Barndoors

Folding doors which are mounted on to the front of a light unit in order to control illumination. (Lighting)
Found on http://www.filmland.com/glossary/Dictionary.html#A

Barndoors

Handy blinders on the sides of lights that can be used to keep light from going everywhere. They can also be used to clip on a lighting gel. They get very hot when a light is on, so it is best to wear work gloves when adjusting them
Found on https://www.encyclo.co.uk/local/21112
No exact match found