diff --git a/.gitignore b/.gitignore
index d90488a..4250a0f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -23,6 +23,9 @@ coverage/
 playwright-report/
 test-results/
 
+# CI security-audit artifact (written by Baton security-audit before lint)
+audit.json
+
 # Editor directories and files
 .vscode/*
 !.vscode/extensions.json
diff --git a/biome.json b/biome.json
index 92cd200..5ce510b 100644
--- a/biome.json
+++ b/biome.json
@@ -152,7 +152,7 @@
     "lineWidth": 120
   },
   "files": {
-    "includes": ["**/*.ts", "**/*.js", "**/*.json", "**/*.html", "!dist", "!node_modules", "!.claude"]
+    "includes": ["**/*.ts", "**/*.js", "**/*.json", "**/*.html", "!dist", "!node_modules", "!.claude", "!audit.json"]
   },
   "overrides": [
     {
diff --git a/src/OpticsLabConstants.ts b/src/OpticsLabConstants.ts
index e899a9d..1cb65d1 100644
--- a/src/OpticsLabConstants.ts
+++ b/src/OpticsLabConstants.ts
@@ -18,8 +18,10 @@
  *  8. Mirror & blocker rendering
  *  9. Glass / lens rendering
  * 10. Light-source rendering
+ * 11+. Grid, gratings, detectors, fiber, carousel, fonts, …
  */
 
+import { GREEN_WAVELENGTH } from "./common/model/light-sources/LightSourceConstants.js";
 import OpticsLabNamespace from "./OpticsLabNamespace.js";
 
 // ── 1. App chrome ─────────────────────────────────────────────────────────────
@@ -79,10 +81,25 @@ export const DEFAULT_FOCAL_LENGTH = 1.0;
 
 export const DEFAULT_MAX_RAY_DEPTH = 200;
 
+/**
+ * Startup default for the `maximumLightRayDepth` query parameter.
+ * Distinct from `DEFAULT_MAX_RAY_DEPTH` (scene / tracer default when unset).
+ */
+export const QUERY_DEFAULT_MAX_RAY_DEPTH = 50;
+
 /** Allowed range for `OpticsScene.maxRayDepthProperty` and `maximumLightRayDepth` query parameter (integer). */
 export const MAX_RAY_DEPTH_PROPERTY_MIN = 1;
 export const MAX_RAY_DEPTH_PROPERTY_MAX = 500;
 
+/**
+ * Length / distance below which a segment or vector is treated as degenerate
+ * (model metres). Used for near-zero guards across model and view code.
+ */
+export const LENGTH_DEGENERATE_M = 1e-10;
+
+/** Maximum number of undo history entries retained by CommandHistory. */
+export const MAX_HISTORY_SIZE = 100;
+
 export const DEFAULT_MIN_BRIGHTNESS = 0.01;
 export const DEFAULT_RAY_DENSITY = 0.5;
 export const RAY_DENSITY_MIN = 0.2;
@@ -145,6 +162,8 @@ export const PANEL_CONTENT_SPACING = 8;
 
 export const BRIGHTNESS_MIN = 0.05;
 export const BRIGHTNESS_MAX = 2;
+/** Step size for brightness NumberControls. */
+export const BRIGHTNESS_CONTROL_DELTA = 0.05;
 
 export const WAVELENGTH_MIN_NM = 380;
 export const WAVELENGTH_MAX_NM = 780;
@@ -155,6 +174,13 @@ export const EMISSION_ANGLE_MAX_DEG = 360;
 export const DIVERGENCE_MIN_DEG = 0;
 export const DIVERGENCE_MAX_DEG = 90;
 
+/** Default divergence half-angle (degrees) for newly created divergent beams. */
+export const DIVERGENT_BEAM_DEFAULT_EMIS_ANGLE_DEG = 10;
+
+/** Element rotation / angle NumberControl bounds (degrees). */
+export const ELEMENT_ANGLE_MIN_DEG = 0;
+export const ELEMENT_ANGLE_MAX_DEG = 360;
+
 export const SPHERICAL_RADIUS_MIN = -20;
 export const SPHERICAL_RADIUS_MAX = 20;
 export const SPHERICAL_R1_FALLBACK = 5;
@@ -164,6 +190,23 @@ export const CONSTRAINED_LENS_RADIUS_MIN = 0.5;
 
 export const REFRACTIVE_INDEX_MIN = 1;
 export const REFRACTIVE_INDEX_MAX = 3;
+/** Step size for refractive-index NumberControls. */
+export const REFRACTIVE_INDEX_DELTA = 0.05;
+
+/** Prism size / leg-length NumberControl bounds (model metres). */
+export const PRISM_SIZE_MIN_M = 0.1;
+export const PRISM_SIZE_MAX_M = 2.0;
+/** Step size for prism size / leg-length NumberControls. */
+export const PRISM_SIZE_DELTA = 0.05;
+
+/** Dimensional glass (slab / parallelogram / Dove) width bounds (model metres). */
+export const DIMENSIONAL_GLASS_WIDTH_MIN_M = 0.1;
+export const DIMENSIONAL_GLASS_WIDTH_MAX_M = 3.0;
+/** Dimensional glass height bounds (model metres). */
+export const DIMENSIONAL_GLASS_HEIGHT_MIN_M = 0.1;
+export const DIMENSIONAL_GLASS_HEIGHT_MAX_M = 2.0;
+/** Step size for dimensional-glass width/height NumberControls. */
+export const DIMENSIONAL_GLASS_SIZE_DELTA = 0.05;
 
 export const ARC_MIRROR_RADIUS_MIN = 0.1;
 export const ARC_MIRROR_RADIUS_MAX = 20;
@@ -193,6 +236,16 @@ export const HANDLE_LINE_WIDTH = 1.5;
 /** Half-width (px) of the invisible filled rectangle used as the drag target for line-segment elements. */
 export const LINE_HIT_HALF_WIDTH_PX = 10;
 
+/** Padding (px) around content bounds for the selection rectangle. */
+export const SELECTION_PAD_PX = 8;
+
+/** Radius (px) of real/virtual image markers in images mode. */
+export const IMAGE_MARKER_RADIUS_PX = HANDLE_RADIUS;
+/** Gap (px) between image marker edge and its label. */
+export const IMAGE_LABEL_GAP_PX = 3;
+/** Horizontal offset (px) from image marker centre to label. */
+export const IMAGE_LABEL_OFFSET_X_PX = IMAGE_MARKER_RADIUS_PX + IMAGE_LABEL_GAP_PX;
+
 // ── 8. Mirror & blocker rendering ────────────────────────────────────────────
 
 /** Shared back-face stroke width for mirrors and blockers. */
@@ -279,10 +332,16 @@ export const PRISM_MIN_VERTEX_DIST_M = 0.05;
 /** Minimum top-face width of a Dove prism (width − height, model metres). */
 export const DOVE_MIN_TOP_FACE_M = 0.05;
 /** Distance threshold below which a vertex position is considered degenerate (model metres). */
-export const PRISM_DEGENERATE_DIST = 1e-10;
+export const PRISM_DEGENERATE_DIST = LENGTH_DEGENERATE_M;
 /** Drag-delta magnitude below which a rotation drag move is ignored (model metres). */
 export const ROTATION_DRAG_DELTA_MIN = 1e-12;
 
+/**
+ * Minimum optical-axis offset (m) of a plano/symmetric lens apex from the
+ * mid-plane. Prevents the apex from crossing flat during curvature drags.
+ */
+export const LENS_APEX_MIN_OFFSET_M = 0.02;
+
 // ── 10. Light-source rendering ────────────────────────────────────────────────
 
 /** Stroke width for the central glow disc circle (point & arc sources). */
@@ -358,9 +417,18 @@ export const REFLECTION_GRATING_GROOVE_LENGTH_PX = 6;
 /** Default groove density for new gratings (lines / mm). */
 export const GRATING_DEFAULT_LINES_DENSITY = 600;
 /** Default wavelength (nm) used when a grating ray carries no wavelength. */
-export const GRATING_DEFAULT_WAVELENGTH_NM = 532;
+export const GRATING_DEFAULT_WAVELENGTH_NM = GREEN_WAVELENGTH;
 /** Maximum diffraction order to compute. */
 export const GRATING_MAX_DIFFRACTION_ORDER = 10;
+/** Default slit-width / line-spacing ratio for new gratings. */
+export const GRATING_DEFAULT_DUTY_CYCLE = 0.5;
+/** Groove-density NumberControl bounds (lines / mm). */
+export const GRATING_LINES_DENSITY_MIN = 1;
+export const GRATING_LINES_DENSITY_MAX = 2500;
+/** Duty-cycle NumberControl bounds and step. */
+export const GRATING_DUTY_CYCLE_MIN = 0.01;
+export const GRATING_DUTY_CYCLE_MAX = 0.99;
+export const GRATING_DUTY_CYCLE_DELTA = 0.01;
 
 // ── 13. Apertured Parabolic Mirror ───────────────────────────────────────────
 
@@ -393,8 +461,17 @@ export const ACQUISITION_DURATION_S = 2.0;
 export const ACQUISITION_PASSES_PER_FRAME = 100;
 /** Initial horizontal offset (px) of the floating chart from the detector midpoint. */
 export const DETECTOR_INITIAL_CHART_OFFSET_X = 200;
+/** Initial vertical offset (px) of the floating chart from the detector midpoint. */
+export const DETECTOR_INITIAL_CHART_OFFSET_Y = 10;
 /** Controls the Bézier bulge of the wire connecting detector to chart. */
 export const DETECTOR_WIRE_NORMAL_MAGNITUDE = 40;
+/**
+ * Maximum hit samples retained by a detector (reservoir sampling).
+ * Caps memory while keeping a uniform random sample of irradiance hits.
+ */
+export const DETECTOR_MAX_HITS = 2000;
+/** Headroom factor applied above the max bin value when autoscaling the chart Y axis. */
+export const DETECTOR_CHART_Y_HEADROOM = 1.25;
 
 // ── 14. Glass model defaults ─────────────────────────────────────────────────
 
@@ -414,7 +491,7 @@ export const PARALLELOGRAM_PRISM_DEFAULT_HEIGHT_M = 0.42;
 
 // ── 15. ContinuousSpectrumSource defaults ────────────────────────────────────
 
-export const CONT_SPECTRUM_DEFAULT_WL_MIN_NM = 380;
+export const CONT_SPECTRUM_DEFAULT_WL_MIN_NM = WAVELENGTH_MIN_NM;
 export const CONT_SPECTRUM_DEFAULT_WL_STEP_NM = 10;
 export const CONT_SPECTRUM_DEFAULT_WL_MAX_NM = 700;
 export const CONT_SPECTRUM_DEFAULT_BRIGHTNESS = 0.5;
@@ -437,6 +514,14 @@ export const FIBER_OPTIC_OUTER_RADIUS_MAX_M = 0.25;
  * coreRadius = outerRadius × this value.
  */
 export const FIBER_CORE_RADIUS_FRACTION_DEFAULT = 0.45;
+/** Core-radius-fraction NumberControl bounds and step. */
+export const FIBER_CORE_FRACTION_MIN = 0.05;
+export const FIBER_CORE_FRACTION_MAX = 0.95;
+export const FIBER_CORE_FRACTION_DELTA = 0.05;
+/** Catmull–Rom tension used when sampling the fiber centreline spline. */
+export const FIBER_SPLINE_TENSION = 0.5;
+/** Sample intervals per Catmull–Rom segment when building the fiber ribbon. */
+export const FIBER_SAMPLES_PER_SEGMENT = 8;
 
 // ── 17. Carousel ─────────────────────────────────────────────────────────────
 
@@ -511,7 +596,12 @@ export const DEFAULT_BEAM_BRIGHTNESS = 0.5;
  * Default wavelength (nm) for newly created beam, divergent-beam, and
  * single-ray sources.  532 nm corresponds to a standard green (Nd:YAG) laser.
  */
-export const DEFAULT_BEAM_WAVELENGTH_NM = 532;
+export const DEFAULT_BEAM_WAVELENGTH_NM = GREEN_WAVELENGTH;
+/** Beam-splitter transmission NumberControl bounds. */
+export const BEAM_SPLITTER_TRANSMIT_MIN = 0;
+export const BEAM_SPLITTER_TRANSMIT_MAX = 1;
+/** Step size for beam-splitter transmission NumberControls. */
+export const BEAM_SPLITTER_TRANSMIT_DELTA = 0.05;
 /** Default brightness for newly created single-ray sources. */
 export const DEFAULT_SINGLE_RAY_BRIGHTNESS = 1;
 /** Default opening half-angle (rad) for newly created arc light sources. */
@@ -564,12 +654,45 @@ export const FACTORY_FIBER_OPTIC_LENGTH_SCALE = 1.5;
 
 // ── 22. Element archetype defaults ────────────────────────────────────────────
 
