*LED (light-emitting diode):
This aquarium light type uses semiconductor technology as its light source. The difficulty in the past (and where many still misunderstand the complexities of LEDs) is correct wave length of the emitters. For example the infrared emitter uses Gallium arsenide (GaAs) and/or Aluminium gallium arsenide (AlGaAs) for its semiconductor material while Blue (460 nm) uses Zinc selenide (ZnSe), Indium gallium nitride (InGaN), Silicon carbide (SiC), and/or Silicon (Si)
Achieving the correct wavelengths in the correct amounts has been the challenge and why a simple LED flashlight has about as much in common to an advanced aquarium LED as paper glider to an airplane. This however is also the advantage as useless green and yellow light spectrums can be omitted as well.
LED aquarium lighting has now become a viable replacement for metal halide and T5 aquarium lighting as soft and hard corals are able to thrive under high output LED’s. These new reef compatible & freshwater plant tank LEDs are likely to take over the market along with the T2, T5, & SHO as they become more readily available, the price comes down and PAR, lumens per watt, & generally aquarium compatibility come up (correct emitter Kelvin technology has been a barrier in the past). In fact the newest generation TMC AquaBeam 500 can easily work for planted freshwater or reef tanks down to 24 inches (60 cm), while the AquaBeam Ultra 1000 LED light tiles can easily penetrate to 30 inches (76 cm) (with specimen placement in the water column being another factor as with any light). (Marine Aquarium to the above left pictured with two TMC Reef White 1000 tiles).
In addition LED lights do not have the heat problems, often last 50,000 hours, produce little useless yellow/green spectrum
From this Aquarium Digest Article: LED Aquarium Lights, Lighting
Also see LED Light Review; Ecoxotic, Double Bright AquaRay, More
