Thursday, May 26, 2011

How White LED display backlights work.

All the new Apple laptops are now using screens backlit by LEDs, I believe. These backlights do not involve red, green and blue diodes, but rather blue diodes encapsulated in a phosphor coated epoxy. This coating absorbs the diode's light and fluoresces, and reemits some of the blue light frequency-shifted to longer wavelengths by way of a physical phenomenon named the Stokes shift. Result, white light, or rather a weird but still smooth spectrum:

White LED technology is displacing CCFL (fluorescent light-tube) technology in laptops, and even in large TV displays; I guess the advantages are low-voltage power supply, no slow flicker and hum,The obvious disadvantage can be seen in the spectrum diagram above: The power output in the longer wavelengths is abysmally low, so you can expect to have a reduced gamut in the reds — no wonder then that demo discs for TV showrooms are heavily stacked toward Ridley Scott bluish decors. 

If your inner geek is still hungry Wikipedia is begging to illuminate. The graph above was excerpted from the linked article.

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