I should be a little careful here, so that I don't degrade the discussion away from the issue, but in regards to the original question, I don't think that having a single light source does much to negate shadows. If you think about it, turn off your lights and light a candle in your room, see the shadows? Now bring in four of your friends, and see how many more shadows you have.
So, assuming that the light source is in the middle of the group, there's plenty of shadows. If there is a light source at both ends of the group, then you get into the situation where you have a well lit hallway that would be hard (or impossible, depending on your interpretation of the rules) to sneak through.
As I said before, I'm more in favor of just putting a big modifier on the hide check (or a bonus on the spot checks) than saying "it can't be done."
Not that this is a fair example, but many action movies have characters that sneak past opponents in well lit hallways, some of them do crazy cool things like climb up the walls, and hide higher than people are likely to look, or duck down below where people look, etc.
I think it lends the game to better play if you just make rolls incredibly difficult instead of impossible. What if the characters do decide to play a game of bones, and the one person who is supposed to be keeping watch actively says they are facing the other way? I'd stab someone quick, if I were that half-orc.