what is a luminous realm?

Where is there more information about the luminous realm? the standard pali is lacking. what is the relationship with jhana? from MN 115 : > “...There are these three elements: the elements of > the sensual realm, the realm of luminous form, and the formless realm. > When a mendicant knows and sees these three elements, they’re > qualified to be called ‘skilled in the elements’.”