How Printers Work

Color Perception

Visible light falls between 380 NM(violet) and 780 Nm (red) on the electromagnetic spectrum. White light comprises roughly equal proportions of all the visible wavelengths, and when this light is shined on or through an object, some wavelengths are absorbed while others are reflected or transmitted. It's the reflected or transmitted light that gives the object its perceived color. Leaves, for example, are usually seen as green because chlorophyll absorbs light at the blue and red ends of the spectrum and reflects back the green part in the middle.

The temperature of a light source, measured in Kelvin (K), affects an object's perceived color. White light, as emitted by the fluorescent lamps in a viewing box or by a photographer's flash, doesn't distort colors and has an even distribution of wavelengths corresponding to a temperature of around 6,000 K. Standard light bulbs, on the other hand, emit less light from the blue end of the spectrum, corresponding to a temperature of around 3,000K, which causes objects to appear more yellow.

Humans perceive color via a layer of light-sensitive cells at the back of the eye called the retina. The key retinal cells in the eye are the cones, which contain photo pigments that render them sensitive to red, green or blue light (the other light-sensitive cells, the rods are only activated in dim light). Light passing through the eye is regulated by the iris and focused by the lens onto the retina, where cones are stimulated by the relevant wavelengths. Signals from the millions of cones are passed via the optic nerve to the brain, which assembles them into a perceived color image.