How To Choose an LED Luminaire We are witnessing rapid and dramatic changes in both the technology and fixture options available for commercial lighting. Technology is shifting; form factors are evolving, and industry forecasts predict that by the end of this decade, solid state lighting (SSL) will account for more than 80% of the general lighting products installed—all but eclipsing traditional technologies. Ongoing improvements in efficiency, color quality and thermal management are enabling the transition, and everyone involved in lighting will benefit. With this opportunity, new players are entering the market, and seasoned manufacturers are also accelerating their own offerings. The aggregate effect is exponentially more SSL products to choose from, with less information for telling them apart. This paper will guide you through various performance, quality, and cost considerations when choosing LED luminaires. With a veritable explosion of LED options and offerings available across all lighting applications – indoors and outdoors, task and volumetric light, from bulbs to high-‐bays, the task of LED luminaire selection can be quite complex. This paper seeks to describe the various attributes for light emitting diode (LED) lighting, highlight certification and industry standards groups that are defining and creating third-‐party testing, and help the reader understand what to look for in order to specify a SSL product for their commercial lighting needs. In choosing a luminaire, there are no one-‐size-‐fits-‐all solutions. Every customer values different attributes and features in a product. Many of these differences align with the various applications within the commercial space such as retail, office, healthcare and education. Within these applications, however, clients are far from homogenous. Take an office work environment, for example, they may value: 1. Performance—the ability to meet minimum illumination standards for efficiency, workplace productivity, safety, insurance requirements. 2. Maintenance—a facility manager will often need or require close to 100% uptime, and will need to manage ways to ensure full operation of all fixtures in the workspace. i 3. Quality—several studies have shown both increased worker productivity and worker satisfaction and retention tied to the quality of the lighting environment. Having general lighting with good color quality is imperative. 4. Controllability—Those same studies have demonstrated that people are more productive and more comfortable in environments where they can control and set their own lighting preferences. In summary, each of these key attributes of LED lighting-‐-‐ performance, value (both economic and environmental) and quality -‐-‐ will help the reader best evaluate different offerings for their needs. How to Choose an LED Luminaire 2 Performance Performance is one of the top priorities for SSL manufacturers’ R&D budgets. Initially, this emphasis was to prove that LED technology could stack up against traditional technologies. More recently, it has become a competitive measure within the SSL marketplace. The following attributes should be considered when evaluating the performance of SSL luminaires and traditional technologies: • Luminaire efficacy—not to be confused with system efficacy, this measures the actual fixture output fully encumbered, taking into consideration optical losses due to the fixture, thermal issues, electrical inefficiencies, and anything else that would reduce luminaire efficacy. One of the reasons this is such a telling metric is that it is blind to the application. Whereas the output of a garage light may be 4,000 lumens, and the output of an under cabinet light may be 300 lumens, they both might post very similar efficacy ratings of 50 lumens per watt. It is similar to a rating system to find the best boxer pound-‐for-‐pound. Knowing and comparing luminaire efficacy can tell you a great deal about inherent luminaire performance, outside of the application. • Lumens—another popular performance metric is output or luminous flux measured in lumens. The lumen is a very misleading, one-‐dimensional metric because it tells you little about how the fixture will interact with its environment. One general lighting fixture, for example, with 3200 lumens may require 8’ x 8’ spacing in an open office because of its light distribution and another fixture with 3200 lumens might be capable of 10’ x 10’ spacing. As important as gross lumens is how the light is distributed. The chart below shows some of the other ways that Thermal Effects in 2 lamp T8 2’ x 4’ Fluorescent Systems Adjustment Factor Output (Lumens) 1.0 5,800 Ballast Factor 0.85 4,930 Coefficient of Utilization 0.7 3,451 Losses for Temp of 45°C 0.91 3,140 Bare Lamp • output can be compromised due to environmental conditions.iiiii Method of Testing—different technologies are tested differently. Unfortunately, this can make comparing technologies difficult if not impossible. Whereas SSL fixtures measure luminaire efficacy, fluorescent performance is derived by a method called relative photometry. Relative photometry takes the bench top readings of the lamp sources out of the fixture at ideal temperatures and multiplies this by a constant fixture efficiency rating factor to approximate How to Choose an LED Luminaire 3 actual output. Due to variance in this fixed rating factor multiplier, the