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Insight - How LED Light Bulb works

Written By: 

Arpit Jain

 

LED bulbs are the future of lighting. Be it automobiles, industries, household or any hobbyist requirement, LEDs form the best solutions in terms of long-term cost savings and power efficiency. Not only are these devices more efficient than traditional lighting devices, they are built to outlast any of their lighting predecessor. Click to know more about LED lighting. The internals of a typical LED bulb will be explored here.
 
A Typical LED Bulb With Power On

Fig. 1: A Typical LED Bulb With Power On

 
A Typical LED Bulb Without Power

 Fig. 2: A Typical LED Bulb Without Power

Externally, a LED bulb might look similar to a conventional incandescent lamp, but the two are quite different. The chassis of the bulb is made of ceramic and houses the electronic ballast. Ceramic is used for its insulating and heat dissipative properties. The LED bulb is housed inside a phosphor coated glass dome. In order to provide output over a constant wavelength and enhance Light output, LED lamps use Remote Phosphor (RP) Technology for coating purposes. This also enables the LED to emit only a single colored light throughout its lifetime while also reducing glare at the same time.
 
Image Showing COB LED Structure of LED Bulb

Fig. 3: Image Showing COB LED Structure of LED Bulb

COB (Chip on Board)

The LED structures become visible once the glass is removed.  LED lights are placed in a COB (CHIP ON BOARD) LED structure. This structure is covered by a plastic disc which once removed, reveals the COB LED Structure as shown in the image above.
The LEDs are mounted on a disc shaped Aluminum substrate that functions as a heat sink for the LEDs. The size of the substrate is kept quite large as compared to the size of the LEDs, as high amount of heat has to be dissipated when the bulb is in operation
These Light Emitting Diodes are made from suitable extrinsic semiconductor materials like Gallium Arsenide or Gallium Arsenide Phosphate. Bulbs made of these diodes consume very less energy and have a longer life than a conventional bulb or a CFL.
The LED structure is covered in a dome shaped silicone or epoxy resin layer. This dome or bubble defines the light distribution angle of the LED, which may vary from a narrow beam to a wide angle. Inside the epoxy, LED semiconductor is in form of a die placed on thermally conductive adhesive.  It is connected to the thermal pad through gold or platinum bond wires whose thickness is in the order of micrometers. These elements are excellent heat conductors and will efficiently help dissipate all the heat generated during LED operation.  There can be multiple dies in a single dome too. In this case there are two domed structures housing individual LEDs. The use of COB LEDs technology, and Gold (Au) and/or Platinum (Pt) bonding wires is the main reason behind the relatively higher cost of LEDs as compared to their other lighting counterparts such as CFL and the incandescent bulb.
The wires on the periphery of the Aluminum disc are connected to the internal circuitry.
 
Image Showing Aluminum Substrate In LED Bulb
 
Fig. 4: Image Showing Aluminum Substrate In LED Bulb

 Electronic Ballast

Lateral view of the LED bulb reveals the insulation layer which separates the LED from rest of the circuitry. Also, adhesives that hold the aluminum substrate to the ceramic chassis are visible.
LED Bulb Electronic Ballast

Fig. 5: LED Bulb Electronic Ballast

 
The internal circuitry is mounted on a double side printed PCB housed in the rear part of the chassis.
 
Image Showing Internal Circuitry In A LED Bulb

Fig. 6: Image Showing Internal Circuitry In A LED Bulb

Base

The images above show both sides of the electronic ballast driver circuit used inside the LED bulb. The use of electronic ballast makes the structure light and power efficient. The electronic ballast driver circuit is a constant current provider that operates at high frequencies and provides current limiting functionality to protect the LEDs.  Moreover, this ballast is very stable at high temperatures and can work for longer durations.
Image Showing How Base of LED Bulb DIffers From That Of Regular Bulb

Fig. 7: Image Showing How Base of LED Bulb DIffers From That Of Regular Bulb

 
The bottom metallic cap of the LED can either be a Bayonet base or Edison base.  Image below shows the internal structure of the Edison base. The red wire connects the power source to the electronic ballast, while the black one provides the grounding.
Bottom Metallic Cap of LED Bulb

Fig. 8: Bottom Metallic Cap of LED Bulb

LEDs are commercially available in both types of the bases so that they can be readily plugged into the holder as replacement to the lesser efficient lamps.

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