Republication of Postings from the U.S. Department of Energy (DOE) Solid-State Lighting Program
by Jim Brodrick, U.S. Department of Energy
As you may know, the U.S. Department of Energy’s (DOE) CALiPER program tests commercially available LED lighting products and publishes the results in a variety of formats — including Application Summary Reports, which focus on specific product types and design scenarios. Late last year, we published CALiPER Application Summary Report 20: LED PAR38 Lamps, which indicated that LED PAR38 lamps had much higher efficacies than conventional sources, while offering comparable lumen output and luminous intensity distributions — at least in the target range of lamps comparable in output to 75 W halogen PAR38s. Most of the LED PAR38 lamps tested had correlated color temperatures that were similar to the conventional lamps they were intended to replace, and color rendering indexes (CRIs) that were good (80s) or excellent (90s).
Earlier this month, DOE published the first in a series of four special investigations intended to extend the findings of Application Summary Report 20. The new report, CALiPER Report 20.1: Subjective Evaluation of Beam Quality, Shadow Quality, and Color Quality for LED PAR38 Lamps, focuses on a subset of lamps from Report 20 and will be the subject of a 60-minute live webinar on Tuesday, December 3, at 1:00 p.m. Eastern Time.
Report 20 showed that, judging by the basic numbers, many LED PAR38 lamps are a good alternative to halogen lamps. But focusing only on standard data from photometric testing doesn’t reveal a lamp’s performance in other areas, such as the smoothness or color consistency of the beam. Unfortunately, many of these facets of lighting quality are not easily quantified using readily available metrics — which can make it hard for manufacturers to make improvements and for consumers to differentiate products. Subjective, comparative evaluations can help identify product attributes that lead to better lighting quality, as well as which attributes specifiers consider desirable.
In order to learn more about lighting preferences and gain a greater understanding of the difference in performance for a set of LED and halogen PAR38 lamps, CALiPER had a demonstration mockup constructed at Pacific Northwest National Laboratory’s facility in Fairview, OR. Members of the local Illuminating Engineering Society chapter viewed the 26 different lamps being demonstrated, and completed a questionnaire on beam quality, shadow quality, and color quality.
Although this wasn’t a rigorous scientific experiment, the results can be used to identify areas of concern related to lighting quality aspects of LED PAR38 lamps — specifically, the relative performance of the LED lamps compared to benchmark halogen lamps, and which features of LED products may lead to more-desirable lighting quality. Among the key findings:
* In each of the quality categories, at least one LED lamp was rated more favorably than the benchmark halogen lamps — which shouldn’t automatically be considered the ideal source for lighting quality.
* LED lamps using a single-emitter design were generally preferred for their beam quality and shadow quality.
* For color quality, the observers generally preferred 3000 K LED lamps over 2700 K LED lamps, but their ranking of color quality did not always correlate with the lamp’s CRI, nor with any other color rendering metric. Based on the wide variation in rankings, the observers likely had a difficult time distinguishing between the color rendering capability of the various lamps, despite differences in performance according to established color quality metrics.
* LED lamps with narrow-spot distributions were generally viewed as having less-acceptable beam quality than their narrow-flood or flood counterparts, although there was substantial variation in perceived quality within any of the groups.
* Poor color consistency within the beam, and stray light outside the main beam pattern, were the attributes most likely to be noted by the observers as negative features.
Although many of the LED PAR38 lamps were ranked higher than the halogen benchmarks, there’s room for improvement for even the best-performing lamps. Furthermore, there remains substantial variability among LED PAR38 lamps — as was also seen among the halogen lamps — which will require buyers to make careful purchases.
Users can’t sense the efficacy or power factor of a light source, but they’re likely to be aware of the quality of the light, which is often about choosing the right product for the application — and in many cases includes minimizing the effects of product shortcomings. Some of a lamp’s limitations may be trivial and easily averted, but identifying areas for potential improvement is important to the continued development of LEDs and other energy-efficient light sources. Even conventional lighting products, which are often considered the standard for comparison, have limitations that shouldn’t be replicated in SSL products. In fact, reducing or eliminating any quality limitations could lead to increased adoption of energy-efficient technologies. In other words, energy-efficiency upgrades may be more likely to occur if they’re coupled with quality improvements, rather than trading off lighting quality for long-term cost savings.
The new report is available online at www.ssl.energy.gov/reports, and more information about the webinar is available on the DOE SSL website. Forthcoming reports in the same PAR38 “20” series will cover flicker, dimming, and power quality characteristics; stress testing; and lumen and chromaticity maintenance.
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