output for a fluorescent system is inflated by 10-‐30%iv. The polar plot below shows the extent to which the data is skewed. The red curve represents the published output of a fluorescent system and the green curve, the actual independent lab measured output based on absolute photometry. If you imagine the different curves representing different light distributions, it’s clear how real world output is going to result in dramatically less light in the space. Because of the imprecision of relative photometry, evaluating fluorescent vs. LED systems on output is an apples-‐to-‐oranges comparison. LED output is measured by LM79 testing, which measures actual light output. Specifiers should insist on LM79 testing for any fluorescent systems that they are interested in specifying in order to assure an apples-‐to-‐ apples comparison. • Trigger Metrics—LEDs have a performance tradeoff between output and quality. The majority of white LED products are phosphor-‐converted, and in order to improve color content, additional phosphor is added which adversely affects emission. Therefore, when evaluating any particular attribute, it is good to keep in mind a corresponding trigger metric. Think of this as the “yes, but what about this” reminder when a metric is considered. For example, when considering luminaire efficacy, the immediate trigger metric should be regarding color rendering index (CRI) or color quality standard (CQS). Simply put, it’s easier to get more efficiency from “cooler” (higher color corrected temperature (CCT)), and lower quality LEDs than warmer ones. Below, is a table of metrics characterizing performance and their corresponding trigger metrics of the current (2011) state of the art LEDs. In commercial applications there is currently parity among best-‐in-‐class SSL and fluorescent products. But with the ongoing rapid improvement in LED technology, it’s clear SSL will soon assume the lead. How to Choose an LED Luminaire 4 Application Metric Value Trigger Metric Trigger Value General Office/ Health Care Luminaire Efficacy 60 Lumens per Watt (LPW) CRI 80 or More Education Task/Under cabinet Output Spacing Power Density Luminaire Efficacy Output 3000 Lumens 80 SF/Fixture 0.6 W/SF 60 LPW 300 Lumens Wattage LPD Uniformity Illuminance Wattage 60 or Less 0.7 or Less 3:1 (Max: Min) 30 FC (Ave) 8 Watts or Lessv Lastly, a discussion of performance would not be complete without touching on performance tests and certification programs. Far and away, the easiest and most accurate way of evaluating a luminaire is to obtain the IES files based on LM79 testing by an independent lab, and to use this data in a mock layout. This way one can evaluate how the luminaire performs within the environment and can observe a three-‐dimensional assessment of its capabilities. In response to confusion and poor measurement methodologies, the Dept. of Energy has introduced Lighting Facts (www.lightingfacts.com), which showcases manufacturers who commit to testing products and reporting performance results according to industry standards. Value Perhaps the most popular trigger metric for the specifier community is price. SSL solutions were originally priced significantly higher than their fluorescent counterparts, yet the pricing direction of LEDs and LED fixtures has been on a sharp downward trajectory with the market impact that today, the total cost of ownership will almost always be lower for the SSL solution. Let’s look at some of the different considerations for accessing value and total cost of ownership in a SSL luminaire: • First cost— Comparing ‘fully burdened’ prices is critical to fairly evaluating first cost. When comparing fluorescent to SSL, remember that all components of an SSL fixture are integral to the fixture, thus it is a ‘fully burdened’ price. Fluorescent luminaires are often quoted without lamps and in many cases without power supplies. Specifying a fluorescent power supply with a high ballast factor—leading to higher system efficiency—will be significantly more expensive. Additionally, since almost every SSL luminaire is capable of dimming, a dimming fluorescent power supply should be included in the quote, a significant cost over standard ballasts. • Total cost of ownership— It is important to consider all the factors when accessing costs of a lighting system. The Life Cycle Cost Benefit Analysis (LCCBA) takes into account the entire lifetime costs for the fixture including installation, relamping, reballasting, and disposal. It also How to Choose an LED Luminaire 5 • • • considers the maintenance component, along with any energy savings and tax effects of depreciation. SSL fixtures almost always have favorable rates of return when compared to traditional fluorescent systems The Illuminating Engineering Society publishes a robust 2nd level analysis methodology in its Lighting Handbookvi. For any large or complex job, performing an LCCBA analysis is highly recommended. A good manufacturer will have these tools at their disposal to help aid the customer in their buying decision. Maintenance costs—Specifiers often vastly underestimate the degree that installation adds to the total cost of the fixture. Considering union labor rates, 10 additional minutes to install a fixture can be the difference between payback making sense or not. Therefore, the user friendliness of maintenance, while it might be considered part of the quality