LED specifications

Building owners are requesting LEDs because of their energy efficiency and long lifespan. Review the basics of LEDs, explain the key aspects of specifying LEDs, and examine lifecycle cost considerations for LEDs.

By Michael Chow, PE, CxA, LEED AP BD+C, Metro CD Engineering, Columbus, Ohio August 18, 2015

Learning objectives

  • Explain the basics of specifying LED lighting.
  • Know the codes, standards, and guidelines that drive lighting specifications.
  • Show designers how to find out the lifespan of LED light sources.

Building owners are requesting LED light sources because of their energy efficiency and long lifecycle. Engineers need to be aware of key aspects when specifying LED light sources. Many specifications discussed in this article are not widely known by specifying engineers and lighting designers.

It was not that long ago when many LED luminaires had claims of 100,000 hr or more. There was also confusion about whether the claimed life was for the LED lamps themselves, the driver, or the entire LED system/luminaire. It is important that engineers understand how to properly specify LED light sources when it comes to critical factors such as rated lifespan.

The efficacy of light sources is measured by lumens/Watt. The higher the efficacy, the better. In 2004, LED light sources had an efficacy of approximately 35 lumens/Watt. Today, many LED products such as troffers have efficacies of more than 100 lumens/Watt. LED light sources are near the top of the efficacy range for commercially available lamp technology (compared to HID and linear fluorescent lamps). The U.S. Dept. of Energy (DOE) estimates that LED packages will have an efficacy of 224 lumens/watt by 2025.

An additional benefit of LEDs is that they do not contain hazardous materials. Fluorescent lamps contain mercury and should be either recycled or disposed at a qualified facility. Because LEDs are solid-state devices, they do not contain mercury, glass, filaments, or gases. These are all reasons why building owners are requesting LEDs.

Specifying LED light sources

Most engineers include specifications within the contract documents for a project. Where included in the scope of the project, these specifications should include LED light sources.

Specifications for LED light sources should take into account certain key parameters and components including:

Adherence to the codes

  • UL listing or label
  • Minimum lumen output
  • Light loss factor (LLF)
  • Illuminating Engineering Society (IES) Light Measurement LM-79: Electrical and Photometric Measurements of Solid-State Lighting Products
  • IES LM-80: Measuring Lumen Maintenance of LED Light Sources
  • IES Technical Memorandum TM-21: Projecting Long Term Lumen Maintenance of LED Light Sources
  •  Minimum lifespan (LED components and driver)
  • Minimum color rendering index (CRI)
  • Color temperature
  • LEDs from the same batch
  • Inrush current
  • Surge protection
  • Radio frequency interference (RFI), total harmonic distortion (THD), power factor
  • Compatibility with dimming controls if applicable
  • Commissioning/functional testing
  • Manufacturer background and longevity
  • Warranty and availability of replacement parts.

Many NFPA 70: National Electrical Code (NEC) requirements refer to "listed" or "labeled" devices and appliances. Specifications for LED light sources should state that they shall have a label from a Nationally Recognized Testing Laboratory (NRTL) that is acceptable to the authority having jurisdiction (AHJ). A UL label is a common requirement found in specifications.

The DOE has a useful publication listing LED standards, codes, and guidelines: SSL Standards and Guidelines.

LED light sources’ lumen output should be included in the specifications because lighting designs and photometric layouts are based upon lumen output. Most other light sources besides LEDs “burn out” and have their “end of life” listed as the time where 50% of the lamps have failed. The lumens from LED light sources decrease over time. The point where the lumen output is at 70% of its initial output is known as L70.

Lighting design and photometric calculations should account for LLF. LLF is based upon luminaire dirt depreciation (LDD) and lamp lumen depreciation (LLD) as well as several other equipment factors such as ambient temperature, driver factors, and other similar items. The L70 value should be used when calculating LLD.

LDD is a number from 0.0 to 1.0 that is based upon the type of environment the LED light source will reside. This is important for LED light sources located outdoors or in harsh environments.

The IES Light Measurement LM-79: Electrical and Photometric Measurements of Solid-State Lighting Products is a publication with a standardized method for photometric and electrical measurements of LED products. As written, the standard measures the total light output (lumens) of general illumination fixtures and also efficacy. LM-79 also requires verification of CRI.The DOE has more information on calculating LLF for LED light sources.

Engineers should specify that IES LM-79 testing for an LED light source be performed by one of the DOE’s LED Lighting Facts-approved labs.

A specification that incorporates IES LM-79 can be found from the United Facilities Guide Specifications (UFGS): Submit test report on manufacturer’s standard production model luminaire. Submittal shall include all photometric and electrical measurements, as well as all other pertinent data outlined under "14.0 Test Report" in IES LM-79.

The UFGS also has a specification that covers test laboratories: Test laboratories for the IES LM-79 and IES LM-80 test reports shall be one of the following:

IES LM-79 does not take into account lumen maintenance. This is addressed by IES LM-80: Measuring Lumen Maintenance of LED Light Sources.