+/**
+ * Wavelength (nm) used when a ray segment has no wavelength (canvas/SVG
+ * rendering fallback) and in the PhET-iO group archetype element state.
+ */
+export const FALLBACK_RAY_WAVELENGTH_NM = 550;
 /**
  * Wavelength (nm) used in the PhET-iO group archetype element state.
- * This placeholder value does not represent any particular preset; it is only
- * used to satisfy the phetioType schema for the archetype element.
+ * Alias of {@link FALLBACK_RAY_WAVELENGTH_NM}.
+ */
+export const ARCHETYPE_DEFAULT_WAVELENGTH_NM = FALLBACK_RAY_WAVELENGTH_NM;
+
+// ── 22b. Observer defaults ───────────────────────────────────────────────────
+
+/** Default observer position X (model metres). */
+export const DEFAULT_OBSERVER_X_M = 0.3;
+/** Default observer position Y (model metres). */
+export const DEFAULT_OBSERVER_Y_M = 0;
+/** Default observer collection radius (model metres). */
+export const DEFAULT_OBSERVER_RADIUS_M = 0.12;
+/** Minimum observer collection radius (model metres). */
+export const OBSERVER_RADIUS_MIN_M = 0.02;
+/** Centre-dot radius (px) for the observer node. */
+export const OBSERVER_CENTER_DOT_RADIUS_PX = 7;
+/** Rim-handle radius (px) for resizing the observer collection radius. */
+export const OBSERVER_RIM_HANDLE_RADIUS_PX = 5;
+
+// ── 22c. Track / spatial-index ───────────────────────────────────────────────
+
+/** Stroke width for track guide lines. */
+export const TRACK_LINE_WIDTH = 2;
+/** Dash pattern [dash, gap] for track guide lines. */
+export const TRACK_LINE_DASH = [8, 4];
+/** Default spatial-hash cell size (model metres). */
+export const SPATIAL_INDEX_CELL_SIZE_M = 2.0;
+/**
+ * Maximum cells traversed along a ray before SpatialIndex falls back to
+ * testing every element.
  */
-export const ARCHETYPE_DEFAULT_WAVELENGTH_NM = 550;
+export const SPATIAL_INDEX_MAX_TRAVERSAL_STEPS = 200;
 
 // ── 23. Fiber optic physics parameters ───────────────────────────────────────
 
diff --git a/src/common/model/detectors/DetectorElement.ts b/src/common/model/detectors/DetectorElement.ts
index d302bae..b24f23f 100644
--- a/src/common/model/detectors/DetectorElement.ts
+++ b/src/common/model/detectors/DetectorElement.ts
@@ -9,7 +9,7 @@
  * Acquisition / histogram logic is delegated to DetectorAcquisition.
  */
 
-import { DETECTOR_NUM_BINS } from "../../../OpticsLabConstants.js";
+import { DETECTOR_MAX_HITS, DETECTOR_NUM_BINS } from "../../../OpticsLabConstants.js";
 import { ELEMENT_CATEGORY_BLOCKER, ELEMENT_TYPE_DETECTOR } from "../../../OpticsLabStrings.js";
 import { BaseSegmentElement } from "../optics/BaseSegmentElement.js";
 import {
@@ -36,9 +36,6 @@ import type {
 } from "../optics/OpticsTypes.js";
 import { DetectorAcquisition } from "./DetectorAcquisition.js";
 
-/** Maximum number of hits stored; older hits are replaced via reservoir sampling. */
-export const DETECTOR_MAX_HITS = 2000;
-
 export type DetectorHit = { t: number; brightness: number };
 
 export class DetectorElement extends BaseSegmentElement implements IAcquirable {
diff --git a/src/common/model/fiber/FiberOpticElement.ts b/src/common/model/fiber/FiberOpticElement.ts
index 0de279c..a680a96 100644
--- a/src/common/model/fiber/FiberOpticElement.ts
+++ b/src/common/model/fiber/FiberOpticElement.ts
@@ -30,6 +30,8 @@ import {
   FIBER_OPTIC_CRITICAL_BEND_RADIUS,
   FIBER_OPTIC_DEFAULT_BEND_LOSS_COEFF,
   FIBER_OPTIC_DEFAULT_OUTER_RADIUS_M,
+  FIBER_SAMPLES_PER_SEGMENT,
+  FIBER_SPLINE_TENSION,
 } from "../../../OpticsLabConstants.js";
 import { ELEMENT_TYPE_FIBER_CORE_GLASS, ELEMENT_TYPE_FIBER_OPTIC } from "../../../OpticsLabStrings.js";
 import { Glass, type GlassPathPoint } from "../glass/Glass.js";
@@ -178,8 +180,6 @@ export class FiberCoreGlass extends Glass {
 
 // ── Catmull–Rom maths ─────────────────────────────────────────────────────────
 
-const TENSION = 0.5;
-
 /**
  * Position on the Catmull–Rom segment from p1 to p2, with context points
  * p0 (before) and p3 (after), evaluated at parameter t ∈ [0, 1].
@@ -187,7 +187,7 @@ const TENSION = 0.5;
 function crPoint(p0: Point, p1: Point, p2: Point, p3: Point, t: number): Point {
   const t2 = t * t;
   const t3 = t2 * t;
-  const tension = TENSION;
+  const tension = FIBER_SPLINE_TENSION;
   const c0 = tension * (-t3 + 2 * t2 - t);
   const c1 = (2 - tension) * t3 + (tension - 3) * t2 + 1;
   const c2 = (tension - 2) * t3 + (3 - 2 * tension) * t2 + tension * t;
@@ -203,7 +203,7 @@ function crPoint(p0: Point, p1: Point, p2: Point, p3: Point, t: number): Point {
  * The tangent at t=0 is τ*(p2−p0) and at t=1 is τ*(p3−p1).
  */
 function crTangent(p0: Point, p1: Point, p2: Point, p3: Point, t: number): Point {
-  const tension = TENSION;
+  const tension = FIBER_SPLINE_TENSION;
   const d0 = tension * (-3 * t * t + 4 * t - 1);
   const d1 = 3 * (2 - tension) * t * t + 2 * (tension - 3) * t;
   const d2 = 3 * (tension - 2) * t * t + 2 * (3 - 2 * tension) * t + tension;
@@ -219,7 +219,7 @@ function crTangent(p0: Point, p1: Point, p2: Point, p3: Point, t: number): Point
  * Used for computing local curvature: κ = |x'y'' − y'x''| / (x'² + y'²)^(3/2).
  */
 function crSecondDerivative(p0: Point, p1: Point, p2: Point, p3: Point, t: number): Point {
-  const tension = TENSION;
+  const tension = FIBER_SPLINE_TENSION;
   const dd0 = tension * (-6 * t + 4);
   const dd1 = 6 * (2 - tension) * t + 2 * (tension - 3);
   const dd2 = 6 * (tension - 2) * t + 2 * (3 - 2 * tension);
@@ -230,11 +230,6 @@ function crSecondDerivative(p0: Point, p1: Point, p2: Point, p3: Point, t: numbe
   };
 }
 
-// ── Number of samples used to approximate the spline ─────────────────────────
-
-/** Intervals per Catmull–Rom segment. Total samples = 4 × N + 1. */
-const N_PER_SEG = 8;
-
 // ── Ribbon path builder ───────────────────────────────────────────────────────
 
 function buildRibbonPath(samples: Array<{ point: Point; tangent: Point }>, r: number): GlassPathPoint[] {
@@ -333,7 +328,7 @@ export class FiberOpticElement extends Glass implements ICompound {
   }
 
   /**
-   * Sample the Catmull–Rom spline at N_PER_SEG × 4 + 1 evenly-spaced
+   * Sample the Catmull–Rom spline at FIBER_SAMPLES_PER_SEGMENT × 4 + 1 evenly-spaced
    * parameter values.  Returns { point, tangent, curvature } triples in model space.
    *
    * Phantom end-points are mirrored so the curve interpolates p1 and p2
@@ -362,9 +357,9 @@ export class FiberOpticElement extends Glass implements ICompound {
         continue;
       }
       const [a, b, c, d] = seg;
-      const kMax = s < segs.length - 1 ? N_PER_SEG : N_PER_SEG + 1;
+      const kMax = s < segs.length - 1 ? FIBER_SAMPLES_PER_SEGMENT : FIBER_SAMPLES_PER_SEGMENT + 1;
       for (let k = 0; k < kMax; k++) {
-        const t = k / N_PER_SEG;
+        const t = k / FIBER_SAMPLES_PER_SEGMENT;
         const tangent = crTangent(a, b, c, d, t);
         const dd = crSecondDerivative(a, b, c, d, t);
         const speedSq = tangent.x * tangent.x + tangent.y * tangent.y;
diff --git a/src/common/model/glass/Glass.ts b/src/common/model/glass/Glass.ts
index e1926fd..d763869 100644
--- a/src/common/model/glass/Glass.ts
+++ b/src/common/model/glass/Glass.ts
@@ -14,6 +14,7 @@
  *     from the previous vertex through the control point to the next vertex.
  */
 
+import { DEFAULT_CAUCHY_B, DEFAULT_REFRACTIVE_INDEX } from "../../../OpticsLabConstants.js";
 import { ELEMENT_TYPE_GLASS } from "../../../OpticsLabStrings.js";
 import {
   arcBounds,
@@ -75,7 +76,12 @@ export class Glass extends BaseGlass {
 
   public path: GlassPathPoint[];
 
-  public constructor(path: GlassPathPoint[], refIndex = 1.5, cauchyB = 0.004, partialReflect = true) {
+  public constructor(
+    path: GlassPathPoint[],
+    refIndex = DEFAULT_REFRACTIVE_INDEX,
+    cauchyB = DEFAULT_CAUCHY_B,
+    partialReflect = true,
+  ) {
     super(refIndex, cauchyB, partialReflect);
     this.path = path;
   }
diff --git a/src/common/model/glass/HalfPlaneGlass.ts b/src/common/model/glass/HalfPlaneGlass.ts
index 7cfce66..4d5256a 100644
--- a/src/common/model/glass/HalfPlaneGlass.ts
+++ b/src/common/model/glass/HalfPlaneGlass.ts
@@ -7,6 +7,7 @@
  * looking from p1 toward p2.
  */
 
+import { DEFAULT_REFRACTIVE_INDEX } from "../../../OpticsLabConstants.js";
 import { ELEMENT_TYPE_PLANE_GLASS } from "../../../OpticsLabStrings.js";
 import { type Bounds, type Point, point, rayLineIntersection, segment, segmentNormal } from "../optics/Geometry.js";
 import type { IntersectionResult, RayCallConfig, RayInteractionResult, SimulationRay } from "../optics/OpticsTypes.js";
@@ -18,7 +19,7 @@ export class HalfPlaneGlass extends BaseGlass {
   public p1: Point;
   public p2: Point;
 
-  public constructor(p1: Point, p2: Point, refIndex = 1.5) {
+  public constructor(p1: Point, p2: Point, refIndex = DEFAULT_REFRACTIVE_INDEX) {
     // cauchyB=0 preserves current behaviour (no dispersion); partialReflect=true
     super(refIndex, 0, true);
     this.p1 = p1;
diff --git a/src/common/model/glass/SlabGlass.ts b/src/common/model/glass/SlabGlass.ts
index 6c2231f..1f0a7ef 100644
--- a/src/common/model/glass/SlabGlass.ts
+++ b/src/common/model/glass/SlabGlass.ts
@@ -1,4 +1,9 @@
-import { SLAB_GLASS_DEFAULT_HEIGHT_M, SLAB_GLASS_DEFAULT_WIDTH_M } from "../../../OpticsLabConstants.js";
+import {
+  DEFAULT_CAUCHY_B,
+  DEFAULT_REFRACTIVE_INDEX,
+  SLAB_GLASS_DEFAULT_HEIGHT_M,
+  SLAB_GLASS_DEFAULT_WIDTH_M,
+} from "../../../OpticsLabConstants.js";
 import { ELEMENT_TYPE_SLAB_GLASS } from "../../../OpticsLabStrings.js";
 import type { Point } from "../optics/Geometry.js";
 import { DimensionalGlass } from "./DimensionalGlass.js";
@@ -22,8 +27,8 @@ export class SlabGlass extends DimensionalGlass {
     center: Point,
     width = SLAB_GLASS_DEFAULT_WIDTH_M,
     height = SLAB_GLASS_DEFAULT_HEIGHT_M,
-    refIndex = 1.5,
-    cauchyB = 0.004,
+    refIndex = DEFAULT_REFRACTIVE_INDEX,
+    cauchyB = DEFAULT_CAUCHY_B,
     partialReflect = true,
   ) {
     super(makeVertices(center.x, center.y, width, height), width, height, refIndex, cauchyB, partialReflect);
diff --git a/src/common/model/gratings/ReflectionGrating.ts b/src/common/model/gratings/ReflectionGrating.ts
index 1985957..1c08594 100644
--- a/src/common/model/gratings/ReflectionGrating.ts
+++ b/src/common/model/gratings/ReflectionGrating.ts
@@ -11,7 +11,7 @@
  *  - dutyCycle:    slit-width to line-spacing ratio (0–1), controls order intensities
  */
 
