i don't think I'd sweat it too much. I took my son on a 12 hour trip -- two 5 hour plane rides and a 2 hour layover -- when he was 20 months old. He also doesn't sleep in the car. He ended up having two 30 min naps (one on each flight) and by the time we got to where we were going it was past midnight! Of COURSE he was OT, so he woke at 8 am the next day. Which was actually fine as it kept us on a fairly normal routine. There was a 3 hour time zone difference, so 8 am there was 5 am at home.

But we just went by the local time -- I just kept A time reasonable.
My son is also VERY sensitive to light etc., and he and I shared a room on this trip -- the room was pretty bright, despite me hanging towels on the windows LOL. But he amazed me by taking 1.5-2 hour naps the whole time we were there. I think he was just exhausted. I never got him to bed before 10 pm once that whole trip, and he only got about 10 hours sleep each night, but it worked out in the end.
I guess what I'm saying is DO NOT FRET. Enjoy your trip! Your son will probably do better than you expect, if for no other reason than he'll be exhausted by all the new stuff going on! The things I found worked great on the plane were a) portable DVD player - my son never watched TV at home, so the DVD player was new and exciting; b) little plastic animals to play with on the airplane tray; c) picture cards with animals on them; d) a couple of new books he hadn't ever seen before; e) some new foods he hadn't eaten -- like juice boxes or foods in fun little packets (goldfish crackers, fruit candies, etc.) I also used lots of smarties (not choc. candies, but sweetart type canides) to bribe him with in the airport and on the plane. That worked a treat! suckers worked well too. Do not underestimate the power of a bribe!
If he has a lovey or uses a paci for sleep, don't forget to bring them on the plane with you. I forgot to put my son's blankey in our carry-on on the way there, and I think things would have gone better with it. On the way back I did bring blankey and while he didn't sleep more, the blankey was a nice cuddle companion!