What is an LED?

LED is an acronym for "Light Emitting Diode" which is self explanatory if you are a geek. Instead of a filament as you would find in normal incandescent or halogen lights, an LED contains things called semi-conductors which are powered by a DC current.

There one is one semi-conductor on the negative side, and another on the positive side of the DC connection and each made from a different type of material. When  DC power is applied to the LED, electrons pass between the two semi-conductors and,  due to their different materials,  the electrons are converted into photons producing a bright light. The "diode" part of LED means that the DC current passes in only one direction from the (-) semi-conductor to the (+) semi-conductor. An important thing to understand is that LEDs are either ON or OFF. In other words they are as bright as they can be when a current is applied or they are not producing any light (when there is no current) there is no "in between".

LEDs pose some interesting design problems that need to be considered if they are to be used in household and commercial lighting:

Filament in an incandescent bulb Electrons flowing between the semi-conductors
  • The actual LED is pretty small, so if you want a bright light you will usually see a number of them bunched together (referred to as clustering) in a light fitting to produce the appropriate amount of light. The number of LEDs affects the look and design of the light. Generally, the brighter the LED downlight, the more LEDs and the larger the diameter of the fitting and the more heat they will produce (see next point). However, LED technology is moving at such a rapid place that more light is being produced in smaller packages and the fitting size and numbers of LEDs will become less of an issue.
  • Although 80% of the energy used is converted to light around 20% remains as heat. The space between the semi-conductors can become extremely hot, therefore you need some way to dissipate the heat otherwise the LED will burnout. This comes in the form of heatsinks (some relatively large) which you see on many LED light fittings.
  • Dimming LEDs involves a little bit of trickery to produce the same results as dimming an incandescent bulb

Regardless of these design challenges LEDs present many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved robustness, smaller size, faster switching, and greater durability and reliability. LEDs powerful enough for room lighting are relatively expensive and require more precise current and heat management than compact  sources of comparable output.

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