sunniness vs lightness

sunniness and lightness both are nouns.

Word	Noun	Adjective	Verb	Adverb
sunniness	Yes	No	No	No
lightness	Yes	No	No	No

As nouns, lightness is a hypernym of sunniness; that is, lightness is a word with a broader meaning than sunniness:

sunniness: lightness created by sunlight
lightness: the visual effect of illumination on objects or scenes as created in pictures

Other hypernyms of sunniness include light.

sunniness (noun)	lightness (noun)
lightness created by sunlight	the trait of being lighthearted and frivolous
the quality of being cheerful and dispelling gloom	the visual effect of illumination on objects or scenes as created in pictures
	the property of being comparatively small in weight
	having a light color
	the gracefulness of a person or animal that is quick and nimble
	a feeling of joy and pride