Fitted Target Efficacy metric promotes discussion
The FTE metric for outdoor luminaires was a major topic for discussion during a Webcast by the DOE’s Energy Star program, which is itself a target for the EPA, writes Brian Owen.
|Pole-mounted luminaires: draft criteria|
At the recent IES Street and Area Lighting Conference in Philadelphia, Tuenge presented an update an the new metric, reassuring the audience that the DOE had listened to the comments submitted from the industry during the commentary period and that the DOE had made modifications and is proposing revisions that reflected these comments where applicable and necessary.
As a review, Tuenge explained that this is an addition to applications for Energy Star Category A and that the draft criteria was first released on July 1st, 2009. These new applications include Pole-mounted area and roadway luminaires, including decorative and historic, but excluding bollards which are already covered in Version 1.1. Also included are Wall-mounted area luminaires or “wall packs” and Ceiling-mounted garage and canopy luminaires, but excludes step lights.
Tuenge addressed why it was determined to add these applications, stating that this is a very active area of the SSL market, there is a high level of interest from energy-efficiency programs, municipalities, and other stakeholders noting that CALiPER testing has revealed a wide range of performance and Demonstration projects indicate potential for large energy savings and most importantly the need for performance guidelines.
Questions regarding ceiling-mounted criteria were addressed and no revisions are proposed. With respect to wall-mounted criteria, the uplight allowances will be eliminated.
Pole-mounted criteria prompted the majority of comments and discussion. Tuenge firstly addressed the IES new luminaire classification system, or the BUG (Backlight, Uplight, Glare) rating system, explaining that FTE evaluates backlight and uniformity. When asked why wasn't BUG incorporated in its entirety and why Lighting Zones are not addressed, the response was that Lighting Zones and BUG ratings cannot be addressed independent of the specific project. A comment received was that the uplight restrictions were too lenient as upward light is wasted and contributes to sky glow and proposed revision eliminates uplight allowances.
Tuenge presented the new pole-mounted FTE metric, which is project-independent, summarizing that it determines the Uniform Pool of illumination unique to each luminaire and sums the luminous flux landing therein, fits a Rectangular Target to surround the Uniform Pool and finds the % of Rectangular Target covered by the Uniform Pool. The summed lumens are scaled (down) by the % coverage and then divided by input wattage (lm/W).
Tuenge cited the benefits as; application-independent; allows for the evaluation of efficacy (lm/W); measures the effectiveness of house-side (HS) shielding; uses distribution shape; and, there are no arbitrary proportions. He noted that there is flexibility for designers and manufacturers, and that effective HS shielding is rewarded, but not required. Also, area of coverage is described, not prescribed, and there is an “apples-to-apples” comparison for similar distributions, independent of MH and illuminance.
Tuenge covered the “how to” of FTE product evaluation by firstly importing IES format absolute-photometry data file into software already developed by DOE and then reviewing the software output.
Comments and responses
One comment concerned consideration of site-specific requirements when establishing criteria, i.e. required illuminance, roadway width and lighting power density (LPD). The response was that site-specific criteria cannot be addressed at the luminaire-qualification level and that appropriate luminaires should be selected by qualified designers. The response to a comment that it would be overly selective to expect LED to outperform 75th percentile HID by 20% was that a proposed revision will reflect a reduction of requirements to the 75th percentile HID performance and that a Mid-Output category will be created.
A comment that dimmable products may not meet requirements in one or more operating modes was addressed with a revision that include a clarification to the criteria sating that luminaires will be tested in their full-output mode. The response to a comment that some distributions are designed for lateral asymmetry and would be unfairly penalized was that the algorithm will be revised and simplified to eliminate the requirement for symmetry. It was noted that FTE is not intended to evaluate luminaires designed for Small Target Visibility (STV).
The response to a comment that the metric should favor larger areas of coverage was that a large area of coverage can reduce initial system cost and embodied energy, but ongoing energy consumption, being the bulk of life-cycle impact, remains the primary concern of Energy Star. It was asked as to whether Target Efficacy Rating (TER) as defined in NEMA LE 6-2008 was considered? The response was that TER was evaluated but not adopted because neither uniformity nor shape of distribution are evaluated and due to improper treatment of backlight. A possible revision, to include to 1.0-MH for Types II-III-IV, would be a major improvement and that a NEMA vote was scheduled for October 7th and that results of the vote are awaited.
Questions and answers
A question and answer period, which followed the presentation, took the majority of the 90 minutes allocated for the Webcast. A comparison was queried between LED versus induction. Tuenge noted that induction has trouble competing with broad pole spacing or shielding on the house side and the long life and lower maintenance benefits of LED. As well, one must still consider lumen depreciation. While induction may be suitable for decorative, there are limitations such as closer pole spacing and a similar sensitivity to heat. Facts became responses to certain questions, such as TM-21 is the standardized forecasting of depreciation and depreciation is highly dependant upon heat-sinking. It is recommended that this be included in warranties. Also with respect to criteria, the CCT lower limit is set to 2700K, as per definition in ANSI C78.377. The FTE metric provides delivered lumens to the target in a useful manner, delivered to uniform pool as compared to the lamp lumens baseline, of which HID is the baseline technology.
