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Dark Sky Lighting: Simple but Effective

By Peter Strasser, International Dark-Sky Association

Low-pressure sodium (LPS) being used in full cut-off fixtures for walkway lighting at a major hospital.
Photos courtesy of International Dark-Sky Association


For 20 years, The International Dark-Sky Association has increased the awareness of light pollution and has sought ways to educate the populace as to its cause and remediation. Dark skies advocates writing about good lighting? How can this be? This is the commonly held misunderstanding, that those who seek dark skies view all lighting as bad. For the record, dark skies does not mean dark ground.

LPS being used for parking lot lighting, both enclosed and open deck. The ones on the top deck are full cut-off. Notice the lack of glare, and the dark sky even in the immediate vicinity of the fixtures.

The IDA sees quality luminaire design and implementation as a critical part of putting a halt to, and inevitably reversing the scourge of light pollution. We often hear that designers appreciate the dark concept and want more information on how to implement these concepts into their work. Dark sky principles are quite straightforward; light when you need it, where you need it, and no more. Anything more than this is wrong for myriad reasons.

Human eyes have greater adaptability and dynamic range than can be rendered in simulations. The eye can adapt, be it to 0.5 foot candles or 2.5. More light does not mean more safe. The opposite of no light is not excessive light. Nature has given us this remarkable ability. It’s time we realize this and that our eyes adapt.

For most landscape lighting, where accent and aesthetics are the principle concerns, the operative word is subtle. Let the eye see the detail and never the source. Contrary to popular misconceptions, there is no need to eliminate lighting. Excellent landscape lighting in general tends to demonstrate the concepts that ambiance, comfort, security and safety are enhanced. Excellent lighting design is one of the great intangibles; good lighting is felt but can’t be touched. You know it when you see it; you feel it when you are in it. It can also be ruined by poorly designed luminaires and poor design practices.

Lighting for dark sky principles includes control, by luminaire selection, lamp wattage, commissioning, and future inspection. That’s not how we do things now, but some things need to change, and inspection and validations should be considered part of the design scheme.

North America at Night. The United States, Canada, and Mexico. A very good way to see the impacts of light pollution.

One of the fundamental methods of controlling light pollution is the simple curfew. In many cases, this dark sky friendly tactic can be implemented immediately. Utilizing simple timers can also make retrofitting existing installations feasible, practical and economical. The darkened exterior of a building, form of a statue, or fronds of a palm tree aren’t an issue of safety.

This is a well lit dining area outdoors. From the standpoint of conspicuous public design, it remains the professional responsibility of the landscape architect to see that good exterior lighting practices are an integral part of their designs.

The goal for the landscape architect is to create ambience. If lighting is ever an afterthought, or delegated to an entity not concerned with the aforementioned ambience, disaster looms. Bright light haphazardly aimed can feel like an interrogation, or perhaps prison yard lighting.

“ Excellent lighting design is one of the great intangibles; good lighting is felt but can’t be touched. You know it when you see it; you feel it when you are in it.”—–Peter Strasser

Be aware of luminaire height and tree growth. Well meaning environmental awareness can backfire. Planting trees to mitigate the urban heat island effect, particularly in parking lots, is a worthy and rational practice. However, conflict often arises when allotting space for said trees and the inevitable (and expected) desirable growth of the trees occurs. Will the illumination of these area lights be impacted by the growth of carbon absorbing, shadow-casting, ambience improving trees? Forethought and cooperation between governing bodies is essential for both daytime shade and nighttime visibility to coexist.

A concept and layout can look exquisite on the plan, with subtle backlighting, accent and walkway luminaires, all properly directed and powered by timer controlled circuits, only to have it all obliterated by the cobra-head on a pole that’s out of your control.

Avoid criminal friendly lighting. A jerk-kneed response to “correcting” a lighting problem is to throw more light on the subject, the more the better. This is most often seen around ATM machines, where liability is in question. The lighting selected can be situated such that the area is sufficiently lit, without harsh glare or shadows, while making the transition from the lighted space to the outer area even and not abrupt. It can be done. However, owing to the excessive lighting practices, all in the name of theoretical litigation, most patrons of ATM machines feel not only well illuminated, but exposed and vulnerable. How, and why this is considered a safe environment? The ubiquitous wall pack, with cheap initial cost and non existent glare control, remains the industry standard for most ATM lighting and area lighting in general, with their deep shadows, harsh illuminance levels, and mounting heights virtually guaranteeing discomfort and disabling glare.