For LED light sources, LM-80 defines lumen-maintenance life as “the elapsed operating time at which the specified percentage of the lumen depreciation or lumen maintenance is reached, expressed in hours.” Different from rated life, the rated lumen-maintenance life is further defined as “the elapsed operating time over which an LED light source will maintain the percentage (p) of its initial light output.” Rated lumen maintenance for LED light sources is typically L70.

The IES LM-80 publication is an approved method for measuring lumen depreciation of LED light sources. IES LM-80 requires a minimum of 6,000 hr of testing with 10,000 hr preferred. The test report for an LED light source for IES LM-80 shows the initial light output and the lumen output as the hours progress towards the 6,000 minimum hour mark and 10,000 preferred hour mark.

The UFGS has a specification for IES LM-80: Submit report on manufacturer’s standard production LED package, array, or module. Submittal shall include:

  • Testing agency, report number, date, type of equipment, and LED light source being tested
  • All data required by IES LM-80.

IES LM-80 does not cover estimating the life of LEDs. IES Technical Memorandum TM-21: Projecting Long Term Lumen Maintenance of LED Light Sources covers this.

The TM-21 publication is an approved method for estimating an LED light source’s lowered lumens as the LED is used over time. This would allow a manufacturer to estimate the amount of L70 hours for an LED light source.

Specifications for LED light sources should state that LEDs shall be tested per IES LM-79, LM-80, and TM-21 parameters. Specifications should require the test reports be submitted to the engineer for review and approval if the engineer is concerned about nonspecified products being submitted with a bid.

Specifications should include the minimum rated lifespan for an LED-light-source system. As stated earlier, rated life is different than rated lumen maintenance. IES LM-79 requires complete luminaire testing. This means the LED lamps cannot be separated from the driver, which could skew the data.

Figure 2 shows a theoretical example of the rated life of an LED system. This LED system is a function of both the LEDs and the driver. The rated life of the combined system is approximately 52,000 hr, which is less than each individual component.

The minimum CRI the engineer requires should be stated in the specifications. IES LM-79 requires that an LED light source’s CRI be verified.

The current CRI is a measure of eight (R1 to R8) color reference samples, which are more pastel-colored. Some LED light sources have difficulty with saturated colors such as strong reds. Color references R9-R12 (saturated solids) are not measured in CRI, but the value of R9 is important when specifying LED light sources. Engineers should consider specifying R9 reference samples in addition to CRI.

CRI and R9 values are dependent upon the type of environment the LED light 

source will be placed. Higher CRI (85+) and R9 (80+) values are generally required for retail environments. Strong red tones with the R9 value are prevalent in skin tones, clothes, meats, and store produce.

Color temperature is important when specifying LED light sources. Engineers need to consult with the stakeholders (building owners, user groups, architects, etc.) when specifying color temperatures for building interior and exterior lighting. “Warm” color temperatures are at the lower end of the color temperature range (2,700 to 3,500 Kelvin). “Cool” color temperatures are typically greater than 3,600 Kelvin.

Currently, the cooler an LED light source, the greater the efficacy. A recent DOE report states that cool white LEDs are approximately 20% more efficacious than warm white LEDs. However, the report states that eventually the difference in efficacy between cool and warm LEDs will be negligible.

All light sources in a room/area should normally have the same color temperature. Mixing of color temperatures is not regarded as good design and can produce undesirable results.

Differences in color temperatures also can occur when placing LED light sources not made in the same batch. Engineers should consider stating in their specifications that LEDs of the same fixture type be supplied from the same batch during manufacturing to help alleviate a potential color temperature issue.

Engineers need to be aware of LED light source inrush currents when specifying and integrating LEDs. Some LED light sources have inrush currents many times the normal steady-state operating current.

These high-inrush currents may trip a circuit breaker depending upon the circuit breaker type. One manufacturer’s LED product specifications state “… to address inrush current, slow blow fuse or type C/D breaker should be used.”

High-inrush currents may also result from dimming LED light sources; there have been known instances of inrush currents 40 times the normal steady-state operating current. Engineers should specify inrush-limiting devices and “pair” the LED/driver and the dimmer to avoid high-inrush currents.

LED light sources, especially in outdoor applications, should have surge protection. LED luminaires have sensitive electronic components that need to be protected against electromagnetic interference (EMI) including high-energy electrical discharges (surges, nearby lightning strike, etc.).

Specifications for LED systems should state that surge-protection devices (SPDs) be provided for each luminaire. SPDs should be UL1449-recognized for all phases (line/neutral, line/ground, and neutral/ground). In addition, IEEE C62.41.2: Recommended Practice on Characterization of Surges in Low-Voltage (1,000 V and Less) AC Power Circuits should be referenced.

The UFGS has a specification for SPDs: LED luminaire surge protection: Provide surge protection integral to luminaire to meet C low waveforms as defined by IEEE C62.41.2, Scenario 1, Location Category C.

Location Category C includes the more severe high-exposure level found in outdoor applications.

It is important that LED light sources limit interference with FM radio and digital-audio-broadcasting systems. Specifications should address this as well as THD and power factor.

