Switching Devices

Automatic controls for street lighting have been available since the days of gas lighting - however, manual switching was still very much the norm for many years due to the automatic controls proving expensive. Lamplighters were employed to go to every lantern in a given area at dusk and activate the gas supply. Most required the lamplighter to go up to the lantern (hence the need for ladder bars on the columns) and light the mantles that way. The lamplighter would then return at dawn and turn the lanterns off again.

The first big change came when a time switch was developed which switched the gas supply on/off automatically. These worked on clockwork and needed to be wound up every few days in order to keep accurate timing. Where gas lighting is employed today, this method is often still used to switch the lanterns on or off. An alternative method these days is to have the gas supply regulated electronically with valves controlled by a photocell.

With the increase in popularity of electric lighting, manual switching again became popular - many lantern companies made their own switches which would fit between the column and the bracket. They were often designed in such a way that the lamplighter could remain on the ground - a long stick with a hook on the end could be used to flick the switch and turn the lantern on or off.

Time switch operation again soon took over with the invention of the 'solar dial' - a device which could automatically change its on and off times depending on the time of year - determined by a date wheel on the dial. The solar time switch quickly became the standard method of controlling lighting loads. Not all units ran the standard dusk-dawn operation - units were developed which allowed for the load to be deactivated at a given time every night (for example, midnight) and then reactivate in the early morning. Other variants included 'dual circuit' time switches - these catered for lanterns designed to run two (or more) lamps. Both circuits would activate at dusk but then one would work part-night, switching off one of the lamps in the hours when traffic flows were less. A problem with some time switch units was that the timing could be 'knocked out' due to power cuts - causing the lanterns to be in use when they were not required and off when they were! Certain units later employed a spring reserve in the mechanism which allowed the dial to continue to turn in the event of a power loss. The reserve typically lasted for several hours - once power was restored, it would immediately start being re-wound by the synchronous motor of the time switch via a slipping clutch.

The popularity of time switches began to diminish in the 1970s when lighting sensors (photocells) were increasing in popularity - such products had been around since just after the Second World War but they were large and, in many cases, unreliable. As electronics improved, photocells could be made smaller - eventually becoming about 76 mm (three inches) in diameter, which is also the standard diameter for 5 and 6 m columns. The popularity of photocells was down to the fact that they required a lot less setting up than a time switch required - if any. The photocells from the 1970s frequently relied on a thermal relay and Cadmium Sulphide detector but it wasn't long before all-electronic photocells were available. The part-nightly option was also available, but the dual-circuit was never an option. At this time, many dual-lamp lanterns had already been replaced by single-lamp lanterns so this was not really a problem.

Nowadays, photocell technology has come on a long way and the switching accuracy has greatly improved since the early days. Certain photocells can now dim lanterns during the early hours of the morning in an attempt to save energy. Special control gear must be provided in order for this to happen however.

Despite this, time switches are not completely confined to history just yet - certain circumstances mean that photocells cannot be used - this is often due to the higher switching capacity of a time switch in comparison to a photocell. Solar-dial time switches are still made to this day - although the spring reserve has now been replaced with a battery back-up system. Some digital time switches can also mimic the operations of a solar-dial nowadays - these are often sold with a 'fit and forget' tagline.

Click here to see the time switches in my collection.

Click here to see the photocells in my collection.



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