1954 Spitlight "P.300.S" (based on a Bedford 5010) 1/1
Swiss made by Gianni Andreoli in Lucern.
Thanks to a powerful carbon arc lamp and an ingenious cooling system, the Spitlight was able to generate a light intensity of 375,000 lumens and project images onto rock faces or artificial clouds over an area of 600 by 600 meters. In 1985, the Spitlight was entered in the Guinness Book of Records as the largest projector in the world.
The projection van celebrated its greatest use in 1956 at the Winter Olympics in Cortina d'Ampezzo, Italy. Among other things, it projected the time, results and advertising emblems onto the rock faces of the Dolomites.
Fun Fact:
The beam of light from the projector is so hot that you can light a cigarette with it.
Spotted at the ENTER museum in Derendingen (SO), Switzerland
I found multiple picture from back in the day that I'll post in the comments as soon as they're open.
Links:
https://enter.ch/de/produkte/spitlight-wolkenprojektor/
https://de.wikipedia.org/wiki/Gianni_Andreoli
https://de.wikipedia.org/wiki/Spitlight