Specifying LED luminaires
- Understand when and where LEDs should be specified in lieu of other lighting options.
- Learn about the standards that govern LEDs.
- Understand what technical requirements should be identified when specifying LEDs and why those technical requirements are important.
LEDs have taken our industry by storm, changing the way we light spaces and use luminaires. Sorting through the hype to find the facts can often be a challenge. Manufacturers and vendors tout their product as being the best in the industry, throw out buzz words like “L70” and “TM-21,” and claim to have products that last 50,000 to 100,000 hours. Beneath the flash and glitz of a lighting product showcase and the rousing testimonies of salespersons are technical and economic factors that can be used to make logical decisions when specifying LED luminaires.
Key aspects of specification
To date there are few standards that dictate the specific lumen output, energy use (efficacy), distribution, and color rendering of LEDs. Each luminaire manufacturer uses its own special blend of LED modules. The Zhaga Consortium has attempted to create a series of standards that LED luminaire manufacturers can use to have interchangeable LED modules, but only a small percentage of LED luminaires are following these standards. When selecting LED luminaires for a project there are a series of steps that can be followed to help weed out the bad products from the good, along with several factors to consider when specifying LED luminaires.
Step 1: Baseline standards
As with the majority of products in the lighting industry, UL has developed a number of standards related to LEDs. The standards cover a variety of different applications, from retrofit conversion kits (UL 1598C), to field-replaceable LED light engines (UL 8753), to LED equipment for lighting products (UL 8750), to mention a few. When specifying any lighting product, it is important to ensure that it has been tested to UL standards or equivalent if allowed by the authority having jurisdiction (AHJ).
The lighting industry through the Illuminating Engineering Society (IES) has developed a few standards related to testing an LED luminaire. Two key standards by the IES are LM-79 and LM-80. LM-79 establishes guidelines for testing LED luminaires for light output, energy use, and color spectrum. LM-80 establishes minimum testing guidelines for LED light sources (i.e., LED chips, modules, or packages used as part of the luminaire), requiring a minimum 6000-hour test where information regarding depreciation of lumen output, energy use, color shift, and failure rates is recorded. When looking at product information for an LED luminaire, one should verify if the product has been tested to LM-79 and LM-80. Many (but not all) manufacturers list this information on the product data sheets. Products that do not follow these two standards should be disregarded. Time and resources permitting, copies of the LM-79 and LM-80 test reports should be acquired from the luminaire manufacturer for review. In specifications for LED luminaires, consider including a statement that the luminaire must be tested to LM-79 and LM-80 standards and that the results of those tests must be submitted to the specifier as part of the submittal review process.
Step 2: Technical requirements
After establishing that the luminaire follows LM-79 and LM-80, the specific technical metrics of the luminaire should be evaluated. Several metrics that should be evaluated are:
Delivered lumen output (initial and end-of-life): Initial delivered lumen output is the value that manufacturers typically list on their cutsheets. The determination of the delivered lumens at end of life will need to be calculated based on assigning a reasonable light loss factor (0.7 or less per IES).
Luminous efficacy (delivered lumens/W): The performance of LEDs is constantly improving. Today, good LED luminaires on the market have efficacies between 70 and 90 lumens/W, with some of the best LED luminaires on the market reaching efficacies between 90 and 110 lumens/W. These values are expected to continue to improve over time.
Color temperature: Color temperatures are relatively consistent between manufacturers and are typically available in the same ranges as fluorescent sources. However, specific color temperatures may be limited from manufacturer to manufacturer. For LEDs, higher color temperatures result in higher lumen output but often result in lower color rendering index (CRI).
Color rendering index: CRI relates to how the colors of an object appear to the eye relative to a baseline comparison. While some reports have shown inconsistency with using CRI as a rating for LED products, it remains a common value used to describe the color rendering of LED products.
Estimated luminaire life: The point in time at which the LED luminaire produces 70% of initial lumen output is referred to as L70. In general, the lighting industry has established a typical industry standard for LED luminaire life of producing L70 at 50,000 hours. Some manufacturers offer longer life at L70, while others offer ratings such as L80, the point in time at which the LED luminaire produces 80% of initial lumen output. The specification for an LED luminaire should identify the minimum length of time (e.g., 50,000 hours) until the luminaire reaches the target percentage lumen maintenance (e.g., L70 or 70%).
Product warranty: To provide a level of certainty that the LED luminaire will perform as indicated without failure, it is recommended that any LED luminaire include a warranty on the entire luminaire, including the driver. The driver can sometimes fail sooner than the LEDs themselves, and therefore require replacement. Requiring a minimum 3- to 5-year warranty helps to protect the client from problems with poor drivers and installation.
In general, the majority of manufacturers provide a 5-year warranty on LED products. Most other manufacturers offer a 3-year warranty as standard for their product and may increase the warranty to 5 years upon request for an additional fee. A few manufacturers are now offering 7- or 10-year warranties on their LED products. Due to the prevalence of 3- and 5-year warranties, products with warranties that are fewer than 3 years should be suspect. It is important to verify that the warranty covers the entire luminaire, including the driver, and not just the LED components. Some warranties include only workmanship and materials, while others include performance. It is important to understand what the warranties cover from different products in order to have a true comparison.
