@Linkat,
We can't really answer this question without any context (observations) on how the dog reacts in the dark.
Just a fun experiment if you're game. Set up a low light security camera where you dog spends most of the time when no one's around. I suspect... like many dogs, they mostly use their nose to keep an 'eye' out on her or his surroundings.
Then again, I figure maybe an older dog might find a lighted room to be more reassuring if his or her senses are fading due to age. It would be kind of difficult to determine the anxiety of an older dog is caused or partially caused by a dark empty house or apartment.
I suspect that the pupper in question wouldn't really care if a light is on or not. That your husband is projecting how he might feel if he was in the dog's place?
Personally, I'd leave some classical music on for the pupper. Sophisticate that pupper up as much as possible! More Debussy for your puppy!