What is an LED
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 through them.
LED's are the brightest technology available today. Diodes are a one way electronic semi-conductor (see diagram) that respond to have current turned on and turned off as happens when displaying moving images
LED's offer brightness, colour saturation and contrast in addition to excellent viewing angles.
The other technologies such as LCD, CRT, Plasma or Projection, just aren't suitable for outdoor full sun applications, which makes LED's the clear winner for a professional application.