-import { GRATING_DEFAULT_LINES_DENSITY } from "../../../OpticsLabConstants.js";
+import { GRATING_DEFAULT_DUTY_CYCLE, GRATING_DEFAULT_LINES_DENSITY } from "../../../OpticsLabConstants.js";
 import { ELEMENT_CATEGORY_MIRROR, ELEMENT_TYPE_REFLECTION_GRATING } from "../../../OpticsLabStrings.js";
 import { BaseSegmentElement } from "../optics/BaseSegmentElement.js";
 import type { Point } from "../optics/Geometry.js";
@@ -32,7 +32,12 @@ export class ReflectionGrating extends BaseSegmentElement {
   /** Slit-width / line-spacing ratio (0–1). */
   public dutyCycle: number;
 
-  public constructor(p1: Point, p2: Point, linesDensity = GRATING_DEFAULT_LINES_DENSITY, dutyCycle = 0.5) {
+  public constructor(
+    p1: Point,
+    p2: Point,
+    linesDensity = GRATING_DEFAULT_LINES_DENSITY,
+    dutyCycle = GRATING_DEFAULT_DUTY_CYCLE,
+  ) {
     super(p1, p2);
     this.linesDensity = linesDensity;
     this.dutyCycle = dutyCycle;
diff --git a/src/common/model/gratings/TransmissionGrating.ts b/src/common/model/gratings/TransmissionGrating.ts
index 37140f5..6cc1959 100644
--- a/src/common/model/gratings/TransmissionGrating.ts
+++ b/src/common/model/gratings/TransmissionGrating.ts
@@ -11,7 +11,7 @@
  *  - dutyCycle:    slit-width to line-spacing ratio (0–1), controls order intensities
  */
 
-import { GRATING_DEFAULT_LINES_DENSITY } from "../../../OpticsLabConstants.js";
+import { GRATING_DEFAULT_DUTY_CYCLE, GRATING_DEFAULT_LINES_DENSITY } from "../../../OpticsLabConstants.js";
 import { ELEMENT_CATEGORY_GLASS, ELEMENT_TYPE_TRANSMISSION_GRATING } from "../../../OpticsLabStrings.js";
 import { BaseSegmentElement } from "../optics/BaseSegmentElement.js";
 import type { Point } from "../optics/Geometry.js";
@@ -32,7 +32,12 @@ export class TransmissionGrating extends BaseSegmentElement {
   /** Slit-width / line-spacing ratio (0–1). */
   public dutyCycle: number;
 
-  public constructor(p1: Point, p2: Point, linesDensity = GRATING_DEFAULT_LINES_DENSITY, dutyCycle = 0.5) {
+  public constructor(
+    p1: Point,
+    p2: Point,
+    linesDensity = GRATING_DEFAULT_LINES_DENSITY,
+    dutyCycle = GRATING_DEFAULT_DUTY_CYCLE,
+  ) {
     super(p1, p2);
     this.linesDensity = linesDensity;
     this.dutyCycle = dutyCycle;
diff --git a/src/common/model/light-sources/ArcLightSource.ts b/src/common/model/light-sources/ArcLightSource.ts
index bb0aa97..73fc636 100644
--- a/src/common/model/light-sources/ArcLightSource.ts
+++ b/src/common/model/light-sources/ArcLightSource.ts
@@ -8,7 +8,7 @@
  * π/2 = down (positive y-axis), consistent with Math.atan2(dy, dx).
  */
 
-import { DEFAULT_ARC_CONE_HALF_ANGLE_RAD } from "../../../OpticsLabConstants.js";
+import { DEFAULT_ARC_BRIGHTNESS, DEFAULT_ARC_CONE_HALF_ANGLE_RAD } from "../../../OpticsLabConstants.js";
 import { ELEMENT_TYPE_ARC_SOURCE } from "../../../OpticsLabStrings.js";
 import type { Bounds, Point } from "../optics/Geometry.js";
 import { normalize, point } from "../optics/Geometry.js";
@@ -38,7 +38,7 @@ export class ArcLightSource extends BaseLightSource {
     position: Point,
     direction = 0,
     emissionAngle = DEFAULT_ARC_CONE_HALF_ANGLE_RAD,
-    brightness = 0.5,
+    brightness = DEFAULT_ARC_BRIGHTNESS,
     wavelength = GREEN_WAVELENGTH,
   ) {
     super(brightness, wavelength);
diff --git a/src/common/model/light-sources/BeamSource.ts b/src/common/model/light-sources/BeamSource.ts
index 30e6a28..325ec06 100644
--- a/src/common/model/light-sources/BeamSource.ts
+++ b/src/common/model/light-sources/BeamSource.ts
@@ -6,7 +6,9 @@
  * the segment.
  */
 
+import { DEFAULT_BEAM_BRIGHTNESS } from "../../../OpticsLabConstants.js";
 import { ELEMENT_TYPE_BEAM } from "../../../OpticsLabStrings.js";
+
 import type { Bounds, Point } from "../optics/Geometry.js";
 import { distance, normalize, point, pointsBounds, subtract } from "../optics/Geometry.js";
 import { BEAM_RAY_DENSITY_SCALE, BRIGHTNESS_CONTINUOUS_THRESHOLD } from "../optics/OpticsConstants.js";
@@ -22,7 +24,7 @@ export class BeamSource extends BaseLightSource {
   /** Second endpoint of the segment perpendicular to beam direction. */
   public p2: Point;
 
-  public constructor(p1: Point, p2: Point, brightness = 0.5, wavelength = GREEN_WAVELENGTH) {
+  public constructor(p1: Point, p2: Point, brightness = DEFAULT_BEAM_BRIGHTNESS, wavelength = GREEN_WAVELENGTH) {
     super(brightness, wavelength);
     this.p1 = p1;
     this.p2 = p2;
diff --git a/src/common/model/light-sources/DivergentBeam.ts b/src/common/model/light-sources/DivergentBeam.ts
index 72f13c1..79c1ae6 100644
--- a/src/common/model/light-sources/DivergentBeam.ts
+++ b/src/common/model/light-sources/DivergentBeam.ts
@@ -6,6 +6,7 @@
  * segment within a finite divergence half-angle.
  */
 
+import { DEFAULT_BEAM_BRIGHTNESS, DIVERGENT_BEAM_DEFAULT_EMIS_ANGLE_DEG } from "../../../OpticsLabConstants.js";
 import { ELEMENT_TYPE_DIVERGENT_BEAM } from "../../../OpticsLabStrings.js";
 import type { Bounds, Point } from "../optics/Geometry.js";
 import { distance, normalize, point, pointsBounds, subtract } from "../optics/Geometry.js";
@@ -18,9 +19,6 @@ import type { SimulationRay, ViewMode } from "../optics/OpticsTypes.js";
 import { BaseLightSource } from "./BaseLightSource.js";
 import { GREEN_WAVELENGTH } from "./LightSourceConstants.js";
 
-/** Default divergence half-angle in degrees. */
-export const DIVERGENT_BEAM_DEFAULT_EMIS_ANGLE = 10;
-
 export class DivergentBeam extends BaseLightSource {
   public readonly type = ELEMENT_TYPE_DIVERGENT_BEAM;
 
@@ -34,9 +32,9 @@ export class DivergentBeam extends BaseLightSource {
   public constructor(
     p1: Point,
     p2: Point,
-    brightness = 0.5,
+    brightness = DEFAULT_BEAM_BRIGHTNESS,
     wavelength = GREEN_WAVELENGTH,
-    emisAngle = DIVERGENT_BEAM_DEFAULT_EMIS_ANGLE,
+    emisAngle = DIVERGENT_BEAM_DEFAULT_EMIS_ANGLE_DEG,
   ) {
     super(brightness, wavelength);
     this.p1 = p1;
diff --git a/src/common/model/light-sources/PointSourceElement.ts b/src/common/model/light-sources/PointSourceElement.ts
index 2e2e390..7bdd64a 100644
--- a/src/common/model/light-sources/PointSourceElement.ts
+++ b/src/common/model/light-sources/PointSourceElement.ts
@@ -5,7 +5,9 @@
  * directions. The angular spacing of rays depends on rayDensity.
  */
 
+import { DEFAULT_POINT_SOURCE_BRIGHTNESS } from "../../../OpticsLabConstants.js";
 import { ELEMENT_TYPE_POINT_SOURCE } from "../../../OpticsLabStrings.js";
+
 import type { Bounds, Point } from "../optics/Geometry.js";
 import { point } from "../optics/Geometry.js";
 import { BRIGHTNESS_CONTINUOUS_THRESHOLD, RAY_DENSITY_SCALE } from "../optics/OpticsConstants.js";
@@ -18,7 +20,7 @@ export class PointSourceElement extends BaseLightSource {
 
   public position: Point;
 
-  public constructor(position: Point, brightness = 0.5, wavelength = GREEN_WAVELENGTH) {
+  public constructor(position: Point, brightness = DEFAULT_POINT_SOURCE_BRIGHTNESS, wavelength = GREEN_WAVELENGTH) {
     super(brightness, wavelength);
     this.position = position;
   }
diff --git a/src/common/model/light-sources/SingleRaySource.ts b/src/common/model/light-sources/SingleRaySource.ts
index 37792df..f474648 100644
--- a/src/common/model/light-sources/SingleRaySource.ts
+++ b/src/common/model/light-sources/SingleRaySource.ts
@@ -5,7 +5,9 @@
  * a second point that indicates direction. Emits exactly one ray.
  */
 
+import { DEFAULT_SINGLE_RAY_BRIGHTNESS } from "../../../OpticsLabConstants.js";
 import { ELEMENT_TYPE_SINGLE_RAY } from "../../../OpticsLabStrings.js";
+
 import type { Bounds, Point } from "../optics/Geometry.js";
 import { normalize, point, pointsBounds, subtract } from "../optics/Geometry.js";
 import type { SimulationRay, ViewMode } from "../optics/OpticsTypes.js";
@@ -18,7 +20,7 @@ export class SingleRaySource extends BaseLightSource {
   public p1: Point;
   public p2: Point;
 
-  public constructor(p1: Point, p2: Point, brightness = 1, wavelength = GREEN_WAVELENGTH) {
+  public constructor(p1: Point, p2: Point, brightness = DEFAULT_SINGLE_RAY_BRIGHTNESS, wavelength = GREEN_WAVELENGTH) {
     super(brightness, wavelength);
     this.p1 = p1;
     this.p2 = p2;
diff --git a/src/common/model/mirrors/BeamSplitterElement.ts b/src/common/model/mirrors/BeamSplitterElement.ts
index cfcaf6a..a35d7d4 100644
--- a/src/common/model/mirrors/BeamSplitterElement.ts
+++ b/src/common/model/mirrors/BeamSplitterElement.ts
@@ -7,7 +7,9 @@
  * in the original direction.
  */
 
+import { DEFAULT_BEAM_SPLITTER_TRANSMIT } from "../../../OpticsLabConstants.js";
 import { ELEMENT_CATEGORY_MIRROR, ELEMENT_TYPE_BEAM_SPLITTER } from "../../../OpticsLabStrings.js";
+
 import { BaseSegmentElement } from "../optics/BaseSegmentElement.js";
 import { dot, normalize, type Point, point } from "../optics/Geometry.js";
 import type {
@@ -24,7 +26,7 @@ export class BeamSplitterElement extends BaseSegmentElement {
   /** Fraction of brightness transmitted (0..1). The rest is reflected. */
   public transRatio: number;
 
-  public constructor(p1: Point, p2: Point, transRatio = 0.5) {
+  public constructor(p1: Point, p2: Point, transRatio = DEFAULT_BEAM_SPLITTER_TRANSMIT) {
     super(p1, p2);
     this.transRatio = transRatio;
   }
diff --git a/src/common/model/optics/CommandHistory.ts b/src/common/model/optics/CommandHistory.ts
index 7ff3f03..3e71c18 100644
--- a/src/common/model/optics/CommandHistory.ts
+++ b/src/common/model/optics/CommandHistory.ts
@@ -1,3 +1,5 @@
+import { MAX_HISTORY_SIZE } from "../../../OpticsLabConstants.js";
+
 /**
  * CommandHistory.ts
  *
@@ -15,8 +17,6 @@
  * The history is capped at MAX_HISTORY_SIZE to bound memory use.
  */
 
-export const MAX_HISTORY_SIZE = 100;
-
 /** A discrete, reversible operation. */
 export interface SceneCommand {
   /** Apply (or re-apply) this command. */
diff --git a/src/common/model/optics/OpticsConstants.ts b/src/common/model/optics/OpticsConstants.ts
index cf70371..e3eeef2 100644
--- a/src/common/model/optics/OpticsConstants.ts
+++ b/src/common/model/optics/OpticsConstants.ts
@@ -6,6 +6,8 @@
  * that file instead.
  */
 
+import { BRIGHTNESS_MAX, DEFAULT_RAY_DENSITY, PIXELS_PER_METER } from "../../../OpticsLabConstants.js";
+
 // ── Intersection tolerance ────────────────────────────────────────────────────
 
