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Color Filters
Kyocera color STN LCDs are known to have brighter, richer colors than competing displays. One reason for
this is that Kyocera manufactures its own color filters.
An LCD subpixel cell operates by transmitting or disrupting light. Each subpixel has a characteristic
color: red, green or blue. The color filter is the film sheet that supplies this color. White light
consists of all colors. When it passes through the color filter, all the other colors are blocked,
leaving only the specific color of that subpixel. A color filter that more aggressively blocks unwanted
colors will produce a display with more saturated colors.
In reflective mode, light passes twice through the color filter, coming in from the environment and
going out as colored light to the eye of the user. So its color filter must let more light through,
compared to the color filter on a transmissive panel. Transflective displays require a compromise color
filter, but one that is designed for the particular reflective components being used.
Chromaticity
Section 6 of of the LCD specification gives the chromaticity coordinates for the red, green and blue colors
of that panel. When plotted on the CIE color space, these points make a triangle whose area is the color
gamut of the display. The more pure the primary colors, the greater the range of colors that can be made
by the display. Chromaticity coordinates are not specified for reflective mode because the color of the
reflected light depends on the color and intensity of the ambient light being reflected. Transflective
displays are measured in transmissive mode. The color gamut is wider for transmissive LCDs than for
transflective LCDs because the color filter is tailored for the transmissive mode.
Here is an example of two color gamuts plotted in the CIE chromaticity color space. This chart shows the
effect of recent improvements by Kyocera in the color filter for transflective panels. It is important
to remember that the primary goal is to produce a liquid crystal display panel that looks better. Color
gamut, brightness, reflectivity and contrast ratio merely quantify different aspects of appearance.
Specifications can be helpful, but prospective customers really must examine LCDs in side-by-side
demonstrations.
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