[alnwlsn]

I meant it's it's physics job to produce light. If it does that efficiently, great! That's one thing you should want.

It's human job is to convey information. If you're measuring efficiency that way, it would be most efficient to have the dimmest screen possible (using the least energy) as long as you can still tell what's happening on screen. If that's already happening, then surely a screen twice as bright as you need it to be would use twice the energy and be half as efficient, even if it physically is equally as efficient making light at any brightness.

You could be using half the energy to do the "same" job.