Got glowsticks? I saw this trick at a recent Oregon AAPT meeting (tip of the hat to Karen Hunter). Light mixing is one of those things that’s always a bit tough to show. You shine a blue and a red light on a surface and it kind of looks magenta. That is, if you have fancy dichroic lights that don’t change intensity across their area of illumination. But most of us don’t. (Though here’s a nice “science snack” using overhead transparencies).
Here’s a really nice visual to illustrate light color mixing. Take three glowsticks, one of each color, crack them to make them glow, and snip off the ends of them. Empty each into a separate test tube or other container. This process by itself is quite pretty — here’s a shot I took of Karen’s leftovers after this process was done.
Then, pipette a little bit of each glowstick up into a pipette, and drop into a cup. Do the same with another glowstick of another color. The mixture will *sort of* look like the color it’s supposed to (e.g., blue + green = yellow). But it works better if you blot a bit of the mixture onto a paper towel. The glowing paper towel looks a lot more like the intended color. The red glowsticks have a bit of red dye in them which make the mixing a bit off.
Here’s a little video of this process — scroll to the end to see the glowstick color mixing.