Source of light in loft or chamber (5)
I believe the answer is:
torch
'source of light' is the definition.
(thesaurus)
'in loft or chamber' is the wordplay.
'in' says the answer is hidden in the clue.
'TORCH' is hidden within 'loft or chamber'.
(Other definitions for torch that I've seen before include "Light carried in the hand" , "Set fire to - hand-held light" , "Small portable battery-powered electric lamp" , "Set fire to; electric lamp" , "Small hand-held battery lamp" .)