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Light Distance From Canopy

Discussion in 'Growroom Design & Setup' started by Ryesty, Jul 14, 2018.

  1. Ryesty


    I was always taught to keep my bulbs 18” from the canopy and allow them to get about 12” from the bulb then pull them back up to 18”. I see a lot of people have there lights several feet from the canopy. Isn’t there a lot of the lights power lost due to this? I thought the inverse square law applied to this.
    GT21 and Ar.BsG like this.
  2. Yeah you are right but there are temp issues and uv and ir from the bulbs could damage the canopy also higher bulbs equals more coverage. If you are able to keep your light at 12” without burning and get a good coverage good for you. It also depends on the type of light you are using. I keep my leds at 18”-20” it works fine.
  3. DGP


    I am using 3500K COBS and the plants can often get within 3 " or so and still do just fine. You must be referring to an HID/HPS type of lamp? My system has no real IR in the spectrum so it doesn't add any radiant heating.....

  4. Yes of course. Mine doesn’t have designated uv an ir diodes either. 18” just gives me good coverage. Since he didn’t specify which type of light he uses i gave a general answer. Also he wrote “bulb” in the post, so probably mh or hps is what i thought.
  5. GT21

    GT21 I like soup Supporter

    Yes but they go for canopy space too... You dont want a light to work best for 1 or 2 plants.. You want it to work best for the canopy.. Mine sit at about 3 ft off the plant because it makes the best light square on the ground
    Toaster79 and CrimsonEcho like this.
  6. Ryesty


    I’m still running hps. Forgot to specify that. I understand heat from the lights and coverage are very important. I run air cooled hoods to keep as much heat away as possible, fans to keep the air in the room moving and an ac to keep the temps in check.
    It just seems like hps lamps would loose a lot of power at 3 feet from the canopy, but that doesn’t seem to be the case from what I’m seeing. I move mine up throughout the grow and some people don’t. They mount them high and let the plants grow to them with great yields.
    CrimsonEcho likes this.
  7. I run 2 gavitas with 12 plants at 1150 W. I have to keep gavitas 3-4 feet above canopy to get proper coverage and heat dispersion. I try to keep my a/c airflow between the top of the canopy and bottom of the lights. It helps so I can keep the lights as close to the canopy as possible. 2BFDFB81-E759-4BD4-8A91-EFEFC1D68F96.jpeg this is in veg at 500w.
    CrimsonEcho and Ryesty like this.
  8. Ryesty


    Very nice! This is exactly what I’m talking about. You have awesome growth and it looks great, I’m not running double ended because I don’t have the ceiling height. I understand they put out a lot of heat. This winter I will be changing my light setup. I’ve been running these hids for a long time. It’s about time to change up. Still researching what’s going to work best in my application.
    1diesel1 likes this.
  9. Inverse square law only applies to point sources of light, not to grow lights.
    The intensity drops off much slower than the inverse square law would indicate.
    Plus there's partial reflection from the walls.
    If the walls were perfectly reflecting, then every photon from the light would hit something, and the light distance wouldn't matter at all.
    Ryesty likes this.
  10. Ryesty


    I was not aware that the inverse square law didn’t apply to grow lights. Thanks for the info, that explains alot