Even if you have no interest in growing plants indoors, you've probably nevertheless heard of LED grow lights if only because they've become something of a hot topic recently and thus show up on places like Amazon and eBay among the latest must-have items.
But why the buzz about what is after all basically a glorified green house lighting system? Well, to understand that you have to first understand why people grow plants indoors and what they need in order to do it successfully.
There are many amateur gardeners and folk who want to grow specimens of an, ahem, recreational nature, but also professional growers of fruit, vegetables and flowers. What they all have in common is the desire to manage the growing environment - temperature, humidity, nutrients and of course light. The aim being to create optimal and reliable conditions and thus increase plant yields and time to reach maturity. In the case of professionals of course, this is reflected on the bottom line as improved profitability.
Now other than fertile soil and sufficient water, all plants depend on two things: air and light. They use a process called photosynthesis to absorb carbon from the CO2 already present in the atmosphere and to convert this into the proteins and sugars that make up organic plant material. The photosynthesis itself is driven by a molecule called chlorophyll that is able to absorb energy from sunlight - but only from specific bands in the spectrum. So most general light is in fact of very little use to a plant.
Historically, attempts to make lights that target these particular regions (two in the blue portion of the spectrum and two in the red) have proved difficult. Incandescent light bulbs produce light almost as an incidental by-product of heating a filament and are thus especially poor at this; fluorescent and high energy discharge lamps are better but bring their own baggage. In all cases, there are issues with waste heat (which obviously affects the micro-climate) and maintenance since the bulbs don't last well given the amount of time they must stay switched on each and every day.
LED grow lights by contrast can be designed to emit light in any part of the spectrum, last easily twenty or more times longer, give off very little heat at all, weigh very little and are easily integrated with automated control systems. If you've had any experience with LEDs you'll know how small and light they are yet also how robust and easy to package in any kind of assembly.
A standard LED grow light panel typically uses four different LEDs, each set to one of the key spectral wavelengths with the capability to switch on/off any possible combination as required. So, for example, during the early stages most seedlings and young plants benefit more from blue light and gradually shift to favouring red light as they mature.
Also, with no significant heat issues, LED grow lights can be positioned much closer which also helps combat the problems associated with the Inverse Square Law as it affects light. Basically, if the distance between lamp and plant is halved, the amount of light it receives goes up by a factor of four (not two). This aspect of LED grow lights is especially beneficial since one of the main factors in promoting plant growth is not just spectral range but sheer power (the amount of light).
Finally, there's a matter of cost. Forget the comparative purchase price between an LED grow light panel and a conventional equivalent. The fact is that grow lights, by definition, stay powered on for much of the day and the running costs associated with fluorescent and HID systems are pretty significant. In contrast to LED grow lights which consume a fraction (about one tenth in fact) of the electricity and thus cost considerably less to operate.
So there you have it - LED grow lights really hit the spot for a variety of reasons, but mainly because they're better at providing exactly what plants need.