Designing for Darkness

Contributed by

Kate Sweater Hickcox, MS, LC
Lighting Research Scientist | Pacific Northwest National Laboratory

e: [email protected]

Kate Sweater Hickcox is a creative thinker in the field of lighting, with over 15 years of experience in both lighting research and lighting design. No matter which hat she’s wearing, her goals are simple – to provide equitable and universal lighting solutions that support humans and the environment. Kate’s unique background blends the artistic with the practical and allows for the discovery of unique design solutions and innovative research-based strategies. 

She has authored or co-authored many technical publications/reports and made several presentations at national conferences. Kate is currently a Lighting Research Scientist at PNNL. She has been a guest critic at Rhode Island School of Design, Parsons/The New School and Rensselaer Polytechnic Institute Architecture Department. She has taught at The New School, Parsons’ School of Constructed Environments and was also the Lighting Fellow for ‘Opening the Edge’, a project of the Design Trust for Public Space, in partnership with the New York City Housing Authority; proposed by Jane Greengold.  

Kate has presented at many lighting conferences, most recently at LightFair Connect 2020.

Poster by Kate Sweater Hickcox

Want a printable version of this poster?
Follow this link for a printable version. If you have any questions or comments, please contact Kate at [email protected].

About the Design for Darkness Artwork

This original poster artwork and the information included were created by Kate Sweater Hickcox. The information on the poster stems from a research project conducted by Dwaal Lighting Design in 2019. This research included a deep dive into the metrics and practices of “dark sky” design. The project started with research and interviews with organizations who were involved in “dark sky” efforts, using or promoting dark sky guidelines, or working on dark sky related research projects. It became clear over the course of many interviews and discussions with stakeholders that the term “dark sky” is fraught with ambiguity, and what falls under the scope of dark sky is not clearly defined by the lighting industry. This led to a search for a clearer definition and approach for lighting-at-night (LAN) concerns. 

All of the topic areas these organizations were talking about, or working on, could be categorized into nine sub-groups of lighting-at-night concerns.

These included

  • Human Health, Comfort, and Safety
  • Concerns about Animals and Wildlife
  • Concerns about Astronomy from both astronomers and the military
  • Energy Waste
  • Preservation of Natural Character (respecting the aesthetics of the natural environment).

These nine sub-groups of LAN concerns could then be divided into three major areas of lighting-at-night concerns in order to create a framework for approaching designing for darkness. The three major LAN concerns include sky glow concerns, human-focused concerns, and ecosystem concerns. 

While each of these areas have very different end-users and design needs, a similar design approach can be adopted in each case. Each of these areas should be addressed using these criteria; timing (duration), directionality, intensity, and spectrum.

The poster illustrates the three major areas of lighting-at-night concerns and gives some detail about how to approach designing for darkness using timing, directionality, intensity, and spectrum. These four approaches are outlined below.

Designing for Darkness Using Timing

  • Allow for controls and dimming
  • Timing is species dependent
  • Ask an expert for ecologically sensitive installations

It would be easy to assume that turning outdoor lighting off during a curfew time period could only have a positive impact on the local ecology, however some species are very sensitive to how and when the lighting changes. Lighting that turns on or off at irregular intervals, or lights that disrupt fixed nighttime patterns, may disrupt the nocturnal behavior of some species. Wildlife and plants are sensitive to changes in both intensity and spectrum during dawn and dusk.

Designing for Darkness Using Directionality

  • Zero direct up-light can greatly reduce sky glow
  • Support wildlife by specifying shielding to prevent direct view of the light source
  • Reduce glare for humans

Controlling the spatial distribution of light, including reduction of direct up light, is one of the most impactful ways to reduce sky glow at the luminaire level. Shielding is a common technique used to reduce impacts from lighting on natural lands and species. Fixtures that allow no light to escape up to the sky are important as this can decrease sky glow and reduce attraction from birds or insects above the fixture.

Designing for Darkness Using Intensity

  • Reduce light output as much as possible
  • Allow for controls: timing and output determined by tasks/needs
  • Less is always better for wildlife and ecology

Regardless of the spectral content, reduction in light output has a significant effect on sky glow. When designing for ecologically sensitive installations, even very low lighting (far below that of the full moon) can have large effects on local wildlife and plants. Lighting codes and recommendations are usually written to support human tasks and needs. The luminous output commonly recommended may be much higher than necessary if you are installing in a rural environment or a natural park.

Designing for Darkness Using Spectrum

Spectrum | Image credit: https://nas/content/live/
  • Limit short wavelengths to help reduce sky glow
  • Spectral selections for ecosystems is species dependent. There is no universal solution.
  • In ecologically sensitive areas, avoid ultraviolet (UV) spectrum and adjacent short wavelengths
  • For humans, spectrum is determined by task
  • Correlated color temperature (CCT) is not spectrum.

Address timing, distribution, and output first; in many cases these will have the greatest impact. When considering spectral choices for an installation, remember that correlated color temperature (CCT) is not spectrum. Two sources with the same CCT can have very different spectra, and thus different impacts on the environment or on wildlife. Finally, keep in mind that there is no universal spectral solution. Across the range of visible wavelengths, there are advantages and disadvantages in each spectral band, depending on the species or environment. Different installations or tasks may require different spectral selections. One rule which can make a big impact, and is relatively easy to enforce, is to avoid any ultraviolet (UV) spectrum and adjacent short wavelengths as some wildlife are highly attracted to ultraviolet radiation.

Call an Expert

If you are specifying lighting or assessing lighting in a place where nocturnal or diurnal wildlife or ecology is a concern, you should consider working with a trusted ecologist or zoological researcher in order to quantify the impact or potential impact from any installation. Just putting lighting at a low light level, using yellow or amber lighting, or adding a dimmer is not enough to say that an installation is ecologically sensitive.

For the same reason that we need an ecologist to help when we are specifying lighting that is sensitive to the wildlife and ecology, an educated lighting specifier is needed to determine lighting solutions that satisfy human needs while mitigating negative side effects.

Who, What, Why?

If you are designing, specifying, or evaluating a lighting system in an outdoor nighttime environment you need to ask:

  • WHO or WHAT will experience this system?
  • WHY is the light necessary here? Do we really need lighting at all?

The who or what can be a wide variety of “end users” or “end scenarios” that should be researched and considered before a lighting solution is reached.  Always ask if the specified lighting is necessary, or could it be removed?

A good lighting specifier knows when not to specify lighting as well as how to specify quality lighting when it is needed.

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