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.
- 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:
- National Voluntary Laboratory Accreditation Program (NVLAP) accredited for solid-state lighting testing as part of the Energy Efficient Lighting Products Laboratory Accreditation Program
- One of the qualified labs listed on the LED Lighting Facts (A Program of the DOE) website.
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.
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