941. There is a debate amongst the teachers in our school as to what are the three primary colors. Some say Red, Green, and Blue, others say Red, Yellow, and Blue. Do you have an explanation? — RS, Farmington Hills, MI
The true primary colors of light are Red, Green, and Blue. This empirical result is determined by physiological characteristics of the three types of color sensitive cells in our eyes. These cells are known as cone cells and are most sensitive to red light, green light, and blue light respectively. Light that falls in between those wavelength ranges stimulate the three groups of cells to various extents and our brains use their relative stimulations to assign a color to the light we're seeing. For example, when you look at yellow light, the red sensitive and green sensitive cone cells are stimulated about equally and your brain interprets this result as yellow. When you look at an equal mixture of red light and green light, the red sensitive and green sensitive cells are again stimulated about equally and your brain again interprets this result as yellow. Thus you can't tell the difference between true yellow light and an equal mixture of red light and green light. That's how a television tricks your eyes into seeing all colors. If you look closely at a color television screen, you'll see tiny dots of red, green, and blue light. But when you back up, you begin to see a broad range of colors. The television is mixing the three primary colors of light to make you see all the other colors.
Incidentally, the three primary colors of pigment are yellow, cyan, and magenta. Yellow pigment absorbs blue light, cyan pigment absorbs red light, and magenta pigment absorbs green light. When exposed to white light, a mixture of these three pigments controls the mixture of the reflected lights (red, green, and blue) and thus can make you see any possible color.