attribute, should also be front and center in pricing discussions. Re-‐lamping a fluorescent fixture has two potential points of failure: first, the lamp connections are brittle and can break, compromising the entire fixture performance and ability to light the task effectively. Secondly, there are compatibility issues often only identified by lamp manufacturers. Specifically, certain lamps need to go with certain ballasts and vice versa. Building engineers often use improper lamps, compromising performance and quality while adding additional costs. The ability of SSL luminaires to “plug and play” as complete systems—especially with a lighting control system -‐-‐ is extremely valuable and underestimated from a soft cost perspective. Specifiers should look for clear installation instructions, lamp compatibility issues and scrutinize the methodology for installing products for each manufacturer. Inherently better lighting controls – Several control techniques are available to improve lighting efficiencies, design and cater lights in a space, and prolong and extend light source lifetimes. Each of these techniques relies on a combination of dimmability, the ability to shut off a light quickly, control the ramp speed of how fast a light turns off or on, and finally, the ability to re-‐ start a light frequently without impacting lifetimes. As a digital light source that can be controlled with literally thousands of light levels (through pulse width modulated dimming), and can be switched on and off 1000s of times per second, forever, with no harm to the fixture, LEDs represent a best-‐in-‐class option of lighting controls. Environmental value— The ability of the luminaire to not be a burden on the environment is becoming an increasingly valuable asset. As SSL bypasses the traditional technologies in efficiency, there are obvious benefits to the technology for both energy savings and lower environmental impact. Not having harmful byproducts such as mercury is a significant advantage of SSL products vs. their fluorescent counterparts. Specifiers should look for RoHS (Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment) compliant products, which assures that no harmful chemicals are included or used in manufacturing of lighting products. How to Choose an LED Luminaire 6 Quality Questions arise around the ability of SSL products to produce the level of quality light versus traditional technologies. Let’s face it: there are a great many unknowns, and new products are appearing all the time. But following are ways that specifiers will be able to confidently select quality SSL products: • Uniformity—because LED luminaires consists of many LEDs working in concert, the issue of optical engineering—how to extract the most light from the fixture while creating a soft, pleasing light—is paramount in considering quality. Soft light in commercial applications is king for a reason: It allows the light to bend around objects and illuminate the space without creating hard, distracting, and multiple shadows. The imagesvii on the left show the light created by two LED luminaires. The top image shows what is common in many LED products. A lack of decent lensing/diffusing techniques has created a harder and inferior quality of light compared to the example below, which has a soft, singular shadow. When evaluating light fixtures, specifiers Assessing Color Quality • Metric Score R9 >50 CQS >80 should slowly wave their hand under the light and look for the presence of multiple, hard shadows. They should also look for a deep “scallop effect” on the walls from installed downlights. Wall shadows should be barely discernable without “hard” lines or steep cut-‐offs between light and dark areas, also indicating poor lensing and diffusing techniques. Color—the images above also serve to illustrate degrees of quality in lighting temperature, or color. The top image shows a color quality that is “cooler,” meaning it is shifted more toward the blue How to Choose an LED Luminaire 7 • end of the white light spectrum than the red. This, in itself, is not an issue as many people and entire cultures (such as Japan) prefer cooler white light solutions that are closer to daylight than incandescent. However, whether the specifier is dealing with warm or cool white light solutions, the most important element is the amount of red in the light. Everyone, regardless of skin tone, has blood vessels at the surface of their skin. Without a considerable red component in the light, skin tones look unnatural and lifeless. The light in the image at the top has considerably less red than the light in the bottom image. Although it is highly beneficial, not all specifiers can physically examine the light fixture and analyze the quality and color of the light. Generally speaking, the more saturated the colors, the easier it is to discriminate between them. Vibrancy is a key element of design. LEDs can deliver this variability as well as provide additional saturation of color, which will improve color quality, even though it may not necessarily change the CRI rating for that light source. viii. Historically, consumers have always had an issue with fluorescent lighting as it has too much green light, which makes people look ghoulish and too little red light, which makes skin tones seem synthetic. Depending on the LED that the fixture supplier is working with, these same issues