Display technologies
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Light emitting diodes
Arrays of LEDs may be put together to form matrix displays. They are most commonly
found in calculators, retail checkout counters and automatic teller devices.
The first LEDs in common use were a deep red. Other colors are available now.
Electroluminescent displays
Some phosphors will produce light when subjected to an electric field, an effect
that is called electroluminescence. One of the conductors must be transparent
to allow the light output, and many discrete elements must be individually
controllable to make a useful display. These panels can be very thin, permitting
a compact display for portable applications.
Multicolor displays
Among the various multicolor visual displays, we will discuss here the three-primary
roster scan CRT.
Three-primary color raster scan
This technology is similar to that of color television. The phosphors, the
resolution and the refresh rates may be different, but it is basically the
same type of device. Three separate phosphors in an array of dots are used
in this type of multicolor display. Only blue, green, and red are present.
Other colors are perceived because the human visual system integrates different
combinations of these three primary colors. If you get close to a color TV
set and look at what would seem to be a "white" area from a distance,
you will see that it is actually a repeating pattern of blue, green and red
dots. The principle involved is the same as in color photography or color
printing .
Spectral energy distribution curve for P22 (sulfide/silicate/phosphate)
phosphor (JDEC, 1975).
Figure 33 shows a plot of light distribution for one set of the P22 phosphors
when all three are excited simultaneously. When all three compounds are simultaneously
excited, the distribution will appear "white" to the eye.
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