# What causes eyeshine at night? **URL:** \ **Category:** Factual Questions\ **Created:** [June 10, 2001, 8:13pm UTC](https://boards.straightdope.com/t/what-causes-eyeshine-at-night/68333 "2001-06-10T20:13:55Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![sethdallob](https://avatars.discourse-cdn.com/v4/letter/s/e36b37/32.png) [@sethdallob](https://boards.straightdope.com/u/sethdallob)\ **Post date:** [June 10, 2001, 8:13pm UTC](https://boards.straightdope.com/t/what-causes-eyeshine-at-night/68333/1 "2001-06-10T20:13:55Z")
What causes cats/dogs/animals eyes to shine an eery red at night when a flashlight is pointed at them? ---
**Author:** ![Scarlett67](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/scarlett67/32/7387_2.png) [@Scarlett67](https://boards.straightdope.com/u/Scarlett67)\ **Post date:** [June 10, 2001, 9:04pm UTC](https://boards.straightdope.com/t/what-causes-eyeshine-at-night/68333/2 "2001-06-10T21:04:27Z")
Not always red – my shepherd/lab mix’s eyes shine bright Kryptonite green! Our springer puppy’s eyes used to shine that color too, but now that she’s older they’re just plain red. I asked my vet once about the color difference, and he had no idea. ---
**Author:** ![rowrrbazzle](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rowrrbazzle/32/414_2.png) [@rowrrbazzle](https://boards.straightdope.com/u/rowrrbazzle)\ **Post date:** [June 10, 2001, 9:09pm UTC](https://boards.straightdope.com/t/what-causes-eyeshine-at-night/68333/3 "2001-06-10T21:09:02Z")
The [tapetum lucidum](http://www.metpet.com/nmerc/tapetum_lucidum.htm). ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [June 10, 2001, 10:20pm UTC](https://boards.straightdope.com/t/what-causes-eyeshine-at-night/68333/4 "2001-06-10T22:20:24Z")
Both my dogs glow green as well. I always wanted to take a slow-exposure photograph of it, but even the Grumpy Old Lady Dog would never stand still for that long. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [June 11, 2001, 3:01am UTC](https://boards.straightdope.com/t/what-causes-eyeshine-at-night/68333/5 "2001-06-11T03:01:11Z")
I suppose you include people in the “animals” definition. In low light levels the pupil dilates and allows you to see the back of the eye, the retina. The lens of the eye concentrates the effect. This is what causes red eye in flash photos. ---
**Author:** ![Mac\_Guffin](https://avatars.discourse-cdn.com/v4/letter/m/2bfe46/32.png) [@Mac\_Guffin](https://boards.straightdope.com/u/Mac_Guffin)\ **Post date:** [June 11, 2001, 11:37am UTC](https://boards.straightdope.com/t/what-causes-eyeshine-at-night/68333/6 "2001-06-11T11:37:48Z")
First a quick quote from that site **zgystardst** posted… > [@](#): > > The tapetum lucidum, “bright carpet”, acts like a mirror bouncing light through the eye. This allows your pet (and other animals with similar eye structures) to make the best use of available light. Cats, partly due to the tapetum lucidum, can see clearly in just 1/6th the amount of light humans need. Here is a question. So it is because of this reflecting membrane that animals have great night vision? So what is to keep us from making a slightly reflective contact lens that has the same effect? Could better night vision be had this way? ---
**Author:** ![Mr.Cynical](https://avatars.discourse-cdn.com/v4/letter/m/ee59a6/32.png) [@Mr.Cynical](https://boards.straightdope.com/u/Mr.Cynical)\ **Post date:** [June 11, 2001, 12:29pm UTC](https://boards.straightdope.com/t/what-causes-eyeshine-at-night/68333/7 "2001-06-11T12:29:50Z")
> [@](#): > > \*Originally posted by particlewill \* > \*\*So what is to keep us from making a slightly reflective contact lens that has the same effect? Could better night vision be had this way? > \*\* Although the reflectivity of the lens would decrease re-transmission of the light to the outside of the eye, the necessary decreased transmissivity inherent in a partially reflective surface would attenuate the amount of light entering the eye in the first place. Think mirrored sunglasses. ---
**Author:** ![Phobos](https://avatars.discourse-cdn.com/v4/letter/p/3d9bf3/32.png) [@Phobos](https://boards.straightdope.com/u/Phobos)\ **Post date:** [June 11, 2001, 1:16pm UTC](https://boards.straightdope.com/t/what-causes-eyeshine-at-night/68333/8 "2001-06-11T13:16:20Z")
> [@](#): > > \*Originally posted by particlewill \* > Here is a question. > So it is because of this reflecting membrane that animals have great night vision? So what is to keep us from making a slightly reflective contact lens that has the same effect? Could better night vision be had this way? Because the flashlight is more effective! 😉 ---
**Author:** ![WindFish](https://avatars.discourse-cdn.com/v4/letter/w/a183cd/32.png) [@WindFish](https://boards.straightdope.com/u/WindFish)\ **Post date:** [June 11, 2001, 4:03pm UTC](https://boards.straightdope.com/t/what-causes-eyeshine-at-night/68333/9 "2001-06-11T16:03:08Z")
> [@](#): > > \*Originally posted by sethdallob \* > \*\*What causes cats/dogs/animals eyes to shine an eery red at night when a flashlight is pointed at them? \*\* I remember this question addressed in the [Straight Dope Mailbag](http://www.straightdope.com/mailbag/meyeshin.html).