 /**
@@ -44,7 +46,7 @@ export const RAY_DENSITY_SCALE = 500;
  * rayDensity was calibrated for pixel coordinates, so this factor (equal to
  * pixels-per-metre) restores the intended ray count.
  */
-export const BEAM_RAY_DENSITY_SCALE = 100;
+export const BEAM_RAY_DENSITY_SCALE = PIXELS_PER_METER;
 
 /**
  * Brightness value at which a source transitions from discrete-ray mode
@@ -59,13 +61,13 @@ export const BRIGHTNESS_CONTINUOUS_THRESHOLD = 1.0;
  * Normalization divisor that maps the brightness property to a [0, 1] per-ray
  * intensity value in continuous-beam mode. Equals the maximum allowed brightness.
  */
-export const BRIGHTNESS_NORMALIZE = 2.0;
+export const BRIGHTNESS_NORMALIZE = BRIGHTNESS_MAX;
 
 /**
  * Reference ray density used to calibrate per-ray brightness.
  * At this density each ray has its "full" brightness.
  * Above this density, per-ray brightness scales inversely with density so that
  * total luminosity is conserved: 2× rays → each at ½ brightness.
- * Should equal DEFAULT_RAY_DENSITY in OpticsLabConstants.
+ * Equals DEFAULT_RAY_DENSITY in OpticsLabConstants.
  */
-export const RAY_DENSITY_REFERENCE = 0.5;
+export const RAY_DENSITY_REFERENCE = DEFAULT_RAY_DENSITY;
diff --git a/src/common/model/optics/RayTracer.ts b/src/common/model/optics/RayTracer.ts
index 14a5a40..e1b8d58 100644
--- a/src/common/model/optics/RayTracer.ts
+++ b/src/common/model/optics/RayTracer.ts
@@ -20,6 +20,7 @@ import {
   DEFAULT_RAY_DENSITY,
   FAR_DISTANCE,
   MAX_TOTAL_SEGMENTS,
+  PIXELS_PER_METER,
   RAY_CONVERGENCE_THRESHOLD,
 } from "../../../OpticsLabConstants.js";
 import { ELEMENT_CATEGORY_LIGHT_SOURCE, VIEW_MODE_RAYS } from "../../../OpticsLabStrings.js";
@@ -407,7 +408,7 @@ export class RayTracer {
    */
   private processObserverImages(allSegments: TracedSegment[], allImages: DetectedImage[]): void {
     const bySource = this.groupObservedSegmentsBySource(allSegments);
-    const thresholdSq = (RAY_CONVERGENCE_THRESHOLD / 100) ** 2;
+    const thresholdSq = (RAY_CONVERGENCE_THRESHOLD / PIXELS_PER_METER) ** 2;
 
     for (const segs of bySource.values()) {
       segs.sort((a, b) => (a.rayIndex ?? 0) - (b.rayIndex ?? 0));
@@ -555,7 +556,7 @@ export class RayTracer {
   private findImagesInSequence(segs: TracedSegment[], images: DetectedImage[]): void {
     // Convergence threshold in model metres (RAY_CONVERGENCE_THRESHOLD is in pixels,
     // 100 px = 1 m).
-    const thresholdSq = (RAY_CONVERGENCE_THRESHOLD / 100) ** 2;
+    const thresholdSq = (RAY_CONVERGENCE_THRESHOLD / PIXELS_PER_METER) ** 2;
 
     const candidates: DetectedImage[] = [];
 
@@ -595,7 +596,7 @@ export class RayTracer {
     }
 
     // Deduplicate candidates that landed in the same threshold cell.
-    const thresholdM = RAY_CONVERGENCE_THRESHOLD / 100;
+    const thresholdM = RAY_CONVERGENCE_THRESHOLD / PIXELS_PER_METER;
     const seen = new Set<string>();
     for (const c of candidates) {
       const key = `${Math.round(c.position.x / thresholdM)},${Math.round(c.position.y / thresholdM)}`;
diff --git a/src/common/model/optics/SpatialIndex.ts b/src/common/model/optics/SpatialIndex.ts
index 3920daf..6fc789a 100644
--- a/src/common/model/optics/SpatialIndex.ts
+++ b/src/common/model/optics/SpatialIndex.ts
@@ -11,19 +11,10 @@
  * separate "unbounded" list and always included in every query.
  */
 
+import { SPATIAL_INDEX_CELL_SIZE_M, SPATIAL_INDEX_MAX_TRAVERSAL_STEPS } from "../../../OpticsLabConstants.js";
 import type { Point } from "./Geometry.js";
 import type { OpticalElement } from "./OpticsTypes.js";
 
-/** Default cell size in model units (metres). */
-const DEFAULT_CELL_SIZE = 2.0;
-
-/**
- * Maximum number of cells to traverse along a ray before falling back to
- * the full element list. Prevents degenerate rays from traversing the
- * entire grid.
- */
-const MAX_TRAVERSAL_STEPS = 200;
-
 export class SpatialIndex {
   private readonly cellSize: number;
   private readonly invCellSize: number;
@@ -38,7 +29,7 @@ export class SpatialIndex {
   private gridMaxCX = 0;
   private gridMaxCY = 0;
 
-  public constructor(elements: OpticalElement[], cellSize = DEFAULT_CELL_SIZE) {
+  public constructor(elements: OpticalElement[], cellSize = SPATIAL_INDEX_CELL_SIZE_M) {
     this.cellSize = cellSize;
     this.invCellSize = 1 / cellSize;
     this.build(elements);
@@ -191,7 +182,7 @@ export class SpatialIndex {
     let tMaxX = xAxis.tMax;
     let tMaxY = yAxis.tMax;
 
-    for (let step = 0; step < MAX_TRAVERSAL_STEPS; step++) {
+    for (let step = 0; step < SPATIAL_INDEX_MAX_TRAVERSAL_STEPS; step++) {
       if (this.isInGrid(cx, cy)) {
         this.collectCell(cx, cy, seen, result);
       } else if (this.isOutOfGrid(cx, cy, xAxis.step, yAxis.step)) {
diff --git a/src/common/view/BaseOpticalElementView.ts b/src/common/view/BaseOpticalElementView.ts
index 9753a10..1f72925 100644
--- a/src/common/view/BaseOpticalElementView.ts
+++ b/src/common/view/BaseOpticalElementView.ts
@@ -22,11 +22,11 @@ import { Emitter, type TReadOnlyProperty } from "scenerystack/axon";
 import { Bounds2 } from "scenerystack/dot";
 import { Node, Rectangle, type RichDragListener } from "scenerystack/scenery";
 import OpticsLabColors from "../../OpticsLabColors.js";
+import { SELECTION_PAD_PX } from "../../OpticsLabConstants.js";
+
 import OpticsLabNamespace from "../../OpticsLabNamespace.js";
 import { unlinkHandleVisibility } from "./ViewHelpers.js";
 
-const SELECTION_PAD = 8; // px of padding around content bounds
-
 export abstract class BaseOpticalElementView extends Node {
   /** Drag listener used to translate the element as a whole. */
   public abstract readonly bodyDragListener: RichDragListener;
@@ -102,10 +102,10 @@ export abstract class BaseOpticalElementView extends Node {
       return;
     }
     this._selectionFrame.setRect(
-      b.minX - SELECTION_PAD,
-      b.minY - SELECTION_PAD,
-      b.width + 2 * SELECTION_PAD,
-      b.height + 2 * SELECTION_PAD,
+      b.minX - SELECTION_PAD_PX,
+      b.minY - SELECTION_PAD_PX,
+      b.width + 2 * SELECTION_PAD_PX,
+      b.height + 2 * SELECTION_PAD_PX,
     );
   }
 
diff --git a/src/common/view/GridScaleIndicatorNode.ts b/src/common/view/GridScaleIndicatorNode.ts
index faf4711..b7422b4 100644
--- a/src/common/view/GridScaleIndicatorNode.ts
+++ b/src/common/view/GridScaleIndicatorNode.ts
@@ -15,6 +15,8 @@ import type { ModelViewTransform2 } from "scenerystack/phetcommon";
 import { Node, Path, Rectangle, Text } from "scenerystack/scenery";
 import { PhetFont } from "scenerystack/scenery-phet";
 import OpticsLabColors from "../../OpticsLabColors.js";
+import { HANDLE_LINE_WIDTH } from "../../OpticsLabConstants.js";
+
 import OpticsLabNamespace from "../../OpticsLabNamespace.js";
 
 // ── Visual constants (view pixels) ────────────────────────────────────────────
@@ -45,7 +47,7 @@ export class GridScaleIndicatorNode extends Node {
     // overlayValueFillProperty is #eee on dark backgrounds, #111 on light ones.
     this._arrowPath = new Path(null, {
       stroke: OpticsLabColors.overlayValueFillProperty,
-      lineWidth: 1.5,
+      lineWidth: HANDLE_LINE_WIDTH,
       lineCap: "round",
       lineJoin: "round",
     });
diff --git a/src/common/view/ImageOverlayNode.ts b/src/common/view/ImageOverlayNode.ts
index c6d7cb1..f9c9c4e 100644
--- a/src/common/view/ImageOverlayNode.ts
+++ b/src/common/view/ImageOverlayNode.ts
@@ -17,12 +17,15 @@ import { toFixed } from "scenerystack/dot";
 import type { ModelViewTransform2 } from "scenerystack/phetcommon";
 import { Circle, Node, Text } from "scenerystack/scenery";
 import OpticsLabColors from "../../OpticsLabColors.js";
-import { FONT_BOLD_9PX } from "../../OpticsLabConstants.js";
+import {
+  FONT_BOLD_9PX,
+  HANDLE_LINE_WIDTH,
+  IMAGE_LABEL_OFFSET_X_PX,
+  IMAGE_MARKER_RADIUS_PX,
+} from "../../OpticsLabConstants.js";
 import OpticsLabNamespace from "../../OpticsLabNamespace.js";
 import type { DetectedImage } from "../model/optics/OpticsTypes.js";
 
-const MARKER_RADIUS = 6; // px
-const LABEL_OFFSET_X = MARKER_RADIUS + 3;
 const LABEL_FONT = FONT_BOLD_9PX;
 
 export class ImageOverlayNode extends Node {
@@ -84,10 +87,10 @@ export class ImageOverlayNode extends Node {
       if (img.imageType === "real") {
         const fillBase = OpticsLabColors.imageRealFillBaseColorProperty.value;
         const strokeBase = OpticsLabColors.imageRealStrokeBaseColorProperty.value;
-        marker = new Circle(MARKER_RADIUS, {
+        marker = new Circle(IMAGE_MARKER_RADIUS_PX, {
           fill: `rgba(${fillBase.r},${fillBase.g},${fillBase.b},${toFixed(alpha * 0.85, 3)})`,
           stroke: `rgba(${strokeBase.r},${strokeBase.g},${strokeBase.b},${toFixed(alpha, 3)})`,
-          lineWidth: 1.5,
+          lineWidth: HANDLE_LINE_WIDTH,
           x: vx,
           y: vy,
         });
@@ -95,10 +98,10 @@ export class ImageOverlayNode extends Node {
         labelFill = OpticsLabColors.imageRealLabelFillProperty.value.toCSS();
       } else if (img.imageType === "virtualObject") {
         const strokeBase = OpticsLabColors.imageVirtualObjectStrokeBaseColorProperty.value;
-        marker = new Circle(MARKER_RADIUS, {
+        marker = new Circle(IMAGE_MARKER_RADIUS_PX, {
           fill: null,
           stroke: `rgba(${strokeBase.r},${strokeBase.g},${strokeBase.b},${toFixed(alpha, 3)})`,
-          lineWidth: 1.5,
+          lineWidth: HANDLE_LINE_WIDTH,
           lineDash: [3, 2],
           x: vx,
           y: vy,
@@ -107,10 +110,10 @@ export class ImageOverlayNode extends Node {
         labelFill = OpticsLabColors.imageVirtualObjectLabelFillProperty.value.toCSS();
       } else {
         const strokeBase = OpticsLabColors.imageVirtualStrokeBaseColorProperty.value;
-        marker = new Circle(MARKER_RADIUS, {
+        marker = new Circle(IMAGE_MARKER_RADIUS_PX, {
           fill: null,
           stroke: `rgba(${strokeBase.r},${strokeBase.g},${strokeBase.b},${toFixed(alpha, 3)})`,
-          lineWidth: 1.5,
+          lineWidth: HANDLE_LINE_WIDTH,
           lineDash: [3, 2],
           x: vx,
           y: vy,
@@ -122,7 +125,7 @@ export class ImageOverlayNode extends Node {
       const label = new Text(labelText, {
         font: LABEL_FONT,
         fill: labelFill,
-        x: vx + LABEL_OFFSET_X,
+        x: vx + IMAGE_LABEL_OFFSET_X_PX,
         y: vy + 3,
       });
 
diff --git a/src/common/view/ObserverNode.ts b/src/common/view/ObserverNode.ts
index a694813..49c89ce 100644
--- a/src/common/view/ObserverNode.ts
+++ b/src/common/view/ObserverNode.ts
@@ -18,18 +18,24 @@ import { Circle, Node, RichDragListener, Text } from "scenerystack/scenery";
 import { Tandem } from "scenerystack/tandem";
 import { StringManager } from "../../i18n/StringManager.js";
 import OpticsLabColors from "../../OpticsLabColors.js";
-import { FONT_11PX } from "../../OpticsLabConstants.js";
+import {
+  DEFAULT_OBSERVER_RADIUS_M,
+  DEFAULT_OBSERVER_X_M,
+  DEFAULT_OBSERVER_Y_M,
+  FONT_11PX,
+  HANDLE_LINE_WIDTH,
+  OBSERVER_CENTER_DOT_RADIUS_PX,
+  OBSERVER_RADIUS_MIN_M,
+  OBSERVER_RIM_HANDLE_RADIUS_PX,
+} from "../../OpticsLabConstants.js";
 import OpticsLabNamespace from "../../OpticsLabNamespace.js";
 import type { Observer } from "../model/optics/OpticsTypes.js";
 
 export const DEFAULT_OBSERVER: Observer = {
-  position: { x: 0.3, y: 0 },
-  radius: 0.12,
+  position: { x: DEFAULT_OBSERVER_X_M, y: DEFAULT_OBSERVER_Y_M },
+  radius: DEFAULT_OBSERVER_RADIUS_M,
 };
 
