light vs room light

light and room light both are nouns.

Word	Noun	Adjective	Verb	Adverb
light	Yes	Yes	Yes	Yes
room light	Yes	No	No	No

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

light (noun)	room light (noun)
any device serving as a source of illumination	light that provides general illumination for a room
a device for lighting or igniting fuel or charges or fires
the visual effect of illumination on objects or scenes as created in pictures
the quality of being luminous; emitting or reflecting light
merriment expressed by a brightness or gleam or animation of countenance
mental understanding as an enlightening experience
a particular perspective or aspect of a situation
public awareness
a visual warning signal
an illuminated area
a person regarded very fondly
(physics) electromagnetic radiation that can produce a visual sensation
having abundant light or illumination
a condition of spiritual awareness; divine illumination

light (adjective)	room light (adjective)
of comparatively little physical weight or density
psychologically light; especially free from sadness or troubles
not great in degree or quantity or number
of the military or industry; using (or being) relatively small or light arms or equipment
(used of color) having a relatively small amount of coloring agent
characterized by or emitting light
(physics, chemistry) not having atomic weight greater than average
of little intensity or power or force
easily assimilated in the alimentary canal; not rich or heavily seasoned
silly or trivial
weak and likely to lose consciousness
having little importance
less than the correct or legal or full amount often deliberately so
designed for ease of movement or to carry little weight
moving easily and quickly; nimble
(used of soil) loose and large-grained in consistency
having relatively few calories
(of sound or color) free from anything that dulls or dims
(of sleep) easily disturbed
marked by temperance in indulgence
very thin and insubstantial
casual and unrestrained in sexual behavior
demanding little effort; not burdensome
(used of vowels or syllables) pronounced with little or no stress
intended primarily as entertainment; not serious or profound

light (verb)	room light (verb)
introduce light into
start or maintain a fire in
begin to smoke
to come to rest, settle
alight from (a horse)
fall to somebody by assignment or lot; passed
cause to start burning; subject to fire or great heat

light (adverb)	room light (adverb)
with few burdens