Being lower, have to shine (4)
I believe the answer is:
glow
'to shine' is the definition.
(I know that glow is a more specific form of beam)
'being lower have' is the wordplay.
'have' indicates the answer is hidden within the clue.
'GLOW' is hidden within 'being lower'.
(Other definitions for glow that I've seen before include "Shine steadily and brightly" , "Radiate or redden" , "Gentle, warm light" , "Send out light and heat without flame" , "Emit light and heat without flame" .)