yes theres multiple kinds of inefficiencies concerning the external circuitry etc, but there is also the intrinsic inefficiency of current LEDs: some of the high energy photon are downcoverted to a low energy photons by phosphors, so there is non-radiative (heat) generation in the phosphor itself. In theory it is perfectly possible to use "quantum cutting" i.e. 1 photon -> 2 photons instead of 1 photon -> heat + photon. There is quite a lot of research on quantum cutting phosphors, both for LED's and for VUV excitation etc, so these higher efficiencies will probably come, but I don't know how far out in the future. If someone knows of commercially available quantum cutting phosphors (or products using them) I would be very happy to know about them for some physics experiments...