Gathering HPS data/Calling all Hps owners

Perhaps it exists.
After 30 years indoors w/shoplights, I'm finally Hp'ed. Thanks all you RUI'ers who helped me realize I was, uhhhh, doing great w/what I had, but capable of so much more.
Now, what's pissing me off is that I can't find any definitive distance-from-the-canopy information. All I see is folks doing the hand jive, which is fine, but awfully case reliant. We all realize conditions vary.
I'm doing this thread to collect distance data, based on these 3 things. Wattage and basic fan/air movement, and distance from the canopy. Room temp is another matter and not relevant to this data.

For example, I'm running 1-600 hps (95,000 lms) currently 26-28" above, with just a fan blowing across between the light and the canopy. No damage.

If enough folks reply, we can get some data that will apply to all but the smallest enclosures.

Also, if you've burned your plant at any distance, it's help if you posted that data, assuming you know the damaging digits.
This needs to be done. There's gotta be something better than a no-time limit mentioned placing of the back of the hand for distance.


A clear window of safety should become apparent. Please help.

very good mr fish i think you have a good point keep up your work +rep to you

i think its a foot for 400 watt and 18 inches for 600. After thst the lumen loss is dramatic. With a vented hood and a fan u dan do that easy. There is a chart and that is the basic sum, it gets passed around alot here in various forms, i looking for it 4 yu. 30 years, well thats awesome.

What I'm after is the distance from the bulb, approximately, to the average canopy with just a fan blowing across the canopy, between the light and the buds.
I'm looking for universal numbers, irregardless of hood types, etc. (except for cool-tube) which I suspect is another ball game, ie: always will be closer?

+ rep for the thread. my two cents for the logic behind the hand test as i think its best for determining the location of the light, assuming you have a hand with nerve endings.

first a few facts - hps lights give off radiant heat that warms the air as well as any surface it hits directly. a thermometer picks up both radiant heat and air temperature and thus will overstate the air temp. a hand can be used to differentiate between the radiant temp and the air temp.

plants flourish in a certain air temp and that is what's quoted for weed - air temp only with the thermometer at the canopy but shaded from direct light. the plant also can take only so much radiant heat. it is the radiant heat that burns the leaves, not air temp.

so, to make a long story short, you need something that measures radiant heat separately from air temp. i guess you could buy an expensive gizmo but the hand works perfectly.

determing light distance by looking at the set up is really difficult because it depends on so many variables. size of light, amount of ventilation, cooling hood or not, etc.

but to help your cause, i use a 600 with an aircooled hood inline with a carbon filter and using a 170 cfm fan and get the light to within 8". it does burn the plant a little at 6".

i was talking lumens man. To get the most outa 400 is like a foot u have to be able to cool the top of the canopy down enuf to where u can get the light close enuf to be a foot away form the canopy. Cooling hoods work the best at this. If u raise the 400 more than a foot and the 600 more than 18 inche the light loss is so great that u really retard the whol point of having that aweome light. U can do it of course it just a waste. So if yu pit a big ol fan on yur light or a ventind hood which works better u can keep the canopy temperature down to 70s and 80s. U measure ur heat with a temp pobe at canopy height in the shade of a leaf so u can get a good reading. U go from there. The thermoters are didgital and u can find a tradio shck for 20 dollars. They are indoor outdoor thermoters.

I fyu can get closer, well u rock. I use a 400 watt in a euro hood from htg and a cheap 30 dollar 6inch duct fan, I can get my temp down to low 80s with lights on. I gonna get a intake fan and better outake to help with this or another outake. That my example. 4x4x6.5 space. I at under a foot. No damage with this space incloset thi ame ystem fried a girl.

Eharmony420 said:

i was talking lumens man. To get the most outa 400 is like a foot u have to be able to cool the top of the canopy down enuf to where u can get the light close enuf to be a foot away form the canopy. Cooling hoods work the best at this. If u raise the 400 more than a foot and the 600 more than 18 inche the light loss is so great that u really retard the whol point of having that aweome light. U can do it of course it just a waste. So if yu pit a big ol fan on yur light or a ventind hood which works better u can keep the canopy temperature down to 70s and 80s. U measure ur heat with a temp pobe at canopy height in the shade of a leaf so u can get a good reading. U go from there. The thermoters are didgital and u can find a tradio shck for 20 dollars. They are indoor outdoor thermoters.

