lightness vs halo

lightness and halo both are nouns.

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

As nouns, halo is a hyponym of lightness; that is, halo is a word with a more specific, narrower meaning than lightness:

lightness: the visual effect of illumination on objects or scenes as created in pictures
halo: an indication of radiant light drawn around the head of a saint

Other hyponyms of lightness include aura, aureole, gloriole, glory, nimbus, sunniness, highlight, highlighting, brightness.

lightness (noun)	halo (noun)
the trait of being lighthearted and frivolous	an indication of radiant light drawn around the head of a saint
the visual effect of illumination on objects or scenes as created in pictures	a circle of light around the sun or moon
the property of being comparatively small in weight	a toroidal shape
having a light color
the gracefulness of a person or animal that is quick and nimble
a feeling of joy and pride