Brussels conference sprouts better understanding of LEDs

LED luminaire manufacturers and LED suppliers were presented with some pretty stark home truths at the recent LEDs conference in Brussels, Belgium. Speakers encouraged the LED community to stop mis-selling the technology as an answer to every lighting situation; to quickly develop standards; to present information about their products in ways that the lighting industry is familiar with; and, in short, to "grow up".

Harsh words indeed. But the intention, for the most part, was to provide constructive criticism. "Don't get me wrong, I think LEDs are an incredibly exciting tool," said Iain Ruxton of Speirs & Major Associates, a lighting design company that has used LEDs in many high-profile projects. "But we need to bridge the gap between LED manufacturers and the lighting community."

This was a theme running throughout the 2-day event, organized by Lighting Equipment News and subtitled "Putting theory into practice: meeting the design and performance challenges." Attendees learned about thermal management issues, which are a key factor in designing luminaries that live up to the long-lifetime claims associated with LEDs. The devices produce heat that must be efficiently removed in order to prevent deleterious effects on various LED properties, including lumen output, emission wavelength and lifetime. Other sessions discussed colour mixing and the responsivity of the human eye to factors such as hue and saturation, as well as new technologies capable of mixing and diffusing light in a highly efficient manner.

The main focus was on addressing the disconnect between what LED producers are delivering and what the lighting companies require, and there were certainly many issues for speakers to get their teeth into. The industry's lack of standardization cropped up again and again, although a number of bodies are making progress, notably the CIE in the area of photometric measurements (see Standardization of LED measurements).

According to Gordon Routledge, managing director of Lumidrives, an LED luminaire manufacturer, a key issue with white LEDs is binning, the process by which LED manufacturers classify their white LEDs. Originally, white LEDs were binned by correlated colour temperature (CCT), but of course devices with the same CCT can appear to have distinct coloured tints depending on their position relative to the black body locus. The leading manufacturers now use new and improved bins, based on MacAdam ellipses - regions on the CIE colour space diagram within which colours are perceived to be the same.

This new binning structure has improved matters but problems remain: the bins are still large enough that differences can often be seen between white LEDs from the same bin, particularly in direct-view applications. Also, colour matching can be problematic if shipments are phased, or if the luminaire manufacturer needs replacements at a later date. At the heart of these issues is a tricky chip-manufacturing process which makes it very difficult to precisely control the LEDs' parameters.

Lack of understanding

By all accounts, LED manufacturers have become much better at providing large amounts of data about their products. The problem is that many luminaire manufacturers don't understand LEDs or the data they are provided with. "Beware of the data sheet," warned Routledge. "Values such as lumen output quoted by the LED manufacturers don't transfer directly to applications."

Partly, problems arise when companies struggle to compare the attributes of different light sources. "The LED community needs to provide designers and engineers with data comparable to industry standard data used for other light sources." said Iain Ruxton.

One result of this lack of understanding is that there are a number of sub-standard LED luminaire products in the market. "It's possible to get away with some pretty bad engineering for a while, since it generally takes some time before major failures occur," said Routledge.

Kevan Shaw, managing director of Kevan Shaw Lighting Design, said that in his opinion people generally have done a poor job of putting LEDs into existing fittings. "They should be adapting existing fittings around LEDs to take into account thermal issues," he said.

The danger is that too many poor products, coupled with unrealistic promises that LED lighting is the answer to every problem, could sour the market. Several speakers likened the situation to that experienced around a decade ago, when fiber-optic lighting was touted as the ultimate lighting solution.

Rapid cycle times

In some ways, LEDs are a victim of their own success, since technological progress is so rapid that the industry struggles to keep pace. "The innovation cycle speed is a cause for concern," said Martin Hartmann, LED product manager with TridonicAtco. "Luminaire manufacturers and lighting designers typically look several years ahead, and by then the technology has changed dramatically." As well as the obvious problem of newly completed projects not having the latest and greatest technology, this situation also results in unproven systems being offered into the market, and proven systems being discontinued as they are overtaken by new developments.

Kevan Shaw summarized this issue in what is coincidentally known as Shaw's Law: "LED lighting products will be out of date by the time they are installed on a project." His talk gave a case study of the new Kuwait Public Institute for Social Security building, which employs nearly a quarter of a million LEDs in 800 fittings, principally to light the building surfaces. Shaw explained that the luminaires driving the light pipes in the installation have already been superceded by much more powerful models. Shaw's concern is that the company might not be able to supply the older model of luminaire in the event of future failure, making matching very difficult.

Advantages?

LEDs have many advantages, but these are often application-specific and sometimes driven by hype. There's no denying the "wow" factor that some LED installations enjoy, or the design and branding potential provided by saturated colors and digital control, or the advantages of small form-factors and the absence of environmental nasties such as mercury and lead. However, energy efficiency claims can be misleading if one takes into account the heat that has to be removed from high-power LEDs, perhaps by adding to the air conditioning load inside a building, for example.

Perhaps the most contentious area is lifetime. Since LEDs generally don't fail catastrophically, any definition of lifetime has to be related to the degradation of output over time. Different conventions have sprung up to quote lifetimes for LEDs as the time taken for the lumen output to drop to either 70% or 50% of its original value. Even setting aside the fact that any measure of lifetime has to reflect the properties of the system in which the LED is positioned, not just the LED itself, these percentage values are out of step with industry conventions to quote the lifetime of fluorescent tubes as the time to fall to 80% of the original illumination level.

If LED light sources that experienced 50% degradation were used in an illumination application where end-of-life output was specified, this could require an overhead of twice as many LEDs, adding considerably to the cost and size of the luminaire (which are already key issues for LEDs in such applications).

Build-up of dirt and dust can also throw a spanner in the works by reducing the light output from a luminaire. An oft-quoted advantage of LEDs is the maintenance savings made by not having to change the light source. However, if the cover is covered in dust and has to be cleaned, or the electrical system needs to be checked at regular intervals, then the light source could be changed at the same time. Hence, the no-maintenance advantage is cancelled out.

Of course, cost is always an issue with LEDs. The high initial cost of LED-based systems is usually justified by reference to significance savings in terms of energy consumption, maintenance costs and replacements costs. Even so, this argument does not always fly. "The expense of LED luminaires is unacceptable on many projects, and cost is often the reason to reject LEDs," said Iain Ruxton. "Whole life cost doesn't interest developers and designers, who don't end up running the building and paying the utility bills."

The range and scale of projects described by various speakers - for example, a bridge between Macau and mainland China, due to be completed before the end of the year, that incorporates almost 1 million high-brightness white LED marker lights - certainly provided convincing evidence of the possibilities that LEDs provide.

"LEDs are part of the solution, they are fantastic for colour-change effects but not for white-light illumination," said Iain Ruxton. "The LED community needs to admit what LEDs are good for and what other sources are better at."