Contrast Enhancement Filters
La = Ambient light level
Lr = Reflected ambient light level
Ld = Display light level
If Ld > Lr the display is readable
If Ld < Lr the display is not readable |
Contrast enhancement filters work by increasing the difference between Lr and
Ld.
Colour Filters improve the contrast by selecting a colour that matches the colour of the display. This filter then eliminates all ambient light of other colours and absorbs a percentage of the light transmitted through the filter
For example: Consider a red filter and a red LED display in strong sunlight.
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La = 200 Lr = 180
Ld = 150
Lr > Ld therefore the display is not readable
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Inserting a red contrast enhancement filter with 60% transmission in the red will give the following results:
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Lc = La - Light absorbed by the filter
Lc = 200 -160 = 40
Lr = Lc x 0.63 = 25.2
Ld = 150 x 0.63 = 96.5
Lr < Ld therefore the display is readable due
to improved contrast
The Contrast Ratio CE = Ld
/ Lr
= 96.5 / 25.2 = 4:1 |
Circular Polarisers
Circular polarisers are highly effective at eliminating "wash out" caused by ambient light reflected from the display.
Circular polarisers modify ambient light as it passes through the filter and traps the mirror image on reflection from the surface of the display. The signal from the display is allowed to pass through the filter and appears as a bright image against a dark background.
Circular polarisers are available in plastic laminations of 0.25, 0.76, 1.83 and 3.3mm thickness. Glass laminates are also available in various thickness from 3.0mm.
Light Control Films
Light control film is a transparent filter material containing micro-louvers which work like a venetian blind to reduce glare and improve contrast. When placed in front of a display, the film directs the signal into a controlled viewing area. On axis light is transmitted with minimum loss of signal and off axis ambient light is prevented from reaching the display and causing "wash out" by reflection.
Light control films are available in sheets 0.76mm thick or as glass or plastic laminates in various thickness from 3.0mm.
Maximum sheet size is currently 250 x 300mm
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