Solid guidelines | 14 April 2011

Martin Valentine specifies LEDs in the Middle East

LEDs are here to stay, but separating manufacturer claims from the reality can be a minefield for the diligent lighting designer. Andy Pearson provides some clarity and a useful checklist for specifiers.

For designers, each innovation in LED technology increases the number of potential applications. But with more applications come new uncertainties as designers struggle to compare LED products from different manufacturers and establish the performance of LEDs compared with traditional products. How can you be sure the LED luminaire you specify is the right product for a particular application?

Designer’s challenge
One of the biggest challenges for designers is to get impartial advice. It is a task made all the more difficult because test houses are struggling to keep up with a torrent of new products. “With the technology evolving at such a pace you often have to rely on manufacturers’ advice because there is very little independently verified product and photometric information for LEDs,” says Mark Jones from lighting designer E+M Tecnica.

Steve Poole, who manages the laboratory for the Lighting Association, sympathises with Jones. “If I was to give a tip to an LED specifier, it would be to ensure suppliers provide independent performance data to substantiate their claims, particularly when developers are looking for long warranties,” he advises.
According to Poole, products from “better” manufacturers are thoroughly tested and will perform as stated. However, he says there are products with “ambitious performance claims”. Such claims are likely to create problems when, for example, contractors opt to replace the specified fitting with a similar cheaper fitting of unverified performance.

The rapid development of LEDs means there are few examples of installations that use the latest technology. To help designers match operational claims for luminaires to traceable data, major UK lighting organisations, including the Society of Light and Lighting, have worked together to produce a template for the specification of LEDs – Guidelines for the Specification of LED Lighting Products. This document does not, however, give examples of successful and unsuccessful LED applications. The guidelines were last revised in January 2011, but don’t expect the publication to remain in its current form for long: “There’s a need to review everything every six to 12 months because LEDs are such a fast moving technology,” says Poole.

The case for consistency
One of the areas where technology is changing fastest is in the manufacture of LEDs, in particular the production of white LEDs. The manufacturing process produces LEDs with slight variations in the shade of white. The LEDs are then tested and ‘binned’ to minimise the variations between devices. However, Poole says recent developments are enabling manufacturers to be more consistent. “Ultimately an LED producer will produce precisely the colour they set out to manufacture,” says Poole.

With change happening so rapidly, Adrian Rawlinson, managing director of LED system manufacturer Marl International, recommends looking at the light output of a lamp rather than its wattage to compare lamps. He says: “A 6W LED today can produce twice as much light as its equivalent a year ago. Many LEDs are delivering 130-140 lumens per watt, but US LED manufacturer Cree has already announced that it has achieved over 200 lumens per watt at its research and development lab.

Although the efficiency of LEDs is improving rapidly, even the most efficient emit heat. Unlike traditional lamps, this heat is largely dissipated to the rear of the luminaire by heatsinks or the device’s housing. Effective dissipation of this heat will help improve the life of the unit. “For suspended ceilings, pay attention to items such as thermal insulation or fire hoods that may cover the luminaire and degrade their output and colour shift or even cause failure,” says Hoare Lea Lighting’s Jonathan Rush.

Good heat management also lets LEDs work at full power over their entire functional life. “Current practice to assess lamp life is a 70 per cent lumen output (L70), or the point at which lumen output drops below 70 per cent of its initial value,” explains Rush. To ensure illuminance levels are maintained for the life of the luminaire, says Rush, lighting calculations should be based on a minimum maintenance factor of 0.7 to cover potential light losses. “Even then, you have to trust the initial output provided by the LED manufacturer,” he says.

Heat is also an issue where LEDs are used for exterior lighting in regions such as the Middle East – but the issue here is ambient temperature, which can nudge 50°C. LEDs are generally tested at an ambient temperature of 25 or 35°C. The high ambient temperature causes the LEDs to run hot and the light output will fall. Since moving to Abu Dhabi, lighting designer Martin Valentine has put in place a performance benchmarking system for exterior LED lighting products (see box, page 30).

Built in for life
Douglas James, a director at lighting consultant Mindseye Lighting, says he is concerned that some LED fittings have not been designed to enable LED chips to be replaced at the end of their useful lives. “The LED is completely integrated into the fitting so the whole unit has to be replaced,” he says.

Brian Glynn of manufacturer Elite Lighting Solutions agrees with James, but says that although it may not be possible to replace the source in fittings such as internal downlighters, the vast majority of new LED fittings, particularly for external use, are of modular construction. Even if you cannot replace the individual chips you will be able to replace the optical array that contains the chip.

To encourage interchangeability between LED modules the industry has created the Zhaga Standard (for more information visit www.zhagastandard.org). One of its objectives is to standardise LED mountings from diverse manufacturers. “Everybody appears to have settled on 1 and 2W LEDs at the moment,” says Glynn

However, it is not the life of the LED but that of the ancillary electronics and control gear where the technology is now evolving fastest. “In the past, the weakest link of any LED fitting has always been its driver,” says Glynn. “It used to be the case that LEDs would last for 50,000 hours but the driver would only last for 15,000 hours,” he explains. He says the situation has now changed. Driver technology has developed to keep pace with developments in LEDs. As a result, drivers should last the lifetime of the product.

Perhaps the most positive aspect of all this innovation in LED technology is that manufacturers have accepted that the technology will continue to develop for some time. Many are developing fittings that will accept new technology as it becomes available. Glynn says: “You make a large investment in a fitting, but most manufacturers I’ve spoken to are building in future-proofing so that if the technology changes or the chips get brighter users will have the option to upgrade the fitting in the future.”

The Dos and Don’ts of LED specification

Do use the LED’s light output rather than wattage to judge a lamp’s performance

Do check the beam angle when replacing a conventional lamp to ensure light levels are the same

Do ensure other luminaire components, such as the driver, have a similar life to the LED unit

Do get hold of a copy of Guidelines for the Specification of LED Lighting Products here

Do ensure an LED’s energy consumption applies to the system and not just the lamp

Don’t forget the performance of an LED depends on its temperature during operation

Don’t buy a fixture if you can hold the heatsink for more than 10 seconds while it is operating without burning your hand. A heatsink is supposed to get rid of heat, not keep it in

Don’t take lifetime claims at face value, ask for evidence of how the tests were conducted

Don’t forget to look for evidence that a unit’s performance has been verified by a third party

Don’t forget to allow for a fall in light output over the life of an LED in a scheme’s design

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About ecoapollo
this is diana zhang from China, with more wishes of beatiful world, so chose to do the pro-enviroment biz(led lighting), bless all!

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