Snoots are used in theatre alot (also called top hats) and are used to prevent light spill and ensure that the only light seen is that reflected off the target, not that from the lamp itself.
Snoots are very useful in the bedroom to allow one to read while not disturbing the other occupants with "light pollution".
Step 1: Measure Twice Cut Once.
-Cardboard (black and thick, flame retardant) DO NOT USE NORMAL CARDBOARD!!!
Alternatively black foil could be used which is obtainable from theatrical shops.....
-PVC tape (Flame retardant)
--Cheap halogen bedside lamp that spills way to much light
Measure the outside of the lamps head (pic 2) and ensure card is long enough.
A piece of A4 should be sufficient for most lamps.
Also measure any protrusions or knobbly bits
Step 2: Cut and Roll
Step 3: Test and Fix
Remove roll and use PVC tape to secure along the outside edge and in a little way inside
Step 4: Done and Tested?
The Snoot can now stay on the lamp or just be slipped off if required.
Ensure the snoot is flame retardant and switch off lamps when not there. Beware fire danger from paper and lamps. Flambar is available from lots of cloth outlets if your require fire proofing.
In the entertainments industry these are generally made of metal, so if your feeling adventurous go with a metal tube, but ensure the inside is matt black!!!