Photocells & Time Switches

1) Photocell's

The Photocell is a device intended to switch the Street Light on as it goes Dark and off in the Morning, this detects the amount of daylight and when it reaches a determent level the resistance increases in the detector and this reenergizes a relay which then closes the contacts and switches on the Street Light, there are various types of photocells on the market some are Thermal which is the simplest this uses a Photo Resistor in series with a Thermal Relay, the Thermal Relay has a small heater which warms up during the day, this intern heats up a Bi Metal switch which open and switches off the Street Light, as it goes dark the resistance is increased on the Photo Resistor this then cools down the Heater and Bi metal switch is closed and the Street Light switches on. Other Photocell's uses a Electromagnetic Relay or a Special Transistor plus a Time delay Circuit which reduces the accidental operation of the Street Light during the Night by Stray Light from Car Headlights say passing over a bridge, and Lightning Storms etc. Today Electronic Part Night Photocells are increasingly becoming Popular for Street Lighting as Energy Prices are Increased and Councils are having to cut back on costs, some Street Lights are being switched off between Midnight and 5.30AM where Roads are empty and/or very little pedestrians are on the streets. or where Street Lights are used in Rural Roads.

UK Photocells

Fisher Karpark SS4 Thermal Photocell circa 1970's

Cableform (Zodion) SS4 Thermal Photocell circa 1990's

Cableform (Zodion) SS5 Electronic Photocell with Photoresistor

Zodion SS6 Electronic Photocell with Blue Housing and Photodiode

Cableform (Zodion) SS8 Heavy Duty Electro-Magnetic Photocell with Photoresistor

Royce Thompson Oasis 1000 Electronic Photocell

Royce Thompson Oasis 2000 Electronic Photocell

Royce Thompson S90 Electronic Photocell

Royce Thompson S300 Electronic Photocell

Royce Thompson SC1000 Electronic Photocell

SELC, Ireland, type 841 Electronic Photocell

SELC, Ireland, type 849 Electronic Photocell

American Photocells

American Fisher Pierce Electronic Photocell for 120 volt Street Lights

American Longjoin JL-2 Electromagnetic Photocell for 105 to 305 volt Street Lights

American Precision Multiple Lighting Controls, Lumatrol, Electromagnetic Photocell for 208 to 277 volt Street Lights

American Area Lighting Research M-480 Electromagnetic Photocell for 420 to 530 volt Street Lights

Part Night Photocells

Royce Thompson "NIGHTSTAR" Electronic Part Night Photocell.

Early 1990's Zodion SS9 Electronic Part Night Photocell

Zodion SS9 Electronic Part Night Photocell showing the Switching Off Times between Midnight & 05.30AM.

Modern Zodion SS9 Electronic Part Night Photocell

Zodion SS19 Electronic Part Night Photocell for use within Fittings

Zodion SS19 Part Night Photocell showing the Switching Off Times between Midnight & 05.30AM.

2) Time Switches

The Time switch were used before Photocells for operating Street Lighting, this consisted of a Time Clock with Solar Dials which automatically adjusted for the Evening and Morning which in tern operated a switch to switch on the Street Light as it goes Dark and off in the Morning, some Time Switches had two switches which operated a twin Lamp Street Light this worked by switching Both Lamps ON as it got Dark, then at Midnight one of the Lamps was switched off then in the Winter the same Lamp would switch Back on at 05.30AM for Rush Hour Traffic and the Both Lamps would switch OFF as it got bright, some Time Switches were Fixed Set Times and were connected in Conjunction with Photocells for Part Night Operations others had a Solar Dial and Fixed Armatures which also was designed for Part Night Operating of Street Lights.

1960's Horstmanns K-Mk2 Solar Time Switch for Street Lighting.

Here you see a 1960’s Horstmann Solar time switch this was commonly used in Street lighting in the UK before Photocells the clock has a Mechanism which tracks the Sun Set and Sun Rise automatically and  are ideal for switching  Street Lights ON at sunset and OFF at sunrise.
 
The Disadvantage of this Time Switch is if there is a Power Failure the Time Switch Motor will Stop, and when Power is Restored the wrong time will occur which could cause the Street Light to switch ON and OFF earlier or Later then it should, and will need to be reset by the Street Lighting department.

Modern Sangamo Q551 Solar Time Switch with Quartz Motor and Battery Back Up

Here you see a Modern Sangamo Q551 Solar time switch this was commonly used in Street Lighting in the UK instead of Photocells, example Group Switched Lighting etc., the clock has a Mechanism which tracks the Sun Set and Sun Rise Automatically and are ideal for switching Street Lights ON at sunset and OFF at sunrise. This model uses a Quartz Motor and Battery Back Up in the event of Power Failure which means they can be left to operate unattended for years.