339
fiber optic technology but many other optical manipulations as well,
including some marvelous fountains of light (light trapped in water
streams via internal reflection) built in the 19
th century.
Color
There are many physical and chemical reasons for color. First, it is
useful to distinguish between the color of a light source (as defined
by its encompassed spectrum of wavelengths) and the color of an
object on which the source shines. Variations in the color of a light
source can be produced by additively combining primary colors—red
(R), green (G), and blue (B)—each associated with specific wavelengths. Additively combining red and green produces the secondary color of yellow. Blue and green produce cyan, and red and blue
produce magenta. White light can be produced by additively combining primary colors with the correct intensities. Red (R), green
(G), and blue (B) are commonly used, but there are actually several
sets of colors that can be combined to produce white light. Selectively adding together these same colors can generate a huge array
of other colors—hence the ubiquitous use of red, green, and blue
lights in common products such as televisions that produce color
additively. Combining two colors that are complementary—say,
cyan and red—can also produce white light, since blue and green
are present in cyan. Any kind of projected light source relies on
additive color mixing to produce the output color. In the section on
solid-state lighting, we will see that red, green, and blue quantum
dots are normally used to produce not only high-quality white light
but other colors as well.
The color that we perceive an object to have when a light source
shines on it is not intrinsic to the object. It depends on the way
wavelengths of the light acting on a surface are absorbed, reflected,
or transmitted. We can only visually respond to the wavelengths
that are reflected from the object and still lie within the visible spectrum. Wavelengths that are absorbed or transmitted are never seen.
The color of an object thus depends on both the spectrum of the
light striking the surface and which wavelengths are reflected.
Let’s consider a light source shining on an opaque surface (one that
can absorb or reflect light wavelengths only, not transmit them).
If white light with a full spectrum strikes an opaque surface that
absorbs all wavelengths present except blue, the surface will appear
blue because the wavelength corresponding will be reflected and
seen by the eye. Here it is useful to think about this effect as being
primarily subtractive in nature. The final colors we see are the result
Light and Optical Environments
fiber optic technology but many other optical manipulations as well,
including some marvelous fountains of light (light trapped in water
streams via internal reflection) built in the 19
th century.
Color
There are many physical and chemical reasons for color. First, it is
useful to distinguish between the color of a light source (as defined
by its encompassed spectrum of wavelengths) and the color of an
object on which the source shines. Variations in the color of a light
source can be produced by additively combining primary colors—red
(R), green (G), and blue (B)—each associated with specific wavelengths. Additively combining red and green produces the secondary color of yellow. Blue and green produce cyan, and red and blue
produce magenta. White light can be produced by additively combining primary colors with the correct intensities. Red (R), green
(G), and blue (B) are commonly used, but there are actually several
sets of colors that can be combined to produce white light. Selectively adding together these same colors can generate a huge array
of other colors—hence the ubiquitous use of red, green, and blue
lights in common products such as televisions that produce color
additively. Combining two colors that are complementary—say,
cyan and red—can also produce white light, since blue and green
are present in cyan. Any kind of projected light source relies on
additive color mixing to produce the output color. In the section on
solid-state lighting, we will see that red, green, and blue quantum
dots are normally used to produce not only high-quality white light
but other colors as well.
The color that we perceive an object to have when a light source
shines on it is not intrinsic to the object. It depends on the way
wavelengths of the light acting on a surface are absorbed, reflected,
or transmitted. We can only visually respond to the wavelengths
that are reflected from the object and still lie within the visible spectrum. Wavelengths that are absorbed or transmitted are never seen.
The color of an object thus depends on both the spectrum of the
light striking the surface and which wavelengths are reflected.
Let’s consider a light source shining on an opaque surface (one that
can absorb or reflect light wavelengths only, not transmit them).
If white light with a full spectrum strikes an opaque surface that
absorbs all wavelengths present except blue, the surface will appear
blue because the wavelength corresponding will be reflected and
seen by the eye. Here it is useful to think about this effect as being
primarily subtractive in nature. The final colors we see are the result
Light and Optical Environments