Recommended light distance won't work for me?

[John Holmes]

I read that the recommended distance from light to plant should be around 41cm/16 inches for a 600w. But when i put the lights even close to that my thermometer sky rockets to close to 30C? Ive got good ventilation and all, 2 oscillating fans. I put my hand right above the canopy to feel if it burns but it doesnt, does that make it good to go?

 

[Johnny5thesim]

I read that the recommended distance from light to plant should be around 41cm/16 inches for a 600w. But when i put the lights even close to that my thermometer sky rockets to close to 30C? Ive got good ventilation and all, 2 oscillating fans. I put my hand right above the canopy to feel if it burns but it doesnt, does that make it good to go?

I wouldn’t go by a generic distance. Your light manufacturer should have recommended distances for height during various stages. I’d start with that, and fine tune to your liking.

 

[Johnny5thesim]

I should mention. I have no idea what light you’re using! I use LED, and wouldn’t feel comfortable seeing 30 degrees.

 

[Bush Doctor 77]

Put your thermometer in the shade.

 

[John Holmes]

Im using a 600w MH with a maxilight reflector

 

[Bush Doctor 77]

I run 1000W HID at about 18 inches, so you should be OK with that light distance. Unless your grow area is open, oscillating fans do not provide ventilation. That's circulation. You need both.

 

[John Holmes]

Yeah i have a extracting fan with carbon filter.

 

[John Holmes]

Put your thermometer in the shade.

Do you have any advice on how to create a shade? Or where i could put the thermometer cable to get a decently correct number?

 

[Bush Doctor 77]

Do you have any advice on how to create a shade? Or where i could put the thermometer cable to get a decently correct number?

A piece of cardboard, under the plants. The problem with where you have your instrument is that you are getting the equivalent of solar gain. Stand in the shade on a bright 70 degree day, and put your hand in the sun. It feels warmer. Plus the glass traps the radiation from the light, like a greenhouse.

 

[John Holmes]

A piece of cardboard, under the plants. The problem with where you have your instrument is that you are getting the equivalent of solar gain. Stand in the shade on a bright 70 degree day, and put your hand in the sun. It feels warmer. Plus the glass traps the radiation from the light, like a greenhouse.

Hmm okay, but shouldnt the thermometer be as close to canopy height as possible?

 

[Bush Doctor 77]

No. You are measuring radiant energy+air temp, not just air temperature. Also, the plants are respirating and have wind chill which your instrument doesn't measure. The evaporation of moisture off the leaves reduces surface temps.