Heat Output

One of LED grow lights' many advantages is the reduction in heat compared to MH and HPS lights. There are two aspects to this: (1) LEDs are more efficient to begin with so they use less energy and therefore create less heat, and (2) the ability to fine-tune the spectrum allows LED grow lights to avoid having a huge spike of infrared light like HPS lights do which only creates heat. (This is why HPS lights burn plants that get too close!)

So, LED grow lights create less heat than HPS lights to get you the same amount of light. They may not heat your plants up as much either. But this doesn't mean that LED lights don't create heat, although many vendors make that claim.

Companies that are honest about the heat their LEDs create are listed above in "The Honest" column; companies that are deceptive about their lights' heat are in "The Deceivers", and companies flat-out lying about it are in "The Liars".

The truth of the matter is that LED, MH, HPS, fluorescent and even incandescent lights will all warm your growing room by exactly the same amount per watt of electricity used. The only difference is the amount of usable light that is also created in the process– but if you have 1000 watts of LED lights running in a sealed tent, it will warm up the air in the tent just as much as 1000 watts of HID lights. However, LEDs provide more light per watt, so you need less cooling for the same amount of light. For example, if you're growing in a small tent with one or two lights, you may not have to worry about cooling with LEDs, though you'd certainly have to worry about it with an equivalent HID.

But if you're using thousands of watts of LED lights, you're going to have to cool the room somehow, just like with HID lights (but with LEDs, you'll need less cooling).

Side note: I'm not saying the effect on the plants will be the same between LEDs and HIDs– you can get LED lights much closer to plants before they show signs of stress, and even then the symptoms are a bit different. With HID lights, leaves turn yellow and then brown and crispy as they get too close to the light; under LEDs they fade to white, and finally if really too close, eventually brown, if the light is intense enough. Some LED light spectrums also allow you to grow with a warmer air temperature which further reduces the need for cooling.

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The Deceivers: Full of Hot Air

Some LED sellers claim that their lights require no cooling; this may be true if you use one or two, but if you use a lot you will need to worry about heat. From the claims I've seen on their sites, I believe that many, if not most of the LED vendors compared on this site, have never personally grown more than a few test plants at a time under one or two of their lights, so they may truly not understand that their lights really do need cooling in larger setups. At the same time, if they've not really grown much with their lights, that's a bit concerning as well, so I'm still going to note the deceptive statements I've found:

  • Illumitex:
    • LED grow lights produce considerably less heat than other lights (3.4 BTUs/hour, compared to 85 for incandescent bulbs) – this should be 3.4 BTUs/hour per watt for the LED lights, and the "85 for incandescent bulbs" is just wrong in this context, they also generate 3.4 BTUs/hour per watt. If they had stated that a 1W LED was comparable to a 25W incandescent bulb somewhere in their text, this statement might make sense– but they didn't. Who's trying to grow with incandescent bulbs anyhow? The whole comparison is just misleading.

The Liars: Don't Let Them Burn You

If a seller claims their LED grow light creates no heat, they're just flat-out lying. Other companies blatantly lie about the heat their fixtures put off with technical information about cooling requirements. Simply stated, BTUs (British Thermal Units) are a measurement of energy. 1 watt of electricity is equal to approximately 3.41 BTUs. This is true whether the wattage is going to an incandescent, fluorescent, MH, HPS, LED, TV, electric toothbrush, refrigerator, anything — 1 watt is 3.41 BTUs. If a company lies about heat/BTUs, you have to wonder what else they may be lying to you about, so I can't recommend buying any lights from these companies:

  • Advanced LED:
    • The lights are just warm to the touch, and they don't heat up the growing area at all, so no additional cooling is necessary. Sorry, they DO heat up the growing area; this is just a lie.
  • G8LED:
    • With the G8-240 [or G8-450] Bloom light there is no need for a ballast and no need to vent extra heat. They're right about the ballast, but if you get a few lights you will need to deal with extra heat- another lie.
  • Kind LED:
    • This revolutionary series of LED grow lights will produce the biggest and best yields, while consuming approximately half the electricity and producing virtually no heat. I certainly wouldn't call 1091 BTUs/hour for their K3-L600 "virtually no heat".
    • Kind LED lights run cool, so cool in fact that no additional temperature control equipment is needed besides the internal circulation fans. This is a lie; you will absolutely need additional temperature control equipment if you put enough of their lights into a room.
  • LumiGrow:
    • On the product pages they claim their Pro 325 model (325 watts) is 800 BTU, though 325 * 3.41 = 1108 BTUs, 38% more than they claim. They say their Pro 650 model (650 watts) puts out 1600 BTUs. 650 * 3.41 = 2217 BTUs, again 38% more than they claim.
  • Lush Lighting:
    • In their comparison to HID lights Lush is apparently compelled to lie about the BTUs of heat a 1000W HPS puts off to make their LEDs look better. The table shows a total 1150 watt draw for the HPS light (presumably this is with a horribly-inefficient magnetic ballast– most of the newer digital ballasts take a lot less than 150 watts). 1150W * 3.41 BTUs/watt = 3921 BTUs of heat, but Lush's table says it requires 7500 BTUs of cooling, almost double the actual number.
  • Mars Hydro:
    • Says their Mars II 1600W light uses 720 watts of power, but they claim it puts out 1883 BTUs of heat (720 watts * 3.41 BTUs/watt = 2455 BTUs). The Reflector-96 draws 200 watts (= 682 BTU) but they say it generates 436 BTU. The Reflector-144 draws 310 watts (= 1057 BTU) but they say it is 467 BTU. The Reflector-192 draws 390 watts (= 1330 BTU) but they claim 567 BTU. The MarsPro 160 draws 360 watts (= 1228 BTU) but they claim 1008 BTU. The MarsPro Cree-256 draws 650 watts (= 2217 BTU) but they say it puts off 1883 BTU. They just seem to be making these numbers up.
  • Platinum LED:
  • Pro Max Grow:
    • Assures us that both of their light models produce little to no heat. They may produce little heat due to their very low wattage, but they still produce 3.41 BTU's per watt like everything else.
  • Pro Source Worldwide:
    • no thermal footprint
  • Spectrum King:
    • Claims on their FAQ page that their 440 watt 400 Series lights produce about 1300 btu's of heat, but 440 * 3.41 = 1500 BTUs their lights put off. They then claim that a Gavita double-ended HPS bulb produces in the neighborhood of 7000 btu's. The most power-hungry fixture Gavita sells pulls 1240 watts when cranked all the way up and produces 4230 BTUs of heat- I wouldn't call that "in the neighborhood of 7000". Spectrum King seems compelled to exaggerate their comparisons to HPS lights; they do the same thing when comparing their reflectors to HPS hoods.


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