(1):

(n.) Illumination; irradiance; brilliancy.

(2):

(n.) The apparent enlargement of a bright object seen upon a dark ground, due to the fact that the portions of the retina around the image are stimulated by the intense light; as when a dark spot on a white ground appears smaller, or a white spot on a dark ground larger, than it really is, esp. when a little out of focus.

(3):

(n.) Act of irradiating, or state of being irradiated.

(4):

(n.) Fig.: Mental light or illumination.