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Values-Centered Outdoor Lighting

Values-Centered Outdoor Lighting Image

Tucson, Arizona, is lit by environmentally sensitive, modern lighting that saves energy. Photo by Bettymaya Foott

On January 28, 2021, the International Dark-Sky Association (IDA) Board of Directors adopted a policy implementing the Five Principles for Responsible Outdoor Lighting. The policy, known as Values-Centered Outdoor Lighting (PDF), is intended to inform and guide IDA’s ongoing work to protect the night from light pollution.


The resolution and its contents

The resolution(PDF) has three main effects. First, it establishes the IDA interpretation of the Lighting Principles, which is that the interplay of all five principles must be considered in the design, installation, and use of outdoor lighting, and that treating the principles in isolation from one another is insufficient to address the growing global problem of light pollution.

Second, it adds to previous IDA guidance on outdoor lighting a number of specifics that are implied by the Lighting Principles.

And third, it codifies two conservation goals for the International Dark-Sky Association: to lower the global rate of outdoor artificial light at night consumption to no more than the rate of population growth in a given region, while not conveying any economic disadvantage to people in developing regions and countries; and to prioritize restoring intrinsic nighttime darkness in circumstances where it is possible to do so.

Download the resolution in these languages: Arabic, Chinese, French, Spanish, and German.

The ten ideas of Values-Centered Outdoor Lighting

     1. Responsible outdoor lighting must consider all five principles in its design and installation and only through attention to all five principles will light pollution be minimized to its practical extent.

     2. Where existing fixtures are replaced, the project should demonstrate how they will reduce light pollution, or at a minimum not increase it.

     3. Where new installation or lighting retrofit projects are proposed, they should be guided by an assessment process to determine if such lighting is necessary and responsible.

     4. To reduce skyglow, glare, spill light, and over-lighting, indoor and outdoor lighting should contain and minimize the emission of light beyond the intended target. Light emitted towards or above the horizon can have extraordinarily high environmental impacts.

     5. To prevent overlighting, actual illumination levels should be as close as reasonably practical to the minimum values recommended by accredited professional bodies (such as IES and CIE) and appropriate for the task and environmental setting. IDA will collaborate with professional bodies to ensure that recommended illumination values are well-founded in science.

     6. New installations should have active controls to reduce illumination levels or extinguish lighting completely based on time of day or occupancy. Such controls are currently underutilized in outdoor lighting and can substantially reduce light pollution and save energy. Energy conservation codes are increasingly calling for active controls.

     7. The spectral content, or color, of light should be limited to only what is necessary for the task. Because of the disproportionate impact on the nighttime environment, particular attention should be paid to reducing the total emissions of short-wavelength or “blue” light (defined for the purposes of this resolution between the wavelengths of 380 nm and 520 nm) through light
source spectrum management.

          a. To minimize negative environmental impacts, IDA recommends using lamps rated at 2200K2 CCT, Phosphor-Converted Amber LED, or some filtered LED.

          b. When higher than 2200K CCT is necessary to meet lighting objectives, keep the total emission of blue light into the environment as low as reasonably possible through low intensities, careful targeting, and reduced operating times.3

          c. Near sensitive sites, such as conservation areas, sensitive wildlife habitat, ecological reserves, parks, astronomical observatories, or stargazing sites, IDA recommends that lighting installations use 0% blue light and a narrower spectrum of emission.

          d. Critically sensitive environments should be kept naturally dark.

      8. IDA recognizes that there is no single solution that will work for all situations; therefore IDA will develop a range of scenarios and guidance for common lighting situations. Solutions that result in no net increase in light pollution should be considered a minimum requirement, whereas best management practices would result in the maximum practical restoration of intrinsic darkness.

     9. Because context matters, IDA recognizes that advocates and lighting professionals need the flexibility to identify how the Principles are best applied within their local area to meet valid needs while observing all regulatory frameworks (guidelines, procedures, standards and codes, and laws). Where required or feasible, such decisions should be guided by an appropriate environmental assessment and supported by monitoring of light levels in the surrounding environment.

     10. IDA will periodically update guidelines in response to changing technology, changes in available
market solutions, evolving social values, and scientific progress.

