Specifying LED luminaires

LEDs are in demand because of their energy efficiency and long lifecycle. This article reviews the key aspects of specifying LEDs, provides a lifecycle comparison to other types of lighting, and discusses the codes that dictate their specification.

08/27/2014


Learning objectives

  • 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.

This article has been peer-reviewed.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.

Figure 1: This flow chart illustrates the categories to consider when specifying LED luminaires. Courtesy: Harley Ellis DevereauxStep 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.

Figure 2: There are several key aspects of specifying LED luminaires. Courtesy: Harley Ellis DevereauxStep 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:

  1. 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).

  1. 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.

  1. 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).

  1. 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.

  1. 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%).

  1. 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. 

Figure 3: This chart illustrates that the lumen output of the fluorescent luminaire stays within a given range over its life. Selecting an LED Luminaire with an initial lumen output greater than the fluorescent equivalent is necessary in order to maintain lighting levels in the space with the LED luminaire over the life of the LED product. Courtesy: Harley Ellis DevereauxIn 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.”


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