How Do Street Lamps Work?
If it were not for street lamps, walking and driving at night would be a much more daunting prospect. Street lamps make sense and have been around for a long time, but they have not always been the automated kind we are familiar with today. Does this Spark an idea?
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Types of Lighting
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Different types of lighting have different energy requirements. Incandescent light bulbs produce light by passing electricity through a wire, which heats up inside the bulb, becoming hot enough to glow. With fluorescent lighting, electricity is passed through a specially-coated glass tube, which uses less energy to produce light. Passing electricity through certain gasses also produces light, using even less energy than fluorescent lighting. This is the type of lighting that street lamps use, according to the Auburn University feature "Ask Aubie."
Design
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The gasses used by street lamps are usually sodium or mercury. The lamps are mounted high on poles or inside the poles, and wires carry electricity to the lamps, supplied by the local power company, in order to allow safe walking and driving at night.
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Considerations
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Street lamps do not have the colors we normally associate with lighting, although their glow is so familiar most people probably never wonder about the reasons for the color choice. In fact, the colors are due to the types of gasses used in the lamps. The color of the light produced by sodium is yellow-orange, while the color of the light produced by mercury is blue. Colored lighting is inappropriate for homes, but orange light in particular works well for the purpose of street lighting, since orange is seen more easily than blue.
History
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Another special consideration for street lights is that to serve their purpose, they must turn on when it gets dark and off when it grows light out. Originally, street lamps burned whale oil, gas or kerosene. A lamplighter walked the streets at dusk carrying a long pole with a torch on the end used to light the street lamps. In the morning, the lamplighter went around and put out the lamps. Later street light designs used ignition devices that struck the flame automatically when the gas supply was activated, according to the Perth & Kinross Council website.
Modern Device
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Today, the flow of electricity to street lamps is controlled automatically. A switch called a "photo cell" is pointed at the sky and responds to light by allowing the flow of electricity when it is dark and blocking it when it is light. The photocells used in street lighting have a delayed reaction to rapidly changing light levels, which is why they do not switch on and off repeatedly during rain storms in daylight hours, and they fail in the "on" mode, according to the Midland Counties Street Lighting website.
Other Systems
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A new type of street lighting fixture using light-emitting diode (LED) units is coming into use. LED units emit white light, last longer than typical street lighting systems (10 to 12 years) and are expected to reduce electricity use and urban light pollution that obscures the stars from view, according to a Feb. 18, 2009 article in Sustainable Business.com. LEDs are semiconductor devices that convert electricity into light.
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References
Resources
- Photo Credit street lamp image by rafalwit from Fotolia.com
