For large screen TVs, no one knows yet.
Basically, for LCDs to work, there needs to be light behind the screen that is allowed through the front of the panel by the LCD.
Current LCD panels all use a fluorescent bulb as a light source. Fluorescent bulbs contain mercury and do eventually burn out, where LEDs do not and last longer. Thus there is a move to replace the fluorescent bulbs in LCD panels with LED arrays for backlighting. Since you need an array of high output LEDs to provide the same output as a high brightness fluorescent bulb, there are a few associated technological challenges, plus LEDs are more sensitive to voltage variations than bulbs are so there have been some problems with backlight flicker in early LED-lit laptop panels.
LED backlighting is also more energy-efficient, so the ultimate power consumption of the set should drop.
It's all somewhat ironic in the wake of the environmentalists' demands that everyone replace incandescent bulbs with compact fluorescents, but I digress.