Optics Lessons: Part 9 - Color and Optical Illusions

When the first television was modified and introduced to the public, there was one major difference between it and the contemporary model: it was in black and white. Society, unhappy with this, strived to change it, gradually modifying the television into color, into the mode of our daily lives. Color is not a definate property. A block of wood is guaranteed to be rough, hard, splintery, but it cannot be definately brown. One person may see it as purple, or even gray. This deviation of our perceptions of the world give rise to a series of topics in physics that have to do with human awareness of light, our discernment of various colors and our view of optical illusions.

Color:

There is a red apple in front you. White light hits it and only waves from the red portion of the visible spectrum are reflected, while the others are absorbed. There is a similar effect when you mix colors. Mix yellow and blue, for instance. The yellow pigment will absorb most of the wavelengths of colors other than it or colors near its area in the spectrum. The same goes for the blue pigment. The green region is near both the yellow and blue regions of the visible spectrum, so not much of it is absorbed and hence is the resulting color you see. This is called the subtractive method of color production:

Well, you may say, it's all fine and dandy that color pigments absorb and reflect certain wavelengths, but how do we make those reflected wavelengths the color we see? How do our eyes make us see the red in that apple or green when blue and yellow are mixed?

How do we see color?

There is not a complete answer to this seemingly simple question. But it is practically impossible for the retina to have a receptor for each color imaginable. Young, the same scientist who conducted the double-slit experiment, suggested that there was a three- color system for receiving color information. More specifically, this theory says there are three different kinds of cones in the retina that each communicates with various parts of the visible spectrum, specifically the red, blue, and green areas, absorbing light from those specific parts. The roles of these three cones overlap somehow to produce what the brain perceives as different colors.

This theory is based on the fact that different intensities of red, blue, and green light can overlap to form most colors. The formation of new colors through overlapping is called the additive method of color production. When two colors from this process combine and seem to form white, then these colors are complementary colors. Red complements cyan; green complements magenta, and blue complements yellow--and vise-versa for each of these three situations.

Also, this theory explains why you see more colors in front of you than at the periphery of your vision. Cones, which transmit higher light intensities and hence help you see more color, are concentrated in the center of the retina, while rods , which transmit mostly black and white color data, are gathered at the periphery of the retina. Rods also react greater to dim light, which explains why you don't see much color in a dark room.

Optical Illusions:

Back Home :: Back to Top
Lessons :: Terms :: Formulas :: Discuss :: Links