-const CENTER_DOT_RADIUS = 7; // px
-const RIM_HANDLE_RADIUS = 5; // px
-
 export class ObserverNode extends Node {
   private readonly modelViewTransform: ModelViewTransform2;
   private readonly observerProperty: Property<Observer | null>;
@@ -50,16 +56,16 @@ export class ObserverNode extends Node {
 
     this.radiusCircle = new Circle(0, {
       stroke: OpticsLabColors.observerCircleStrokeProperty,
-      lineWidth: 1.5,
+      lineWidth: HANDLE_LINE_WIDTH,
       lineDash: [5, 3],
       fill: OpticsLabColors.observerCircleFillProperty,
       pickable: false,
     });
 
-    this.centerDot = new Circle(CENTER_DOT_RADIUS, {
+    this.centerDot = new Circle(OBSERVER_CENTER_DOT_RADIUS_PX, {
       fill: OpticsLabColors.observerDotFillProperty,
       stroke: OpticsLabColors.observerDotStrokeProperty,
-      lineWidth: 1.5,
+      lineWidth: HANDLE_LINE_WIDTH,
       cursor: "move",
     });
     this.centerDot.tagName = "div";
@@ -71,7 +77,7 @@ export class ObserverNode extends Node {
       fill: OpticsLabColors.observerLabelFillProperty,
     });
 
-    this.rimHandle = new Circle(RIM_HANDLE_RADIUS, {
+    this.rimHandle = new Circle(OBSERVER_RIM_HANDLE_RADIUS_PX, {
       fill: OpticsLabColors.observerRimFillProperty,
       stroke: OpticsLabColors.observerRimStrokeProperty,
       lineWidth: 1,
@@ -127,7 +133,7 @@ export class ObserverNode extends Node {
         const current = observerProperty.value ?? DEFAULT_OBSERVER;
         observerProperty.value = {
           position: current.position,
-          radius: Math.max(0.02, startRadius + accR),
+          radius: Math.max(OBSERVER_RADIUS_MIN_M, startRadius + accR),
         };
       },
     });
@@ -156,7 +162,7 @@ export class ObserverNode extends Node {
     this.centerDot.y = cy;
 
     this.labelNode.centerX = cx;
-    this.labelNode.bottom = cy - (CENTER_DOT_RADIUS + 3);
+    this.labelNode.bottom = cy - (OBSERVER_CENTER_DOT_RADIUS_PX + 3);
 
     this.radiusCircle.x = cx;
     this.radiusCircle.y = cy;
diff --git a/src/common/view/RayPropagationView.ts b/src/common/view/RayPropagationView.ts
index 5b5db6e..c05ac9e 100644
--- a/src/common/view/RayPropagationView.ts
+++ b/src/common/view/RayPropagationView.ts
@@ -27,6 +27,7 @@ import {
   EXT_LINE_DASH,
   EXT_LINE_WIDTH,
   EXT_R,
+  FALLBACK_RAY_WAVELENGTH_NM,
   RAY_ALPHA_BUCKETS,
   RAY_ALPHA_SCALE,
   RAY_ALPHA_SKIP,
@@ -302,7 +303,7 @@ export class RayPropagationView extends CanvasNode {
         return;
       }
 
-      const c = VisibleColor.wavelengthToColor(seg.wavelength ?? 550);
+      const c = VisibleColor.wavelengthToColor(seg.wavelength ?? FALLBACK_RAY_WAVELENGTH_NM);
       let obsAlpha = seg.isObserved ? Math.min(1, alpha * 1.4) : alpha;
       if (additive) {
         obsAlpha = Math.min(1, obsAlpha * CONT_SPECTRUM_RAY_ALPHA_MULTIPLIER);
@@ -365,7 +366,7 @@ export class RayPropagationView extends CanvasNode {
         continue;
       }
 
-      const c = VisibleColor.wavelengthToColor(seg.wavelength ?? 550);
+      const c = VisibleColor.wavelengthToColor(seg.wavelength ?? FALLBACK_RAY_WAVELENGTH_NM);
       context.strokeStyle = `rgba(${c.r},${c.g},${c.b},${toFixed(alpha, 3)})`;
       context.beginPath();
       context.moveTo(clipped[0], clipped[1]);
@@ -440,7 +441,7 @@ export class RayPropagationView extends CanvasNode {
       const baseX = mx - ux * (ARROW_LENGTH * 0.5);
       const baseY = my - uy * (ARROW_LENGTH * 0.5);
 
-      const c = VisibleColor.wavelengthToColor(seg.wavelength ?? 550);
+      const c = VisibleColor.wavelengthToColor(seg.wavelength ?? FALLBACK_RAY_WAVELENGTH_NM);
       context.fillStyle = `rgba(${c.r},${c.g},${c.b},${toFixed(alpha, 3)})`;
       context.beginPath();
       context.moveTo(tipX, tipY);
diff --git a/src/common/view/RayStubsProperty.ts b/src/common/view/RayStubsProperty.ts
deleted file mode 100644
index ef0fa80..0000000
--- a/src/common/view/RayStubsProperty.ts
+++ /dev/null
@@ -1,28 +0,0 @@
-/**
- * RayStubsProperty.ts
- *
- * Singleton properties that control the "ray stubs" display mode.
- * When enabled, only a short stub of each ray segment is rendered from its
- * start point, hiding the full ray path.  This gives a clean directional
- * indicator without the visual clutter of complete ray traces.
- *
- * rayStubsEnabledProperty  – toggles the mode on / off
- * rayStubLengthPxProperty  – length of each stub in view pixels (default 50)
- */
-
-import { BooleanProperty, NumberProperty } from "scenerystack/axon";
-import { Range } from "scenerystack/dot";
-import OpticsLabNamespace from "../../OpticsLabNamespace.js";
-
-export const RAY_STUB_LENGTH_DEFAULT_PX = 50;
-export const RAY_STUB_LENGTH_MIN_PX = 10;
-export const RAY_STUB_LENGTH_MAX_PX = 200;
-
-export const rayStubsEnabledProperty = new BooleanProperty(false);
-
-export const rayStubLengthPxProperty = new NumberProperty(RAY_STUB_LENGTH_DEFAULT_PX, {
-  range: new Range(RAY_STUB_LENGTH_MIN_PX, RAY_STUB_LENGTH_MAX_PX),
-});
-
-OpticsLabNamespace.register("rayStubsEnabledProperty", rayStubsEnabledProperty);
-OpticsLabNamespace.register("rayStubLengthPxProperty", rayStubLengthPxProperty);
diff --git a/src/common/view/SceneSVGExporter.ts b/src/common/view/SceneSVGExporter.ts
index 851aceb..35cb5b0 100644
--- a/src/common/view/SceneSVGExporter.ts
+++ b/src/common/view/SceneSVGExporter.ts
@@ -15,6 +15,7 @@ import {
   EXT_LINE_DASH,
   EXT_LINE_WIDTH,
   EXT_R,
+  FALLBACK_RAY_WAVELENGTH_NM,
   PIXELS_PER_METER,
   PROTRACTOR_SCALE,
   RAY_ALPHA_BUCKETS,
@@ -158,7 +159,7 @@ function addRayPathNodes(
       const shape = getOrCreateExtensionShape(extensionShapes, alphaBucket);
       shape.moveTo(x1, y1).lineTo(x2, y2);
     } else {
-      const wavelength = seg.wavelength ?? 550;
+      const wavelength = seg.wavelength ?? FALLBACK_RAY_WAVELENGTH_NM;
       const wavelengthColor = getCachedWavelengthColor(wavelengthColorCache, wavelength);
       const bucket = getOrCreateForwardBucket(forwardBuckets, wavelengthColor, alphaBucket);
       bucket.shape.moveTo(x1, y1).lineTo(x2, y2);
diff --git a/src/common/view/ToolsPanelIcons.ts b/src/common/view/ToolsPanelIcons.ts
index 24e9be2..df744df 100644
--- a/src/common/view/ToolsPanelIcons.ts
+++ b/src/common/view/ToolsPanelIcons.ts
@@ -82,7 +82,7 @@ export function extendedRaysIcon(): Node {
   const spreadY = 4;
   return new Node({
     children: [
-      new Line(startX, cy, endX, cy, { stroke: c, lineWidth: 1.5, lineDash: dash }),
+      new Line(startX, cy, endX, cy, { stroke: c, lineWidth: HANDLE_LINE_WIDTH, lineDash: dash }),
       new Line(midX, cy, endX, cy - spreadY, { stroke: c, lineWidth: 1, lineDash: dash }),
       new Line(midX, cy, endX, cy + spreadY, { stroke: c, lineWidth: 1, lineDash: dash }),
     ],
@@ -130,7 +130,10 @@ export function rayArrowsIcon(): Node {
     .lineTo(tipX - headH, cy + headW)
     .close();
   return new Node({
-    children: [new Line(left, cy, right, cy, { stroke: c, lineWidth: 1.5 }), new Path(headShape, { fill: c })],
+    children: [
+      new Line(left, cy, right, cy, { stroke: c, lineWidth: HANDLE_LINE_WIDTH }),
+      new Path(headShape, { fill: c }),
+    ],
   });
 }
 
@@ -143,8 +146,8 @@ export function rayStubsIcon(): Node {
   const gap = 2;
   return new Node({
     children: [
-      new Line(cx - gap / 2 - stubLen, cy, cx - gap / 2, cy, { stroke: c, lineWidth: 1.5 }),
-      new Line(cx + gap / 2, cy, cx + gap / 2 + stubLen, cy, { stroke: c, lineWidth: 1.5 }),
+      new Line(cx - gap / 2 - stubLen, cy, cx - gap / 2, cy, { stroke: c, lineWidth: HANDLE_LINE_WIDTH }),
+      new Line(cx + gap / 2, cy, cx + gap / 2 + stubLen, cy, { stroke: c, lineWidth: HANDLE_LINE_WIDTH }),
     ],
   });
 }
diff --git a/src/common/view/detectors/DetectorChartPanel.ts b/src/common/view/detectors/DetectorChartPanel.ts
index 52cf4d1..7101582 100644
--- a/src/common/view/detectors/DetectorChartPanel.ts
+++ b/src/common/view/detectors/DetectorChartPanel.ts
@@ -28,9 +28,11 @@ import OpticsLabColors from "../../../OpticsLabColors.js";
 import {
   DETECTOR_CHART_HEIGHT,
   DETECTOR_CHART_WIDTH,
+  DETECTOR_CHART_Y_HEADROOM,
   DETECTOR_NUM_BINS,
   FONT_9PX,
   FONT_BOLD_9PX,
+  HANDLE_LINE_WIDTH,
   PANEL_CORNER_RADIUS,
   PANEL_X_MARGIN,
   PANEL_Y_MARGIN,
@@ -123,7 +125,7 @@ export class DetectorChartPanel extends Panel {
     // Reference tick marks crossing the bottom border of the chart
     const chartTicksPath = new Path(buildChartTicksShape(chartTransform), {
       stroke: OpticsLabColors.detectorTickStrokeProperty,
-      lineWidth: 1.5,
+      lineWidth: HANDLE_LINE_WIDTH,
       lineCap: "round",
       pickable: false,
     });
@@ -267,7 +269,7 @@ export class DetectorChartPanel extends Panel {
         }
       }
     }
-    this.chartTransform.modelYRange = new Range(0, maxVal * 1.25);
+    this.chartTransform.modelYRange = new Range(0, maxVal * DETECTOR_CHART_Y_HEADROOM);
 
