DS1 is 9 and needs dark to sleep. He shares a room with DS3 who is 7 and scared of the dark. He wants to have his side light on but I have vetoed this saying I'll leave the hall light on and the door open.
DS1 says it's still too much light.
The argument is still ongoing up there and it's after ten now.
My DD's are a little like this,I have put them in bunk beds,and the one who wants the light has a Nightlight that is a Torch and a clock with a light.I put a bookcase up against the bed,so the top shelf becomes her "bedside table".She has all the light she needs up there without it bothering anyone.
Alternatively,you can get bed tents from Ikea quite cheaply which keeps them in the dark.
Oh dear, sounds familiar - have had this with my DDS. Haven't really got an answer i am afraid. We did what you are doing - left hall light on with door open a crack. Time seems to have helped, DD2(8Y) now is much less worried about the dark, but last year I was up and down the stairs sorting the disagreements out.
My ds used to say he was afraid of the dark, but even if we left the light on he still didn't sleep well. Eventually we moved him in with dd and he slept fine, in the dark. The distraction of having someone in the room with him seemed to make him forget the initial fear iyswim. Is there something you can distract your ds with without having to leave light on? e.g. some kind of comfort object, or even torch for under bedclothes in case he needs to see.
Ds doesnt like the dark and we used to have to leave the hall light on. however we got him a new cheap argos bedside clock with large (cos he's short sighted) green luminous numbers on. This actually gives off enough of a green glow that we no longer have to leave the light on yet isn't too bright to be a nuisance