A solar dial is a type of

time switch A time switch (also called a timer switch, or simply timer) is a timer that operates an electric switch controlled by the timing mechanism. Intermatic introduced its first time switch in 1945, which was used for "electric signs, store window lig ...

used primarily for controlling lighting. The benefit of a solar dial over a conventional 'on-off' time switch is the ability to 'track' the

sunrise Sunrise (or sunup) is the moment when the upper rim of the Sun appears on the horizon in the morning. The term can also refer to the entire process of the solar disk crossing the horizon and its accompanying atmospheric effects. Terminology A ...

and

sunset Sunset, also known as sundown, is the daily disappearance of the Sun below the horizon due to Earth's rotation. As viewed from everywhere on Earth (except the North and South poles), the equinox Sun sets due west at the moment of both the spring ...

times for a particular

latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pol ...

(which is specified when the unit is purchased). The solar dial 'adjusts' itself by a fractional amount each day, thereby ensuring that

street lighting A street light, light pole, lamp pole, lamppost, street lamp, light standard, or lamp standard is a raised source of light on the edge of a road or path. Similar lights may be found on a railway platform. When urban electric power distribution ...

is switched on and off when required throughout the year. Many dials also have an additional 'part night' facility allowing for a switch-off in the middle of the night, and then back on in the morning if needed. This 'part night' option was widely adopted in the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...

for street lighting in the 1970s and 1980s in order to conserve energy. Some solar dial switches have a

clockwork Clockwork refers to the inner workings of either mechanical devices called clocks and watches (where it is also called the movement) or other mechanisms that work similarly, using a series of gears driven by a spring or weight. A clockwork mec ...

or battery 'reserve' to maintain time accuracy in cases of power outage. If this is lacking, the switch would have to be reset every time the power fails, a labour-intensive task. Frequently, one time switch with a heavier switch rating is used to control a whole series of lighting columns, perhaps one side of a street, and another to control the opposite side. Many columns are however fitted with individual clocks, especially on alleyways, pathways, and areas in which a single column stands alone. Sometimes the time switch is housed in a box fitted to a wall or

telegraph pole A utility pole is a column or post typically made out of wood used to support overhead power lines and various other public utilities, such as electrical cable, fiber optic cable, and related equipment such as transformers and street lights. It c ...

, and the lanterns are powered/switched by means of an extra (fifth) core on the overhead cables.

Obsolescence

The solar dial time switch has largely been superseded by

photocell Photodetectors, also called photosensors, are sensors of light or other electromagnetic radiation. There is a wide variety of photodetectors which may be classified by mechanism of detection, such as photoelectric or photochemical effects, or b ...

control, which is cheaper and requires less maintenance. Solar dials are still used for lighting stairwells and car parks, and in some cases local authorities may request them for street lighting, though this is rare. Solar dials are often found in the rural

, but as these fail they are sometimes replaced by a photocell, usually on a new lantern and sometimes with a whole new column. More recently, digital sunrise/sunset tracking time switches have appeared on the market, but these are generally too expensive for large scale use in street lighting and have not been adopted for this purpose, except in a few rare instances. Sangamo still manufacture and sell three models of solar dials from their factory in Port Glasgow. Solar dials continue to be used in retail premises, security systems, lighting and industrial heating systems. Old examples from the 1950s, 1960s and 1970s are collected by enthusiasts.

References

External links

Incatron Time Switch and Lighting Control Archive
{{DEFAULTSORT:Solar Dial Clocks Control devices

Obsolescence

See also

References

External links