By using multiple junctions and stacking them, top one converting the most energetic photons, then the second-most etc, one can approach the theoretical limit of about 95% or whatever it is. However in practice it's very expensive and difficult as I understand. AFAIK the current state of the art is about 6 stacked junctions at around 60% efficiency, at great cost.

And as you say the LEDs aren't 100% efficient either, though both deep red and bright blue are among the most efficient, about 85% there.

So that leaves you with about 50% overall just from those two.