There's definitely situations where both are useful. Is most or all of your group in LoD's cone area, and do they need healing? If so, then duh - cast LoD. In 5-mans there are a lot of situations (particularly in a melee-heavy group) where all 4 other members of your party are in its range, and I see no problem with doing it then. Certainly there are bad times to use it, but it's not universally bad in 5-mans like the mystery yeller seems to think.

Basically, this, but I'd stress that those situations are not common.
1) The RDF tends to put people in groups with other classes, so you're unlikely to have two rogues or two warriors or what have you.
2) Your ranged group members will usually spread out from each other by default. It's a habit to avoid AoEs.
3) Bosses are big, and the melee people will often be standing behind the boss, making them further away from the tank.
Because of all this, the frontal cone that includes the whole 5-man is not common, and difficult to find when it's there. If you can find a pug that is willing to cluster up for Radiance or LoD, then more power to you, because they've been hiding from me.