Temperatures and hps height

I have some plants in dwc under a 400w hps. The tallest plant is about 12 inches. Measured at the base of the plants, the temp is about 76. But up at the top of the tallest plant, under the light, it is 88. The bulb is about 14 inches above that point.

1. Is there a problem?
2. I try to keep temps in the upper 70s, not much over 80, but at what point is that measured when they get some height?
3. What to do?
a. not worry
b. dim the dimmable hps to 250w
c. raise the light

88 isn't too bad. Best thing to do is raise the light a bit and adjust the height of the shorter plants buy putting the pots on top of wood scraps, books etc so that they're all equal.
If your doing hydro that's impossible of coarse.

you can raise the light.. i would go close to 18 inches... unless your plants are stretching for light, it is probably too close.

1. put a fan on em
2. bend or tie the plant down so most of the vegetation is at the same height as the rest of the plant
3. dont worry, I have a 1000w hps at 18 inches and could go closer but I need the area coverage that the height affords
4. if the plants arent burning its not too close, plant growth halts at around 85 degrees (depending on strain)
so, a) dont worry, unless you notice the plant growth halting!

oh btw, check the water temp, thats just as important as air temp when doing hydro, cold water holds more dissolved oxygen, warm water is will slow growth and invite pathogens like algae and the like hope that helps

FYI, it is hydro so I can't change plant height. If the temps are taken at the plant tops, I don't see how they can be kept below 80 unless the light is much higher.

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