1. The quality of having extraordinary mental capacity or talent: The luminosity of the character in the first act of the play as created by Ms. Scully, was astonishing, well deserving of the standing ovation which she received.
2. The energy radiated per second by a celestial body; such as, a star: John and the astronomers were using new equipment to measure the luminosity of the newly discovered star in the southern hemisphere.
3. The visual perception of the extent to which an object emits lucence: Due to the cataracts in his eyes, Mr. Smithson felt that the luminosity of his reading light had declined.
4. The fact or process of giving off brilliance; the quality of an object that produces shine: When certain botanical microscopic life in the sea are exposed to sunlight, their luminosity is increased, causing the sea to appear to shimmer.

A standard measure of the responses of the eyes to monochromatic (one color) light at various wavelengths: As part of her research, the ophthalmologist, Dr. Robinson, studied the changes in the luminosity functions of the eyes of her patients.

The fulgent power output of the sun or any other star: Tom and the other astronomers used highly technical telescopes to study the changes or variations of the solar luminosity during the phases of the calendar year.