ray, light
光 centers on visible radiance: a ray of light or light itself. The two given meanings are essentially the same concept at different scales.
光 is a pictograph of a person kneeling under a flame or light source, representing light or radiance. The modern form retains the top ⺌ (a simplified fire/light element) and the bottom 儿 (legs), though the original kneeling figure is now stylized.
The top ⺌ looks like a small flame or light, and the bottom 儿 resembles legs. Picture a person holding up a light, making rays shine out: 光 is light.
For コウ, imagine a bright light shining on a coal (コウ) mine: coal -> コウ, and the light illuminates the dark mine.
light
sightseeing; tourism
to shine; to glitter; to be bright
scene; spectacle; sight; view
sunlight; sunshine; sunbeams
glory
optics
honour; honor; glory; privilege
ray (of light); beam; light
emission (of light); radiation (of light); luminescence
brilliance; polish; lustre; luster; glossy finish
moonlight; moonbeam
light-year
sunshine; sunlight
bright light
footlight; limelight
lightning
to shine; to glitter
sunbathing; basking in the sun
brightness; splendour; splendor
brilliance; splendour; splendor; lustre; luster
optical character recognition; OCR
cost of fuel and lighting; cost of heat and electricity; energy bill; utility cost
fluorescent lamp; fluorescent light