Map Reading Light Sheild

[Keith Orpin]

Guys,
A very good freind of mine dropped off a very rare piece of kit today. See attached photos of said piece. It's a map reading sheild, fitted to gun tractors and anti aircraft tractors. Personally, I've never seen one, has anyone else come across one, either fitted or not ?. Internally, it looks like it was once painted white, with a light at one end, and a cover which moves though about 90 degrees. Look forward to any feedback on this one.
Regards
Keith