I didnt upgrade my lights for electricity savings per say, as power is pretty cheap here.. I just hated having 1 light source trying to blanket 10 plants.. And i hated having the extraction fan running non stop, ballast fans running, bulb changes, etc, etc... My low temps are also happening as i am only doing 4 plants right now and am only running one panel.. Once both panels are up and going i dont think the heater will kick on at all.. With one panel around 300-350w , my tent stays at about 22c, I've found that the girls like 25c..I have one of those heavy duty canvas tents(called premium canvas), and it seems to hold the temps in well.. Ive only had it come on once while ive been in the tent.. I bought one of those inkbird temp controllers that u plug a heater in and you extraction fan and it will regulate whatever temp u want... They work fantastic..
Cheers