LCD panels consist of a number of “layers.” Here are layers common to
most LCD panels: 1) Vertical filter film to polarize the light as it enters,
2) Glass substrate with electrodes, 3) Twisted nematic liquid crystals,
4) Glass substrate with common electrode, 5) Horizontal filter film to
block/permit light to pass, 6) LCD surface screen.
lighting conditions, without generating
excessive heat.
The major problem is outdoor ambient
light on the LCD screen when the chartplot-
ter is mounted on the flybridge or at an open
helm station. As the ambient light gets
brighter, the contrast ratio decreases because
more light is reflected by the display. When
the ambient light gets bright enough, the
contrast ratio is reduced to 1.0 and the dis-
play can’t be read at all. In other words, the
reflected ambient light overpowers the back-
light and the display appears “washed out.”
In recent years, anti-reflective (AR) coat-
ings have been developed which, when
applied to the front screen of the LCD, can
reduce the surface reflectivity by over 90%,
dramatically improving the high-ambient
light legibility and image clarity. Modern
chartplotter screens treated with
AR coatings present clearly legible
and readable screen images in
direct sunlight without the need
for high-power consumption
backlighting.
Backlighting
Until recently, all LCD monitors used
cold-cathode fluorescent lamps (CCFL) for
backlighting. CCFL technology has been
around for a long time but is being replaced,
especially in high-end units, by light-emitting
diode (LED) backlighting.
CCFL has a number of disadvantages. For
example, light output is temperature depend-
ent and can lose as much as 40% of its light
intensity when the temperature drops 68 to
32 degrees centigrade. At the lower tempera-
tures it can suffer from flickering and cold
starts. But its biggest drawback in chartplot-
ter (and TV) applications is its inability to
accommodate local dimming, which is where
full-array LED backlighting shines. There are
two versions of LED backlighting: edge-lit
and full-array. Both have advantages over
CCFL, but only the full array LED is capable
of local dimming.
