Thoughts about temps

[curlybud]

Been wondering about this for a while now as I prob have heat issues in my box..

How do you effectively measure temps in a growbox? Where do you place the little probe thingie some digital thermometers come with, usually intended for outdoor use? Do you place it a) right under your light, close to your plant, to get an idea of the temps the plant will be facing? or b) somewhere not directly in the light, maybe a bit above the plant, where you can get the circulating air temp? If a, you might be getting readings a bit higher than the actual temp since you're dorectly under the light. If b, how do you make sure you plant isn't getting too much heat from the lights?

I get an approx 5 degrees celsius difference depending on where I place my thermometer and the little probe. If we're talking 22C, then fine, but if we're approaching the 30s in the box, I feel getting a reading 5 degrees below the actual temp is approaching the danger point.

Right now, I try to point my fans towards the lights to try and carry the warm air away from them. Should I be trying to point it at the plant instead to try and keep the warm air away?

Seems like the more I think about it, the more confused I get.
Any form of, uh.. light... shed here would be much appreciated!

 

[glitch]

Take this with a grain of salt as I haven't actually done a grow yet, But I would suggest you do the following:

Use 2 probe thermometers. You need probe thermometers so you can mount the temp display outside of the grow box. That way you can view the temps while it's closed and it will be more accurate.

Put the first thermo's probe about where you estimate the top of the plant will reach (so 6" below the light or whatever, depending on your setup). Make sure the probe is directly below the light and that it is directly illuminated by the light (so no shadows). If it's off to the side of your box or in the shadows it will give you an inaccurate reading. It may require a bit of rigging to suspend the probe in mid-air . Put the second thermo's probe roughly 2/3 between the light and the bottom of your box. So 1/3 away from the bottom of the box. It can pretty much hang against the side of the box and it will be accurate enough. This will give you a pretty decent idea of the lower temp boundary and the upper temp boundary.

It can also help to measure yet another set of data. Use the two probe thermos again. One should be measuring the air coming in through your intake and the other should be measuring the air going out of your exhaust. That will give you your T-diff, which will tell you how much heat is being either produced by or absorbed by your grow box.

Also, you should know that there are 2 main ways your plant is receiving its heat: via radiation and conduction/convection. Radiation is direct heat in the form of infrared light coming directly from the light source to the top of your plant. Conduction/convection is the warm air flowing around your plant and transferring its heat to the plant. If your plant is too close to the light source, then it will be burned via radiation and no amount of pointing fans at anything is going to help you. The plant cannot get too close to a hot light source or it will be damaged, period. However, if the air in the box is too hot then you just need better ventilation. Having your intake fan blow across your lights can help to disburse the heat, but you probably just need more air moving in and out of the box.

To any people who actually have experience: of course feel free to shoot my idea full of holes here