Best Way to Control Street Lights Intensity Using High Intensity Discharge Lamps

Each time your car crosses through the street light, ever spared a thought about the street lights? No, I guess. So let me take your attention to what actually constitutes the street lights.

A Sneak peek into traditional Street Lights using High-Intensity Discharge Lamps

A high-intensity discharge lamp works on the principle of electrical discharge by gas ionization. It consists of two tungsten electrodes inside a glass tube filled with neutral gas and metal. The electrodes are connected through ballast (coil) to the voltage source. When the ballast is ignited or current passes through the ballast, it supplies high voltage to the electrodes such that a sufficient amount of current flows to ionize the gas to create an electric arc between the electrode.  As the metal salts come in contact with the arc, they get heated up and thus get ionized, causing the electrons to jump to their excitation level, and as they fall back to their actual state, they emit photons, thus producing light. An HID lamp generally produces light at an intensity of 50-100 lumens/watt.

A Mercury Halide HID lamp
A Mercury Halide HID Lamp

5 Reasons why HID Lamps can prove to be Inconvenient

  • They are more failure-prone. Failure can result from the impact of goods or improper positioning of the lamps or scratches on the surfaces.
  • They are not safe. Mere contact with water can cause a fire. Even using incompatible ballasts can also cause a fire.
  • They do not start instantly and take the time to start. A maximum starting period of 10 minutes is taken.
  • They are prone to self cycling, i.e. they turn off on their own, due to overheating of the tube.
  • The intensity cannot be controlled easily.
  • A slight fluctuation in the voltage can trip off the bulbs.

So all these limitations are what paves the way for a new technology of street lights and that’s where the role of LED-based lamps comes.

How a LED lamp does look like?

A LED Street light consists of an array of LEDs with a heat sink and placed inside a base. An LED lamp consists of a glass dome coated with phosphorus, with the led bulb housed inside. LED or Light Emitting Diode consists of a semiconductor material that has the property of emitting light as the junction gets sufficient potential to allow the charge to flow. LEDs used in street lights are generally white light LEDs which is either produced by mixing red, blue, and green light from LEDs to produce white light or using a phosphor incorporated blue LED which produces yellow light and when this blue light mixes with yellow light, white light is emitted.

An LED street lamp
An LED Streetlamp

8 Reasons why LED Streets Lights are being Preferred: 

  • They have a longer-lasting time. This is due to the fact that LED lamps do not contain toxic materials like mercury and sodium which can easily burn out when subjected to some reactions. A typical LED light can last for about 10000 hours.
  • They are highly energy-efficient and draw quite less amount of power, only 8 W or less. It achieves about 80% energy efficiency.
  • They provide a high intensity of light. It can range from 80-200 lumens/watt.
  • They have a high CRI rating, about 80-90. It implies that LED lamps allow for high fidelity of identifying objects. In plain words with LED lamps, objects’ color appears as it is actually.
  • They are easily controllable by varying the applied voltage.
  • They are safer to use.
  • They can start up instantly.
  • They are more environmentally friendly as they do not use toxic products.
  • They are not affected by voltage fluctuations.

2 Reasons why still LED street lights have not completely replaced HID street lights

  • They produce directional light and cannot produce glow in all directions.
  • Their cost of installation is very high, about 1000 dollars.

A Simple Demonstration Depicting Controlling LED Based Street Lights to Glow with Vehicle Detection.

The basic idea is to control the glowing of led lights based on the sensor inputs and changing the LED light intensity with respect to the distance of the approaching vehicle.

The system consists of three main components:

  • A controller: Here a microcontroller is used. It is programmed to carry out the required tasks.
  • A sensor: Here number of IR sensors is used. The IR sensor is a combination of an IR transmitter – IR LED and an IR receiver-Photodiode.
  • LED array: Here an array of LEDs is used, which are a substitute for the actual LED street lights.

    Block Diagram showing the system
    Block Diagram showing the system

In normal conditions, when there is no interruption between the IR LED and the photodiode (placed on opposite sides of the road), the latter conducts, causing the transistor connected to its output to conduct, resulting in low voltage output to the microcontroller. The microcontroller receives this output and makes the LEDs glow for a low period of time by sending a low duration pulse.

Now when a vehicle approaches the street lights and comes in between the IR LED and the photodiode, an interruption is created, causing the connected transistor to conduct less, causing an almost high logic output given to the microcontroller. The microcontroller accordingly makes the LEDs glow for a larger amount of time by sending a higher duration pulse.

Thus using pulse width modulation the microcontroller controls the intensity of street lights as the vehicle approaches near the street lights.

So by now, you must be ready to spare a moment to think about the street lights which show you the way in darkness. Not just that, do spare a thought to check the type of street lights you see and do tell here if you spot LED street lights anywhere.

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