OP - my man is extremely conscious of spending money on electricity so he cuts it off wherever he can - I can't run my hairdryer if he's got coffee on the burner at the same time, cuz he doesn't want to spike the usage, etc.
My man also has VERY "OCD" like behaviors, has joked for years about himself in this regard:
- he is obsessive about certain methodologies, and things being in their right place - but this arises from having always had his stuff stolen from him by his abusers. (like a child who grows up in an orphanage has to fight to keep any one thing their "own" so it isn't taken by someone else) .. so this is PTSD related, not OCD.
- he has "routines" that he MUST follow before he can feel enough relief from his anxiety to leave the house - but this stems from both the above realities, AND the fact that he is PTSD-DID and so his memories don't transfer from short to long term memory the way it should, so he honestly cannot remember IF he did this or that (lock the back door? turn off the furnace? make sure the refrigerator door is closed tight? windows locked?) .. he was abused to such extremes most of his early life, that he is always expecting some thief or betrayer to come across his path at any time and take everything he has - because this has happened to him over and over. I tend to walk through the routine WITH him, now, cuz he also hates stressing me out by always being late for things which in turn puts more anxiety on HIM .. but if I SEE him do a thing, then he can ask me in the car (instead of doubling back to the house to re-do the routine!) - Did I remember to turn the furnace down? Did you see me click the bolt lock? ... etc. :)
SO .. all that to say - I can't comment on the QUALITY of the light vs. dark shower, but maybe it's just a money saver. Agree with other posters above - you can just ASK him, but I have found I have to be careful how I ASK, too .. cuz that could be a trigger, or he might instantly feel I'm either questioning his judgment OR somehow disdainful of some of the side-effects of his PTSD which he can internalize, cuz he really struggles with feeling ashamed because of his "quirks."
Then again, it really could be as simple as "Why do you like taking showers in the dark?" :) :) Oh dear, we can so easily complicate things! LOL
~S2B