     // Update live bars
     const liveData = liveBins.map((v, i) => new Vector2((i + 0.5) / numBins, v));
diff --git a/src/common/view/detectors/DetectorView.ts b/src/common/view/detectors/DetectorView.ts
index 3c65b54..7e6241d 100644
--- a/src/common/view/detectors/DetectorView.ts
+++ b/src/common/view/detectors/DetectorView.ts
@@ -29,7 +29,9 @@ import OpticsLabColors from "../../../OpticsLabColors.js";
 import {
   ARC_MIRROR_SAMPLE_COUNT,
   DETECTOR_INITIAL_CHART_OFFSET_X,
+  DETECTOR_INITIAL_CHART_OFFSET_Y,
   DETECTOR_WIRE_NORMAL_MAGNITUDE,
+  HANDLE_LINE_WIDTH,
   LINE_HIT_HALF_WIDTH_PX,
   MIRROR_BACK_WIDTH,
   MIRROR_FRONT_WIDTH,
@@ -50,8 +52,6 @@ import {
 import type { ViewOptionsModel } from "../ViewOptionsModel.js";
 import { DetectorChartPanel } from "./DetectorChartPanel.js";
 
-const INITIAL_CHART_OFFSET_Y = 10;
-
 export class DetectorView extends BaseOpticalElementView {
   public readonly bodyDragListener: RichDragListenerType;
   private readonly backPath: Path;
@@ -64,7 +64,7 @@ export class DetectorView extends BaseOpticalElementView {
   private readonly chartPanel: DetectorChartPanel;
 
   /** View-space offset of the chart center from the detector midpoint. */
-  private chartOffset = new Vector2(DETECTOR_INITIAL_CHART_OFFSET_X, INITIAL_CHART_OFFSET_Y);
+  private chartOffset = new Vector2(DETECTOR_INITIAL_CHART_OFFSET_X, DETECTOR_INITIAL_CHART_OFFSET_Y);
 
   // Properties driving the WireNode (updated imperatively in rebuild / chart drag).
   // Initialized with separated positions to avoid zero-length cubic bezier crash.
@@ -101,7 +101,7 @@ export class DetectorView extends BaseOpticalElementView {
     });
     this.ticksPath = new Path(null, {
       stroke: OpticsLabColors.detectorTickStrokeProperty,
-      lineWidth: 1.5,
+      lineWidth: HANDLE_LINE_WIDTH,
       lineCap: "round",
       pickable: false,
     });
diff --git a/src/common/view/edit-controls/EditControlHelpers.ts b/src/common/view/edit-controls/EditControlHelpers.ts
index 7306278..08b4a39 100644
--- a/src/common/view/edit-controls/EditControlHelpers.ts
+++ b/src/common/view/edit-controls/EditControlHelpers.ts
@@ -14,6 +14,9 @@ import type { Tandem } from "scenerystack/tandem";
 import { StringManager } from "../../../i18n/StringManager.js";
 import OpticsLabColors from "../../../OpticsLabColors.js";
 import {
+  ELEMENT_ANGLE_MAX_DEG,
+  ELEMENT_ANGLE_MIN_DEG,
+  FONT_11PX,
   SEGMENT_LENGTH_MAX,
   SEGMENT_LENGTH_MIN,
   SLIDER_THUMB_HEIGHT,
@@ -31,7 +34,7 @@ export type { EditControlsResult } from "./EditControlsResult.js";
 
 export const SLIDER_TRACK_SIZE = new Dimension2(SLIDER_TRACK_WIDTH, SLIDER_TRACK_HEIGHT);
 export const SLIDER_THUMB_SIZE = new Dimension2(SLIDER_THUMB_WIDTH, SLIDER_THUMB_HEIGHT);
-export const LABEL_FONT = "11px sans-serif";
+export const LABEL_FONT = FONT_11PX;
 
 // ── Private widget helpers ────────────────────────────────────────────────────
 
@@ -282,7 +285,7 @@ export function buildSegmentAngleControl(
   triggerRebuild: () => void,
   tandem: Tandem,
 ): { control: Node; refresh: () => void } {
-  const A_RANGE = new Range(0, 360);
+  const A_RANGE = new Range(ELEMENT_ANGLE_MIN_DEG, ELEMENT_ANGLE_MAX_DEG);
   const angleProp = new NumberProperty(segmentAngleDeg(element.p1, element.p2), {
     range: A_RANGE,
     tandem: tandem.createTandem("numberProperty"),
@@ -342,7 +345,7 @@ export function buildDirectionAngleAboutP1Control(
   triggerRebuild: () => void,
   tandem: Tandem,
 ): { control: Node; refresh: () => void } {
-  const A_RANGE = new Range(0, 360);
+  const A_RANGE = new Range(ELEMENT_ANGLE_MIN_DEG, ELEMENT_ANGLE_MAX_DEG);
   const angleProp = new NumberProperty(segmentAngleDeg(element.p1, element.p2), {
     range: A_RANGE,
     tandem: tandem.createTandem("numberProperty"),
@@ -411,7 +414,7 @@ export function buildDirectionAngleControl(
   triggerRebuild: () => void,
   tandem: Tandem,
 ): { control: Node; refresh: () => void } {
-  const A_RANGE = new Range(0, 360);
+  const A_RANGE = new Range(ELEMENT_ANGLE_MIN_DEG, ELEMENT_ANGLE_MAX_DEG);
   const angleProp = new NumberProperty(radiansToDisplayDeg(getDirectionRadians()), {
     range: A_RANGE,
     tandem: tandem.createTandem("numberProperty"),
diff --git a/src/common/view/edit-controls/GlassEditControls.ts b/src/common/view/edit-controls/GlassEditControls.ts
index ee5cc52..55dd47b 100644
--- a/src/common/view/edit-controls/GlassEditControls.ts
+++ b/src/common/view/edit-controls/GlassEditControls.ts
@@ -16,8 +16,19 @@ import {
   CONSTRAINED_CURVATURE_MAX,
   CONSTRAINED_CURVATURE_MIN,
   CONSTRAINED_LENS_RADIUS_MIN,
+  DIMENSIONAL_GLASS_HEIGHT_MAX_M,
+  DIMENSIONAL_GLASS_HEIGHT_MIN_M,
+  DIMENSIONAL_GLASS_SIZE_DELTA,
+  DIMENSIONAL_GLASS_WIDTH_MAX_M,
+  DIMENSIONAL_GLASS_WIDTH_MIN_M,
+  ELEMENT_ANGLE_MAX_DEG,
+  ELEMENT_ANGLE_MIN_DEG,
   FOCAL_LENGTH_MAX_M,
   FOCAL_LENGTH_MIN_M,
+  PRISM_SIZE_DELTA,
+  PRISM_SIZE_MAX_M,
+  PRISM_SIZE_MIN_M,
+  REFRACTIVE_INDEX_DELTA,
   REFRACTIVE_INDEX_MAX,
   REFRACTIVE_INDEX_MIN,
   SEGMENT_LENGTH_MAX,
@@ -108,7 +119,7 @@ function buildSphericalLensAngleControl(
   triggerRebuild: () => void,
 ): { control: NumberControl; refresh: () => void } {
   const controlStrings = StringManager.getInstance().getControlStrings();
-  const A_RANGE = new Range(0, 360);
+  const A_RANGE = new Range(ELEMENT_ANGLE_MIN_DEG, ELEMENT_ANGLE_MAX_DEG);
   let prevAngleDeg = segmentAngleDeg(element.p1, element.p2);
   const angleProp = new NumberProperty(prevAngleDeg, { range: A_RANGE, tandem: Tandem.OPTIONAL });
   let angleDriving = false;
@@ -149,7 +160,7 @@ function buildGlassPrismAngleControl(
   triggerRebuild: () => void,
 ): { control: NumberControl; refresh: () => void } {
   const controlStrings = StringManager.getInstance().getControlStrings();
-  const A_RANGE = new Range(0, 360);
+  const A_RANGE = new Range(ELEMENT_ANGLE_MIN_DEG, ELEMENT_ANGLE_MAX_DEG);
   let prevAngleDeg = prismPathAngleDeg(path);
   const angleProp = new NumberProperty(prevAngleDeg, { range: A_RANGE, tandem: Tandem.OPTIONAL });
   let angleDriving = false;
@@ -187,7 +198,7 @@ function buildDimensionalGlassAngleControl(
   triggerRebuild: () => void,
 ): { control: NumberControl; refresh: () => void } {
   const controlStrings = StringManager.getInstance().getControlStrings();
-  const A_RANGE = new Range(0, 360);
+  const A_RANGE = new Range(ELEMENT_ANGLE_MIN_DEG, ELEMENT_ANGLE_MAX_DEG);
   const initDeg = (((element.rotation * (180 / Math.PI)) % 360) + 360) % 360;
   const angleProp = new NumberProperty(initDeg, { range: A_RANGE, tandem: Tandem.OPTIONAL });
   let angleDriving = false;
@@ -412,7 +423,7 @@ export function buildSphericalLensControls(
         controlStrings.refractiveIndexStringProperty,
         element.refIndex,
         new Range(REFRACTIVE_INDEX_MIN, REFRACTIVE_INDEX_MAX),
-        0.05,
+        REFRACTIVE_INDEX_DELTA,
         (v) => {
           element.refIndex = v;
         },
@@ -578,7 +589,7 @@ export function buildSymmetricLensControls(
         controlStrings.refractiveIndexStringProperty,
         element.refIndex,
         new Range(REFRACTIVE_INDEX_MIN, REFRACTIVE_INDEX_MAX),
-        0.05,
+        REFRACTIVE_INDEX_DELTA,
         (v) => {
           element.refIndex = v;
         },
@@ -744,7 +755,7 @@ export function buildPlanoLensControls(
         controlStrings.refractiveIndexStringProperty,
         element.refIndex,
         new Range(REFRACTIVE_INDEX_MIN, REFRACTIVE_INDEX_MAX),
-        0.05,
+        REFRACTIVE_INDEX_DELTA,
         (v) => {
           element.refIndex = v;
         },
@@ -814,7 +825,7 @@ export function buildHalfPlaneGlassControls(element: HalfPlaneGlass, triggerRebu
         controlStrings.refractiveIndexStringProperty,
         element.refIndex,
         new Range(REFRACTIVE_INDEX_MIN, REFRACTIVE_INDEX_MAX),
-        0.05,
+        REFRACTIVE_INDEX_DELTA,
         (v) => {
           element.refIndex = v;
         },
@@ -840,7 +851,7 @@ export function buildRefractiveIndexControls(element: BaseGlass, triggerRebuild:
         controlStrings.refractiveIndexStringProperty,
         element.refIndex,
         new Range(REFRACTIVE_INDEX_MIN, REFRACTIVE_INDEX_MAX),
-        0.05,
+        REFRACTIVE_INDEX_DELTA,
         (v) => {
           element.refIndex = v;
         },
@@ -863,8 +874,8 @@ export function buildEquilateralPrismControls(
       makeControl(
         controlStrings.sizeStringProperty,
         element.size,
-        new Range(0.1, 2.0),
-        0.05,
+        new Range(PRISM_SIZE_MIN_M, PRISM_SIZE_MAX_M),
+        PRISM_SIZE_DELTA,
         (v) => {
           element.setSize(v);
         },
@@ -876,7 +887,7 @@ export function buildEquilateralPrismControls(
         controlStrings.refractiveIndexStringProperty,
         element.refIndex,
         new Range(REFRACTIVE_INDEX_MIN, REFRACTIVE_INDEX_MAX),
-        0.05,
+        REFRACTIVE_INDEX_DELTA,
         (v) => {
           element.refIndex = v;
         },
@@ -896,8 +907,8 @@ export function buildRightAnglePrismControls(element: RightAnglePrism, triggerRe
       makeControl(
         controlStrings.legLengthStringProperty,
         element.legLength,
-        new Range(0.1, 2.0),
-        0.05,
+        new Range(PRISM_SIZE_MIN_M, PRISM_SIZE_MAX_M),
+        PRISM_SIZE_DELTA,
         (v) => {
           element.setLegLength(v);
         },
@@ -909,7 +920,7 @@ export function buildRightAnglePrismControls(element: RightAnglePrism, triggerRe
         controlStrings.refractiveIndexStringProperty,
         element.refIndex,
         new Range(REFRACTIVE_INDEX_MIN, REFRACTIVE_INDEX_MAX),
-        0.05,
+        REFRACTIVE_INDEX_DELTA,
         (v) => {
           element.refIndex = v;
         },
@@ -929,8 +940,8 @@ export function buildPorroPrismControls(element: PorroPrism, triggerRebuild: ()
       makeControl(
         controlStrings.legLengthStringProperty,
         element.legLength,
-        new Range(0.1, 2.0),
-        0.05,
+        new Range(PRISM_SIZE_MIN_M, PRISM_SIZE_MAX_M),
+        PRISM_SIZE_DELTA,
         (v) => {
           element.setLegLength(v);
         },
@@ -942,7 +953,7 @@ export function buildPorroPrismControls(element: PorroPrism, triggerRebuild: ()
         controlStrings.refractiveIndexStringProperty,
         element.refIndex,
         new Range(REFRACTIVE_INDEX_MIN, REFRACTIVE_INDEX_MAX),
-        0.05,
+        REFRACTIVE_INDEX_DELTA,
         (v) => {
           element.refIndex = v;
         },
@@ -962,8 +973,8 @@ export function buildSlabGlassControls(element: SlabGlass, triggerRebuild: () =>
       makeControl(
         controlStrings.widthStringProperty,
         element.width,
-        new Range(0.1, 3.0),
-        0.05,
+        new Range(DIMENSIONAL_GLASS_WIDTH_MIN_M, DIMENSIONAL_GLASS_WIDTH_MAX_M),
+        DIMENSIONAL_GLASS_SIZE_DELTA,
         (v) => {
           element.setWidth(v);
         },
@@ -973,8 +984,8 @@ export function buildSlabGlassControls(element: SlabGlass, triggerRebuild: () =>
       makeControl(
         controlStrings.heightStringProperty,
         element.height,
-        new Range(0.1, 2.0),
-        0.05,
+        new Range(DIMENSIONAL_GLASS_HEIGHT_MIN_M, DIMENSIONAL_GLASS_HEIGHT_MAX_M),
+        DIMENSIONAL_GLASS_SIZE_DELTA,
         (v) => {
           element.setHeight(v);
         },
@@ -986,7 +997,7 @@ export function buildSlabGlassControls(element: SlabGlass, triggerRebuild: () =>
         controlStrings.refractiveIndexStringProperty,
         element.refIndex,
         new Range(REFRACTIVE_INDEX_MIN, REFRACTIVE_INDEX_MAX),
-        0.05,
+        REFRACTIVE_INDEX_DELTA,
         (v) => {
           element.refIndex = v;
         },
@@ -1009,8 +1020,8 @@ export function buildParallelogramPrismControls(
       makeControl(
         controlStrings.widthStringProperty,
         element.width,
-        new Range(0.1, 3.0),
-        0.05,
+        new Range(DIMENSIONAL_GLASS_WIDTH_MIN_M, DIMENSIONAL_GLASS_WIDTH_MAX_M),
+        DIMENSIONAL_GLASS_SIZE_DELTA,
         (v) => {
           element.setWidth(v);
         },
@@ -1020,8 +1031,8 @@ export function buildParallelogramPrismControls(
       makeControl(
         controlStrings.heightStringProperty,
         element.height,
-        new Range(0.1, 2.0),
-        0.05,
+        new Range(DIMENSIONAL_GLASS_HEIGHT_MIN_M, DIMENSIONAL_GLASS_HEIGHT_MAX_M),
+        DIMENSIONAL_GLASS_SIZE_DELTA,
         (v) => {
           element.setHeight(v);
         },
@@ -1033,7 +1044,7 @@ export function buildParallelogramPrismControls(
         controlStrings.refractiveIndexStringProperty,
         element.refIndex,
         new Range(REFRACTIVE_INDEX_MIN, REFRACTIVE_INDEX_MAX),
-        0.05,
+        REFRACTIVE_INDEX_DELTA,
         (v) => {
           element.refIndex = v;
         },
@@ -1053,8 +1064,8 @@ export function buildDovePrismControls(element: DovePrism, triggerRebuild: () =>
       makeControl(
         controlStrings.widthStringProperty,
         element.width,
-        new Range(0.1, 3.0),
-        0.05,
+        new Range(DIMENSIONAL_GLASS_WIDTH_MIN_M, DIMENSIONAL_GLASS_WIDTH_MAX_M),
+        DIMENSIONAL_GLASS_SIZE_DELTA,
         (v) => {
           element.setWidth(v);
         },
@@ -1064,8 +1075,8 @@ export function buildDovePrismControls(element: DovePrism, triggerRebuild: () =>
       makeControl(
         controlStrings.heightStringProperty,
         element.height,
-        new Range(0.1, 2.0),
-        0.05,
+        new Range(DIMENSIONAL_GLASS_HEIGHT_MIN_M, DIMENSIONAL_GLASS_HEIGHT_MAX_M),
+        DIMENSIONAL_GLASS_SIZE_DELTA,
         (v) => {
           element.setHeight(v);
         },
@@ -1077,7 +1088,7 @@ export function buildDovePrismControls(element: DovePrism, triggerRebuild: () =>
         controlStrings.refractiveIndexStringProperty,
         element.refIndex,
         new Range(REFRACTIVE_INDEX_MIN, REFRACTIVE_INDEX_MAX),
-        0.05,
+        REFRACTIVE_INDEX_DELTA,
         (v) => {
           element.refIndex = v;
         },
diff --git a/src/common/view/edit-controls/LightSourceEditControls.ts b/src/common/view/edit-controls/LightSourceEditControls.ts
index 47ffb7f..893e542 100644
--- a/src/common/view/edit-controls/LightSourceEditControls.ts
+++ b/src/common/view/edit-controls/LightSourceEditControls.ts
@@ -9,6 +9,7 @@ import { Range } from "scenerystack/dot";
 import { Tandem } from "scenerystack/tandem";
 import { StringManager } from "../../../i18n/StringManager.js";
 import {
+  BRIGHTNESS_CONTROL_DELTA,
   BRIGHTNESS_MAX,
   BRIGHTNESS_MIN,
   DIVERGENCE_MAX_DEG,
@@ -51,7 +52,7 @@ export function buildArcLightSourceControls(element: ArcLightSource, triggerRebu
         controlStrings.brightnessStringProperty,
         element.brightness,
         new Range(BRIGHTNESS_MIN, BRIGHTNESS_MAX),
-        0.05,
+        BRIGHTNESS_CONTROL_DELTA,
         (v) => {
           element.brightness = v;
         },
@@ -92,7 +93,7 @@ export function buildPointSourceControls(element: PointSourceElement, triggerReb
         controlStrings.brightnessStringProperty,
         element.brightness,
         new Range(BRIGHTNESS_MIN, BRIGHTNESS_MAX),
-        0.05,
+        BRIGHTNESS_CONTROL_DELTA,
         (v) => {
           element.brightness = v;
         },
@@ -137,7 +138,7 @@ export function buildBeamSourceControls(element: BeamSource, triggerRebuild: ()
         controlStrings.brightnessStringProperty,
         element.brightness,
         new Range(BRIGHTNESS_MIN, BRIGHTNESS_MAX),
-        0.05,
+        BRIGHTNESS_CONTROL_DELTA,
         (v) => {
           element.brightness = v;
         },
@@ -184,7 +185,7 @@ export function buildDivergentBeamControls(element: DivergentBeam, triggerRebuil
         controlStrings.brightnessStringProperty,
         element.brightness,
         new Range(BRIGHTNESS_MIN, BRIGHTNESS_MAX),
-        0.05,
+        BRIGHTNESS_CONTROL_DELTA,
         (v) => {
           element.brightness = v;
         },
@@ -232,7 +233,7 @@ export function buildSingleRaySourceControls(element: SingleRaySource, triggerRe
         controlStrings.brightnessStringProperty,
         element.brightness,
         new Range(BRIGHTNESS_MIN, BRIGHTNESS_MAX),
-        0.05,
+        BRIGHTNESS_CONTROL_DELTA,
         (v) => {
           element.brightness = v;
         },
@@ -271,7 +272,7 @@ export function buildContinuousSpectrumSourceControls(
         controlStrings.brightnessStringProperty,
         element.brightness,
         new Range(BRIGHTNESS_MIN, BRIGHTNESS_MAX),
-        0.05,
+        BRIGHTNESS_CONTROL_DELTA,
         (v) => {
           element.brightness = v;
         },
diff --git a/src/common/view/edit-controls/MirrorEditControls.ts b/src/common/view/edit-controls/MirrorEditControls.ts
index 3a3fafd..1bc3023 100644
--- a/src/common/view/edit-controls/MirrorEditControls.ts
+++ b/src/common/view/edit-controls/MirrorEditControls.ts
@@ -17,13 +17,27 @@ import {
   ARC_MIRROR_CURVATURE_MIN,
   ARC_MIRROR_RADIUS_MAX,
   ARC_MIRROR_RADIUS_MIN,
+  BEAM_SPLITTER_TRANSMIT_DELTA,
+  BEAM_SPLITTER_TRANSMIT_MAX,
+  BEAM_SPLITTER_TRANSMIT_MIN,
   DETECTOR_BINS_MAX,
   DETECTOR_BINS_MIN,
+  ELEMENT_ANGLE_MAX_DEG,
+  ELEMENT_ANGLE_MIN_DEG,
+  FIBER_CORE_FRACTION_DELTA,
+  FIBER_CORE_FRACTION_MAX,
+  FIBER_CORE_FRACTION_MIN,
   FIBER_OPTIC_OUTER_RADIUS_MAX_M,
   FIBER_OPTIC_OUTER_RADIUS_MIN_M,
   FOCAL_LENGTH_MAX_M,
   FOCAL_LENGTH_MIN_M,
+  GRATING_DUTY_CYCLE_DELTA,
+  GRATING_DUTY_CYCLE_MAX,
+  GRATING_DUTY_CYCLE_MIN,
+  GRATING_LINES_DENSITY_MAX,
+  GRATING_LINES_DENSITY_MIN,
   LINES_DENSITY_CONTROL_DELTA,
+  REFRACTIVE_INDEX_DELTA,
   REFRACTIVE_INDEX_MAX,
   REFRACTIVE_INDEX_MIN,
 } from "../../../OpticsLabConstants.js";
@@ -321,7 +335,7 @@ export function buildSegmentControls(
 
