400 W HPS- Distance to Canopy

SO I am 17 days into flower are things are moving slow. I am seeing some pointing in the leave tips so I moved the light as High above as I can in my tent about 19"
I have an aircooled fan so thought 12" would be good. but I am trying this distance for a day or so and seeing what happens

use the back of your hand as a heat guide, if its to hot for you its to hot for them.
i generally have mine about 1 to 1 1/2ft off the tops check my sig for results

lykarckstar420 said:

SO I am 17 days into flower are things are moving slow. I am seeing some pointing in the leave tips so I moved the light as High above as I can in my tent about 19"
I have an aircooled fan so thought 12" would be good. but I am trying this distance for a day or so and seeing what happens

Click to expand...

Check out the charts below. They are a good reference for distance/watt
View attachment 2477345 View attachment 2477346

Delvite's suggestion is also a good rule of thumb.

if you have a cool tube or hood on you should be able to keep it close, yes use the charts and sure to put your hand in and feel for yourself its a good way to see if they are to hot, but with a cool tube on a 400W 12" sounds ok, look for heat stress (edges of the leaf`s is pointing up)

I have a 600W and had it at around 20" before I got a coolhood, now I can keep it 12-15" away, witch according to my light meter, give me around 7K foot candles at the tops and about 5K at the Buds sites just below and then it fate out quickly bottom half of my plants only get between 1 and 3K foot candles

OK wow good info . I have seen thAt chart concerning lamp height per watt and this is the thing.. I guess It may be a water/ over Nute issue.. I have an air cooled glass enclosed HPS 400W. My hand stays NOT HOT as close as 8-11" but thats pushing it.
My other issue is that the MAX height for my light is 44" from the bottom of the garden. Meaning I guess when I am close to being ready for harvest I will hopefully have 8-12" distance only. I am gorwing 7 plants in a 4'3'5' tent , too many i know but the clone guy gave me two free as a first time buyer.. not bad ( blue dream ) Yummm... I moved the light to the MAX right now about 18" above the tallest plants ( on outside of my garden ) so tonight @9pm i will check when the light goes on and again over the next few hours and in the morning again b4 the light goes off I will see ..and if things look good I will lower it . Kind of opposite of what the book says ... raise the light with the plants ... but in this case I think I am fine since I am only at 19" above my garden 17 days into flower...

Hour before day time. 757PM PST lamp at max height ...wait n see

I just had a berry bomb that during the stretch was litterally growing into the fixture so about 2 inches from it and it was fine. THat being said im sure its strain dependent. I just flowered with the 400 about 6 inches away. I just kept getting super fluffy buds with it 12 inches away. Sealed fixture tho.

those look like they're loving life brother.

I've got a 400w HPS in a small cabinet, cooled hood of course. I'm getting nervous because the canopy has just exploded since I put them in flower 2 weeks ago and now I'm about 12" from the glass (14" from the light), and I think I'm going to run out of room. Long story.

Anyways onto your dilema and mine also, Temps at the canopy are about 81, right at the top of the glass is about 84. My experienced grower friend said it's no problem they can even touch the glass except for a small area right under the light where the glass is much hotter. They're going to get up there all I can do it drop down my ballast to 250w if it becomes a problem. Hopefully you will be okay, sounds like you will...Mine are handling the heat well. Good luck..

Thanks Fyre- I also have a ballast I can dial DOWN the temp but do I really WANt TO ??? Heard both sides of the argument.
My light is also air cooled nad have read that 6-12" in more than FINE... but I am a conservative fella and would rather it be on the high end than the low...

Thanks peeps

Put a small fan between the glass and the plants it helps with the heat the fixture gives off. I said about the 6 inch from the fixture i should add it was a cold grow room maybe 60-70 then the heat from the light might be a different story during the summer.

I say its bullshit that you can dim a light and it still run proper. If you run a 400 at 250 theres no way the spectrum the light produces is what its supposed to. All the dimmable ballasts i think are a gimic and a scam.

Awesome chart been looking for awhile thx. Those distance losses are crazy tryin to keep canopy at 6.My closet is cooled w/outside air on a t-stat set about 72 at bulb hieght. I had to check but I'm at 5" on a couple tops got there w/back of hand method. The distance changes dramatically w/temp.

LadyJane420 said:

Check out the charts below. They are a good reference for distance/watt
View attachment 2477345 View attachment 2477346

Delvite's suggestion is also a good rule of thumb.

Click to expand...

Great chart LadyJane420