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DLC’s Testing & Reporting Requirements for LED-based Horticultural Lighting

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A new specification issued by the DesignLight Consortium (DLC) provides detailed criteria for assessing various performance aspects of LED lighting

In this article, we’ll provide details on the DLC specification, “Testing and Reporting Requirements for LED-based
Horticultural Lighting,” and discuss how this document can help lighting manufacturers provide accurate and
objective information on the unique performance characteristics of their products.


Innovations in agricultural production, including indoor farming and other forms of controlled environment agriculture, will be an essential component in the effort to meet the projected global demand for nutritious food in the second half of the 21st century. However, just as in outdoor agricultural settings, successful indoor plant growth depends on a number of environmental variables, such as ambient temperature, water quality and lighting conditions. Further, individual plant types generally require a unique combination of each of these variables to help ensure optimal growth.

LED lighting fixtures offer significant advantages over high-pressure sodium (HPS) lamps and other lighting technologies previously used in indoor farming facilities. First, they represent a far more energy-efficient source of light, using only a fraction of the power previously required. This helps make LED lighting a more environmentally friendly alternative to conventional lighting.

More importantly, various aspects of the light emitted by LEDs are, in theory, infinitely adjustable. Characteristics such as photosynthetic photon flux (PPF), photosynthetic photon intensity distribution (PPID) and spectral quantum distribution (SQD) are lighting performance variables that can be integrated into the design of the LED fixture to deliver the specialized lighting “recipe” that is unique to each plant. In this way, LED lighting fixtures can support the creation of an optimal indoor environment for a given plant type and help to maximize growth and production yields.

Current standards for LED horticultural lighting

Until now, available standards applicable to LED-based lighting have focused primarily on safety considerations. The most commonly-applied standard, ANSI/UL 1598, the Standard for Safety of Luminaires, is an American National Standard (ANS) that addresses safety issues and describes testing required for all lighting fixtures that are hard-wired in a fixed location, including LED luminaires and fixtures used in horticultural lighting applications. A 4th Edition of ANSI/UL 1598 was published in August 2018 and includes modifications to several existing requirements while also adding a number of new requirements.

Another standard applicable to LED-based horticultural lighting is IEC 62471, Photobiological Safety of Lamps and Lamp Systems. This standard deals with human safety considerations associated with exposure to optical radiation generated by many types of lighting systems, including those based on LED technology, and defines radiation measurement parameters and exposure limits. Again, however, the focus of IEC 62471 is primarily on safety, not on lighting performance.

In addition to these safety standards, there are also available other documents and test methods that are used in connection with luminaires and lighting systems. The Illuminating Engineering Society (IES) has issued several design and testing guides, notably its LM 79 and LM 80 series of measurement specifications, that are applicable to a variety of lighting fixtures, including LEDs. And the DLC has previously released several testing and reporting specifications intended to assess the energy efficiency of lighting fixtures, in support of its Solid-State Lighting (SSL) Qualified Product List (QPL) program. But none of these documents directly address key performance aspects of LED-based horticultural lighting fixtures related to plant growth and development.

About the DLCs horticultural lighting testing and reporting requirements

In an effort to address this void, the DLC has recently finalized new testing requirements exclusively for LED-based horticultural lighting fixtures. Published in November 2018, “Testing and Reporting Requirements for LED-based Horticultural Lighting” represents the first technical specification that focus primarily on lighting performance factors that have a direct impact on plant growth and development. LED light fixtures that are found compliant with the DLC’s testing and reporting requirements are eligible for listing on the DLCs new Horticultural Lighting QPL.

The DLC’s specification requires testing of, and reporting on, the following critical characteristics of LED-based horticultural lighting fixtures:

  • Output characteristics—Testing of the output of a lighting fixture involves an assessment of four individual parameters, as follows:
  • Photosynthetic photon flux (PPF): This parameter measures the total lighting output of a device over a specified range of wavelengths, as well as specific
    output in the wavelengths associated with blue, green and red light.
  • Far-Red photon flux (PFFR): This represents the measurement of the lighting output of a device over the “far-red” band. Far-red light is linked to premature
    flowering in many plant species.
  • Spectral quantum distribution (SQD): This parameter represents the measurement of the distribution of photon flux per photon wavelength over the photosynthetic and far-red range of wavelengths.
  • Photosynthetic photon intensity distribution (PPID): This parameter measures the distribution of PPF density emanating from the device.

