Something that is nonluminous does not produce its own light.
Nonluminous things are usually dark and need light from something else to be seen.
Examples:
The moon is nonluminous; it reflects light from the sun.
The nonluminous room was dark until we turned on the lamp.
She pointed to the nonluminous stars in the night sky.
The nonluminous cat was hard to see in the dark room.
The nonluminous cave was so dark, I couldn't see my hand in front of my face.
The nonluminous fish in the deep ocean are hard to find because they don't make their own light.