It's light to carry (5)
'it's light' is the definition.
(torch is a kind of light)
'to carry' is the wordplay.
I cannot really see how this works, but
'to' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for torch that I've seen before include "Set fire to (something)" , "Hand-held lamp or burning stick" , "Link" , "Flashlight" , "may get one glowing" .)
(Other definitions for lantern that I've seen before include "Light in a transparent protective case" , "It illuminates" , "outside D [DECORATION]" , "Top of lighthouse" , "Enclosed light" .)