Earlier in the presentation, Tuenge discussed the FTE software and a question was raised that there were difficulties in its employment. Tuenge stated that properly formatted IES files should only be used with the software and that any errors are usually related to non-standard or poor formatting. He advised participants that should they encounter any problems, they could send him their photometric file and he could likely correct the issue easily and quickly for them. Asked about the BUG rating system, the relative detail can be found in IES TM-15-07, Addendum A.
Tuenge was asked as to whether the issue of IR radiation into the sky from the heat sink been considered and he responded that he doesn’t think that it is substantial but they (the DOE) will look into it.
Tuenge commented that the Energy Star criteria is setting a reasonable bar of quality with LED not achievable with competing technology. There must have been a few competing technology proponents participating as 2 separate questions were asked about the eligibility of HID or induction for Energy Star, with the response being that scope of the criteria is for LED only.
A number of questions were asked about correlations and dependence, such as ‘Does FTE depend on mounting height? with the response being no as with respect to uniformity and the uniform pool in relation to MH, the relationship is preserved. It was also asked if there was a correlation between FTE and LPD and Tuenge responded that there was no strong correlation, further stating that is was expected and fundamental that the luminaire will be appropriately applied by a designer.
Tuenge responded to question regarding the inclusion of additional specifications for controls such as dimming, stating that although the benefits are recognized, it is best evaluated at a project level and considered separately. Asked whether there would be a category for luminaires with integral controls, Tuenge responded that the problem is the site-specific nature or requirements, which are not clear-cut, therefore would not be incorporated into specifications.
When asked about IES involvement in the development of the criteria, the DOE's Richard Karney said, "We have relied on IES standards and test methods to the greatest extent possible for these criteria. For example, we use the BUG criteria, IES uniformity criteria, and LM-79 generated IES photometric files as the basis for these criteria. DOE has a close working relationship with the IES and always welcome their input and involvement in our Energy Star criteria setting."
The Roadway Lighting committee of the IES may have had a different opinion going into this process, but hopefully with most of the comments addressed, there will a be a general satisfaction with the criteria. At a recent RLC meeting, held annually after the IES Street and Area Lighting Conference, this year in Philadelphia, the RLC is also hard at work getting the long overdue revision of the RP-8 ‘Recommended Practice for Roadway Lighting’ into publication and practice, including the new BUG luminaire classification system. A question was posed as to whether there has been any field verification of the FTE metric. Tuenge’s short answer was that FTE is relatively new and no, but in checking the results of GATEWAY Demonstrations, there has been good correlation between FTE and performance in the project depending as to whether the selected luminaire is well suited for the project. Asked if other metrics were considered, such as the NEMA TER, the answer was yes, but TER didn't fit requirements and that FTE is a better metric for the purposes of the criteria.
Dark skies and dark days for DOE
As described in a recent LEDs Magazine article, the International Dark-Sky Association (IDA) raised alarms regarding bluish-white light. Tuenge commented that the DOE is aware of the concerns and that it is an ongoing area of research, admitting that more research is required but that it is not currently something that can be directly applied to lighting practice. Tuenge also commented, “We (the DOE) don't feel that it is something to cause alarm.”
In addition to the Webcast subject, another target was hit in recent days, as the DOE Energy Star program became the target of the Environmental Protection Agency (EPA) – see News. Richard Karney, DOE Energy Star Program Manager answered a question posed, explaining that is hoped that this criteria will be finalized within 4-6 weeks and then handed over to EPA for implementation.
I asked Shirley Coyle, President of Ruud Lighting Canada (BetaLED) for her comments on the webcast. “Jason Tuenge of PNNL did a good job of explaining why they have decided to use the FTE (Fitted Target Efficacy) metric for achievement of Energy Star for LED outdoor lighting. “ said Coyle, adding “The FTE metric is an improvement over the simplistic and sometimes misleading LPW (lumens per watt) efficacy rating because it goes beyond LPW to evaluate the LED luminaire’s ability to uniformly distribute light to a target area. Tuenge made it clear that the FTE is intended strictly a product-level approval and still requires a lighting designer / specifier at the project level, who knows the application, to choose the appropriate Energy Star LED product to achieve a successful design that is both energy efficient and functionally effective.” Coyle was one of many industry professionals who were originally quite sceptical about the ‘efficacy’ of the metric itself, but with the proper application and consideration or necessary revisions, has seen where the metric can be beneficial.
When asked as to the difficulty for a manufacturer meeting Energy Star criteria for Outdoor Luminaires, Coyle commented, “Achieving Energy Star will not be a short putt for SSL luminaire manufacturers. The standard has been written to assure that any LED luminaire making the cut is able to compete against the cream of the crop in today’s current HID luminaires, the top 25% of incumbent HID technology.” Noting “At BetaLED / Ruud Lighting, we certainly believe LED lighting can earn its place on a project based on competing against best-in-class HID systems.”
At the conclusion, Tuenge noted that the DOE would determine if a 2nd comment period might be necessary.