Click to expand...

the problem with this is that plant leaves burn even when the measured air temp is within the right range. the leaves get super heated due to radiant heat which the air can cool only if you are getting sufficient ventilation. however, you reach a point in distance where no matter how much ventilation you have the plant will still burn.

you have to use something to test radiant heat directly. that''s why everyone suggests using your hand.

The hands fine . . . it's the amount of time each individual would need to do so to get a reading that I question. I mean, should it be uncomfortable at, say, 45 seconds and hurt at 90? I think there needs to be a "standard" time for this to be all inclusive?

ah, i finally understand your question. must be the dope. your hand will heat up right away - that's the way radiant heat works. fifteen seconds should be fine.

400w HPS bulb about 14 to 18 inches from the tops with strong ocillating fan blowing across the tops. Room temps between 75 and 80(F).

I have read (don't remember where) that if the lights are too close (but not close enough to burn) that it will inhibit the pistil color change. The "hairs" will stay white. Anyone debunk or verify this?

MrFishy said:

The hands fine . . . it's the amount of time each individual would need to do so to get a reading that I question. I mean, should it be uncomfortable at, say, 45 seconds and hurt at 90? I think there needs to be a "standard" time for this to be all inclusive?

Click to expand...

Shouldn't hurt *ever*

Hoods do matter. You gave an exception to a cool-tube. An air cooled hood is a cool tube (in mechanics). Duct in and duct out and glass covered. No a plain hood is open and doesn't help at all.

Now if I can ask you a Q. Prefer T8 or T12 for veggin?

BigBudBalls said:

Shouldn't hurt *ever*

Hoods do matter. You gave an exception to a cool-tube. An air cooled hood is a cool tube (in mechanics). Duct in and duct out and glass covered. No a plain hood is open and doesn't help at all.

Now if I can ask you a Q. Prefer T8 or T12 for veggin?

Click to expand...

Definitely T-12. Price, convenience, heat, horizontal coverage. Get parts from 7-11, etc.
However, I've never used T-8's and know little of them.
I can barely keep up with the veg growth under 6 40W T-12's. After the clones take, I use 40W gro-lux 12's in every other slot.

The hood not mattering is simply a phrase I used to try and make this apply to anyone not cool-tubed, which I'm guessing is, initially many.

i have a 400watt and had my lamp (with fan only blowing across the tops) at about 10-12" from the top of my plants and it was to close for them burnt them right up lifted it to 15-18" and they are doing just fine heat/light wise.

MrFishy said:

Definitely T-12. Price, convenience, heat, horizontal coverage. Get parts from 7-11, etc.
However, I've never used T-8's and know little of them.
I can barely keep up with the veg growth under 6 40W T-12's. After the clones take, I use 40W gro-lux 12's in every other slot.

The hood not mattering is simply a phrase I used to try and make this apply to anyone not cool-tubed, which I'm guessing is, initially many.

Click to expand...

Thanks man. Re doing both rooms. Got a 400W HPS for flowering so I'm curious to this thread also.

saturnlily said:

i have a 400watt and had my lamp (with fan only blowing across the tops) at about 10-12" from the top of my plants and it was to close for them burnt them right up lifted it to 15-18" and they are doing just fine heat/light wise.

Click to expand...

Now this example is written in a way that would really help in actually being able to decypher the data and make some all but all inclusive claims in relationship to light/distance guidelines. Thanks.

sure thing here to help by my own trial and error i've learned. i get help here so its easy to pass on the love. just remember "people keep it real and keep people high"

Thus far, it appears one can hang a 400W at 14/15"-18" w/only a canopy fan, without damage. I moved my 600W down to 24" and saw slight tip burning (in 2-3 hrs) so it's back at 28".

my personal experience with an open back ended diy cool tube with its own exhaust and also an additional exhaust to remove just cab air, and an oscillating fan blowing the canopy is that i can keep my 400w hps 6 inches from the canopy without burning. I also have two intake holes. one is connected to my central a/c because my grow is in my attic and it gets to be like 130 degrees up there in the dead of summer and the other is the exhaust fan hose from one of my bathrooms that used to go directly out of my roof. i just disconnected that hose from the roof attached it to my cab and now use an additional hose from my exhaust to go right back out the vent that bathroom exhaust hose used to use. with this setup i can keep air temps between 70-80.
also, the space i use is 2ft wide by 2ft long by 6ft high.
i must admit this is very tricky to do as the light must be moved every day and during the beginning of flowering when plants are growing taller i have had to move them twice in one day. because i have definitly had burning at under 6 inches

Another go around, please.