L2, L4, L5, L6, L7 and U2 all use a five watt Luxeon.
The L2 and L4 are small and pocket sized. They're similar to the other E series lights. Due to their small reflector, they tend to be mostly flood, with little throw (no tight spot). The L2 is two stage (high and low) while the L4 is single staged (high setting only).
The others have a larger body (C sized) with a larger, deeper reflector. They give a tighter spot that will light up objects better at a distance (more throw). Each one has its own unique characteristics:
- L5: single stage, runs on two cells
- L6: single stage, runs on three cells for longer runtime
- L7: single stage, runs on rechargeable cell pack
- U2: multi stage (six settings from low to high), runs on two cells
I'm over simplifying some things a bit, such as options like the two stage tailcap for the L4, or the possibility of using an 18650 cell in the U2. But, for the most part, all of these lights will put out somewhere in the neighborhood of 100 lumens, give or take depending on the lottery. Their main differences lie in the reflector choice and power supply.