Solar dial
Encyclopedia
A solar dial is type of time switch
used primarily for controlling lighting. They were/are primarily manufactured by the companies Venner
, Horstmann
and Sangamo.
and sunset
times for a particular latitude
(which is specified when the unit is purchased). The solar dial 'adjusts' itself by a fractional amount each day, thereby ensuring that street lighting 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
for street lighting in the 1970s and 1980s in order to conserve energy. Some solar dial switches have a clockwork
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, and the lanterns are powered/switched by means of an extra (fifth) core on the overhead cables.
, but as these fail they are invariably 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.
Although they are now mostly obsolete, Sangamo still manufacture solar dials. Old examples from the 1950s, 1960s and 1970s are collected by enthusiasts and are increasingly hard to find in good working condition.
Time switch
A time switch is a timer that plugs into an electric socket, between the socket itself and a power plug. This physical arrangement allows the connected device to automatically receive power for a desired duration of time...
used primarily for controlling lighting. They were/are primarily manufactured by the companies Venner
Venner
Venner is a surname, and may refer to:* Charlie Venner* Thomas Venner* Stephen Venner, a bishop of the Church of England* Venner, a 1960 Norwegian film-See also:* Bamses Venner, Danish musical group*Venner...
, Horstmann
Horstmann
Horstmann can refer to:* Horstmann suspension - Type of armoured fighting vehicle suspension.* Horstmann technique - Therapeutic massage technique working with blocked "energy".* Horstmann Cars - a British car manufacturer....
and Sangamo.
Benefits
The benefit of a solar dial over a conventional 'on-off' time switch is the ability to 'track' the sunriseSunrise
Sunrise is the instant at which the upper edge of the Sun appears above the horizon in the east. Sunrise should not be confused with dawn, which is the point at which the sky begins to lighten, some time before the sun itself appears, ending twilight...
and sunset
Sunset
Sunset or sundown is the daily disappearance of the Sun below the horizon in the west as a result of Earth's rotation.The time of sunset is defined in astronomy as the moment the trailing edge of the Sun's disk disappears below the horizon in the west...
times for a particular latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
(which is specified when the unit is purchased). The solar dial 'adjusts' itself by a fractional amount each day, thereby ensuring that street lighting 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
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
for street lighting in the 1970s and 1980s in order to conserve energy. Some solar dial switches have a clockwork
Clockwork
A clockwork is the inner workings of either a mechanical clock or a device that operates in a similar fashion. Specifically, the term refers to a mechanical device utilizing a complex series of gears....
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, 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 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 United KingdomUnited Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
, but as these fail they are invariably 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.
Although they are now mostly obsolete, Sangamo still manufacture solar dials. Old examples from the 1950s, 1960s and 1970s are collected by enthusiasts and are increasingly hard to find in good working condition.