Unlike fluorescent lamps that have generally been standardized, LED luminaires can vary greatly between manufacturers. Therefore, it becomes necessary to define the performance parameters when specifying LED luminaires. Specifying these parameters as part of the description of the luminaire provides a common denominator to be used between different LED products and manufacturers, allowing for competitive bidding between manufacturers while still adhering to design criteria. For example, a description for the technical performance of an LED luminaire may include a statement similar to the following:
“The LED Luminaire shall have at least 4000 initial delivered lumens, a luminous efficacy of at least 90 lumens/W, a color temperature of 3500 K, a CRI of at least 80, an estimated life of at least 50,000 hours at 70% lumen maintenance, and shall include a minimum 5-year warranty on the entire luminaire including the driver. The luminaire and LEDs shall have been tested in accordance with LM-79 and LM-80.”
Step 3: Quality recommendations
In addition to reviewing technical requirements from a performance perspective, it is also important to look at the technical requirements of the luminaire from a physical quality and maintenance perspective. These elements are more subjective, and the specifier should decide which of these elements are required and which are optional for the specific project. While this is not intended to be an exhaustive list, here are several items to consider in terms of the physical quality of the luminaires:
Modular components: Many manufacturers are designing their LED luminaires with replaceable LED modules. This typically allows an individual to unplug a plug-and-play type connector within the luminaire and then remove the LED module or chip boards by removing a few screws. Then, a new module can be installed in its place. This sort of modularity is important for future proofing the LED products. Other manufacturers are designing their luminaires around established prebuilt LED modules. For example, the Zhaga Consortium has established a series of standards regarding replaceable LED components with the intent that in the future LED components would be swappable between LED luminaires of different manufacturers. When specifying an LED luminaire, it would be advisable to establish if the product has such modular components. Additionally, if a standard prebuilt LED module is available from multiple luminaire manufacturers, one could specify that that specific LED module must be used. This would provide a consistent platform of performance between multiple manufacturers. When a luminaire without modular components no longer performs adequately, the entire luminaire must be replaced.
Passive versus active heat dissipation: Heat is the enemy of LEDs. Some manufacturers rely on passive heat dissipation (i.e., heat sink, natural ventilation, etc.) while others rely on active heat dissipation (i.e., fans). It is important to identify which sort of heat dissipation a luminaire uses. Active heat sinks allow the luminaire to run cooler, allowing it to produce more lumens. However, adding a fan to the luminaire results in an additional component that could fail. The specific performance of the luminaire must be weighed against the heat dissipation method used, as well as the maintainability of the luminaire.
Luminaire construction and appearance: A picture is no substitution for viewing a luminaire in person to assess its construction and appearance. Viewing a physical sample can reveal if the LED chips are clearly visible to the user, can identify potential glare issues, and can showcase the quality of light emitted from the luminaire. Side-by-side tabletop comparison is the best way to evaluate the color rendering of the luminaire.
MacAdam ellipses: A “MacAdam ellipse” (standard deviation color matching) is a testing method that defines how close the color difference is between two sources. The lower the number, the closer the difference; a 1-step MacAdam ellipse is tight enough that the colors should essentially be indistinguishable to the eye. ANSI C78.377 defines the range allowed for a standard color temperature of LED (e.g., 2700 K is defined as 2725 K ± 145 K); this equates to approximately a 7-step MacAdam ellipse for a given standard color temperature. The visual difference between two sources next to each other at the same color temperature but on different ends of the allowed range is quite apparent. As the MacAdam ellipse approaches a 4-step to 2-step difference, it becomes much harder to discern differences in the color temperature. Some LED manufacturers have information related to how tight their binning process is, or how few MacAdam ellipse steps they have within their binning process. Comparing the step differences between different manufacturers’ products can help one determine how narrow the color difference is between products.
Step 4: Optional testing reports
Several other standards exist related to performance testing and reporting for LED luminaires. Specifiers may wish to consider using these standards in their analysis of appropriate LED luminaires. The following are two testing and reporting methods for consideration:
IES TM-21: TM-21 establishes guidelines that limit the hours of life that a manufacturer can claim to be no more than six times the number of hours that the fixture was tested for under LM-80 for a test sample size of 20 units or more. While not all manufacturers follow TM-21, those that do are providing an additional level of assurance related to the estimated life of their product.
CALiPER: The Commercially Available LED Product Evaluation and Reporting program (CALiPER) run by the U.S. Dept. of Energy is a testing process for LED luminaires. These tests evaluate the LED luminaire to see if it performs as the manufacturer claims. This is similar in some ways to reports from TM-21 and LM-79; because CALiPER tests are performed by a third party and not the manufacturer, they give an unbiased view of the LED luminaire’s performance.
Lumen maintenance: How long will it last?