1 Outdoor light emission in the ultraviolet portion of the spectrum (below 380 nm) should also be avoided as it often has deleterious consequences for wildlife while providing no benefit or human utility.
2 IDA recognizes that there is no widespread agreement on a more relevant metric than CCT for spectrum evaluation and will continue to advocate that one is developed. In the interim, CCT may be used as a placeholder, although it should be verified that the source emits no more than 8% blue light emissions.
3 IDA has captured many examples of how lighting with higher blue content can be done in a responsible manner. IDA’s Community-Friendly Sports Lighting Certification is one such example.


Resources for users

One-page ‘explainer’

This brief document summarizes why IDA adopted the new resolution, what it contains, and how it affects IDA’s work.
IDA Values-Centered Lighting Resolution Explainer (PDF)

Frequently Asked Questions

Q: What prompted this change?

A: We now know more about the physiology of vision and the possibilities enabled by modern lighting technology than when we last considered these issues; e.g., establishing 3000K as an upper limit for most outdoor lighting in 2014. It’s confusing to policy makers and consumers, and evolving technology will make metrics like correlated color temperature (CCT) a forever-moving target. Rather than being overly prescriptive about all of the technical characteristics, we came to realize that a flexible approach recognizing the interconnected nature of the characteristics stays more true to what we know (and don’t know) about lighting and its effects, and offers the chance to increase voluntary cooperation by giving lighting designers, lighting manufacturers, property owners, consumers, and policy makers more options from which to choose.

We recognize that our 3000K upper limit became a de-facto design standard. Although never intended to be used in this manner, it was working against advocates advancing progressive lighting solutions. The resolution attempts to correct this course and provide guidance based on the best available evidence.

Q: How can this new guidance be incorporated into lighting designs?

A: By first clearly identifying the need for light in a given situation and then considering how illumination levels, timing, spectrum, and targeting can be used together to meet the identified need and reduce wasted light. 

Q: What does this mean for IDA’s Fixture Seal of Approval (FSA) program?

A: The Fixture Seal of Approval program addresses two of the five principles, namely Targeting and Color. Because it certifies the fixture and not how it is installed or used, it established an upper CCT limit of 3000K CCT. Today, many good options exist at lower Kelvin ratings and we encourage consumers to seek them out. The FSA program is introducing a new “innovation category” to recognize best in class lighting with lower CCT. Over time as more low CCT products become available, we will revisit our guidance.

Q: What does this mean for the International Dark Sky Places (IDSP) program?

A: The International Dark Sky Places Program guidelines have broadly adhered to the IDA Fixture Seal of Approval standards since 2014 in the recognition that IDSPs are intended to be highly visible exemplars of quality outdoor lighting. The new values-centered lighting approach will not formally apply to any of the IDSP categories until the next major revision of the program guidelines expected in 2022. At that time, the program requirements will be adapted consistent with values-centered principles. Until that time, the current (2018) program guidelines requirements will remain in effect.

Q: Isn’t brighter and whiter light more safe?

A:  A 2200k LED is considered to be “white” by ANSI standards. There is such a thing as “too white” where the color has a decidedly bluish appearance, increasing glare and causing veiling luminance within the structure of the eye that starts to inhibit visibility the brighter and bluer the source. If the decision is made to use white light with higher blue content, steps must be taken to reduce illumination levels and otherwise control the light. By doing this, light pollution can be reduced and visibility enhanced.

Q: Doesn’t this mean more blue light going into the environment?

A: Not necessarily — we must start to think about the “integral” over all the different lighting characteristics; e.g., a 3000K white LED source at high intensity that is on all night emits more blue light in total than does a 4000K source operated at a much lower intensity and on a motion sensor. We think that following this new approach will mean a decreased light consumption overall, which will help offset situations where end users choose higher CCT. 

Q: How does this resolution address the impact of blue light on human health?

A: There is a growing body of evidence that exposure to short wavelength, “blue light” emissions is correlated with a variety of diseases. Less is known about the dose, timing, and precise wavelengths that lead to these impacts. IDA is adopting a precautionary approach and encourages everyone to take steps to reduce the overall quantity of blue light emitted into the environment by considering all five principles.

