There is a new
backlighting method that is challenging the way that
LCDs are currently driven, and it may significantly change the balance in the ongoing
flat TV war. That change is switching from
fluorescent lamps to LEDs to illuminate the display.
A liquid-crystal display (LCD) is basically a variable light filter. The liquid crystals are trapped between two sheets of glass and walled off from one another into the image bits called pixels. These crystals twist and untwist to let polarized light through, and filters placed in front of the pixels create the colors that come out. Since it only modifies light, not creates it, an LCD is only as good as the spectrum of light coming into it from the rear.
The light behind the LCD currently comes from a fluorescent lamp, very similar to that in the ceiling of your office. The exact type is called a cold-cathode fluorescent lamp (CCFL). This lamp is coiled behind the display and is the biggest power drain. The biggest problem is that CCFLs only produce an approximation of white, not true white light. Since an LCD can only make color within the spectrum of the light it receives, a CCFL-based LCD has a color gamut (the extent of the mix of color a display is capable of producing) smaller than a cathode-ray tube (CRT) or a Plasma display, as they use energized phosphors to create purer colors.
The strength of LED backlighting is in its ability to generate pure colors with spectral accuracy. Using Red, Green, and Blue LEDs in a backlight (as Sony and Samsung among others are developing) and mixing their colors creates (by definition) “pure” white light. Since the source light is “whiter” since it uses clean primary colors, an LED-backlit LCD can deliver more color (110% of the color gamut) than the original NTSC (good ol’ fashioned TV standard) color spec! In addition, since the color balance of the white balance can be adjusted (being made up of RGB light) the color balance of the screen can be maintained accurately over operating life of the display.
In addition to increased durability (LEDs are not nearly as fragile as CCFLs) and decreased weight (the drive electronics are not as massive), another significant advantage of LEDs is that they have a functional lifetime far longer than CCFL tubes, so an LED-LCD would operate almost as long as a CRT (about 10+ years).
IMPORTANT SIZE NOTE:
This technology can be applied to LCD screens of any size, and specifically refers to laptop-sized displays and up. Handheld device displays are almost all exclusively lit by LEDs already. The displays Sony and Samsung are working on will be 50+ inches.
UPDATE 2010 - Large-screen LED-driven LCD TVs are now beginning to dominate the high end.