How do 2 wavelengths of light mix to make a color? Does the light itself mix to make a color or do the cones in our eyes see the 2 wavelengths and interpolate a color?

Answer 1

Simply put, light is additive. When measuring with a light meter, you may need two lights in order to reach a desired exposure level. In the same way that light is additive with exposure, light is also additive in color information. Light is recorded on a digital cameras sensor by millions of picture elements called pixels. With this in mind, you can cast two light sources with different colors on the same surface. This will result in a color mixture on the surface. A red light at f/4 mixed with a yellow light at f/4 will create an orange light at f/4.5-f/5.6. Not only is your color going to change, but your exposure will increase as well. It is here that you can choose the hue and saturation of the color. A brighter exposure will create a lighter shade with lower saturation. Whereas a darker exposure creates deeper colors and increased saturation relative to your cameras exposure setting.