can be manifest in the LED systems. When analyzing an LED light source, it is important to watch for a green hue in skin tones. An indicator of sufficient red light is to look for veins and blood vessels at the skin level. An LED with a good portion of red will show these veins along with other red elements in the skin. It is strongly encouraged that the specifier be able to view the light generated by all the LED products under consideration. The issue of naturalness is at stake when we rely on metrics alone, and nothing can compare to putting a hand under a light source to see how it renders skin tones. The Right Supplier—With LED fixtures becoming popular, selecting the right supplier is critical to ensuring product quality, dependability and support. LED products are not meant to be disposable; they are durable goods that need to be built to last. The following are criteria for vendor selection: o LEDs—the quality of the components is imperative to the color quality and durability of the system. Of course, it is important that these components are engineered correctly—such as providing a robust thermal path from the junction to the outside environment in order for the fixture to meet expected lifetime estimates. o Power Supply—the weakest link in almost every LED fixture is the power supply. Most specifiers know very little about this esoteric component, making it difficult to evaluate. When running multiple strings of dynamic device LEDs, it is important to regulate current across the strings. Does the supplier use metal–oxide–semiconductor field-‐effect transistors MOSFETs, some other type of passive device, or none at all? What type of capacitor is used? Is the fixture going to be in a warm environment like a recessed ceiling can? Evaporation of electrolytic can be an issue. Specifiers need to ask as many questions about the power supply as they do for the fixture. How to Choose an LED Luminaire 8 o Documentation—one of the easiest ways to determine higher quality LED fixtures is in the level of documentation that a supplier provides. Independent lab testing—specifically LM79 testing -‐-‐ is imperative for EVERY LED manufacturer. There are only a handful of labs that are accredited for actual LM79 testing and specifiers should make sure that the lab is accredited by the Department of Energy. http://www1.eere.energy.gov/buildings/ssl/test_labs.html o DesignLights Consortium—DLC is a collaboration of utilities and energy efficiency concerns. The requirements for DLC accreditation are much stricter than current Energy Star requirements and more specific to SSL products. Most of the few rebates available today flow out of the DLC specification. o Warranty—The current industry norm is a 3 year warranty—anything less should raise a red flag. While there is no pressure on other technologies to increase their warranty term, LED fixture manufacturers are being asked to show a warranty that is more in line with their 50,000 hour lifetime metric. The trend is toward 5 years, and it is expected to increase with more testing data available. Summary Fixture Selection Checklist Selection Criteria Value Lumen Efficiency 1. Seek fixtures with published LM-‐79 test data 2. Target fixtures for general purpose lighting with at least 60 lumens/watt, and 80 CRI performance or better Total Cost 1. Seek fixtures with published LM-‐80 lifetime performance data 2. Consider combining LED fixtures with advanced lighting systems to gain full dimming and controllability benefits of LED technologies Quality 1. Target fixtures with either Design Lighting Consortium (DLC) or EnergyStar certification for third party validation of quality In conclusion, there are a great many things to consider and evaluate when specifying an LED solution. Not only does each customer have a unique set of requirements and desires that drive their purchasing decision, the SSL attributes that are meeting these requirements can be moving targets. Thankfully, How to Choose an LED Luminaire 9 they are moving in the right direction, and the benefit of owning SSL becomes more compelling every day. With this growing opportunity, there is increased competition for market share making evaluation and selection of quality suppliers more difficult. Hopefully the metrics described in this paper increase your understanding of what is important when specifying LED suppliers. i A recent study by Gensler reported that workers would work an extra hour per day in a more comfortable workspace. (See: http://www.bnet.com/article/office-‐design-‐how-‐to-‐build-‐a-‐better-‐office/190221 for more details.) ii NLPIP Lighting Answers Thermal Effects in 2’ x 4’ Fluorescent Lighting Systems iii Coefficient of Utlization describes the efficiency that a luminaire might extract light. In this example, a lensed troffer, the fixture efficiency is stated as 70%, which is consistent with Department of Energy testing iv Peifer D Apps and Answers LD+A v For a more complete data and reports on up-‐to-‐date tested performance of LED lighting applications, see the Dept of Energy’s CALiPER program here: www.ssl.energy.gov/reports.html. vi th IESNA Lighting Handbook, 10 edition vii Peifer D Apps and Answers LD+A, April 2011 viii For additional information on CQS, please see Color Rendering of Light Sources, on the NIST website. http://www.nist.gov/pml/div685/grp05/vision_color.cfm How to Choose an LED Luminaire 10