|MadSci Network: Zoology|
Hey there, Although I wasn't able to pin down any scientific data to answer your question, I'm just going to tell you what I know and extrapolate from that. As you know, when you shine visible light onto many animals' eyes, you get a very shiny, often greenish reflection. This reflection is from a layer behind the retina called the tapetum lucidum, which basically is a living mirror. In humans, light that passes through the retina without being seen is absorbed so no stray light goes bouncing around in our eyes to cloud our vision. Cats, deer, and other wild and/or nocturnal animals depend on night vision to live, though. The tapetum lucidum gives them another chance to "see" light that has already been through their retinas once. Because the light doesn't always bounce straight off the tapetum, they don't know exactly where it came from. So, their vision isn't as sharp, but it is much more sensitive at night. The infrared spectrum begins where the visible spectrum ends in the reddish colors. The cut- off for infrared and visible red isn't exact. But the animal needs to see reds at the far end of the spectrum, so I imagine the reflectance of the tapetum extends a ways into the infrared also. Unfortunately, I couldn't find a reflectance profile to tell you exactly what wavelengths of the electromagnetic spectrum are reflected by the tapetum. I imagine it also reflects ultraviolet quite well too. Anyway, the tapetum may be slightly hotter than core body temperature, but not much hotter. What's happening is that it's just reflecting a lot more infrared than the animal's body is. Hope that helps answer your question, Tom
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