Luminosity is a transparency type in the Transparency Tool. This uses the grayscale equivalent of the color to control the luminosity (or Value) of underlying objects. Note that Luminosity has no effect on gray, white or black underlying objects.

The color of the object with Luminosity applied:

Gray & White - increase the luminosity of underlying objects. White has the greatest effect, producing saturated color.

Black - remains as a black object.

Other colors - convert the color to the equivalent shade of gray. (Yellow gives light gray, Red dark gray.) Then increase the luminosity of underlying objects.