Frontlight
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A frontlight is a system of illuminating a display device, usually an LCD, so that the apparent brightness of such a display is not diminished in the presence of ambient light.
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[edit] The problem with LCDs
LCDs work by changing the polarization of light using a refractive medium that can change its light-bending properties in response to electrical charge. No light is emitted in this process, rather the path of existing light is changed by the display. Because of this, LCD screens are not self-illuminating. In their "normal" form they require light to be supplied from outside, which is then reflected back through the LCD so it can be viewed. In the more common backlight system, a light source is placed behind the LCD (in place of the reflective medium used to reflect ambient light) so that the screen appears to glow, like a more conventional Cathode ray tube (CRT) display. This requires a different form of LCD to be manufactured, and the light source to be of equal area to the display.
[edit] Implementation
In a front-lit display system, a light source is built into the display in front of the LCD itself. This has the advantage of requiring minimal additional engineering, because the LCD itself is unmodified, retaining the reflective backing of an unlit system; ergo, if conditions warrant, the front light can be deactivated and the LCD can still retain useful visibility. The source of the artificial light is usually a light-emitting diode (LED), as they are small and consume very little power. Backlight systems are usually fluorescent in nature, due to the fact that the bulbs are capable of covering a larger area.
[edit] Limitations
The frontlight system's main drawback is that of colour fidelity - if the built-in light source is not particularly powerful, or if its colour deviates somewhat from pure white, the display may take on a "washed-out" look, lacking the more vivid colour definitions of a backlit LCD or conventional CRT display.
Frontlight systems are also limited to relatively small displays - the very nature of their layout dictates that the light source must be placed around the sides of the display. This precludes their use in applications such as television or laptop computer screens.
