Cold Lights

A few weeks ago I visited Urban Ore with some friends, one of whom, a fellow digital tech, pointed out some old-ish theatre fresnel spot lights. They were only $20 so we each picked one up with the intent on retrofitting them to use standard light bulbs. Somewhat surprisingly the light still had a fully functioning lamp, drawing 500W and demonstrating why they're called "hot lights".

The power for the light is provided by a special plug used for lighting called a Bates plug, or formally a Stage Pin Connector, which is basically a chunky, but flat, plug and socket. I wanted my retrofit to be as minimal as possible, so I decided to keep the plug and swung by my local grip shop to get a matching receptacle to splice onto a standard power cable. With the power sorted it was time to move on to the lamp.

The existing socket used a special bulb, and while there are apparently drop-in LED replacements available they cost as much as the entire light did, and I wanted to be able to automate the light with Home Assistant. A second trip to Urban Ore was in order to rummage through the bins of light sockets. I found a nice ceramic one which had mounting holes I could use to attach it to the focussing slide in the light. Again, I wanted to make as few modifications to the original light as possible, so the question of how to actually wire the new socket up remained.

The original wiring was fairly specific to the original socket. I could have just cut the terminals off on each side and crimped them together, but instead I designed a little terminal block which could be mounted on a convenient hole in the back of the housing. It was just a matter of 3D printing it, and a couple of attempts at screwing everything together, and I had a new task light!

I wanted the light to be as bright as possible, any LED was going to be much dimmer than the original 500W lamp, so I tested a a bunch of bulbs I had in my collection. The geometry of the fresnel and reflector made the bulb selection and interesting challenge. The brightest bulb I had, at 1500 lumens, was indeed bright, but was too tall, resulting in poor overall performance. I eventually settled on an 840 lumen bulb that placed the actual light emitting portion at the correct height. Interestingly both bulbs gave a roughly equivalent output through the fresnel when measured with a light meter.

I eventually mounted the light to some pipes in the ceiling of my loft, pointed at a shelf to highlight my camera collection. Hanging from the rafters is where this light was meant to be used after all.