Light bulb distance from canopy using 600 watt HPS

I've read a bunch about the distance a bulb needs to be from the canopy, but am confused.

Some information I read says a 600 watt HPS should be anywhere from 10-18 inches from the top of the canopy. Other information says to get it as close as possible without burning the plants.

Also, do I count the distance from the top of the plants to the bulb, or from the top of the plants to the bottom of the reflector hood's glass lens? In my setup, that's a four inch diffference, so it could be substantial if distance is really important.

Using Lumatek 600W HPS with 600W Digilux HPS bulb.

you need to get it as close has you can without it burning, depends on fans ect, personally my 600w hps is a minium 24" above my plants any closer and it starts to slowly cook them..

The average 600w bulb with sufficient cooling needs to be more than 13" away from the plants at all times. The plants should be spaced at about 17" for maximum light usage, adequate vertical growth room and to keep the plants small. Move the lights back to 17" each morning.

Again, this is only with enough lamp cooling that heat is not a factor when determining bulb distance.

You measure distance from the bulb. Just note the space between the bulb and lamp glass, then use that much less space.

Thanks for responding, this is a very cool website. I'm currently at 16 inches from the 600 watt hps bulb. I have duct cooling with a 6" vortex. Heat is mostly not an issue. I already had to tie two plants down a little to keep them at 16 inches from the bulb. My other two plants are presently minding their distance at 17 inches.

I'm not sure if I should tie the two 16 inch distance plants down even more? They haven't gone vertical in a few days.

I'm at around day 25 of flower. Does this time frame normally mean no more vertical growth? Or, could I still get a vertical growth spurt? I'm hoping for bud growth only at this point, since I'm not able to raise my light any further without some major redesigning.

I have Blueberry, Sharksbreath, MK Ultra, and Afgan Kush growing. I took a couple of pictures, but it's in the HPS light. Still, you can probably see that heat or 16 inches from the bulb isn't bothering them very much right now.

looks like you got it about right mate, good growing..

im not running a 600 but a 400 and im about 3-4 inches away air cooled. temps make it possible and im not showing any signs of burning. u talking air cooled or open?

shortshack13 said:

im not running a 600 but a 400 and im about 3-4 inches away air cooled. temps make it possible and im not showing any signs of burning. u talking air cooled or open?

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Using air cooled right now. Even with that, the temperature at the canopy is anywhere from 75 to 80 degrees with the light on. I don't think I can get much closer with my current setup.

id just keep it as close as you can then. the lumen intensity just starts to diminish the further away from the bulb. if you ever get board pick up a light meter and check this at different spots on your canopy you will see it goes down something like 25% a ft not sure of exact numbers but my 400 only gets full light 3ft or under and after that the growth is just holding back the rest aka fluffy. thats why i am so close and at 2.5 ft finish height.

ps plants look good. you may still see a little vertical but not to much.

shortshack13 said:

id just keep it as close as you can then. the lumen intensity just starts to diminish the further away from the bulb. if you ever get board pick up a light meter and check this at different spots on your canopy you will see it goes down something like 25% a ft not sure of exact numbers but my 400 only gets full light 3ft or under and after that the growth is just holding back the rest aka fluffy. thats why i am so close and at 2.5 ft finish height.

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Inverse square law from wiki For quick approximations, it is enough to remember that doubling the distance reduces illumination to one quarter;[SUP][4][/SUP] or similarly, to halve the illumination increase the distance by a factor of 1.4 (the square root of 2), and to double illumination, reduce the distance to 0.7 (square root of 1/2). When the illuminant is not a point source, the inverse square rule is often still a useful approximation; when the size of the light source is less than one-fifth of the distance to the subject, the calculation error is less than 1%

taking the inverse square law into account if your 17" away the strength in lighting would be more even from top to bottom. At 4 inches the light at the top is much much brighter than on the bottom. so I would argue a balance between how much fall off you can tolerate in the light.

Im not taking heat into consideration at all

crash000001 said:

Inverse square law from wiki For quick approximations, it is enough to remember that doubling the distance reduces illumination to one quarter;[SUP][4][/SUP] or similarly, to halve the illumination increase the distance by a factor of 1.4 (the square root of 2), and to double illumination, reduce the distance to 0.7 (square root of 1/2). When the illuminant is not a point source, the inverse square rule is often still a useful approximation; when the size of the light source is less than one-fifth of the distance to the subject, the calculation error is less than 1%

taking the inverse square law into account if your 17" away the strength in lighting would be more even from top to bottom. At 4 inches the light at the top is much much brighter than on the bottom. so I would argue a balance between how much fall off you can tolerate in the light.

Im not taking heat into consideration at all

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It would be nice if this one made their point without the college thesis