One night, Aunt Judy was reading a book in the living room. Uncle Jim turned off the light, leaving the room completely dark. Aunt Judy continued to read. How is this possible ?

He was in a different room

Uncle Jim was in a different room OR Aunt Judy was reading on a backlit tablet and could see even if the light was turned off

Aunt Judy is blind and reading in Braille

she had a light source in hand