Without lights, computers can be useful. Ursula Le Guin once said in an interview that the advantage for an author of using a computer is that she can write poetry in the dark.

However, even in the dark it may not always be necessary, given that for performers the printed music is often more of an aide-mémoire than anything else. I once heard a broadcast concert of a concerto in which applause broke out in the middle of a movement, a most unusual thing at a classical concert. Afterwards the announcers explained that the lights had gone out but the players kept on going. The applause came when the lights turned back on.