As LEDs have become famous with recent advancements, and with growing technology, you can get LED glow lights that are long lasting, bright and quite inexpensive. These lamps emit light of wavelength that corresponds to the peak of absorption of the typical photochemical process of a plant.
LED grow lights are better than other grow lights, since they do not consume a lot of electricity, and they do not need ballasts. And they also produce less heat. So you can easily put these lights closer to your plants. And since plants do not transpire a lot, heat is reduced, and thus you do not have to water them very often.
For carotenoids and chlorophyll, there are many absorption peaks, and thus the LED grow light might have to use multiple LED colors that overlap these peaks.
You can save about 75% of power when you switch from HID to LED. And you wouldn't need cooling systems as well. Your plants can use up all the energy that is emitted from LED growth lights. HID lights on the other hand release a lot of light along with a lot of heat.
There are various recommendations for LED designs. According to a US patent, using 6 orange 612nm, 1 blue 470nm 12 red 660nm LEDs is optimal. But this works if the ratio of blue: red and orange light comes out to be 6%-8%
LEDs are generally preferred for vegetative growth, when the LED light is of wavelength of about 400nm. And these lights do not produce any noise, and produce only the light that is needed for your plants to grow fast.
Early LED growth lights used several small LEDs and they were not bright enough to replace HID growth lights. With newer advancements, there are LED growth lights that use multiple watt bright LEDs.
Main Advantages of LED Grow Lights
Targeted Light Wavelengths: LED Grow lights can use targeted wavelengths of light used by plants for photosynthesis.
Low Heat Emission: LED grow lights output up to 90% less heat than traditional grow lights.
Very Low Voltage: LED lights are very low voltage devices, which makes them a very safe option for the home.
No Ballast Required: This means that LED grow lights are much lighter and have fewer parts that need replaced over time.
Long Life: The life of an LED light is up 100,000 hrs, which is up to 50 times more than a HPS grow light.
No Reflector Required: Traditional grow lamps emit light in every direction. LED Grow lights have their own reflectors so an external light reflector is not required.
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I have also written a more in depth led grow lights review at http://hubpages.com/hub/LED-Grow-Lights-