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Name:  Bill
Status:  other
Age:  60s
Location: N/A
Country: N/A
Date: 2000-2001


Question:
Many people hit deer while driving at night. Why can't you see deer eyes glow at night when you drive past them?


Replies:
The commonly observed phenomena of animals' eyes "glowing in the dark" is a result of some exterior light, usually a flashlight, spotlight or headlight, reflecting back from the animal's eyes. You will not see it unless you, the light, and the animal are at the right angles - you will only see a deer's eyes glow in headlights if the deer is more or less in front of the car and its eyes turned just right toward you.

J. Elliott


This is a complex area of optics. It involves the same "red eye" effect in flash photography. Different animals reflect different colors. The keywords to look this up include: retroreflectivity and dew heiligenschein. Robert Greenler refers to this in a chapter on diffraction in his book _Rainbows, Halos, and Glories_ , Cambridge University Press 1980.

This effect is used by 3M in their reflective tapes and in highway paint. Small spheres reflect the light back. Two other technologies -- corner cube reflection (Stimsonite) and parabolic reflectors (illumiNITE) -- are also retroreflective, but you can skip those in your search.

---Nathan A. Unterman---


Bill,

Many animals with 'night vision' have reflective pigment behind the retinal photoreceptors at the back of their eyes. Light coming into the eye therefore stimulates the photoreceptors on the way in and once again as it reflects back through them. That doubles their perception of the light's brightness. If you shine a light directly into their eyes at night, you see the reflected light from that pigment on the back of their eyes. Unless the animal looks directly at the source of the light, you won't get the full effect.

CED


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