[Richard Coutts-Smith]

Came across this electric Lucas Demister the other day, Post War British, I thought maybe Ferret or similar as it is only 10 inches long. Do they work by just heating the glass or do they need air movement as well? I have done a search on the numbers, but no result.
LV6/MT3 2540 99 803 654
DEMISTER No1 Mk2
LU78033
Any ideas as to what where and why?
Rich.