You could use Solar Beam in the dark.
Scene:
Red was battling Blue in Mt. Moon.
Red: Ivysaur use Solar Beam
Blue: Ha, you can't use Solar Beam because it is very dark. I'm going to de-
Blue was interrupted mid-sentence when Red's Ivysaur defeated Blue's Charmeleon using Solar Beam.
Blue: .... I'm done for life now...