The DLC specification contains no specific requirements for any of these four parameters. Instead, the reporting of assessment results is required to provide validated technical information regarding a lighting fixture’s performance.

  • Efficacy - The evaluation of a lighting fixture’s efficacy characteristics involves testing of its photosynthetic photon efficacy (PPE), which is the output of the fixture over the specified range of wavelengths. All fixtures are required to have a PPE of > 1.9 micromole per joule (µmol/J), the threshold defined in the specification.
  • Long-term performance – A lighting fixture’s long-term performance and reliability is assessed in accordance with the following five parameters:
    • Photon flux maintenance, photosynthetic (PFMP) and photon flux maintenance, far-red (PFMFR): These parameters measures the ability of a lighting device to maintain consistent output within the given ranges over time. The Q90 for PFMP must be greater than or equal to 36,000 hours. The Q90 for PFMFR does not have to meet a stated threshold value, but must be reported.
    • Driver lifetime: This parameter measures the anticipated lifetime of the lighting fixture driver under anticipated in-situ temperature conditions. The DLC specification stipulates a minimum driver lifetime of >50,000 hours.
    • Fan lifetime: This parameter assesses the anticipated lifetime of any on-board cooling fans in a given fixture. Again, the DLC specification stipulates a minimum lifetime of >50,000 hours for cooling fans.
    • Warranty: The DLC specification requires a product warranty that covers the complete lighting fixture for a period of not less than five years.
  • Electrical performance and power quality - The electrical performance and power quality of a lighting fixture is evaluated according to the following two
    parameters:
    • Power factor: Lighting fixtures must demonstrate a measured power factor of >0.90 at any rated input voltage and maximum designed power output.
    • Total harmonic distortion, current (THDi): Lighting fixtures must also demonstrate a measured THDi of <20% at any rated input voltage and maximum
      designed output power.
  • Safety certification - Finally, to address safety-related considerations, lighting fixtures must be certified in the U.S. by an OSHA NRTL or in Canada by an SCC-recognized body in accordance with the safety requirements and standards applicable to horticultural lighting products.

Why DLC qualification is important for LED-based horticultural lighting producers

The DLC testing and reporting requirements for LED-base horticultural lighting provide an important set of performance specifications for producers seeking to
quantify the quality and effectiveness of their lighting products in horticultural applications. Testing in accordance with the DLC specification results in an independently validated lighting “profile” that enables lighting manufacturers to accurately characterize the performance of their products. And that profile can be used by operators of indoor farms and other controlled environment growing facilities with the information they need to select the lighting products that are most appropriate for their agricultural operations.

The DLC specification also helps support the wider adoption of LED lighting in horticultural applications. The performance advantages of LED lighting fixtures, combined with greater energy efficiency, make them the logical choice for optimizing the output of agricultural products produced in controlled environments while also making an important contribution to larger environmental goals and objectives. The specific performance issues addressed in the DLC specification can also serve to foster further innovation in LED lighting technology, potentially producing even greater benefits for everyone.

How TÜV SÜD Can Help

TÜV SÜD has been an NRTL-recognized testing laboratory for more than 12 years and is currently recognized to test and certify LED-based horticultural
lighting products in accordance with UL 1598, UL 8800 and other relevant lighting standards. We are also recognized by the DLC to conduct testing required under its horticultural specification in support of listings to the DLC’s Horticultural QPL. As a single source for testing and certification of all types of lighting systems and products, we are also equipped to conduct customer-specific testing to assess performance, functionality and durability consistent with
end-use requirements. With four recognized testing lab locations across the U.S., TÜV SÜD America is uniquely positioned to provide manufacturers and distributors, regardless of their location, with convenient access to our full suite of testing and certification services.



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