Originally Posted by Kino
There are some scientific articles written by Peter Mole on the development of movie lights here (you might have seen them):
I got John Anton's book "Painting with Light". It gives very comprehensive overview of the luminaries used in that Era. Most interestingly, it mentioned in somewhere about the use of lens diffusion disk made of glass to be placed in front of the fresnel lens...this is something different from wire scrim we use nowsdays and it was used for close-up face shot especially actresses. Obviously glass diffusion disk does not alter the directionality & spread of the beam and its effect is different from putting a silk/spun glass/frost on the barndoors or scrim frame that gaffers use these days.