When comparing one LED luminaire to another, whether LED or a conventional lamp, it is important to compare the delivered lumens values at the end of life of the two products. This is done by evaluating the components to derive the light loss factor. For example, when comparing a linear fluorescent product to an LED, it is necessary to account for the fluorescent luminaire efficiency as well as ballast factor losses and lamp depreciation losses.
The lumen maintenance of an LED luminaire is often overlooked when comparing an LED luminaire to a conventional source, such as a fluorescent lamp. Most LED manufacturers adhere to a minimum L70 standard. The LED product will continue to produce light beyond this point, though that light will continue to depreciate. As lighting designers and specifiers, we typically design the lighting in a space such that it maintains the proper light level for the task at the end of source life, to ensure adequate light levels throughout the life of the design. Therefore, for an LED luminaire that produces 70% of it is initial light output at the end of its rated life, a designer must design the space so that it is properly illuminated at 70% of the initial light output. In comparison, a 28 W T5 lamp produces 90% to 95% of its initial light output at the end of its rated life.
The benefits of the extended life must be weighed against the initial cost of the LED luminaire and compared to the initial cost plus the lamp replacement costs of conventional luminaires. Additionally, for task areas that require a specific and critical amount of lighting (such as in a hospital), it may be necessary to require a higher level of LED lumen maintenance (L80 or above) or to consider scheduled testing of the LED luminaire light output and performing LED module replacement to maintain lighting levels. Alternately, an automatic control system that regulates the light output of the LED luminaires and reports when the lighting level approaches the minimum required values could be used to ensure that the minimum required lighting levels are being maintained. If none of these options is viable, it may be necessary to use conventional sources that can be maintained to produce the required level of lighting.
Lifecycle comparison to other light sources
When evaluating the cost impact over the life of the LED luminaire, initial cost is weighed against the maintenance, lamp replacement, controllability, and energy savings to make a final determination. The initial cost for LED luminaires has typically been a major hurdle in the use of LED technology. Prices for LED luminaires can vary from as much as a conventional luminaire to more than twice as much as a conventional source. In some cases, the long life of LED luminaires far exceeds conventional lamps to such an extent that the savings in maintenance and relamping over the life of the luminaire outweighs the initial cost of the LED fixture.
One feature that assists in bringing the initial cost of an LED luminaire closer to a conventional source is the inherent availability of dimming. Most LED luminaires include a dimming driver either standard or as a minor cost addition. Therefore, when comparing the cost for an LED luminaire with dimming to a conventional luminaire with dimming, the price difference between the two becomes much smaller. In some cases, an LED luminaire with dimming has shown to have a lower initial cost than a conventional fixture with dimming. As a result, LED luminaires are ideal for daylight harvesting applications, where diming control is needed. Dimming LEDs also assists in complying with energy code requirements to provide multiple levels of lighting in some areas (e.g., ASHRAE Standard 90.1-2010, California Title 24 – 2013). While no long-term studies have been performed, some manufacturers claim that dimming LEDs will increase the rated life, as dimming will reduce the amount of heat generated in the LED. Additionally, dimming allows the user to correct for the lumen depreciation of the LED to maintain a minimum lumen output over the product life.
The number of lamp changes needed for conventional sources to match LEDs can vary greatly. For conventional sources with few relampings, it may not be worthwhile from a maintenance perspective to use LEDs. However, luminaires in inaccessible spaces having a higher maintenance cost may be good candidates for LED luminaires that have a long rated life. An understanding of the maintenance costs, including relamping and cleaning, is necessary to fully evaluate the savings from eliminating the need to periodically relamp luminaires.
Energy savings is often touted as a primary reason to use LED technology. This energy savings can vary, as the need to over-light a space initially to compensate for the depreciation of the LED minimizes the energy savings when compared to a conventional source. In other cases, savings up to or greater than 45% can be achieved from using LEDs. It is important to not make assumptions and to perform calculations to validate potential energy savings. Selecting luminaires with high lumens/W ratios, long life, and high lumen maintenance improves the likelihood of gaining energy savings from using LED luminaires. As energy codes become more stringent, more people are looking to LED luminaires to help produce energy savings. As LEDs continue to evolve and their anticipated longevity moves from an extrapolated value to a proven value, it is anticipated that more energy savings will be achieved with the use of LED luminaires.
The past decade has seen LED luminaires move from niche decorative products with low lumen output to a wide variety of functional and energy efficient luminaires covering every market. From parking lots and landscapes to offices and factories, there are now LED products for virtually every application on the market. Where projects once would only specify LEDs in limited applications, now LEDs can be used to specify entire projects. Even so, it is the responsibility of the specifier to examine the pros and cons of using LEDs for a specific project, evaluating the products from an economic, technical, and performance perspective. Understanding key characteristics of specifying LED luminaires allows specifiers to look beyond the buzz around LEDs and see the true potential available in the products at hand.
Brian Fiander is an electrical engineer at Harley Ellis Devereaux specializing in lighting design and specification. He serves as one of the firm’s sustainable design champions, acting as a resource for other staff members regarding green design, LEED certification, lighting, and electrical systems. He has participated as a panel speaker for the IES Detroit chapter on LED installation and application due to his understanding and specification of LED luminaires.