Types of LEDs

Because the LED form factor is so versatile they can be made into all types of lighting from down lights to strip lighting to individual bulbs.. There are three basic types of LEDs that can be used for lighting:


  • T-type LEDs
  • Surface Mount Device (SMD) LEDs (sometimes called sub-mounted device)
  • Chip-on-Board (COB) LEDs

All these LEDs use N-node and P-node semi-conductors to produce light.

T-type LED

This is the conventional shaped and easily recognised  LED that has been around for years. The T-type LED encloses the semi-conductors in a plastic housing (common size is 3.5mm but can be larger or smaller) for the wired LED. The shape of the lens determines the light emission angle. It has a reasonably low lumen output and the early LED lights were based on using many of these T-type LEDs clumped together.


SMD LEDs have their own housing each containing a single chip and the entire component is glued directly to the circuit board and the contacts are soldered. There are two types of SMD LEDs: 3528 or 5050, the numbers indicating the size in millimeters of the chip (3.5mm x 2.8mm or 5mm x 5mm). The picture on the right show 3 SMD LEDs forming a "G4" bulb for garden or boating lighting.


With COB technology the LED chip does not have a housing but instead is placed directly on a circuit board possibly next to many other chips. The whole construct is then sealed to protect it sometimes making it look similar to an egg yolk.


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