 export function buildApertureControls(element: ApertureElement, triggerRebuild: () => void): EditControlsResult {
   const controlStrings = StringManager.getInstance().getControlStrings();
-  const A_RANGE = new Range(0, 360);
+  const A_RANGE = new Range(ELEMENT_ANGLE_MIN_DEG, ELEMENT_ANGLE_MAX_DEG);
 
   // Build an angle control that rotates the aperture (p1/p2) while preserving
   // the fractional positions of the gap endpoints (p3/p4) along the line.
@@ -383,7 +397,7 @@ export function buildGratingControls(
       makeControl(
         controlStrings.linesDensityStringProperty,
         element.linesDensity,
-        new Range(1, 2500),
+        new Range(GRATING_LINES_DENSITY_MIN, GRATING_LINES_DENSITY_MAX),
         LINES_DENSITY_CONTROL_DELTA,
         (v) => {
           element.linesDensity = v;
@@ -394,8 +408,8 @@ export function buildGratingControls(
       makeControl(
         controlStrings.dutyCycleStringProperty,
         element.dutyCycle,
-        new Range(0.01, 0.99),
-        0.01,
+        new Range(GRATING_DUTY_CYCLE_MIN, GRATING_DUTY_CYCLE_MAX),
+        GRATING_DUTY_CYCLE_DELTA,
         (v) => {
           element.dutyCycle = v;
         },
@@ -418,8 +432,8 @@ export function buildBeamSplitterControls(
       makeControl(
         controlStrings.transmissionRatioStringProperty,
         element.transRatio,
-        new Range(0, 1),
-        0.05,
+        new Range(BEAM_SPLITTER_TRANSMIT_MIN, BEAM_SPLITTER_TRANSMIT_MAX),
+        BEAM_SPLITTER_TRANSMIT_DELTA,
         (v) => {
           element.transRatio = v;
         },
@@ -449,7 +463,7 @@ export function buildFiberOpticControls(element: FiberOpticElement, triggerRebui
     controlStrings.claddingRefractiveIndexStringProperty,
     element.refIndex,
     new Range(REFRACTIVE_INDEX_MIN, REFRACTIVE_INDEX_MAX),
-    0.05,
+    REFRACTIVE_INDEX_DELTA,
     (v) => {
       element.refIndex = v;
     },
@@ -460,7 +474,7 @@ export function buildFiberOpticControls(element: FiberOpticElement, triggerRebui
     controlStrings.coreRefractiveIndexStringProperty,
     element.coreRefIndex,
     new Range(REFRACTIVE_INDEX_MIN, REFRACTIVE_INDEX_MAX),
-    0.05,
+    REFRACTIVE_INDEX_DELTA,
     (v) => {
       element.coreRefIndex = v;
     },
@@ -470,8 +484,8 @@ export function buildFiberOpticControls(element: FiberOpticElement, triggerRebui
   const coreFractionControl = makeControl(
     controlStrings.coreFractionStringProperty,
     element.coreRadiusFraction,
-    new Range(0.05, 0.95),
-    0.05,
+    new Range(FIBER_CORE_FRACTION_MIN, FIBER_CORE_FRACTION_MAX),
+    FIBER_CORE_FRACTION_DELTA,
     (v) => {
       element.coreRadiusFraction = v;
     },
diff --git a/src/common/view/glass/GlassView.ts b/src/common/view/glass/GlassView.ts
index ad90ce0..f7b62d9 100644
--- a/src/common/view/glass/GlassView.ts
+++ b/src/common/view/glass/GlassView.ts
@@ -19,6 +19,7 @@ import { Tandem } from "scenerystack/tandem";
 import OpticsLabColors, { glassFill } from "../../../OpticsLabColors.js";
 import {
   GLASS_STROKE_WIDTH,
+  HANDLE_LINE_WIDTH,
   HANDLE_RADIUS,
   PRISM_EDGE_ADD_RADIUS,
   PRISM_VERTEX_REMOVE_RADIUS,
@@ -204,9 +205,9 @@ export class GlassView extends BaseOpticalElementView {
         new Circle(PRISM_EDGE_ADD_RADIUS, {
           fill: OpticsLabColors.prismAddFillProperty,
           stroke: OpticsLabColors.prismAddStrokeProperty,
-          lineWidth: 1.5,
+          lineWidth: HANDLE_LINE_WIDTH,
         }),
-        new Path(plusShape, { stroke: OpticsLabColors.prismAddStrokeProperty, lineWidth: 1.5 }),
+        new Path(plusShape, { stroke: OpticsLabColors.prismAddStrokeProperty, lineWidth: HANDLE_LINE_WIDTH }),
       ],
     });
 
