Oh, I thought it was the goal of the gameplay to actually do it without a lightsource and then find something like that. Explored almost the whole abyss just by drawing the fluorescent fishes near me and wondered why this part of the game is so hard and frustrating.
So, to make it clear, there is a light source to be found, that is not hidden in the abyss?
addit: ha! I got out of that pearl cave without light, I'm so happy ;_;