Tapetum Lucidum: 3D Eyeshine Ray Model

Flashlight position

Drag the dot — center = aligned with camera

Species preset

Eye optics

Tapetum reflectivity R 0.65

Absorption per pass a 0.22

Ambient light level 30

Pupil dilation 0.6

Live readouts

Total captured

39%

Sensitivity gain

×1.8

Alignment angle

0.0°

Eyeshine visible

100%

How it works

Each frame this scene ray-traces a real chief ray: it leaves the draggable flashlight, refracts toward the eye's optical axis at the pupil (a simplified lens), hits the tapetum lucidum — a concave mirror behind the photoreceptors — and reflects by the actual law of reflection about the local surface normal at that point:

P_total = P1 + (1 - P1)·R·P2
d_reflected = d_in - 2(d_in·n)n

Because the mirror is curved, only a ray that entered close to the optical axis reflects back out along a direction close to its own incoming path — real retroreflection geometry, the same reason a cat's eyes flash in headlights but not in ambient room light off to the side. Orbit the camera or drag the flashlight pad away from center and watch the exit ray miss the camera — the sensitivity gain from the double pass never changes, but the visible glint does.

Photoreceptor layer Tapetum (mirror) Ray path

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