Higher Temps after LED upgrade

I just upgraded from the “600 watt” LED that came with my grow tent to an HLG 300L Rspec. This light is brighter at its dimmest setting than my other light at 100%! I adjusted the height to 18 inches. My tent temps have climbed to 78 degrees at 50%RH. I still have about 3-4 weeks left on this grow. In case the plants like this light at 100%, how hot is too hot?

This is the light that came with the tent.


78 is fine. If you’re growing sativa dominant strains they like it even hotter. Check your seed supplier for specifics. Or the main site, seed store, if they have your strain it’ll list it’s preferred climate. 78/50 usually falls close in range of most vpd charts. But gotta measure the temp of your leaves to use accurately.

Any questions just ask. Each chart is for a different difference in leaf and room temperatures.


You can also increase the speed of your exhaust fan to keep temperatures under control.


I have the sensor hanging at the 18 inch mark which is where most of the colas are. Is that what you mean by leaf temps?

Nope. I mean actually measuring the leaf temperature with an infared thermometer.
Like this, just gotta be really close to the leaf.

The exact one I use.
Plants use dissipation just like us. We sweat, it evaporates, we cool down. This is why the leaves will be cooler than the environment. Water is evaporating off them. So the difference you’re looking for is between the leaf temp and your sensor hanging near colas.

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I have the AC Infinity 6 inch on auto. 78 degrees is with it maxed at 10.

Nothing wrong with 78. I like it a little warmer. I run mine at 84


18 inches is fine my Frosty gelato has grown about 6-8 inches from my hlg 260 xl because I cant raise it anymore since shes at the edge of my closet it doesnt hurt her she sucks up water 1.5x faster then the other girls do though and I run a humidifier 24 7 temps don’t really matter until you are below 60 or above 90 as long as your above 45% humidity they’ll do great


Wow i have that same y00 w light and i have some 260xls and the 600w runs about the same heat as the 600. How are your vents setup. Maybe u need to het a bigger exhaust fan to move more heat out

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Me too. This is closer to what it takes to get proper leaf surface temp with led lights.


Thanks for the responses everyone. It’s my first grow and I’m a little paranoid on keeping things in range. I assumed cooler temps were always better. You may be onto something with the exhaust fan. The fan itself is strong but due to where I placed the tent, it has a very long duct attached to it. The nearest window is 25 feet away. About 1 minute after I open the flap to water, my tent temps drop to 75. Increasing the intake vents didn’t affect the temperature. I’m going to try a small fan blowing across the LED. That should tell me if it is the exhaust fan or simply the hotter LED. Good info for future use.

I keep all the vent flaps closed. For intake, I have a AC Infinity Raxial 6inch. Exhaust is a T6 with carbon filter. The T6 does have a 25 foot run to the window.

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Just a heads up. You only need the filter when your flowering and they start to smell.
Running it when its not needed and they aren’t smelling(veg state) can saturate the carbon before its needed.

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Damn, what did you use to raise and lower the old one with, an engine tow? Jk but in the pic, without any reference point, it looks thick and stout.

I believe @dbrn32 has mentioned that this method for measuring leaf temp is not really very accurate.


They will work fairly close if emissivity is set properly.


I have the same 6 inch for my 2x4 tent and love that little fan. Lol. Just ordered a 8 inch to put in my bathroom to see if it will help haul out some of the heat from in there it seems to stay a bit warm. If u have exhaust issues all u jave to do is order a cheapo inline booster like the raxial kind and install it aboit midway helping the original one move the air thru all the tube. They r cheap at home depot ect i got a 8 inch for like 28 bucks or so

It is pretty beefy looking with the built-in fans. Dimensions are 11 1/2in x 13in x 3in.

Yea, that was the original intention when I ordered this Raxial 6in booster fan. I wasn’t venting the venting outside this room at first and didn’t see the need… I bought it just in case. It just increased the room temperature which in turn increased the tent temperature. It didn’t become an issue until flowering and I turned up the power (and heat) on the first LED. Maybe I’ll pick up a second booster fan to use on the exhaust side just to help the T6 not work so hard.

Lux only measures light. So no it’s not remotely good if you don’t have a reputable light. It will give you readings that seem good but aren’t. Although, if you know your light is good like an hlg, lux can 100% be used to gauge the approximate height you should hang it at. Like if I threw a crap ton of 6500 LED t8, lux be off the chart. But I’d have a crap ton of bright heavy blue light. Not very useful. Ppfd refers particularly to photosynthetic light. While I replied to you, I’m very aware you probably already know this. Was just sharing the information with any one wondering why.

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