Re: why does a television have red green and blue electron guns?

Hi Matt, Thanks for your question. You have discovered that different groups of people use the same description for different things and this is very confusing! Artists use the phrase 'primary colors' to mean red, yellow and blue. You can make any other color from these paints-red plus yellow makes orange, blue plus yellow makes green and so on. But when scientists say primary colors, they mean red, green and blue. If you mix red and green light you get yellow, red and blue light gives you "magenta" and so on. In this system you can also get any color, but by changing the intensity of the red, green or blue.

The difference is that with paints, you get colors by taking away other colors (this is called 'subtractive color'), but with light, colors are made by adding colors ('additive color'). Remember a paint doesn't make any light of its own, it just reflects or absorbs whatever light falls on it. So a red paint absorbs blue and green light and reflects what is left (red) and it appears red. A yellow paint absorbs blue light and reflects the red and the green, so it appears yellow. If you mix red (absorbs green and blue, reflects red) and yellow (absorbs blue, reflects red and green) you get a 'red plus green=yellow plus more red', or what we call orange. Perhaps this little diagram might help; RGB stands for red, green and blue.

Light(RGB)---->hits red paint, green and blue removed----->red reflected
Light(RGB)---->hits blue paint, red and green removed----->blue reflected
Light(RGB)---->hits yellow paint, blue removed---->red plus green=yellow

So a television has red, green and blue because the color that you see comes straight to your eyes from the light in the TV.

This can be a bit confusing at first, there are some very nice web sites that tell you all about colors. Try these:
http://www.colormatters.com/rgb.html
This one is very good.
http://wwwchem.csustan.edu/chem1002/colors.htm
http://www.beer.org/~tpark/color.html

Neil Saunders