light reflex vs reflex action

light reflex and reflex action both are nouns.

Word	Noun	Adjective	Verb	Adverb
light reflex	Yes	No	No	No
reflex action	Yes	No	No	No

As nouns, reflex action is a hypernym of light reflex; that is, reflex action is a word with a broader meaning than light reflex:

light reflex: reflex contraction of the sphincter muscle of the iris in response to a bright light (or certain drugs) causing the pupil to become smaller
reflex action: an automatic instinctive unlearned reaction to a stimulus

light reflex (noun)	reflex action (noun)
reflex contraction of the sphincter muscle of the iris in response to a bright light (or certain drugs) causing the pupil to become smaller	an automatic instinctive unlearned reaction to a stimulus