Illuminating a common misconception about light and vision

When I ask “How is it that light allows us to see?” What I’m really asking is: “how does information over there get over here to where I can sense it?”

This may seem like an intuitive and easy to answer question, but for hundreds of years it baffled even the greatest thinkers. Aristotle, Euclid, Ptolemy, Galen and others all shared a common, fundamental misunderstanding about the familiar phenomenon of sight.

Extromission Theory of vision

The common, prevailing theory for a very long time of how we were able to see was: Laser Eyes. Yes, Laser Eyes. In other words, something shot out of our eyes, and “touched” the thing we saw.

This theory makes sense on a number of levels, and was, in fact, backed up by what seemed like solid evidence at the time. The first place we look when we don’t understand something, is to the closest thing to it that we do understand. When we want to feel something, we extend our arm and reach out to touch it. Why should vision be any different?

It turns out, this idea is deeply grounded in our intuitive sense of things. If you know that this is NOT how we see, you likely had to unlearn it first.

There were a number of possibilities presented as to what exactly it was that extended from our eyes to bring vision into our experience, but one of the most popular was fire. Yup. Fire. This was what Aristotle believed – and most thinkers tended to agree. Why, you may ask, if we are shooting fire out of our eyes do we not engulf the things we look at in flames? Aristotle had an answer: it is a gentle fire.  Okay.



And, there was evidence to support the idea that fire  was  emitted from our eyes. Have you ever seen a deer,  or  other animal, at night with “glowing” eyes like this     one? Well, that’s the “evidence” that we emit fire from   our eyes – you can see it, can’t you?


And then there is the most obvious question: If there is fire coming out of my eyes, why can I not see it at night? There was a”reasonable” answer for this as well. Basically, you need two fires; the internal one and another, external one, to create an image. The two fires (lights) must “mingle and coalesce” to form the image.

I know. Really? But yes, really. And what there is to take away from this is that an intuitive sense of something is really, really, really hard to interrupt. Its so hard to interrupt that a 1996 study* found that up to 70% of first graders and one third of college students have the same misconception!  One third of college students!

Kids need to un-learn the idea that something is emitted from our eyes in order to begin to understand light and vision. 

The persistence of this misunderstanding is likely why it is specifically and explicitly addressed in the Next Generation Science Standards PS4 at both the first and fourth grade levels.

NGSS 1-PS4 – Waves and their applications in technologies for information transfer:           Objects can be seen if they are illuminated or if they give off their own light.
NGSS 4-PS4: Waves and their applications in technologies for information transfer:                  Develop a model to describe that light reflecting from objects and entering the eyes allows us to see.

And it is not enough to simply present the “right” model. Simply presenting the less intuitive, although correct model does not necessarily disrupt the deeply imbedded misconception.

vision model

We have published an activity designed specifically to address this common misperception about light and sight. It also meets NGSS 1-PS4 and 4-PS4. It’s called the Classroom Cave and you can download it for FREE.




*Development in the understanding of perception: The decline of extramission perception beliefs. Cotrell, Jane E.; Winer, Gerald A. Developmental Psychology, Vol 30(2), Mar 1994, 218-228.