Color and Chromaticity
Return to Luminescence Menu | Next Topic Color Our perception of color is determined by what wavelengths of radiation reach our eye and the sensitivity of the receptors in our eye to various colors The eye has rods and cones containing chromophores which convert light into electrical impulse that the brain uses to perceive images. This the opposite of what you see in light emitting diodes in which electricity causes emission of light.
The rods function under low intensity conditions and provide images in shades of black, grey, and white This is referred to as scotopic vision
The cones process images of high intensity in color which is referred to as photopic vision.
Cones come in three varieties which correspond roughly to blue, green, and red sensitivities; if all three cones are simultaneously excited, then the image will appear white.
If wavelengths of light from a certain region of the spectrum are absorbed by a material, then the materials will appear to be the complementary color Thus, for instance, if violet light with wavelength of 400nm is absorbed, the material will look yellow. If the material absorbs blue you will see the color orange.
| Color absorbed | Color seen |
|---|---|
| Violet | Yellow |
| Blue | Orange |
| Green | Red |
| Yellow | Violet |
| Orange | Blue |
Note that green is not indicated in the figure; this is because materials that appear green actually absorb in the red and the blue (i.e., about 650 nm and 425 nm)