LED stands for Light Emitting Diode, which is exactly what they are. They emit light rather than reflect it when they are in a position of having current passed thru them.

LED's are the brightest technology available today. Diodes are a one way electronic semi-conductor (see diagram) that respond in milliseconds to having current turned on and turned off as happens when displaying moving images.

LEDs' offer brightness, colour saturation & contrast in combination with excellent viewing angles.

The other technologies such as LCD, CRT, Plasma or Projector, just aren't suitable for outdoor full sun applications, which makes LED the clear winner for the professional application.