Activity 9
Color
Background Information
Shadows are produced when one object blocks some of the light that is hitting another object. Outside on a sunny day, you can see a sharp shadow of your foot on the ground. You can also see shadows of leaves on the ground, but notice how sharp—or rather how fuzzy—is the border of these shadows. You can see the same effect in a dark room by turning on a single frosted bulb. Because the bulb and the sun are extended light sources, they make shadows with a penumbra region, a fuzzy border around the shadow illuminated by some, but not all, of the light source.
The size of this fuzzy border is directly proportional to the distance from the object to the screen. The top of a flagpole, or even better a tall building, casts a fuzzy shadow indeed.
Color is produced by the eye and the brain. The corresponding physical property of light is the wavelength. Visible wavelengths range from about 0.4 X 10[-6] m to 0.7 X 10[-6] m. Light with a wavelength in this range stimulates the eye and brain to produce a spectral color, as shown by the spectral colors of sunlight formed by a prism (the index of refraction of the prism glass depends on the wavelength of light). These spectral colors are also produced by combinations of lights with different wavelengths. Red light plus green light produces light we see as yellow. Sometimes these color combinations contain white, and the result is an unsaturated color. Such a combination would be a red, green, and blue light, with a second blue light added, which would be seen as a pale blue. In a saturated color, there is no white. Saturated colors are often called “strong” or “intense.” As different colored lights are progressively turned on to illuminate a screen, more and more light falls on the screen, which looks brighter and brighter. In the drawing of the three overlapping disks on page 247, the central area, illuminated by light of all three colors, would be the brightest area and would be white.
Overlapping colored filters gives quite different results. As more and more filters are overlapped, the light transmitted is less and less, so the stack of filters looks dark. Typically a filter passes a range of wavelengths, which correspond to a range of colors, so two overlapped filters pass only those wavelengths that both pass in common.
Color
Background Information
Shadows are produced when one object blocks some of the light that is hitting another object. Outside on a sunny day, you can see a sharp shadow of your foot on the ground. You can also see shadows of leaves on the ground, but notice how sharp—or rather how fuzzy—is the border of these shadows. You can see the same effect in a dark room by turning on a single frosted bulb. Because the bulb and the sun are extended light sources, they make shadows with a penumbra region, a fuzzy border around the shadow illuminated by some, but not all, of the light source.
The size of this fuzzy border is directly proportional to the distance from the object to the screen. The top of a flagpole, or even better a tall building, casts a fuzzy shadow indeed.
Color is produced by the eye and the brain. The corresponding physical property of light is the wavelength. Visible wavelengths range from about 0.4 X 10[-6] m to 0.7 X 10[-6] m. Light with a wavelength in this range stimulates the eye and brain to produce a spectral color, as shown by the spectral colors of sunlight formed by a prism (the index of refraction of the prism glass depends on the wavelength of light). These spectral colors are also produced by combinations of lights with different wavelengths. Red light plus green light produces light we see as yellow. Sometimes these color combinations contain white, and the result is an unsaturated color. Such a combination would be a red, green, and blue light, with a second blue light added, which would be seen as a pale blue. In a saturated color, there is no white. Saturated colors are often called “strong” or “intense.” As different colored lights are progressively turned on to illuminate a screen, more and more light falls on the screen, which looks brighter and brighter. In the drawing of the three overlapping disks on page 247, the central area, illuminated by light of all three colors, would be the brightest area and would be white.
Overlapping colored filters gives quite different results. As more and more filters are overlapped, the light transmitted is less and less, so the stack of filters looks dark. Typically a filter passes a range of wavelengths, which correspond to a range of colors, so two overlapped filters pass only those wavelengths that both pass in common.