SSL Product-Growth Barriers

Experts for general-illumination, light-emitting-diode (LED) and other solid-state lighting (SSL) see several reasons for product-growth barriers – one oft-stated reason is the multiple technologies required for standard LED-lamping systems. Although this may be somewhat true, such products as televisions, computers, cell-phones and other electronic gadgets, which are, in many respects, more high-tech than LEDs, have gained notorious success. These systems have penetrated the mass market much faster than LED-based lighting systems that are equipped with the necessary standards adoptions. So, what’s the problem?

General-illumination, LED-lamping systems threaten to overhaul the screw-base (Edison-type), lamp-type products and their 100-year infrastructure, which dominates the lighting field. The decades-old, fluorescent-lamp systems also face this barrier. Fluorescent lamps, introduced in 1939, experienced similar acceptance challenges as they’ve tried to replace the century-old infrastructure (and our familiarity) with warm, white light.

Earlier, high-tech products such as television, computers and cell phones didn’t replace technologies that provided the same functionalities; thus, they didn’t contend with an existing infrastructure and historic marketbase.

Still, fluorescent lamps, although dubiously successful in the beginning, have improved in terms of brightness, correlated color temperature (CCT), efficacy, size and cost per application. Further, fluorescent’s improved systems require no changes in existing fixtures or wiring layouts, which gives LEDs a more difficult task when replacing them.

In a previous column, I discussed the technical and business challenges LED manufacturers face when attempting to overtake such incumbent products. Precisely, these challenges – uncertainties – dampen the progress of LED-standard developments, despite the product’s potential long-term environmental and cost benefits.

Lighting companies’ manufacturing tasks are daunting. To implement a wide-based adoption of LED-lamping systems, they, essentially, must obsolete their own products. They’re faced with such challenges as developing new (standard) fixtures, electrical feeds and other systems that enhance LED usage. Developing such complex products isn’t easy, because technology provides myriad present and future engineering options. They must also add marketing efforts that lead, hopefully, to general acceptance by architects, builders – and consumers.

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Compatibility
To gain full acceptance, LEDs or other SSL systems require both mechanical and electrical compatibility with current lighting fixtures, while matching the existing light quality. In order words, for white LEDs to replace current, household lamps, they must twist into existing Edison-type, lamp sockets, as do the now popular, compact-fluorescent lamps (CFLs) introduced in 1979, while providing similar light properties.

Similarly, commercial-building SSL- or LED-type luminaires (the complete lighting unit, including lamp, reflector, ballast, socket, wiring, diffuser and housing), to be accepted, must coalesce with regular 120/220VAC systems. Such electrical or mechanical fixture systems (and requirements) aren’t necessarily the most efficient solution for SSL light quality, longevity and cost, but developers recognize that most residential and commercial users won’t accommodate non-conventional fixtures or voltages.

Currently, special retailers offer low-brightness (20-150 lm) Edison-socket/ballast-type, white LED lamps in limited quantities and quite a few are Underwriter Laboratories (UL)-listed – a comfort for users. However, without more offerings in the 700–1,000-lm brightness range (much higher for commercial applications), broader adoption into the general lighting market will be restrained.

Retailers such as Home Depot and Lowe’s want lower-cost, standard SSLs with a quality equal or higher than current products — but a Catch-22-type question delays this outcome: How does the SSL supply chain afford to develop standards for general lighting products when the current technology offers comparable lamps, fixtures and outlets with lower upfront costs?

Even as the technology advances, to meet the cost and quality demand, are we better off leaving the bulb sockets and electrical requirements as they are? Perhaps this task isn’t as simple as it first seems.

Standards within standards
Standards for mechanical forms, electrical connections and current lighting measurements set aside, specific standards for LEDs or SSLs are, now, a broad and expanding field. Currently, for example, LED lamps suit diverse applications, both existing and new; each may have certain standards and requirements. Further, LED luminaires have various levels of integrated components (sub-assemblies), each requiring its own standards level, that is, if the sub-assemblies are to become commodities.

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Manufacturers must also consider safety standards (such as those employed by UL) and standard LED lamp criteria for lumen/watt, brightness, color-rendering index (CRI) and CCT, plus new, LED-specific quantities, such as lumen degradation over time, and useful lifetimes.

Developing LED standards for such niche applications as signage may be somewhat easier, because signs are commercial applications that compromise a larger system level, meaning, illuminated signs are larger and more easily managed enclosures. Also, signs, operated or maintained by skilled professionals, bypass the actions of ordinary people.

