The View From 32


JULY 13, 2007  

Here's exactly what I saw, I think.

As I was reading, sitting in a sunny spot in the backyard this morning, I noticed that the shadows cast by my fingers were bright blue-green. Unusual. I looked around for something that might be reflecting the sunlight in such a way as to create these colorful shadows. After a minute I decided it must be the bright red T-shirt I was wearing.

I thought this was worth a picture. Could be helpful when talking about how light and color are related.

When I looked at the picture I was even more surprised. Move your mouse over the picture to see what the camera actually recorded.

The whole book actually has a reddish cast to it, but that's not what I saw. I saw white pages with blue shadows. My brain was automatically adjusting my perception to make the pages look white. Why? Because I knew they were white. I saw what I expected to see. According to Wikipedia, "This feature of the visual system is called chromatic adaptation, or color constancy; when the correction occurs in a camera it is referred to as white balance."

The camera, having no such brain, shows them as they actually were, bathed in a reddish light reflected from my shirt.

The smaller photo shows how the book looked when I took off the red shirt, the pages their "natural" white color.

For more information about light and shadows, try this Exploratorium activity, Colored Shadows, or another from the Teachers' Lab.

Related concept: color is in the mind, not in the world.


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