The Ray Box: Part Two

Law of Refraction The law of refraction for light states that a light ray is bent away from its original direction when it passes from one medium to another if it strikes the interface between the two media at a nonzero angle of incidence. Air Glass Incident Beam Refracted Beam ii RR Normal

Refraction is the reason why swimming pools look more shallow than they really are. Refraction is the property that explains the operation of telescopes, binoculars, eyeglass lenses, projector lenses, etc.

Introduction In today’s experiment you will continue to use the properties of reflection and refraction. The concepts of color addition and color subtraction also will be studied. A short description of light transmission and reflection with color filters follows.

When light passes from one medium into another, part of the light is transmitted into the next medium and part of the light is reflected back into the first medium. To show this look at the white light below that is incident upon a red filter. There would be multiple reflections inside the filter, but they would become weaker with each reflection.

Color Addition

Through color addition you are able to see a wide range of colors from a color TV or color projector which actually only emit three different colors. These colors are red, green, and blue. They are called the additive primaries. Your vision system “adds” these together to see a single color from a single location illuminated by more than one color. You can even see colors that don’t appear in the continuous emission spectrum of the sun. Red, green, and blue are used as the additive primaries because this set of three will produce the widest range of colors that you visually experience.

On the next slide you will see what happens as you add colors to produce other colors.

Note that cyan is the addition of green and blue. Note that yellow is the addition of red and green. White Red Green Blue Yellow Cyan Magenta Colors in White Note that magenta is the addition of red and blue. You can see that these three add to give white.

To summarize, see color addition circles on next slide.

Blue Magenta Red Yellow Cyan Green What you are about to see is what you would get with three partially overlapping spotlights reflecting off a white screen. Color Addition Circles Red Green Blue Yellow Cyan Magenta

Color Subtraction

Through color subtraction you are able to see a variety of colors from printings, paintings, etc. If you have ever bought printer inks, you will notice that the ones used to provide a variety of colors in printing are yellow, cyan, and magenta. They are called the subtractive primaries. In subtraction colors are eliminated by the absorption of colors that were in the original illuminating source. This particular set of three colors, yellow, cyan, and magenta, will produce the widest range of colors that you visually experience.

On the next slide you will see what happens as you remove different colors from white light.

White Yellow Take away yellow and what is left? You get blue. Blue Colors in White

White Red Take away cyan and what is left? Cyan You get red. Colors in White

Magenta White Take away magenta and what is left? You get green. Green Colors in White

To summarize, see color subtraction circles on next slide.

Blue Yellow Red Cyan Green Magenta Color Subtraction Circles What you are about to see is what you would get with three partially overlapping transparencies on an overhead projector. Magenta Red Yellow Green Cyan Blue

Any two colors that add to give white are said to be complementary colors. Of the primary colors, both additive and subtractive, the following pairs are complementary colors. Red and Cyan Green and Magenta Blue and Yellow Complementary Colors

When complementary colors are used in color subtraction, generally black is produced. One exception will show this in the demonstration that follows. Your laboratory assistant will now demonstrate color subtraction using only complementary colors.

On the next slide you will see what happens as white light passes through the blue and yellow filters.

A yellow filter lets this through. A blue filter lets this through. It is obvious that green will get through both filters.

This situation only occurs with this particular combination of filters. It is because filters pass a range of colors and in this case with blue and yellow, the ranges overlap because blue and yellow are fairly close to each other in the color spectrum.