Hi sorry I've been a stranger...little obsessed about my own grow, I guess
So, as far as burning your house down goes, it's pretty unlikely.
Does something different happen if you switch the lamp off versus unplug it? Like, is there a cooling fan that stays on?
My guess is it has to do with the temperature of the glass. Glass hates to change temps rapidly and unevenly. The other day, my wife took out the glass shelf from our
cold fridge and tried to clean it in the sink under
hot water. Oh yeah, you guessed it,
glass-explosion!
I used mercury lamps in a microscopy lab for awhile, and the rule with them was: if you turn it off, leave it off for 30mins before turning it on again. Turning a high-heat lamp like HPS off and on frequently can cause uneven heating and lead to the glass breaking.
In your situation, where you'll be turning it off for 6-12 hours at a time, there shouldn't be a problem. Hope this helps!