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I teach an after school tutoring class where my students constantly amaze me. Since the class is small and informal, students ask just about anything. Today one of my students asked me a science related question that I wanted to share. She asked, "Miss you know when you turn the lights off at night, and you can't see and then after a few minutes you can...why is that? I am not a science teacher, but have thought about that before. I told her that I wasn't sure but I think it had to do with your pupil dilation. How would some of you explain this? Also, have any of you come across situations similar to this?

Hi Shanae,
I can't explain it as well as Dr. Bill Robertson, but I will summarize what he says in his Book Chapter: All About the Eyeballs, from one of his books in his Stop Faking It Book Series (Light). You can access this chapter in the NLC.
He says, 'When you shone a flashlight in one of your eyes, you
saw your iris expand and contract. That’s because little
muscles in your eye react to the amount of light coming in
and adjust the opening accordingly. Too much light makes
it really difficult to see things, so when you shine light in
your eyes, the opening gets smaller.' (p. 86)
I am assuming that if you turn all the lights off in a room to make it dark, your eyes have to adjust - the iris needs to expand again. Once the iris expands enough, any little bit of light can be used to help you see in the dark. If it is truly, totally dark (absence of light), then you cannot see!
The book chapter does a much better job of explaining it :-)
Carolyn

Thanks Shanae Hatchell, That is a great topic to discuss with students and even better that a student thought of that question. It makes us feel good knowing their brains are working and wondering about the world around them. Thanks for sharing. Helen

I wanted to ditto what Carolyn shared. I used to work for an opthalmologist as well as an optometrist prior to becoming a teacher (as this was my first choice of career). In general, and in simplest terms, yes, this is what is occuring. It's the same as when you step out of the movie theatres into the brightly lit sunshine, your eyes need time to "adjust" or you "can't see". A non-dilating pupil can also be a sign of brain/spinal/nerve injuries and that is why the medics often shine a light back and forth in front of your eyes. They are making sure that the pupils are reactive to light. The pupils are like the automatic flash/aperture of a camera, it needs to focus and adjust the size of the area which allows light in, in order to make for the best "picture".

A great expansion would be to have the students discuss why you can "see" a bright image still after they close their eyes. I can see their brains turning right now as they come up with their own answers for why this occurs.........

It is due to pupil dilation. In bright light your pupils do not need to be dilated so much because there is so much light. But when the light is turned off, your eyes need time to "adjust" or dilate so that it can gather enough light to be able to see. If your class is small and you have access to the internet, this would be a good time to show students how to do research. You could also throw in the fact that you cannot trust all the information that is available on the internet and how to pick and choose which ones to believe.

I have always encouraged my students to ask questions, like many of you I'm sure.. There are so many times when a simple question can turn into a 45 minute discussion/lesson. Every year when I teach body systems my students come up with amazing questions. That is one of the reasons why these community forums are so wonderful. We can ask eachother and share and give feeback to eachother. Ricki Luster

That is fantastic that your students are curious. I would definitely keep this little idea up my sleeve for a good hook for a lesson.