Salt water dimmers at Alexandra Palace Theatre

Salt water dimmers, which are an early example of liquid rheostats, were used in theatres after the introduction of electric

stage lighting Stage lighting is the craft of lighting as it applies to the production of theater, dance, opera, and other performance arts.

to control the brightness of the lights on stage.

Electric lighting

Electric lighting replaced

gas light ''Gas Light'' is a 1938 thriller play, set in 1880s London, written by the British novelist and playwright Patrick Hamilton. Hamilton's play is a dark tale of a marriage based on deceit and trickery, and a husband committed to driving his w ...

s in theatres from the 1880s. The first theatre to replace the gas lighting totally with electric lighting was the

Savoy Theatre The Savoy Theatre is a West End theatre in the Strand in the City of Westminster, London, England. The theatre was designed by C. J. Phipps for Richard D'Oyly Carte and opened on 10 October 1881 on a site previously occupied by the Savoy ...

in 1881.

Salt water dimmers

A dimmer consisted of a glass jar filled with

salt water Saline water (more commonly known as salt water) is water that contains a high concentration of dissolved salts (mainly sodium chloride). On the United States Geological Survey (USGS) salinity scale, saline water is saltier than brackish wate ...

with a metal electrode at each end. As the upper electrode was moved away from the lower electrode, the resistance increased and the lights got dimmer. The brightness also depended on the concentration of salt in the water. The switchboard built at

Her Majesty's Theatre His Majesty's Theatre is a West End theatre situated in the Haymarket, London, Haymarket in the City of Westminster, London. The building, designed by Charles J. Phipps, was constructed in 1897 for the actor-manager Herbert Beerbohm Tree, who ...

, London in 1897 had a dimmer scale of 0 to 10, whereas gas lighting only had 3 levels. The salt water need to be refilled regularly, the metal electrodes corroded, and the dimmers emitted a strong smell. The dimmers were hazardous both because of the flammable gases produced and the potential for electric shocks. Salt water dimmers were gradually replaced by semiconductor dimmers, the last dimmers in London theatres being replaced in 1959. An example of a saltwater dimmer can be seen backstage at

Alexandra Palace Theatre The Alexandra Palace Theatre was originally built in London, England, in 1873 for the performance of opera and ballet, but within a few weeks was burnt to the ground with the rest of the Alexandra Palace. The Palace, including the theatre, w ...

in north London.{{Cite web , title=Salt water dimmer at the Alexandra Palace Theatre {{! Theatres Trust , url=https://database.theatrestrust.org.uk/resources/images/show/7075-salt-water-dimmer-at-the-alexandra-palace-theatre , access-date=2024-10-04 , website=database.theatrestrust.org.uk

References

Theatre Lighting