I try to keep my thermometer and hygrometer in the canopy. About where your white one hangs. That's the area that's getting the most stress wherein I may have to intervene. So that's where I keep it.
I have a fan blowing directly on my bulb 600 watt HPS, that air is blowing across the bulb and hood and to my exhaust, two more fans are blowing air up from the floor, So I just figured thats my average. The intensity of the light at the top gives me a false reading of my room temp, in all actuality to get a accurate average you would need 3. One on top of the room, one at canopy and one on the floor... divide for your average.... but thats just not nessisary for me to worry about ya know?
I was kinda scared to point mine directly on her but it does give quite accurate readings, my brother is electrician so I just happened to have one laying around the house, never needed one myself lol. Useful for sure, probably one of the most useful tools for a first time grower for accurate real time readings of temps.
I used to keep a thermometer/hygrometer near the canopy, but took it out after the batteries ran out. Nothing really changes. I keep a similar device outside the room to keep an eye on the ambient temps/humidity. I do use a laser thermometer on occasion and would recommend one to other growers. It gives an instant readout as to the temp anywhere in the room, even on a leaf. Very useful.
Simon
$ 50 at the grow shop but have seen them too at hardware stores and walmart for less
