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2 January 2007


DOE study sheds light on commercial LED lamp efficacies

A pilot test of four LED lamps by the US Department of Energy’s solid-state lighting (SSL) Commercial Product Testing Program (CPTP, introduced in a workshop in October) has found that they all fall short of their claimed light output in lumens per watt.

During the program’s development phase, the pilot tests examined two‘downlights’ (the type of spotlight that is typically recessed into a ceiling) as well as a task light and an under-cabinet light. The four different products were selected to represent a range of applications, designs, and manufacturers. The LED makers claimed lighting efficacies
of 36-55lm/W, while the pilot test found efficacies of 11.6-19.3lm/W, placing them below compact fluorescent lamps (CFLs) in lighting efficacy.

The study suggests that manufacturers are relying on measurements of how much light an isolated LED produces rather than how much the light an LED lamp actually delivers. However, the results show that traditional lighting performance metrics (primarily based on lamp efficacy rather than overall luminaire efficacy) do not provide an
adequate indication of an SSL luminaire’s performance; it is
inappropriate to suggest that a high LED luminous efficacy (lamp efficacy) indicates that a luminaire using those LEDs has high efficacy. It could therefore be misleading if lamp efficacy is used to compare the light output or energy efficiency of an SSL product to a product using another light source, says the DOE. So, lamp efficacies should not be used in luminaire product literature to indicate luminaire performance at this time.

Nevertheless, measures of LED efficacy can be useful for manufacturers to evaluate the performance of available lamp components, it adds. Developers of individual LEDs are achieving significant gains in efficacy. In October Cree Inc said that it had developed a white-light LED that produces up to 85lm/W. DOE helped fund the development of the LED, which can output as much as 160lm. White LEDs have since been demonstrated with luminous efficacies of over 100lm/W by South Korea’s Seoul Semiconductor (the P4, launched in early December) and 150lm/W by Japan’s Nichia in mid-December. By 2025, DOE’s goal is to achieve
160lm/W in cost-effective, market-ready, solid-state lighting products.

Since SSL technologies are undergoing rapid change and improvements, products arriving on the market exhibit a wide range of performance, says the DOE. Industry groups, standards setting organizations, and the DOE are therefore moving to develop the standards and test procedures
needed for SSL products. In the meantime, manufacturers could knowingly or unknowingly take advantage of the novelty of SSL, of the public’s lack of familiarity with it, and of the lag in appropriate standards and rules to promote products as energy efficient, whereas in fact they perform more poorly than incandescent or fluorescent lamps, the DOE warns.

Until standards and testing procedures are established and rulings are adapted to account for particularities of SSL technologies, industry professionals should use their vigilance to help ensure that product performance data is not used misleadingly, the DOE advises, adding that
manufacturers, testing laboratories, energy experts, and regulators have a key role in protecting the potential of SSL. Until the field of SSL technologies and supporting knowledge matures, any claims regarding the performance of SSL luminaires should be based on overall luminaire
efficacy (i.e. from testing of the entire luminaire, including LEDs, drivers, heat sinks, optical lenses and housing), to avoid misleading buyers and causing long-term damage to the SSL market.

Further CPTP testing is planned to better understand the discrepancies observed: i.e. to gain a clearer understanding of how to assess the performance of SSL products compared to products using traditional light sources; to identify how different testing procedures may affect results; and to clarify how traditional photometric practices apply or do not apply to SSL products.