Cooling LEDs By Heating The Water Saves On Electricity

[Matthias] swapped out his twin-tube florescent aquarium lights for LEDs. By running tank water through the aluminum LED mounts he’s transferring excess heat into the water in the tank, in turn saving some of the electricity that would have been used to heat the tank. Couple this with roughly 35 Watts saved by moving away from fluorescent tubes and he’s got a great energy-saving hack. The LEDs used in the last aquarium light conversion were cooled by heat sinks and fans. We’d love to see this concept incorporated into that design.

32 thoughts on “Cooling LEDs By Heating The Water Saves On Electricity

  1. This guy must live in the arctic. Heating the tank is rarely a problem for me. The ambient temperature plus the heat created by the pumps, lights and other equipment are usually all I need to keep it at 79 degrees. If anything it overheats and I have to constantly battle with cooling it.

  2. I’ve long thought that the lights belong at the base of the tank and behind it, with just a mirror up top to reflect the light into the tank. That way the heat from the led or bulbs will rise away from the light controller, ballasts, boards, or whatever the design uses — rather than up into them.

  3. If the LED’s are the beefy kind (1,3,5+ watt each) then they will definitely need heat sinks, the little tiny LED’s you see in Pen lights don’t need heat-sinking, but the stronger ones do…

  4. Are there guides for LED wavelength output for flora and fauna? I have been curious about the subject of light and life. Usually it comes down to I use brand x of bulb and in my tests it works better than y z. I am not questioning the tests of the plant and animal aficionado. What I wonder specifically is what amount and wavelengths of light do various common plants and animals need for better health.

  5. Not ‘energy saving’, it’s reducing energy.

    Saving energy would be to get rid of the aquarium and not incur the costs of the luxury. But, if it makes you feel like you’re saving the world, go for it.

  6. @damntech

    I think it’s easy to know which LED will fit for plants growing, just compare the spectrum of aquarium fluorescents (just look in the box of it) with the spectrum showed in power LEDs’ datasheets.

    The power needed is another thing… you should look for the lumens and the spawn angle of the led.

  7. So let’s see – you’ve gone from a fluorescent tube (relatively thermally inefficient) to a more illumination efficient LED system that also heats a bit of water?

    Since you’ll have to make up the rest of the heat with a resistance heater, wouldn’t it make more sense to go with a *less* efficient light source and use *all* the waste heat?

  8. first problem Aluminum leaking as stated
    second temperature overheating
    third -if led lights burn human eyes if looking close to it– what about the fish – are we going to blind the fish – that why the fish are at bottom to get away from the light

  9. planted tanks like this don’t need heat unless it’s in your garage or cold basement. there doesn’t seem to be much room for fish in there. on the other hand, my coralife 96w has four fans on it for cooling and i still have to heat the water to keep the fish happy…

  10. @scott: no, because transferring the waste heat to the water is probably not as efficient as as straight up resistance heater. Also the more power you are able to control, the better, say if you want zero heating on a warm day.

  11. Sorry fo being late, i haven t noted that this treat has grown this much
    to answer the main questions:
    1.)Pure Aluminum sure is dangerous for the fish, but in my case its eloxadized and also for outdoor use w/o getting stained. So i think it will not contact the water that much. Also the tube will get an algae layer inside due longer flooding time.
    2.)The energy “harvest” is not enough to keep the tank heated up to the desired temperature while the average temperature in my living room is at night 17degC(62F) and at day 20degC (68F) in winter times(Central Europe -Germany) It’s rather to waste not the energy loosing of the LEDs and saddle them with huge heatsinks.
    The insulating tube is detachable for warmer outside temperatures to let the heat flow in the ambient air.
    3.)Yep i have fish in there, but make a portrait of every one is not the subject here ;)
    4.)The LEDs and datasheet you ll find here: (site is in english too)
    5.) When every aquarium owner gives up his (luxury)hobby there can be switched off much carbon firing and atomic power plants. If the half reduces power by changing to efficient light there can switched off some of them.

  12. HI, if you have some basic skills to work with metal, you sure can build it from the pics on flickr. Important is to use eloxated aluminum as tube. Pure Al will kill your fish!
    The beta point at this version is the connection between the square al-tube and the stainless input/output tubes. Looking forward to get my lathe ;)
    At the moment i got not much time to do a howto, but you can contact me on fb if you like. I ll sure answer any question to this theme.

  13. I have been contiplating this myself. Espicially with planted and coral and larger LEDs required. Id do it radiantly through the bottum or back of the tank with a sealed system. Than you dont have to worry about plugging pipes or contamination issues. Glad im not the only one thinking about this.

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