Student apt to open up when the lights are low? (5)
I believe the answer is:
pupil
'student' is the definition.
(pupil can mean a student at a school)
'apt to open up when the lights are low?' is the wordplay.
I cannot really see how this works, but
'up' is within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for pupil that I've seen before include "Aperture in an eye" , "Dark centre of the eye" , "that shrinks from brightness" , "I learn" , "School learner" .)