Went in front, having source of light (3)
I believe the answer is:
led
I believe this is a double definition.
'went in front' is the first definition.
'source of light' is the second definition.
(abbreviation for light emitting diode)
'having' acts as a link.
(Other definitions for led that I've seen before include "Guided; small light" , "Went first to show the way" , "was in the van" , "Something emitting light" , "induced to" .)