@@ -266,9 +267,9 @@ export class GlassView extends BaseOpticalElementView {
         new Circle(PRISM_VERTEX_REMOVE_RADIUS, {
           fill: OpticsLabColors.prismRemoveFillProperty,
           stroke: OpticsLabColors.prismRemoveStrokeProperty,
-          lineWidth: 1.5,
+          lineWidth: HANDLE_LINE_WIDTH,
         }),
-        new Path(xShape, { stroke: OpticsLabColors.prismRemoveStrokeProperty, lineWidth: 1.5 }),
+        new Path(xShape, { stroke: OpticsLabColors.prismRemoveStrokeProperty, lineWidth: HANDLE_LINE_WIDTH }),
       ],
     });
 
diff --git a/src/common/view/glass/PlanoLensView.ts b/src/common/view/glass/PlanoLensView.ts
index b22ffc0..a8ccaa6 100644
--- a/src/common/view/glass/PlanoLensView.ts
+++ b/src/common/view/glass/PlanoLensView.ts
@@ -13,14 +13,15 @@
 
 import type { ModelViewTransform2 } from "scenerystack/phetcommon";
 import { Tandem } from "scenerystack/tandem";
+import { LENS_APEX_MIN_OFFSET_M } from "../../../OpticsLabConstants.js";
 import OpticsLabNamespace from "../../../OpticsLabNamespace.js";
+
 import type { GlassPathPoint } from "../../model/glass/Glass.js";
 import type { SphericalLens } from "../../model/glass/SphericalLens.js";
 import type { ViewOptionsModel } from "../ViewOptionsModel.js";
 import { SphericalLensView } from "./SphericalLensView.js";
 
 /** Minimum distance (model units) the apex must sit past the corner midpoint. */
-const APEX_MIN_OFFSET = 0.02;
 
 export class PlanoLensView extends SphericalLensView {
   /**
@@ -28,7 +29,7 @@ export class PlanoLensView extends SphericalLensView {
    * along the optical axis:
    *   −1 for PlanoConvexLens  (r2 < 0, apex on +dp side → relProj > 0, reqSign = −r2Sign = +1)
    *   +1 for PlanoConcaveLens (r2 > 0, apex on −dp side → relProj < 0, reqSign = −r2Sign = −1)
-   * Stored as −r2Sign so the clamp condition is simply relProj * apexReqSign >= APEX_MIN_OFFSET.
+   * Stored as −r2Sign so the clamp condition is simply relProj * apexReqSign >= LENS_APEX_MIN_OFFSET_M.
    */
   private readonly apexReqSign: 1 | -1;
 
@@ -86,10 +87,10 @@ export class PlanoLensView extends SphericalLensView {
     const midY = (v1.y + v3.y) / 2;
     const relProj = (v2.x - midX) * dpx + (v2.y - midY) * dpy;
 
-    if (relProj * this.apexReqSign < APEX_MIN_OFFSET) {
+    if (relProj * this.apexReqSign < LENS_APEX_MIN_OFFSET_M) {
       // Apex has crossed to the wrong side (or is too close to flat) — snap back.
-      v2.x = midX + APEX_MIN_OFFSET * this.apexReqSign * dpx;
-      v2.y = midY + APEX_MIN_OFFSET * this.apexReqSign * dpy;
+      v2.x = midX + LENS_APEX_MIN_OFFSET_M * this.apexReqSign * dpx;
+      v2.y = midY + LENS_APEX_MIN_OFFSET_M * this.apexReqSign * dpy;
     }
 
     this.rebuild();
diff --git a/src/common/view/glass/SymmetricLensView.ts b/src/common/view/glass/SymmetricLensView.ts
index ff24467..2ec48cd 100644
--- a/src/common/view/glass/SymmetricLensView.ts
+++ b/src/common/view/glass/SymmetricLensView.ts
@@ -19,14 +19,15 @@
 
 import type { ModelViewTransform2 } from "scenerystack/phetcommon";
 import { Tandem } from "scenerystack/tandem";
+import { LENS_APEX_MIN_OFFSET_M } from "../../../OpticsLabConstants.js";
 import OpticsLabNamespace from "../../../OpticsLabNamespace.js";
+
 import type { GlassPathPoint } from "../../model/glass/Glass.js";
 import type { SphericalLens } from "../../model/glass/SphericalLens.js";
 import type { ViewOptionsModel } from "../ViewOptionsModel.js";
 import { SphericalLensView } from "./SphericalLensView.js";
 
 /** Minimum distance (model units) the apex must sit past the corner midpoint. */
-const APEX_MIN_OFFSET = 0.02;
 
 export class SymmetricLensView extends SphericalLensView {
   /** +1 for BiconvexLens (r1 > 0), −1 for BiconcaveLens (r1 < 0). */
@@ -78,9 +79,9 @@ export class SymmetricLensView extends SphericalLensView {
       const midY = (v0.y + v4.y) / 2;
       const relProj = (v5.x - midX) * dpx + (v5.y - midY) * dpy;
       const reqSign = (this.rSign === 1 ? -1 : 1) as 1 | -1; // −rSign
-      if (relProj * reqSign < APEX_MIN_OFFSET) {
-        v5.x = midX + APEX_MIN_OFFSET * reqSign * dpx;
-        v5.y = midY + APEX_MIN_OFFSET * reqSign * dpy;
+      if (relProj * reqSign < LENS_APEX_MIN_OFFSET_M) {
+        v5.x = midX + LENS_APEX_MIN_OFFSET_M * reqSign * dpx;
+        v5.y = midY + LENS_APEX_MIN_OFFSET_M * reqSign * dpy;
       }
       // Re-derive r1 from the (now-clamped) apex and mirror to r2.
       const { r1 } = this.lens.getDR1R2();
@@ -100,9 +101,9 @@ export class SymmetricLensView extends SphericalLensView {
       const midY = (v1.y + v3.y) / 2;
       const relProj = (v2.x - midX) * dpx + (v2.y - midY) * dpy;
       const reqSign = this.rSign; // +rSign
-      if (relProj * reqSign < APEX_MIN_OFFSET) {
-        v2.x = midX + APEX_MIN_OFFSET * reqSign * dpx;
-        v2.y = midY + APEX_MIN_OFFSET * reqSign * dpy;
+      if (relProj * reqSign < LENS_APEX_MIN_OFFSET_M) {
+        v2.x = midX + LENS_APEX_MIN_OFFSET_M * reqSign * dpx;
+        v2.y = midY + LENS_APEX_MIN_OFFSET_M * reqSign * dpy;
       }
       // Re-derive r2 from the (now-clamped) apex and mirror to r1.
       const { r2 } = this.lens.getDR1R2();
diff --git a/src/common/view/guides/TrackView.ts b/src/common/view/guides/TrackView.ts
index a8e1ac7..ea4b307 100644
--- a/src/common/view/guides/TrackView.ts
+++ b/src/common/view/guides/TrackView.ts
@@ -11,6 +11,8 @@ import type { ModelViewTransform2 } from "scenerystack/phetcommon";
 import { Path, type RichDragListener } from "scenerystack/scenery";
 import type { Tandem } from "scenerystack/tandem";
 import OpticsLabColors from "../../../OpticsLabColors.js";
+import { TRACK_LINE_DASH, TRACK_LINE_WIDTH } from "../../../OpticsLabConstants.js";
+
 import OpticsLabNamespace from "../../../OpticsLabNamespace.js";
 import type { TrackElement } from "../../model/guides/TrackElement.js";
 import { BaseOpticalElementView } from "../BaseOpticalElementView.js";
@@ -24,9 +26,6 @@ import {
 } from "../ViewHelpers.js";
 import type { ViewOptionsModel } from "../ViewOptionsModel.js";
 
-const TRACK_LINE_WIDTH = 2;
-const TRACK_LINE_DASH = [8, 4];
-
 export class TrackView extends BaseOpticalElementView {
   public readonly bodyDragListener: RichDragListener;
   private readonly trackPath: Path;
diff --git a/src/common/view/mirrors/AperturedParabolicMirrorView.ts b/src/common/view/mirrors/AperturedParabolicMirrorView.ts
index f327c95..039f220 100644
--- a/src/common/view/mirrors/AperturedParabolicMirrorView.ts
+++ b/src/common/view/mirrors/AperturedParabolicMirrorView.ts
@@ -14,6 +14,7 @@ import { type Circle, Path, type RichDragListener } from "scenerystack/scenery";
 import type { Tandem } from "scenerystack/tandem";
 import OpticsLabColors from "../../../OpticsLabColors.js";
 import {
+  APERTURED_MIRROR_MAX_APERTURE_FRACTION,
   LINE_HIT_HALF_WIDTH_PX,
   MIRROR_BACK_WIDTH,
   MIRROR_FOCAL_MARKER_SIZE_M,
@@ -246,7 +247,10 @@ export class AperturedParabolicMirrorView extends BaseOpticalElementView {
 
     const chordLen = distance(p1, p2);
     const halfAperture = chordLen / 2;
-    const effectiveHalfWidth = Math.min(this.mirror.apertureHalfWidth, halfAperture * 0.99);
+    const effectiveHalfWidth = Math.min(
+      this.mirror.apertureHalfWidth,
+      halfAperture * APERTURED_MIRROR_MAX_APERTURE_FRACTION,
+    );
 
     const allPoints = this.mirror.computePoints();
 
diff --git a/src/preferences/opticsLabQueryParameters.ts b/src/preferences/opticsLabQueryParameters.ts
index 55dc536..42ada7a 100644
--- a/src/preferences/opticsLabQueryParameters.ts
+++ b/src/preferences/opticsLabQueryParameters.ts
@@ -6,12 +6,17 @@ import { logGlobal } from "scenerystack/phet-core";
 import { QueryStringMachine } from "scenerystack/query-string-machine";
 import {
   DEFAULT_RAY_DENSITY,
+  GRID_SPACING_M,
   GRID_SPACING_MAX_M,
   GRID_SPACING_MIN_M,
   MAX_RAY_DEPTH_PROPERTY_MAX,
   MAX_RAY_DEPTH_PROPERTY_MIN,
+  QUERY_DEFAULT_MAX_RAY_DEPTH,
   RAY_DENSITY_MAX,
   RAY_DENSITY_MIN,
+  RAY_STUB_LENGTH_DEFAULT_PX,
+  RAY_STUB_LENGTH_MAX_PX,
+  RAY_STUB_LENGTH_MIN_PX,
 } from "../OpticsLabConstants.js";
 import OpticsLabNamespace from "../OpticsLabNamespace.js";
 
@@ -31,7 +36,7 @@ const opticsLabQueryParameters = QueryStringMachine.getAll({
    */
   maximumLightRayDepth: {
     type: "number" as const,
-    defaultValue: 50,
+    defaultValue: QUERY_DEFAULT_MAX_RAY_DEPTH,
     public: true,
     isValidValue: (value: number) =>
       Number.isInteger(value) && value >= MAX_RAY_DEPTH_PROPERTY_MIN && value <= MAX_RAY_DEPTH_PROPERTY_MAX,
@@ -47,7 +52,7 @@ const opticsLabQueryParameters = QueryStringMachine.getAll({
   // Spacing between major grid lines, in model metres (same range as preferences / scene grid size).
   gridSpacing: {
     type: "number" as const,
-    defaultValue: 1,
+    defaultValue: GRID_SPACING_M,
     public: true,
     isValidValue: (value: number) => value >= GRID_SPACING_MIN_M && value <= GRID_SPACING_MAX_M,
   },
@@ -106,9 +111,9 @@ const opticsLabQueryParameters = QueryStringMachine.getAll({
   /** Length of ray stubs in view pixels when ray-stubs mode is active. */
   rayStubLength: {
     type: "number" as const,
-    defaultValue: 50,
+    defaultValue: RAY_STUB_LENGTH_DEFAULT_PX,
     public: true,
-    isValidValue: (value: number) => value >= 10 && value <= 200,
+    isValidValue: (value: number) => value >= RAY_STUB_LENGTH_MIN_PX && value <= RAY_STUB_LENGTH_MAX_PX,
   },
 
   /** Show the background grid at startup. */