Home▸Biology▸Tapetum Lucidum: Why Eyes Glow at Night

Tapetum Lucidum: Why Eyes Glow at Night

2D ray-diagram cross-section of a nocturnal eye's tapetum lucidum — trace light through the photoreceptors, off the reflective tapetum, and back for a second pass to see why eyeshine only appears when the light source lines up with the viewer.

Biology2DEasy60 FPS📱 Mobile-adapted⇄ 3D version

Details

CategoryBiology

RenderingCanvas 2D

DifficultyEasy

Target FPS60

ControlsDrag the flashlight handle along the arc to change the incidence angle (or use the angle slider), plus sliders for tapetum reflectivity, photoreceptor absorption per pass, ambient light level and pupil dilation, with the same species presets; drag the canvas to pan and scroll to zoom the ray diagram.

tapetum-lucidumeyeshineopticsnight-visionhalloween

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A ray-traced cross-section of a nocturnal eye showing the real double-pass optics behind eyeshine: light enters the pupil, is partly absorbed by the photoreceptor layer, and whatever survives reflects off the tapetum lucidum for a second pass through the receptors before escaping the eye. Adjust tapetum reflectivity, per-pass absorption, ambient light and pupil dilation to see the sensitivity trade-off, and drag the flashlight to see why the escaping glow is only visible to an observer standing close to the light source's own line of sight.

⚙ Under the hood

2D ray-diagram cross-section of a nocturnal eye's tapetum lucidum, tracing light through the photoreceptors, off the reflective tapetum, and back for a second pass to show the real double-pass optics behind eyeshine.

tapetum-lucidumeyeshineopticsnight-visionhalloween

2D · HTML5 Canvas 2D · 60 FPS target · runs fully client-side, no install