The spellbook of light is among the easiest spells. After reading this, the scroll of light is even more useless.

Casting the spell of light has the same effect as an uncursed scroll of light: a circular area with 5 squares radius around your position (while casting) is permanently made lit.

At first, the spell is useful to train up divination, and to light you way in the Gnomish Mines if you have enough energy. Since you have to see what you can target, it can help you use a polearm or jump in dark parts of the dungeon. However, casting takes up a turn, making jumping less powerful. This spell also helps you save lamp oil during protracted battles, especially on the stairs up where covetous monsters like to retreat. It can also be used to mark the area you have already searched for the vibrating square.