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LED Lighting Explained

Ever since Philips Lumileds created the high power LED over 10 years ago, the rapid advancement and development of solid state lighting components has facilitated exciting new applications and innovations. If we gaze around our environment, we notice just how wide. spread the use of LED technology has become.

by Ross Spina (RMS Parts Pty Ltd

LEDs are everywhere, in just about every household appliance, in our automobiles, in our computers and also in our lighting fixtures.

In fact it is the lighting industry which is gaining the most in the use of LED Technology. The push for greener, environmentally friendly lighting solutions means that LEDs have become the viable alternative solution to incandescent and fluorescent lamps.

Click for larger image
The LED Dazzler, from our February 2011 issue used 3 high-brightness Seoul Semiconductor LEDs and came with a warning: don’t look into it!

Where the reliability of CFL products is questionable, LEDs are being promoted as more reliable, consuming lower power and more adaptable in their applications.

However the adoption rate of LED lighting in consumer homes is still relatively low. This is due to the high expectations which have been placed on the cheap imports and their failure to deliver.

Within the industry there are many myths about the reliability of LED products. The most common relates to the lifetime of LEDs. There is a general belief that LED fittings will last 50,000 hours with 70% of the initial lumen output. This is simply an exaggeration.

To put this statement into perspective, a LED fixture would need to be utilised for 12 hours a day over more than 11 years before we could expect partial or total failure. Any electronics engineer will know that the fitting is only as good as its weakest link. Given that LEDs often require complex circuitry and adequate cooling to operate, it is unrealistic that we should expect this level of reliability.

It may be useful to summarise some of the

terminology used in High Brightness LED specifications. LED distributors are often asked to explain some of these terms to clients.

Luminous Flux (or Lumens)

This is probably the most prominent information provided by any high-power LED manufacturer – and also one of the least understood.

It simply measures the total amount of light emitted by the light source and is measured in lumens (lm). On its own, this information is not very useful other than to provide a comparison of the total output of one light source when compared to another. Accordingly it is likely that this information will be marked on the packaging of most light bulbs or light fixtures.

Traditionally the output of low power or indicator LEDs has been measured in candelas (cd) or milli-candelas (mcd). This is still a valid unit of measure for LEDs as it measures the luminous intensity of a light source in a given direction.

If you focus a LED light source into a narrow beam, this will increase the light intensity, thus increasing the candela rating. While this is a practical measurement for indicator LEDs, it has no real purpose for lighting applications. LED lighting needs output in much more than one direction.

However, it is still common to be asked for the relationship between candela and lumen output despite the fact they are measuring different lighting characteristics.

There is no direct correlation, suffice to say that the narrower the beam angle of the light source, the greater the cd/lm ratio.

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