Designation of Filters for Theatrical Lighting - 1938 DB Judd


Well-Known Member
Mar 1, 2012
Rochester, NY
This year I read a paper published in 1938 regarding how gels are named and numbered. In the year prior members of the Illuminating Engineering Society (you've heard of them, the IES founded in 1905 in NYC) had approached the esteemed color researcher DB Judd to solve the problem of how to name or number gels in a way that was simple and described the properties well. That way transmissive filters from different companies could quickly and easily be compared. Judd correctly determined that it was in fact the spectral properties of the filter that were important to designers, as small variations in the transmissivity of different wavelengths affected the way different colored materials appeared on stage. Even a blue gel with a slight bit of transmissivity near 580nm could make a yellow dress appear to glow. So Judd devised a system of 7 digits corresponding to different parts of the spectrum which could describe to designers the properties of the filter.

Of course, this would have been very expensive for manufacturers to implement. Color measurement at the time was even more limited than it seems to be today. Besides, giving customers an easy way to find replacements for your product probably didn't interest the manufacturers. Anyway, I thought I would share the paper here.

I also read some interesting things regarding the founding of the IES and the relationship to lighting designers of the day, but I think that story will have to wait til another day when I can pull up that research again.

Happy Holidays!


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