Temps at top of foliage

This is dwc under a 400w hps. They are ending the second week of flowering. This is my first time using the hps. I have had the temp gauge on the lid of the reservoir, but as plants grow it became shaded. Temps were 73 with light on. I rigged up a way to suspend the gauge directly under the light at the height of the top of the tallest plant. The temp was 91.

I guess the Q is obvious: should I measure temp there? Is 91 too high for that location?

I did raise the light a couple inches. I hate to raise it more than necessary because light won't penetrate as deeply. I did jack up the fans and the air circulation. Any thoughts appreciated?

temperatures above 85F generally stop plant growth, unless its genetics are born from hot environments, but even then they still won't grow to full potential. Have you ever seen an outdoor grow in a hot area of the world in a video or something? They sometimes put shade screens over the top to keep the temperature down. Just make sure you are pulling the heat out from the top of your growing area and keep the ambient temperature outside of your growing area as low as you can to balance out the inside temps. Your space might be a little too constricted so you might look into getting a cooltube?

everywhere i read says keep it between 70-75 for best growth. but i'm a new grower so i wouldn't just take my word for it. good luck with the grow

I should probably have added that they are growing like crazy and look healthy as can be. New bud sites are popping up all over. I wonder if temperature should be considered as an average across several locations? I also think I need to raise the light some more, but damn, I hate to essentially reduce their light when visually they are doing so well.

Average rule is... put ur hand level with ur top foliage. Hold steady for a couple minutes, if top of ur hand gets hot then raise light untill it doesn't. You don't wanna go higher then 12 inches, if u got a air cooled hood u shouldn't have problem gettin it even closer.

I keep my 400w(330w technically) CMH about 8 inches away with OPEN hood and my foliage temps don't go over 80.

The most accurate way to measure ur temp is at ur foliage. U def wanna keep it below 85. Make sure ur thermometer isn't in direct light from ur hps or it will give false readins.

lostNug, thanks! One Q though - you say not to put therm in direct light. I have been doing that. My reasoning is that the light is directly over the foliage, so why measure temp off to the sides where there are visibly less lumens and presumable heat?

Illegal Smile said:

lostNug, thanks! One Q though - you say not to put therm in direct light. I have been doing that. My reasoning is that the light is directly over the foliage, so why measure temp off to the sides where there are visibly less lumens and presumable heat?

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good point