Move your head back and forward looking towards the center and you'll feel like the glow is.... well, growing!

What: This illusion, created by Alan Stubbs in 2006 [1], has the neat effect of a growing light (or shadow if you customize above to those colors) when you move your head towards and away from the image. It has the extra effect of making you look like you’ve forgot your glasses and are trying to read whats on screen, or like you’re straight up a chicken.

How To: Sit straight on from the screen and move your head back and forth, like a bird. When you’re closer the gradient within will appear to grow, and when you dip out it will shrink back again. You can mess with a few settings here to see different effects, it works great with a dark gradient, and the contrasting colors can give you a bigger or weaker effect.

Cites and Extras:

I've researched these illusions in my spare time but am clearly not any kind of expert and my explainations are pretty smooth brained, if you find something mis-cited, earlier examples, or general mistakes please new let me know via, be kind!