March 18, 2016 admin

Tech History- Saltwater Dimmers

The history of film and theatre-from the ancient Greeks to Marvel Studios, milestones in advancement and artistic achievement are well known and well documented.wireless dimmers

Sadly,  film and theatre tech history has only recently become a hot commodity so there is not a lot of valid info available. Lighting has such a rich history that even with little info available, I could go on for days- but one bit of info has always intrigued me.

Years ago I was spoke with a lighting designer who told me about her time doing tech for shows at a state fair. The equipment, she said was outdated and a little terrifying. Terrifying? Yes, terrifying. They used saltwater dimmers. Say what? Oh yes saltwater dimmers that made all your arm hairs stand up when you operated them-I had to find out more….

The first dimmers were directly controlled through the manual manipulation of large dimmer panels, but this meant that all power had to come through the lighting control location, which could be inconvenient and potentially dangerous, especially with systems that had a large number of channels, high power lights or both.

Early examples of a rheostat dimmer include a salt water dimmer or liquid rheostat; the liquid between a movable and fixed contact provided a variable resistance. In a salt water dimmer, there were two metal contacts in a glass beaker. One contact was on the bottom, while the other was able to move up and down.

The closer the contacts to each other, the higher the level of the light. Using salt water dimmers was a tedious and precarious task that included filling the beakers with water, checking the concentration of the salt, and raising or lowering the top contact. Salt water dimmers were not efficient due to the evaporation of water and the corrosion of the many metal pieces. These dimmers were colloquially known as “pis pots”, for obvious reasons. Many old theatre electricians still recount stories of how they were initiated into the art by being requested to “top up a pot” and receiving a shock, as unbeknownst to them the pot was live…

Well we have certainly come a long way! Can you imagine what those old stagehands would think about our wireless dimmers? They would probably be shocked!



Comment (1)

  1. Loved the article on saltwater dimmers – brought back memories. As a kid at ten I built them for a theatre in my parents’ basement: could not afford auto-transformers. Only needed to dim six 75-watt spots.

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