help with a 600 watt hps in a 2'x2' cab

I have a 600 watt hps in a 2x2 cabinet. My thermometer probe is taped to the side of the compartment and after the light has been on for a few hours it reads up to 90ºF. I've since learned the difference between radiant heat and air temperature but it is impossible to make shade in this tiny space with such a powerful light. I made a 1"x1"x1" cube with slits in the sides to put around the probe and it lowered the reading to 88º but i still think it is reading high because the utility/exhaust room (similar to NGB Design) temperature is only 85º and thats with the air comming fom the light vent and ballast heat.

I guess my question is: Does anyone know a good way to determine true air temperature under a HID and when i hear to keep it under 85º is that refering to radiant heat?

ambient temp should be under 85. use ur hand under the light, if its too hot for ur hand its too hot for the plants.

if ambient temp is 85 even, when that light kicks on its gonna skyrocket, esp in small space, i guess, as u didnt mention a unit of measurement.

ugzkmk said:

ambient temp should be under 85. use ur hand under the light, if its too hot for ur hand its too hot for the plants.

if ambient temp is 85 even, when that light kicks on its gonna skyrocket, esp in small space, i guess, as u didnt mention a unit of measurement.

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The ambient temperature is around 70ºF when the light comes on it travels thru the mother chamber 2'x2'x4.5' and then into the Flower chamber 2'x2'x6'. The thermometer reads 88º in the flower chamber but i believe that is radiant temperature because the temperature in the utility chamber drops 3º. I can touch the glass on the hood and its slightly warm but not hot at all. How can I measure air temperature without the radiant heat screwing up the reading?

Sativa Hybrid said:

The ambient temperature is around 70ºF when the light comes on it travels thru the mother chamber 2'x2'x4.5' and then into the Flower chamber 2'x2'x6'. The thermometer reads 88º in the flower chamber but i believe that is radiant temperature because the temperature in the utility chamber drops 3º. I can touch the glass on the hood and its slightly warm but not hot at all. How can I measure air temperature without the radiant heat screwing up the reading?

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Dunno if its too late but you could take a measurement of the temps by hanging the therm. higher than the lights so the light doesn`t mess up the reading

I would also take a black pot or something, cover it with whatever to block the lights and get it right next to the plants, make sure you let the cab get nice and hot before checking temps. I would personally take the average of the 2 readings since there is air circulating in the cab. (more readings makes the avg more accurate)

600W in 2x2 seems like a fucking LOT. any way you cud increase grow space? I mean I think you could get alot more with that much light if you could increase by like a foot or two vertically

Sounds like you need more airflow. Also you it sounds like you have a problem blowing warm air from the mother chamber into the flower chamber. I'd add a fan blowing fresh air into the flower chamber. Blow fresh air into both sides and have a central exhaust. Don't know if you have an exhaust fan but I wouldn't recommend one, just an open vent for the exhaust and fans blowing fresh air in, you can restrict the airflow out if you have a fan for exhaust also.

Thanks for the tip Mr. Holland. I want to do what you suggest by placing the probe above the light but I will have to rerun the line on the next grow attempt (I'm experiencing problems which are probably due to temp ph and nute (this has been a learning experience but marijuana should never be called weed again!)

Rachface, I KNOW!!! originally I had planned on a 250 watt hps but the 600 was a recommended design change by a close friend who knows much more about this than I. The cabinet is built and if I make any changes it will be to try and trade the ballast and drop the watts to 400. I don't know if 400 would make alot of temp difference but the hood isn't designed for anything smaller than 400 :\

Thanks for the reply, La9. The mother chamber has 4 26 watt cfls and a passive intake. I have a 6" flexible duct that pulls air from the top and delivers it to the bottom of the flower chamber. The 600 hps is in a radiant hood that is sealed and has three 4" openings. 2 are pulling air from the top of the flower chamber and the third has a 4" flexible duct that delivers the air to the utility chamber where it is pulled thru a carbon filter and is sent into the attic by a 6" inline fan.

i agree...air flow is your best option, i bought one of those IR heat sensors and i measure the temp of the leaves

fat sam said:

i agree...air flow is your best option, i bought one of those IR heat sensors and i measure the temp of the leaves

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I'd love to borrow that for a few days

I guess I'll keep posting my trials and errors so taht anyone searching for info might be able to use some of it. I have seven 2.5" holes for my passive intake that i figure gives me 34.37 sq inches of intake and the 6" duct that puts air into the mother chamber is 28.26 sq inches. After reading Mr.'s post I decided to try putting more fresh air in the flower/veg chamber so I drilled seventeen 1" holes giving me 13.35 sq inches of cooler room air in addition to the 6" duct of warmer air from the mother chamber. I still havent solved the temperature probe problem yet but I hope to be able to tell if the problem is getting better by utility chamber temperature and plant condition.