How Do Street Lights Work

How are street lights powered?

street light, light pole, lamppost, street lamp, light standard, or lamp standard is a raised source of light on the edge of a road or path. When urban electric power distribution became ubiquitous in developed countries in the 20th century, lights for urban streets followed, or sometimes led.

“By 1980, lamp sizes had ranged from 35 to 1,000 watts; with most types attaining 24,000 hour estimated operating hour life, creating much competition with mercury lamps of the time …. Efficiencies of the late 1990s range from 64 lumens per watt for the small 35-watt lamps to 140 lumens per watt for the 1,000 watt size. Common HPS lamp wattages are 35, 50, 70, 100, 150, 200, 250, 400, and 1,000. Medium base lamps are available through 150 watts; all are otherwise produced with mogul screw threads.”

purpose of street lights

The purpose of street lighting is to assist drivers, pedestrians, and cyclists in finding their way in the dark. Many neighborhood groups believe that extra illumination helps prevent crime, and business district lighting also may help create a pleasant environment.

Street lights are very crucial. They automatically start if it becomes dark out, providing a little bit of light time. They help drivers view objects out and give pedestrians light. … Thu purpose mainly to light the streets ad make people (Walking – Cars – Bicycle) see what is going on.

Street lighting provides a number of important benefits. It can be used to promote security in urban areas and to increase the quality of life by artificially extending the hours in which it is light so that activity can take place. Street lighting also improves safety for drivers, riders, and pedestrians.We are committed to providing good street lighting using the latest technology available.

How do street light sensors work?

Photocells detect if light is needed. Photocells are light-sensitive sensors that respond to the amount of light detected. When the light is too low, such as at dusk or under heavy overcast skies, the sensor tells the computing unit within the streetlight to activate the flow of electricity. When the photocell detects too much light, the sensor will deactivate the streetlight (e.g., at dawn).

Electricity is sent through high-intensity discharge lamps. A high-intensity discharge lamp emits light by an arc of electricity created between two electrodes. The electrodes are in a transparent tube filled with gas and metal salts. The electrical arc generates heat, which works with the gas and metal to create light-emitting plasma.

Streetlights use bypass technology. Through use of either isolation transformers or film cutout technology, streetlights are able to pass the voltage through to other streetlights when they are burned out. Much like older Christmas tree lights, streetlights are connected in series design; the current to operate five streetlights on the same street flows from light 1 through 2, 3 and so on. 

Streetlights are carefully planned. Streetlight issues include light pollution of the night sky and interference with night vision of drivers. A sudden inability to perceive lighting and distance at night due to street lighting is because of the accommodation reflex of the human eye as cars move from a darkened area to an area illuminated by a streetlight. 

A common light-sensing component is the cadmium sulfide photo-resistor, also known as a CdS cell. A photo-resistor changes its resistance based on the amount of light that hits it. When a lot of light hits it, it has almost zero resistance — it conducts electricity very well. When no light hits it, it has high resistance — it conducts electricity poorly.

In an extremely simple circuit, you would wire a CdS cell directly to a relay (see How Relays Work), so that a lot of light would energize the electromagnet and a small amount of light would not. Usually, however, a CdS cell cannot draw enough current to activate the relay when light hits it. Therefore you need to add a transistor to amplify the current that flows through the CdS cell. A typical circuit might look like this.

The most commonly used component in streetlights is called a cadmium sulphide photoresistor, or a CdS cell for short. The CdS cell changes the resistance of a circuit depending on the amount of light shining on it. When lots of light falls on a CdS cell, then the resistance is very low, which means it conducts electricity well. When there is not much light, the photo-resistor has a high resistance which means not much current can flow.

This change in current can then be used to control a relay. A relay is basically an electromagnetic switch; when the electromagnet has a high current (lots of light falling on the photo-resistor – daytime) then it pushes the switch open so no current can fl ow to the streetlight. When it gets dark, then not much current can flow to the electromagnet so the switch closes and allows electricity to flow to the streetlight, turning it on.


With the above, you hopefully now have a basic gist of how do street lights work, especially in areas without much access to electricity. The portable and environment-friendly nature of a LED street light can make them an ample replacement for ordinary street lights, and perhaps a sound option as well for areas without access to an electrical grid.

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