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Distance from Light to Plants

Discussion in 'Lighting' started by Kolchak420, Jan 11, 2011.

  1. I'm running a 600-watt HPS inside a DayStar air-cooled hood with 6" flanges. About how close can it be to the tops of mature flowering plants, without harming them?
  2. As close as temps will allow. If you can hold the back of your hand to the light at plant-top height for 30 seconds comfortably then it's OK for the plants.
  3. OK, thanks. I have a good air-cooled hood and a good fan to cool it. Assuming that, can you give me a ballpark guess at how close the 600 HPS can be to the tops of healthy plants? Six inches? Twelve inches? Eighteen inches? I'm just trying to make sure my grow room has enough height, but not too much.

  4. when i run my 600 w i have 2 lights that are air cooled by a 435 cfm fan and an oscillating fan that blows on the plants. i can keep the lights about 8 inches away from the tops without the temp rising above 81-82 degrees f.
  5. get a small thermometer/hygrometer and put it right where the tops of your plants are, i use a scrog so i just keep my thermometer on the screen
  6. Agree with Kolchak, probably about 8 inches would be my initial expectation but monitor with a thermometer at plant-top height under the light.

    How many plants though? If you are covering more than about 4-6 good-sized plants then as you move the light closer you are delivering stronger light intensity directly under the light but you are cutting down the angle for coverage on the outer edges.

  7. this would be a problem if i had more plants. im only running 2 under each 600 rright now, but if i were running 4 id probably have the light about 14 inches up to cover it.

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