1938 lightbulb brightness testing machine - photo

[Jon]

1938 lightbulb brightness testing machine. I believe this may be some sort of Integrating sphere.

Test electric light bulbs for Uncle Sam. Washington, D.C., March 21. Purchasing on an average of 4,000,000 electric light bulbs annually, Uncle Sam is probably one of the largest users of light in the country. The National Bureau of Standards sees that the government gets value received in purchases by continually testing the incandescent lamps to determine their life and the amount of light they give. Using a special machine designed by the Bureau, Louis Barbrow is shown measuring the amount of light given by a lamp, 3/21/38

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Test electric light bulbs for Uncle Sam. Washington, D.C., March 21. Purchasing on an average of 4,000,000 electric light bulbs annually, Uncle Sam is probably one of the largest users of light in the country. The National Bureau of Standards sees th
https://en.wikipedia.org/wiki/Integrating_sphere

Previously:

How spiral compact fluorescent bulbs are formed - GIF
Drone changing a lightbulb - GIF

[McDesign]

I work in Commercial Lighting R&D, and we still use the same integrating spheres.
Where those incandescent lamps were ~8-12 lumens per Watt just for the bare lamp itself, we have lots of LED FIXTURES with power supplies and smart controls that produce ~170+ lumens per input Watt, with lifetimes measured in decades. Typically we'll quote less than 10% light reduction in 100,000 operating hours.

Forrest (McCanless) in Atlanta - no, really - look me up - I have lots of lighting patents.
I mean, chicks dig plaques, right?