We’re talking about getting burned in the metaphorical sense of course. An LED grow light (like LEDs of all kinds) produces very little heat at all and is quite safe to touch while in operation (unlike the conventional alternatives). However, as with most new technologies there are always suppliers only too keen to bamboozle the ignorant and unwary with inferior products that are guaranteed to disappoint.
The best defense against being ripped off in this way is to arm yourself with information and the first thing to understand is what makes a good grow light of any type and what’s special about LED. There are two key elements: light density and light color.
Many people think that light density is the same as brightness but it’s not exactly; that’s because brightness is a subjective measure. Humans can perceive light only between certain wavelengths (the visible spectrum) and so we cannot for example see X rays. Light density measures the number of light photons falling on a given area regardless of which part of the spectrum they belong to (in other words, regardless of whether they seem bright or even visible at all to us).
The color of grow lights means something too… Light color is short hand for wavelength, so 430 and 453 nanometers are in the blue part of the spectrum while 642 and 662 nm sit in the red. And the important point about these particular wavelengths (or colors) is that they correspond to chlorophyll absorption peaks – the specific types of light that plants need to drive photosynthesis. Quite a few people simply don’t realize that just as we cannot see certain types of light so it is with plants.
Now, whereas conventional incandescent (including high intensity discharge) lamps emit light broadly across most of the visible spectrum, LED lights emit at one particular wavelength and furthermore the wavelength can be easily set during the manufacturing process. So an LED grow light can be constructed with individual modules each tuned to one of the chlorophyll absorption peaks.
So when considering LED grow lights you should first establish that they are genuinely outputting light at specific wavelengths (and not just vaguely “red” or “blue”) and second check the intensity. The easiest way to do this is to simply find out the power consumption per LED. This should ideally be 1 watt – anything below that will not penetrate foliage and anything greater will work but be aware that LED power does not scale linearly (a 2W LED is not twice the intensity of a 1W one). Typically the total number of LEDs and total power consumption is given so just divide the latter by the former to obtain the individual rating.
