Guided by small light (3)
I believe the answer is:
led
I believe this clue is a double definition.
'guided' is the first definition.
('lead' can be a synonym of 'guide')
'small light' is the second definition.
(light emitting diode)
'by' is the link.
(Other definitions for led that I've seen before include "Something emitting light" , "showed the way ahead" , "Came first" , "induced to" , "Took by the hand and showed the way" .)