So when we are talking temperature.........
- Thread starter Tee Five
- Start date
desertrat
Well-Known Member
ok, here's the deal on temperature. the guidelines for room temp are for a thermometer at the top of the plant canopy but shaded from direct light. if you don't shade it the thermometer will read ambient air temp and radiant heat combined. you test for radiant heat by using your hand as a temp gauge lower the light as far as you can keeping your hand comfortable. you can get an aircooled hps light to within a foot without burning.
Tee Five
Active Member
I would suggest a heat gun would do a far better job than a thermometer.
But you're saying...that lower til your hand doesn't become uncomfortable. Well at what temp does your hand get uncomfortable--at 60 C. So how does the temp drop from 60C to 24C within a foot?
Im sure a cooled hood helps and so does fans and AC....but I find it impossible to believe that the plants at canopy-level is a comfortable 24 C with a HID (I know you have recitied commonly accepted guidelines---and im not calling you a liar or anything...and I also know that success has come from that formula). So im playing a bit of Devil's advocate here.
but 24C at canopy level with a HID light (even at 2 feet away)---Im sorry Im having trouble understanding the real temperature for a HID at the canopy level
But you're saying...that lower til your hand doesn't become uncomfortable. Well at what temp does your hand get uncomfortable--at 60 C. So how does the temp drop from 60C to 24C within a foot?
Im sure a cooled hood helps and so does fans and AC....but I find it impossible to believe that the plants at canopy-level is a comfortable 24 C with a HID (I know you have recitied commonly accepted guidelines---and im not calling you a liar or anything...and I also know that success has come from that formula). So im playing a bit of Devil's advocate here.
but 24C at canopy level with a HID light (even at 2 feet away)---Im sorry Im having trouble understanding the real temperature for a HID at the canopy level
Nukulhedd
Active Member
it does not matter what the opperating temp of an hid light at the bulb the only thing that matters is keeping it far enough from your plants to not burn them. that means keep your temp at the canopy of your garden at a nice comftorble temp for the plants. if it comftorble for you it is also for the plants. my canopy stays around 75-77f and my ambient room temp stays around the same with proper ventilation and my girls love it. i get 1-2 inches growth every day for a good 60 days of veg and my plants are huge by time i flower.
CDXX
Active Member
If you are using T-5s you can have them a few inches above the plant, I've seen some people do 2-3 inches. T5s spread the heat they generate over a wider surface than regular HID lights. Because the heat is distributed evenly, you can put the light closer. I keep my t5s extremely close to the canopy, and have never gotten burnt. However, I do use 2 small clip fans to blow air across the light/canopy, so perhaps this plays a part.
desertrat
Well-Known Member
you need to understand the difference between radiant heat and ambient temperature. radiant heat passes through the air and directly heats an object - as an extreme radiant heat is what cooks an egg on the sidewalk on a hot day in the desert. the ambient temp of the air is in the 30c range but the egg is cooking at greater than 100c due to the radiant heat. and i guarantee you the air is still in the 30c range within a couple of inches of the egg.
the trick in growing is to keep the ambient air cool and circulating enough to overcome the radiant heat generated in the leaves themselves. so, in short you keep the lights as close as you can without the radiant heat burning them. and a hand is a lot cheaper and 100% reliable compared to a heat gun. just saying.
Tee Five
Active Member
10"...is that not way too far away? Why so far?
Tee Five
Active Member
@Desertrat
Well maybe thats the thing im not getting?
I would find it hard to believe that it would be hot enough to fry an egg on the sidewalk--but the air around the egg is comfortable.
Are we saying that radiant heat has no effect on the temperature of the surrounding air? Because isn't that all amibent temp is air temp--is it not?
Well maybe thats the thing im not getting?
I would find it hard to believe that it would be hot enough to fry an egg on the sidewalk--but the air around the egg is comfortable.
Are we saying that radiant heat has no effect on the temperature of the surrounding air? Because isn't that all amibent temp is air temp--is it not?
Tee Five
Active Member
I keep mine at 1-2 inches--and im saying too myself--why not even closer? I could lick my T5s at operating temperature.
But we have a similar set up--I just want to know how you took that pic...unless you are rather short
PS: thanks for posting a pic
This is how close I keep it
@desertrat--You've helped with the shade on the thermo advice, I really didn't take that into account (but i still wished I had a heat gun)--you can see my clip-on gauge on the middle planter in my pic--so thanks...im going to try that.
desertrat
Well-Known Member
air does absorb radiant heat energy from the sun but air is a relatively transparent medium to infrared radiation, so it's absorbing a small fraction of the total energy. the earth absorbs most of the energy but is so large it acts as a heat sink and doesn't increase in temp much. the same principals apply in a grow room except you achieve the effect by sending relatively cool air over the plants taking away much of the radiant heat they absorbed. sorry, chem engineer geek running free here
genuity
Well-Known Member
i like to try and have atleast an inch of node spaceing,and it helps with not haveing to move the light so much..
SmokesLikeBob
Well-Known Member
desertrat got it in a nutshell! +rep to you man!
SLB
SLB
Tee Five
Active Member
Well--I'll bet you the reality is very few people have the kind of cooling to carry away all that heat. A Low Pressure Sodium runs at around 200C--thats fuckin hot! As in car engine hot. Now whether a LPS runs hotter than a HPS or MH--I can't seem to find that information.
If you took 20 growers (with HIDs) and aimed a temperature gun at the crown of their plants--I'll bet you most of those plants tops are going to be well over 25C.
If someone has a temp gun and wants to post a picture of that--I'll give out rep like candy.
If you took 20 growers (with HIDs) and aimed a temperature gun at the crown of their plants--I'll bet you most of those plants tops are going to be well over 25C.
If someone has a temp gun and wants to post a picture of that--I'll give out rep like candy.
desertrat
Well-Known Member
i run two 600 watt air cooled lights, the pane of glass is cool enough to touch, and i keep my plants within 12 inches with a cool flow of co2 enriched air that i am not even venting out of the room. instead i have a closed loop a/c keeping the air in the 70's, and that's plenty low enough to keep radiant heat from being a problem for the plants. really, i'm smoking it now so i'm pretty sure i'm not imagining things.