A little light, but of double density (3)
I believe the answer is:
led
'a little light' is the definition.
'led' can be an answer for 'light' (light-emitting diode). I am not certain of the 'a little' bit.
'of double density' is the wordplay.
'of' says the answer is hidden in the clue.
'LED' can be found hidden inside 'double density'.
'but' is the link.
Can you help me to learn more?
(Other definitions for led that I've seen before include "showed the way ahead" , "Went first to show the way" , "Guided; small light" , "was in the van" , "Came first" .)