What was the spell did harry potter use in the prisoner of Azkaban to make light?

Answer 1

Two spells. Lumos and Lumos Maxima

The former lights up the tip of the wand giving it a torch-like use. The latter sends a larger span of light ahead and lights up the distance - for instance, you see this in the Half-Blood Prince when Dumbledore lights up the cave.

However in the Prisoner of Azkaban, we see Harry say this spell without its effect happening. It gives a short Lumos effect (as opposed to Lumos Maxima's effect, as it was meant to). In the short time that he produces light under his sheets, we see a spell book. We can assume that as the light did not go far as it was intended to, and did not stay on for long, Harry was practicing the spell and had not yet mastered it.