A sample specification addresses this: LED drivers shall be electronic, labeled as compliant with radio frequency interference (RFI) requirements of FCC Title 47 Part 15, comply with NEMA SSL 1, have a sound rating of “A,” and be rated for a THD of less than 20% at all input voltages with a minimum power factor of 0.90.

Controls and commissioning

Engineers should specify dimming controls that are compatible with the specified LED light sources and their drivers. Some dimmers require a minimum wattage (e.g., 25 W to 40 W) to operate. Engineers also need to consider the maximum number of LED light sources (total wattage) per control. And it is required starting with the 2011 edition of NEC to include a neutral conductor to be installed with all dimming controls.

Specifications for dimmable LED drivers should include a requirement that the drivers be capable of dimming without LED strobing or flicker across their full dimming range.

Commissioning of lighting systems including LED light sources should be included in the specifications. Commissioning lighting systems helps reduce energy consumption and operating costs. Other benefits include client/user satisfaction and acceptance of lighting-control systems. Requiring commissioning of any system will add cost to the project and typically stretches far beyond just the lighting systems.

The commissioning authority ideally reports directly to the building/facility owner and should be contracted with the owner directly. The commissioning authority should also be contracted at the predesign stage.

Including commissioning of lighting should cover not just the lighting fixtures, but also should add the lighting controls to be tested, and roles and responsibilities of the commissioning authority and the contractor(s). These items help reduce or even eliminate conflicts and issues during commissioning tasks such as functional testing. For example, a commissioning specification may state, “The contractor shall notify the commissioning agent in writing at least 14 days in advance of all prefunctional testing.”

Energy codes and LEED certification have made commissioning of lighting controls a requirement. ASHRAE Standard 90.1-2010 requires functional testing of lighting controls and systems.

U.S. Green Building Council LEED v4 (the latest version) uses ASHRAE 90.1-2010 as the baseline energy code. Not only does Standard 90.1-2010 require functional testing of lighting controls and systems, but LEED Version 4 certification also requires that lighting systems be commissioned. Functional testing is a core component of commissioning.

Excellent resources for commissioning include the IES DG-29-11: The Commissioning Process Applied to Lighting and Control Systems and the ACG (AABC Commissioning Group) Commissioning Guideline.

Design specifications

Many public projects require that alternate manufacturers other than those listed in the specifications and drawings be considered.

For example, a recent public state project required that the contracted engineering firm review LED light sources that were not listed in the lighting fixture schedule (also known as the luminaire fixture schedule). The state mandated that all lighting fixtures or luminaires that met or exceeded the written specifications be considered and be reviewed for approval by the specifying engineer.

A contractor on this state project submitted his bid with LED light sources from a company that was only 1 yr old and was based overseas. The specifications were not very specific on key issues such as warranties, independent lab-testing and verification of component lifespan, lumen output, and other related key items.

The contractor’s LED product did not meet many of the parameters that should have been in the specifications, such as independent lab-testing of light output. The engineer and project manager with the state decided to rebid the project with more detailed specifications. These revised specifications included the missing parameters, and the contractor was not able to submit the LED products that were submitted with the original bid due to these new specifications.

There are numerous manufacturers of LED light sources. How does one know the good from the bad? Engineers may try to limit the LED light sources to brand-name manufacturers. However, as we have seen from a previously discussed example, sometimes engineers may be required to consider other manufacturers’ products.

Engineers can state in the quality assurance section of their lighting specifications that the LED system manufacturer shall have a minimum number of years’ experience in the manufacture of LED systems. Engineers may want to consider using an LED product from a newer manufacturer if the manufacturer is able to provide evidence of financial stability.

Specifications for LED light sources should require warranties that are at least 5 yr long. The warranty should cover the complete mechanical assembly, the electrical and LED components and the driver. It is also important to specify that replacement parts be available for at least 10 yr.

Lifecycle considerations

Several factors need to be considered when performing a lifecycle cost analysis for LED light sources.

Engineers should give thought to the lifetime, reliability, warranty, serviceability, sustainability, and cost for their lighting project. For example, a building lighting-renovation project is expected to last for 10 to 15 yr. Does it make sense to go with products that last at least 20 yr at a higher initial cost for this example? Instead, it may be better to use a less expensive product with a shorter useful life, but higher reliability. Sustainability should also be taken into account when choosing products based upon a longer useful life.

LED systems that have easy serviceability usually have a modular design that allows components to be replaced or upgraded easily. A technician’s time and rate for replacing parts should be accounted for in the lifecycle cost analysis.

Building owners are requesting LED light sources because of their energy efficiency and long lifespan. Engineers that are able to include effective specifications for their LED light sources will help these owners achieve their goals.

Michael Chow is the founder and owner of Metro CD Engineering. He holds a BSEE from Ohio Northern University and is a member of the Consulting-Specifying Engineer editorial advisory board and is a 2009 40 Under 40 winner. Chow has won six IES Illumination Awards of Merit including four awards in 2015.

The December 2014 Consulting-Specifying Engineer article “Commissioning Lighting Systems” provides more detail on commissioning.

Watch the webcast Lighting: LED codes and standards for more information.