Temperature regulation, ventilation

A question from a fellow grower:

i have a 4ft by 2 ft by 3 ft tall grow box using 6 4ft t5 bulbs my problem is my lights are creating 90 degree temps while on using 90 cfm exhaust fan when lights are off temp will drop to around 67 will this be a problem and should i shut down ventilation during 4 hr dark period any help or suggestions would be greatly appreciated by the way doing autos thanks

There is a formula to figure “cfm” for a grow space. the temp you mentioned ; 67 degrees’s is OK for night time “light’-out”. many run fans 24/7 but also many turn off fans a night - consider the later - what’s your daily temp’s? When you open the tent are you "blasted "by a heat-wave?

(90f) lights on is about 5f above safe and 10-15 above optimum for best healthy growth here are some simple options to consider use a faster fan with speed controller.
Add a second bigger fan to exhaust and use 90cfm fan to bring in cool fresh air. Cool mist humidifier vent your lights by placing a glass sheet under them and forcing air between light and sheet? remove or allow top of light shade to protrude top of box so it can vent heat