There are four chlorophyll absorption peaks and LED grow lights use four different types of LEDs to hit all four peaks (two red and two blue).[3] Early LED grow lamps used hundreds of fractional watt LEDs and were not effective replacements for HID lamps. Newer advanced LED grow lamps use automotive grade 2-3 watt LEDs and have shown similar results to HID lamps.

[edit] Use
Grow lights are usually used for indoor gardening, plant propagation and food production, including indoor hydroponics and aquatic plants. Although most grow lights are used on an industrial level, some small-scale/domestic usage of these lamps has also been found.

According to the inverse square law, the intensity of light radiating from a point source (in this case a bulb) that reaches a surface is inversely proportional to the square of the surface's distance from the source. So if an object is twice as far away, it receives only 1/4 the light. This is a serious hurdle for indoor growers, and many techniques are employed to use light as efficiently as possible. Reflectors are thus often used in the lamps to maximize light efficiency. Plants or lights are moved as close together as possible so that they receive equal lighting and that all light coming from the lamps wind up on the plants (rather than partly besides it). Often, the distance between lamp and plant is in the range of 24 inches (with incandescent lamps), up to 4 inches (with other lamps as compact, large and high-output fluorescent lamps).[4] Many home gardeners cover the walls of their grow-room with a reflective material, or alternatively, white paint to maximize efficiency.