Further, electronic-display signage and channel-letter LEDs have less demanding, white-light requirements.

Standards measurement
Many organizations collaborate to create LED standards, namely, the Illuminating Engineering Society of North America (IESNA); the American National Standards Institute (ANSI); Underwriters Laboratoriess (UL); the International Commission on Illumination (CIE); the National Electrical Manufacturers Assn. (NEMA); the Dept. of Energy (DOE) and the Next Generation Lighting Industry Alliance (NGLIA).

Within the past year, this group formed the ANSI C78-09 and IESNA (TPC-Testing Procedures Committee) subcommittees, to study and develop LED standards for lighting applications. Dr. Kevin Dowling, VP of innovation, Philips Solid-State Lighting Solutions (Burlington, MA), is leading the standards effort. The focus: developing LED standards for chromaticity, luminous flux, lumen depreciation, SSL definition, photo-biological safety, color quality and electrical safety.

After approximately two hours of continuous operation, LEDs (particularly those used in high-brightness applications) reach a steady-state stage, and the brightness drops to 85% of the initial value. Such factors emphasize the importance of testing criteria. The industry also needs specific LED light-output, measuring standards, because LED radiation patterns differ from those projected by incandescent and fluorescent lamps. This procedure, then, requires standards for placing the photodetector and measurement methods.

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Because standards depend upon measurements, it’s important to create a standardized means to accredit those who conduct the measuring. Additionally, accredited laboratories (e.g., the National Institute of Standards and Technology) must apply the standards via high-quality, measurement equipment, built by established companies. Clearly, laboratory-accreditation procedures, determined for testing and calibration, must be in place prior to any general standards implementation.

White, high-brightness LEDs (HB-LEDs) face the most difficult technical challenges, especially for color quality and stability. Still, accurate and meaningful measurements are crucial for HB-standards adoption and, although some general standards appear imminent, vendor-spawned variations make product standards and specifications difficult to pin down. Furthermore, ongoing, rapid technology advancements, particularly from top manufacturers, magnify the challenge.

Electrical-driver technology, another technical aspect, also impacts general illumination. LEDs require a constant-current power source, that is, a DC electrical drive, a converter that’s connected to an existing AC voltage outlet. In household applications, manufacturers can integrate the contrivance into the luminaire. In most signage applications, the device’s relevant bulk is equal to or less than standard transformers.

Signage standards
The primary challenges are cost and successful implementation. Standards play a key role in successful implementation, especially for larger market penetration. Some general-illumination, LED standards also apply to signage, although in different quantitative ranges. Also, standards for binning of luminance and color may be less stringent than those for general illumination.

Many signage products require white and color LEDs, which add additional standards. In electronic-display signage, electronic controls can adjust luminance and color. LCD displays are tuned through pulse-width-modulation (PWM) correction methods that utilize color mixing that’s applied electronically,to obtain uniformity. These sophisticated techniques, as opposed to extreme binning methods (for consistent flux, color and forward voltage), will become more mainstream over time.

Further technology and standards advancement will boost SSL into the signage industry over the next several years.

Still, signage and display manufacturers who, today, utilize LEDs in their products can affect the standards adoption for the general industry. They realize – or will soon learn – that hundreds of LED and SSL-luminaire suppliers exist, but a limited number produce quality products. Signmakers, then, should select accredited suppliers. They should also demand LED-specific requirements, such as binning, correction methods, and, in the display field, onsite testing of screens under specific conditions.

Signmakers should also ensure that luminaire suppliers have tested the products they sell, under rigorous conditions, to determine product lifetime and warranty liabilities.

Manufacturers should provide comprehensive product literature, with specifications that sign designers can use and understand. The pages should display nominal values and acceptable standard deviation; and product-safety information. Also, the product itself should be certified by UL or an equivalent organization.

Despite the lack of standards, LED-signage applications continue to grow. In truth, both manufacturers and signmakers don’t need measurements to determine if light output is useful — but standards are still necessary to ensure consistency, supply metrics for fair comparison and keep the aspects of all measurements equivalent. Only with adequate standards will we purge the current industry cloud of confusion, hype and frustration.

Opteolectronic and SSL Technologist Dr. M. Nisa Khan has bachelor’s degrees in physics and mathematics, and a master’s and doctorate in electrical engineering; she has 18 years’ experience in the semiconductor and telecommunication industry.