1. Color Mixing light

2. Misconceptions and problems Mixing light can get very confusing to many students because most have never done it. We have mixed pigments (paints etc.) and try to apply that to mixing light. Light is the reverse of mixing pigments so it causes some disbelief.

3. Color by addition Unlike pigments each time you add a color of light you are just adding more to the mix, not subtracting. If you add all colors you should get white. To make black you remove all light (turn them off). Look at a T.V. or computer screen. When they are off they are black. They can make white (and every other color) by adding different colors of light to the screen. This is the opposite of a piece of paper!

4. Additive Primary Colors The additive primary colors are red, blue and green. You will notice these are the three color controls on TV’s and a computer screen Complimentary colors (made by mixing two primary colors) are magenta, cyan and yellow.

5. Mixing Primary Light Colors

6. Mixing the additive primary colors in equal concentrations Red BlueGreen Yellow Magenta Cyan *Almost identical to the pigment triangle, just rotated. White

7. Pure and mixtures Red BlueGreen Yellow Magenta Cyan White The primary colors are considered pure, the complimentary colors are mixtures. True primary red is only red light yellow is a mix of green and red. This means they should or should not separate in a prism, diffraction grating etc.

8. Why things look different in different sources of light. The most obvious is under a “dingy” light (yellowish) This happens when a gas light gets old, it doesn’t put out the high end of the spectrum (blue) like it should so the light is yellow. These are found in several parking lots. Even though the pigment on your car, shirt or skin may reflect blue; if there is no (or little) blue present, it can’t be reflected.

9. So that means… Things will look odd under that light (all blue has been subtracted out). This also happens with the differences between incandescent, fluorescent, and sunlight.

10. Homework Read section 28.5 Pg 575-6 Do Questions 9-11; 25-33