LED

Definition – A lightemitting diode (LED) is a two-lead semiconductor light source. It is a p–n junction diode, which emits light when activated. When a suitable voltage is applied to the leads, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons.

LEDs are a solid state device and do not require heating of a filament to create light. Rather, electricity is passed through a semiconductor material that is excited and generates light. LEDs are not bulbs or lamps in the true sense.To make it usable asbulb are placed on a circuit board or other material that allows electricity to pass through at a specific voltage and current and with components required to operate them at specific voltages.

Enclosures are plastic, aluminum or metal composites with various types of lens/covers.

A group of LEDs set in a square, rectangular or linear pattern and formatted to be operated at a specific voltage.

CONSTRUCTION OF LED FIXTURES

An LED light consists of small-small LED chips which are connected in series & parallel combinations. Each LED chip is designed for 3V, 3.5V DC and 350mA, …900mA current. These LED chips are connected in series & parallel on a PCB (Printed Circuit Board) according to the design of light. These lights are designed for either constant voltage or constant current. Accordingly each PCB is required a particular voltage which may vary from 12V to 50V. This is provided by a control circuit called driver. A driver receives 230VAC & gives DC voltage to PCB. As driver is an electronic circuit, the functions of driver are –

  1. To reduce input single phase ac supply, 230VAC to 12V – 50V, on which LED operates as per design,
  2. It is designed to control the power factor of the light more than 0.9,
  3. It is designed to control the harmonics which are generated during operation of lights,
  4. It is designed to protect light from surge voltage. For example – indoor lights are designed for 2KV or 3KV surge protection & outdoor lights are designed for 5KV -10KV surge voltage protection.

(Note: – When LED glows, it generates heat. This heat plays an important role in the performance of driver. Hence, proper heat dissipation is very important factor for long life of the drivers. That is why in LED lights, fire resistant PCB (Printed Circuit Board) is used for the driver.)

Heat dissipation is done by using metallic baseforLED lights. In some lights this driver is installed inside the case of the light & in some cases outside. Outside installed driver is better for long life of the driver.

ADVATAGES OF LED LIGHTS

  • They don’t generate heat.
  • LED lights are energy efficient& its estimated energy efficiency is 80% – 90% when compared with traditional Incandescent bulb.
  • No toxic chemicals are used in LEDs as compared to fluorescent bulb that contains mercury.
  • Asno UV emission is done by LED, they are useful where UV sensitive material /objects like museum art galleries, archeological sites etc.
  • LED light scan be designed in any shape & lighting effect because individual LEDs can be controlled.
  • LEDs are suitable to operate in all weather conditions without any problem. While in fluorescent bulb, low temperature affects the operation of bulb.
  • Low voltage supply is required to operate LED which is suitable for outdoor activity and very useful for lighting in rural area.
  • LED lights are suitable for outdoor lighting system as they are resistant to shock, vibration, external impacts. Also These lights can be easily focused at one location.

 

DISADVANTAGES OF LED LIGHTS

  • Expensive – LED lights are very expensive as compared to fluorescent or incandescent light.
  • Color change – LEDs can change itscolour due to age & temperature.
  • Brightness – LEDs emit lower output levels over a very long period of time and become less bright.
  • Expertise – LEDs must be supplied with correct voltage or current & this required highly engineering expertise.

SELECTION OF LED LIGHTS

Following points should be considered while selecting an LED light –

  • Luman /watt – These days LED lights are designed between 80 -120 Lumens/Watt. It means intensity of light is directly proportional to the lumen, higher the lumen means higher the light intensity. Therefore, we should select higher lumen/watt light. Higher lumen per watt light saves energy also.

Ex. – Suppose 1000 lumens are required for an area. First let us select 80Lumens/watt. So for 1000Lumes – 12.5W (1000/80= 12.5W)LED light is required while for 110 lumens/watt – 9W LED light is required for same 1000lumes light.

  • Burning Hours – We should ask for maximum burning hours of the light. Number of burning hours depends on the operating hours of the light. For 24X7 operations, number of operating hours less as compared to 12X7 operating hours. These days, internal & external light fixtures are available for 50000 burning hours while LED lamps are available for 25000 burning hours.
  • Built-in protection – We should ensure built-in protection provided in the light fixtures like power factor, surge protection, THD (Total Harmonics Distortion),
  • Make of Driver & LED Chip – We should ensure that make of driver & chip should be of reputed make.
  • Warranty – We should ask for the warranty of the light fixture.
  • Ask for LM 79 & 80 reports of LED lights.

LM 79 & 80 REPORTS

LM 79 Report– This report ensures the overall performance of LED fixtures which includes light output (lux level), wattage (electrical power), lumens per watt, drive current (mA), color temperature, efficiency & intensity distribution.

  • LM 80 Report– This report ensures the performance of LED in terms of lumen maintenance which measures the lumen depreciation of LEDat various temperaturethrough testing hours between minimum 6000 hrs to 10000 hrs.