Q: Why are you continuing to use CCT when it is widely acknowledged that it is a poor metric for the spectral characteristics of light?

A: Despite its shortcomings, CCT is the dominant metric used by the global lighting industry to convey information about the color qualities of lighting for both indoor and outdoor applications. We acknowledge those shortcomings, as well as the reality that for the time being we must continue to speak the industry’s language in order to influence its actions. At the same time, IDA has begun to advocate for long-term changes that we hope will culminate in identification of an appropriate metric or metrics to replace CCT and that provide more useful information to lighting designers and end-users in order to make better decisions when choosing lighting products.

Q: If IDA’s recommendation is to light to the minimum level recommended by professional bodies, does that preclude further dimming?

A: No. Rather, we believe that illumination levels of outdoor spaces should scale reasonably according to actual use patterns. Consistent with considering all five Lighting Principles, and in particular the notion that lighting should be provided in amounts and quantities consistent with, but not exceeding, user needs, quality outdoor lighting design should consider reducing or extinguishing light at times and under circumstances where the necessity of lighting has not been established.

Q: I’ve heard that some recommended lighting levels (e.g., EN 13201) are either not based on evidence or are otherwise too high. What can you say in response to that?

A: IDA is not a standard-setting body, and we expect that the organizations that set lighting standards to do due diligence in ascertaining safe lighting levels through empirical research and then setting their recommendations accordingly. In instances where international standards appear to be lacking in evidence, we will press the bodies that set those standards to justify their recommendations with scientific data or otherwise revise them downward consistent with the best available evidence from lighting design practice. Furthermore, focusing on only one of the five Lighting Principles in isolation from the others is what the resolution advises against. 

Managing all five light principles — even while potentially accepting higher light levels in the short term — will help further reduce light pollution.

Case Study: Tucson, U.S.

What happens when a large city considers all elements of the five Lighting Principles in designing a new street lighting system? Read about how the City of Tucson, Arizona, decreased street light emissions by 60% during its transition to LED lighting technology while maintaining safe illumination levels on city streets, realizing a 7% reduction in skyglow over the city.

Case study: Sahuarita, U.S.

To illustrate the practical application of Values-Centered Outdoor Lighting, consider outdoor sports lighting installed at Quail Creek-Veterans Municipal Park in the town of Sahuarita, Arizona, in 2015. The state-of-the-art lighting system considers all Five Principles for Responsible Outdoor Lighting in its design, yielding exceptionally effective athletic field lighting with nearly no off-site impacts.

Athletic field lighting at Quail Creek-Veterans Municipal Park in the town of Sahuarita, Arizona. Photo by Pete Strasser.

Athletic field lighting at Quail Creek-Veterans Municipal Park in the town of Sahuarita, Arizona, showing extreme control of the light distribution near the edge of the field. Photo by Pete Strasser.

Tennis courts at Quail Creek-Veterans Municipal Park in the town of Sahuarita, Arizona. The lighting design careful controls placement and intensity of the light to restrict it to the courts. Photo by Pete Strasser.

The design incorporates carefully controlled white LED lights whose area distributions are precisely tailored to the site conditions. The lighting system is network-enabled, providing dynamic control of light levels. The lights are automatically extinguished after sporting events end each night. In recognition of this outstanding installation, the Sahuarita Town Council was recognized publicly by IDA in 2019.

Drawing from all Five Principles for Responsible Outdoor Lighting, the Quail Creek-Veterans Municipal Park athletic field lighting design is:

  • Useful — meeting the needs of athletes and spectators, enabling safe play and viewing of nighttime sporting events
  • Targeted — light is positioned where needed on the playing fields and tennis courts, avoiding light spill into adjacent parking and residential areas
  • Correctly illuminated for the task — illumination levels follow the Illuminating Engineering Society minimum values appropriate to the ‘class of play’
  • Controlled — individually network-addressable light towers are actively controlled to provide the correct amount of light for the sport being played and the lighting is automatically switched off at the conclusion of play
  • Mindful of light spectrum — lighting at a correlated color temperature of 4000 kelvins yields high color rendition for athletes, while lower light levels results in overall reduced blue light emissions compared to most conventional outdoor sports lighting designs

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