From The Aquarium Wiki
LED stands for Light Emitting Diode. This is a diode that has been altered so that it's primary function is to emit light.
What is a Diode?
A diode is an electronic component that allows current to flow in only one direction.
Pros of LED Lighting
- Efficient. Uses less electricity and produces less heat than other lamps.
- Polarised point type light source. (Makes the water "shimmer")
- Long life. Typically ~40,000 hours with only 20% output fall.
Cons of LED Lighting
- Narrow colour spectrum.
- Takes many of them to produce sufficient light output.
- Good LEDs are expensive.