50-ampere light? (4)
I believe the answer is:
lamp
'light?' is the definition.
(lamp is a kind of light)
'50-ampere' is the wordplay.
'50' becomes 'l' (Roman numeral).
'ampere' becomes 'amp' (synonyms).
'l'+'amp'='LAMP'
(Other definitions for lamp that I've seen before include "Florence Nightingale was the Lady with the . . . ." , "Source of artificial light" , "Appliance producing light" , "Lighting device in palm" , "Device providing illumination" .)