Advantages: Researchers report approximately 40% yield win from using LED lights. They use about a tenth the energy of high-pressure sodium lights.
Life: LEDs last about 50,000 hours. Plants grow best with 16 hours light a day - that's 16 hours total sunlight + LED light. The amount of sunlight obviously varies depending on climate and latitude, but if you lived in a cave, you'd be using the growlights 16 × 365 hours a year: 5840 hours a year so they'd last 8.5 years. Factoring in sunlight, they should last at least 20 years.
Color: Plants need a mixture of blue (wavelength of 458nm) and red lights (wavelength of 640nm), with the red lights about six times brighter than the blue.
Brightness: Plants need about 30,000 lux (lumens per square meter)
Commercial growlights vs DIY: This is a commercial growpanel with 225 LEDs for $34 plus shipping. It may be cheaper to buy loose LEDs.
- Here are Red LEDs for 9c each at a brightness of 0.3 lumens. Blue LEDs for 41c each at a brightness of 1.5 lumens.
-  has 5m led strips for $7.88
Large High-Output LED Array for Plant Growth slidshow by orbitech