ideal temperature...... under lights or in room?

read a lot of posts and bits of information stating the ideal temperature is between 70 and 80 degrees, out of curiosity i took an indoor/outdoor thermometer and place the outdoor electrode underneath of the lights.

both readings were taken on the floor so obviously things are warmer higher up, however room temperature about 3 feet away from the light is 77 degrees directly under the light with the light about 3.5 feet off the ground is 90 degrees.

this poses the question of the 70 - 80 degree reading, are folks taking the temperature based on room temperature or temperature under the lights where the plants actually are?

Where the plants actually are is the best place to take temps. Rule of thumb is to place your hand just over your plants for 30 seconds, and if its uncomfortably to your hand than its to hot for your plants. Hope this helps. Ideal temps at the plant should be 76-86 ish.

Room temperature. Don't put the meter or the sensor under the light because you'll get a false reading. I had to correct the same problem a week ago.

so which is it, at plant height or bottom of room?

I keep my sensor even with the height of my light in my tent and off to the side out of the light.

The distance your plant should be from the light is based on how much heat your light is radiating.

ok, but how much heat is the light radiating if your sensor is in the shade??

I have an aircooled 400w light, so not very much heat until about 5 inches away and my hood is cool to the touch.

Every set-up is different. What are you trying to figure out exactly?

well... I'm trying to get the light as close to my plants as I can.

The light is about 12" from the tops, and i'm getting 90F when the meter is placed under the light, at 20" approx from it. Good ventilation.

I think my 90F is erroneous is because the sensor is in direct light. So I should stick the sensor on the roof of my growbox and place plants 6" from light?

Hard to get a fixed answer on this.

Like said in the second post, use your hand to measure how close until you feel heat. Too much then back it off a little.

Just make sure the temp in the whole grow area doesn't break 85F.

420God said:

I keep my sensor even with the height of my light in my tent and off to the side out of the light.

The distance your plant should be from the light is based on how much heat your light is radiating.

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The ideal temperatures have everything to do being under the light. It is possible for a "room" to have varying temperatures in different areas. We are growing plants. The temperature should be checked at canopy level under the lights.

Older thermometers would give you problems but the new digital ones with probes have no issues being in the light. You need your temperature on your plants to be ideal. Anywhere else in the room really doesn't matter. Putting a thermometer anywhere else is just worthless. Who cares if it's 75 against the wall of your room if your plants are at 90?

phillipchristian said:

Older thermometers would give you problems but the new digital ones with probes have no issues being in the light. You need your temperature on your plants to be ideal. Anywhere else in the room really doesn't matter. Putting a thermometer anywhere else is just worthless. Who cares if it's 75 against the wall of your room if your plants are at 90?

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i agree lol. mine says 81.

You should have good enough airflow in your grow room that the temp is pretty even around the room anyways.

I got one of these (similar) and it's proven to be even better than expected. Point and shoot....excellent for exact leaf temps, soil temps, containters, equipment, etc. etc. I think mine ranges from -45F to 600F. They are awesome!

http://www.thetoolwarehouse.net/p-4803-raytek-mt6.aspx

Here's Jorge using one in the field:

http://www.youtube.com/watch?v=AS5GiJdXaYM