The Book of Light and Day is a holy text of the Menaphite Pantheon. The text is known to contain the story of Tumeken's Dream, during which Tumeken created the gods Crondis, Apmeken, Het, and Scabaras.
According to Reldo's comments on the website version of Tumeken's Dream, the Book of Light and Day is typically written in the Menaphosian language, which is likely related to or synonymous with that of the greater Menaphite people.
Although the text itself cannot be obtained by players, an excerpt containing Tumeken's Dream can be found on the Official RuneScape website. The Sphinx in Sophanem also recounts Tumeken's Dream in detail. It is unknown what other information the book contains.