psy, it's either excessive air temp or radiant heat from that silly tanning light that's causing the stretch in the tall plant. T'ain't natcheral, son. Get it out of there.
Back to my op for a minute... Cooltubes are still working like a champ, pinning the room temp between 23.0 - 24.5C, except for one weird glitch.
A couple days ago, I checked my peak mem thermos. There are 2 in this room, just to be sure. One is an indoor/outdoor type, which measures air temp in the immediate vicinity of the thermo; it also has a remote 'outdoor' sensor, which I have put in the cooltube exhaust duct so I can monitor that the cooling system is working correctly. The cooltube EGT is usually about 32-33C with an air intake temp of about 20-21C.
Scarily, I had a big room air temp spike the other day. One of the thermos recorded a flowering room air temp peak of 29.5C and the other 27.5C! Amazing, considering ambient air available to be drawn into the op was at a cool 21C.
For temps to spike as high as 27-29.5C, my main exhaust blower or entire room air ventilation system would have to have failed for an entire lights on period... and I am fairly confident all the ventilation blowers are OK. The main vent thermostat seems to be switching stuff on and off OK, to the best of my knowledge. I have checked and rechecked all the connections in the ventilation system electrics and all looks OK. This really is a bit of a mystery to me.
If the main ventilation system is working and the cooltubes are being ventilated normally, the room will be right between 23.0 & 24.5. Cooltube EGT will be about 32-33.
29.5 is seriously hot and would cause plant damage or stretchy buds.
It's been OK for a couple of days now, not deviating from the 23-24.5 range, lights on or off... I'll keep watching it tho... something's amiss- and it may just be highly intermittent and hard to identify.