The iPhone 4 Retina display uses technology called IPS (in-plane switching) — the same technology used in the Apple LED Cinema Display and iPad — to achieve a wider viewing angle than on typical LCDs.
LED backlighting.
The Retina display includes LED backlighting and an ambient light sensor that automatically adjusts the brightness of the screen for the best viewing and battery life possible. So you can focus on more important things. Like destroying aliens.