Light and Color

Why do objects appear to be certain colors? The color of an object depends upon which wavelengths of light shine on the object and which wavelengths are reflected.

An object appears a certain color because it absorbs the light of all colors except the light whose color is the same as the apparent object’s color. Serway/Faughn Physics pg 465

Additive Colors Because white light can be dispersed into elementary colors, it is reasonable to assume that they can be combined to form white light. This can be done with a lens, or with filters.

When two primary colors are combined, a complementary color is formed When two primary colors are combined, a complementary color is formed. When light passed through a red filter is combined with green light, a patch of yellow light appears.

If the yellow light produced is combined with blue light, the resulting light will be colorless, or “white” light.

The primary colors of red, green, and blue light produce compliments of cyan, magenta and yellow respectively.

A television screen uses the principal of additive colors. Pixels are small luminous dots that glow either red, green, or blue. Varying the brightness of different pixels in different parts of the picture produces a picture that appears to have many colors present at the same time.

The human eye can see color because of the three kinds of color receptors in the eye. Each receptor, called a cone cell, is sensitive to either red, green, or blue light. Light of different wavelengths stimulates a combination of these receptors so that a wide range of colors can be perceived.

Subtractive Colors Blue pigment mixed with yellow pigment results in green (not white as with mixing light). Pigments rely on colors of light that are absorbed, or subtracted, from incoming light.

Pigments rely on colors of light that are absorbed, or subtracted, from incoming light. Yellow pigment subtracts blue and violet colors from white light, and reflects red, orange, yellow and green light. Blue pigment subtracts red, orange, and yellow from light and reflects green, blue, and violet. When yellow and blue pigments are combined, only green light is reflected.

When the three primary colors are mixed together in the proper proportions, all the colors are subtracted from white light, and the mixture is black.

Because most pigments found in paints and dyes are combinations of different substances, they reflect light from nearby parts of the visible spectrum. Without the knowledge of the light-absorption characteristics of these pigments, it is hard to predict exactly what colors will result from different combinations.

3-D Viewing In a movie theater, the reason why you wear 3-D glasses is to feed different images into your eyes just like a View-Master does. The screen actually displays two images, and the glasses cause one of the images to enter one eye and the other to enter the other eye. There are two common systems for doing this:

Red/Green or Red/Blue Although the red/green or red/blue system is now mainly used for television 3-D effects, and was used in many older 3-D movies. In this system, two images are displayed on the screen, one in red and the other in blue (or green). The filters on the glasses allow only one image to enter each eye, and your brain does the rest.

The polarized 3D system viewing system gives the best images.

Polarization of Light Waves Light waves from a typical source consists of waves that have electric fields oscillating in random directions. This is unpolarized light. A light filter that polarizes light only allows light to pass at a certain angle.

Polarized sunglasses filter out some light rays to reduce glare

The polarizing layer in polarized lenses acts like millions of microscopic mirrors. These mirrors are angled away from your eyes field of vision. When light waves hit the polarization layer at any angle that is not perpendicular to your lens it is reflected away rather than allowed through to your eye. This results in unwanted glare from roads, water and car windows being either dulled out or dramatically reduced allowing the sunglass user to see the field of vision they want.