LEDs: a matter of quality

LEDs hold great promise as a new light source for general illumination. They can be highly energy efficient at a time when governments around the world are seeking alternatives to incandescent lamp technologies. They can have a very long life (claims of 50,000 hours and even 100,000 hours are not uncommon), an attractive feature for facility managers and others responsible for building maintenance. While there are some excellent products available, LEDs are beset by quality problems and many in the marketplace fail to match suppliers’ claims of efficiency, longevity and other critical parameters. For this reason, Lighting Council Australia has introduced a quality scheme for LEDs.

What is an LED?

Light emitting diodes differ from traditional light sources in the way they produce light. In an incandescent lamp, a tungsten filament is heated by electric current until it glows or emits light. In a fluorescent lamp, an electric arc excites mercury atoms, which emit ultraviolet (UV) radiation. After striking the phosphor coating on the inside of glass tubes, the UV radiation is converted and emitted as visible light.

An LED, in contrast, is a semiconductor diode. It consists of a chip of semiconducting material treated to create a structure called a p-n (positive-negative) junction. When connected to a power source, current flows from the p-side or anode to the n-side, or cathode, but not in the reverse direction. Charge-carriers (electrons and electron holes) flow into the junction from electrodes. When an electron meets a hole, it falls into a lower energy level and releases energy in the form of a photon (light). The specific wavelength or colour emitted by the LED depends on the materials used to make the diode.

Benefits of LEDs

• Highly energy efficient - comparable to fluorescent technology
• Long life - ideal for locations where access is difficult
• Durable - ability to withstand vibration and shocks
• No warm-up period - full brightness when switched on
• Ability to withstand rapid on-off switching
• Do not contain mercury
• Dimmable
• Highly flexible technology - will lead to rethink of lighting applications

Why do some LEDs have quality problems?

Solid-state lighting is a complex technology - much more so than incandescent and fluorescent lighting. While LEDs have been with us for quite some time, the technology is still under development. It is only in very recent years that the technology has allowed area lighting. LEDs are a point source of light and are excellent for applications such as brake lights, traffic signals and flashlights. However, area lighting - such as illuminating a room or a road - is much more challenging.

Heat dissipation from the p-n junction in a LED is a significant challenge for manufacturers. If the heat is not dissipated correctly, degradation of the LED material and phosphors can lead to colour shift. This is important in side-by-side applications, as the human eye is particularly good at discerning differences in colour temperature among lighting fixtures. Excess heat can also degrade the lighting fixture and lead to premature failure. The need for a substantial heat sink explains why it remains difficult for an LED to directly replace the small MR16 downlights so common in Australian homes - although this does not stop many suppliers claiming to have such products.

Governments in Asia in particular are encouraging LED production. This has led to a huge number of new manufacturers, literally in the thousands, most of whom have no previous experience in lighting. It is, therefore, not surprising that many make mistakes along the way.

Another problem is the immaturity of standards. A great deal of work is now occurring internationally to develop LED standards. However, until this work is complete it remains difficult to judge a particular LED product. The absence of standards, unfortunately, has allowed some unscrupulous suppliers to claim outlandish lifetimes for their product without supporting evidence.

Poorly performing LED products can undermine confidence among users and discourage early adopters of the technology. An underperforming product has the potential to delay or otherwise compromise the substantial energy savings potential of LEDs.

Lighting Council Australia has therefore introduced its SSL Quality Scheme - a certification program for LED products. A minimum set of critical parameters is reported by participating suppliers to accurately reflect the performance of their products. The scheme participants provide test reports or other evidence verifying their claims. Lighting Council Australia registers the product on a database on its website (www.lightingcouncil.com.au) and authorises use of a label indicating conformance to the parameters.

A sample SSL Quality Scheme label with an explanation of the six critical parameters. The sample label and further material on the Scheme appears on Lighting Council Australia’s website www.lightingcouncil.com.au. In addition to the main label appearing above, Scheme members are able to apply a miniaturised version to their product.

The critical parameters appearing on the SSL Quality Scheme Label are:

• Luminaire efficacy (energy efficiency of the entire fitting)
• Light output of the luminaire
• Measured input power
• Test voltage
• Correlated colour temperature
• Colour rendering index

SSL Quality Scheme Label

When Scheme requirements have been met, Lighting Council Australia issues a label for a specific light fitting containing LEDs or a family of LED fittings.

If you are considering investment in LEDs you are strongly encouraged to look for this label.

SPARC 2011 - International Lighting Event

Doltone House, Darling Harbour, Sydney

6-8 June

www.sparcevent.org

SPARC is an exposition of modern lighting technologies - including LEDs - combined with a program of top international and Australian speakers covering modern lighting design and other lighting topics.

International keynote speakers include Mark Major, Director of Speirs and Major, London; Chou Lien, Partner, bpi Brandston Partnership, New York; Rogier van der Heide, Chief Design Officer in Lighting, Philips; and Klaus Vamberszky, Executive Vice President - Technology, Zumtobel Group.

SPARC 2011 is partnering with Vivid Sydney (27 May to 13 June), a festival of light, music and ideas featuring the stunning illumination of the Sydney Opera House sails.