brightness; splendor; radiance
Refers to a brilliant, shining light or glory, often with a poetic or formal tone. Used for literal light, as well as metaphorical brilliance of achievements or character.
The brightness of the sun filled the room.
His achievements will shine with eternal splendor.
The jewel gave off a brilliant radiance.
His life was filled with splendor.
栄光 refers specifically to glory or honor earned through achievement, while 光輝 can describe either literal shining light or a more general sense of splendor.
好機 (a good opportunity) and 光輝 (brightness, splendor) are pronounced identically as こうき but have completely unrelated meanings.
Compound of 光 (light) and 輝 (radiance), both kanji carrying meanings of brightness and shining. The reading こうき is the on'yomi for both characters.