Science Photo of the Day


Why are this alligator's eyes glowing?

Fantastic job. Its eyes are glowing because of light from my camera flash, reflecting from the back of the gator's eyes. This reflective layer is called the tapetum lucidum, and it is just behind the retina. Light enters the eye, passes over the light sensitive cells of the retina, reflects from the tapetum lucidum, and hits the cells of the retina again. That should make the image look twice as bright, a big advantage for creatures that are active at night, but there is more to it.

When we looked at the oil on water photo, we saw that two waves that meet when they are in sync cause constructive interference, making the light brighter. Constructive interference lets the tapetum lucidum improve night sight as much as 600%.

Many animals, from rabbits to cats, deer to wolves have eyeshine due to a tapetum lucidum, but humans do not. The red eye seen in photographs is light reflected directly from the retina, not a tapetum lucidum.

I took this photo in the Everglades, but I was not worried. Alligators don't usually bother people, unless they are used to being fed by people or the people are bothering them. This one was much more interested in looking for a nice duck to eat.

science101 wrote on Mon, 09/07/2009 - 15:58:

I think it is because of the camera flash, it is the light reflecting off of the back of the retina. It is more intense than humans because he has superior night vision.

Anonymous wrote on Fri, 09/04/2009 - 18:36:

maybe the reason the aligators eyes are because red,when the camera flashed it's eye's when the camera flashes it turns red.

from your incredible fan,

Anonymous wrote on Fri, 09/04/2009 - 15:19:


I have a fue questions first i think his eye's are red becuase the
flash is making it come out like this becuase sometimes it happens
to us to thats wat i think.

Alsoe were you scared allot alsoe it looks like its looking at the
camara with glaring eyes were you in a park or were you near your
house mabye???

your big fan!!!!
Carina from Mrs.
Webber's class

Anonymous wrote on Fri, 09/04/2009 - 14:21:

Dear Mr. Krampf,

Our first guess is that the sun is reflecting off of the alligator's eyes.
The second guess is that the alligator's eyes are naturally red, which makes him look very fierce.
Or maybe it's not the reflection or by nature, but instead it's due to the flash of a camera making its eyes red.

We were wondering if you were on a boat when you took that picture. If so, were you super scared?

You are a daring scientist!

Have a fabulous weekend!

Your young scientists,
Mrs. Webber's 4th grade class

Anonymous wrote on Fri, 09/04/2009 - 10:11:

PS Maybe his eyes are not reflecting a camera's flash but a bonfire on shore. ??? Obviously, :-) we are not sure.

The Andrews

Anonymous wrote on Fri, 09/04/2009 - 10:09:

The alligator's eyes are glowing because of the camera's flash. Or at least, that is what we think. Sometimes, people's eyes are red in a picture. (Danny)

Abbie is wondering if the alligator's eyes are like cats eyes that you can see in the dark. Tacy wonders if their eyes get so much water when they are under the water that they just glow when they get above water.

Abbie asks: Do cats eyes really glow in the dark?

Thanks! The Andrews Family