The rigorous training of the landscape architect lends itself to analyze, envision and design a nighttime ambiance solution that defines the exterior space in a manner that is aesthetically and artistically pleasing, functional and safe. In so doing, the night time environment is transformed where people live, work and recreate. It becomes so comfortable that people want to stay in it, often subconsciously, but with the distinct notion that where they are is the place to be, without any intrinsic reason to leave.

Presently, the most common question posed about dark sky lighting is how to incorporate “nostalgia” luminaires into designs where the streetscape is included. These nostalgia luminaires are often referred to as “acorns” because of the resemblance the glass portion has to the seeds of some oak trees. For most dark sky advocates these acorns a truly “nuts.”

From a holistic viewpoint, it is important for the overall lighting design to utilize energy saving component products. An area lighted by low voltage produces an environment that is pleasing, to the point where common higher wattage area lights, like wall packs, will not be tolerated.

Nostalgia luminaires are sought after and installed for their appearance in daytime. Contemporary lamp wattages routinely provided with them are so high that one cannot begin to contemplate the beauty of the design, let alone look anywhere near them because of the intense, uncomfortable glare they produce.

The public needs a little history lesson here. This Old World post top design had an Old World lumen output, in that they contained a flame. That is why the Victorian lexicon has the term “Lamplighter” and not “high intensity discharge lamp.”

The light given off by these flame-driven luminaires was sufficient for the task at hand. In the present conformations, the pole height is similar, the optics are similar (if one allows for acrylics as well as glass), but the light source and the expected tasks are astonishingly different.

Allow for the biological fact that the eye adapts to lighting levels and architectural details are revealed with lower levels as seen on this patio, and obscured with higher ones. Making something brighter will not make everything more visible. Quite the contrary. High light level will diminish detail by creating glare. Glare is never good.

They are typically lamped with sources exceeding 10,000 lumens, at the same height as the old world, flame-containing luminaire. They are also expected to light up the roadway, public areas and the surrounding environs. When lamped with an HID source, people are exposed to harsh glare and discomfort.

An acorn luminaire should not be considered for illuminating a roadway. They are simply the wrong mounting height for illuminating a street and without being a source of disabling glare. Another flaw in the design is the lack of light control. Light is thrown in every direction.

What can be a solution to the problem is selecting the best light control design available, lamp them with lower lumen output, certainly below 1,000 lumens, and light the roadway only at conflict points/intersections with a conventional full cut off streetlight.

Regardless of the quality of the installation and a majority opinion that the lighting level is good, there will always be those who feel that an installation it is too dark or insecure. Habituation to “seeing the source” as proper and necessary for “good lighting” is commonplace.

A view of a parking lot, one lit by glary lighting. Can you see the criminal? Blinded by glare.

Same view, but with a flash photograph to show where he is. Can you design a better, safer installation? The great fear is a criminal lurking in the shadows. Lurking in the shadows has two important components; a place to lurk and a shadow in which to do it.

A new concept for encouraging better lighting practices has been in place for several years, the LEED building certification program. Regrettably this program remains cursory when it comes to discouraging poor lighting design. While LEED has the Sustainable Sights Credit #8, The Light Pollution Reduction Credit, it remains an option. From the public’s viewpoint, it can make a LEED certified building a laughingstock and put a black eye on the LEED certification program. A LEED certified building can have the most egregious examples of bad lighting design, wasting energy while shining any amount of light in all directions, with no thought of containment, curfew or control. Lighting systems reserved for stadium lighting could be blasted on a building and it will still achieve LEED certification. Until Credit #8 becomes a requirement, light pollution can be a problem on even the most presumably energy efficient structures.

It is entirely appropriate for municipalities to take pride in their history, facilities, monuments or plantings. Well-designed lighting also has a place here as well. But statues, buildings, other structures and plants are not vain. They do not require illumination at all hours of the night. Communities should set reasonable curfews for lighting such objects.

Wasteful lighting destroys and disrupts the livability found in otherwise well designed spaces, and then extends beyond the living space to obscure the firmament, the space of the starry heavens. Why has this ever been considered an acceptable practice, let alone condoned? Waste is never good, with the single exception that its very nature will lead to its demise. As energy resources become scarcer and increasingly expensive, our society can no longer behave with the ill conceived notion of having the luxury and right to waste.

The Dark Sky cause has a powerful, professional ally in the effort to curtail and reverse light pollution. Such can be achieved with a well thought out lighting scheme, eliminating light trespass and having no contribution to light pollution. Good lighting practices will reverse the trend of over lighting, and as that happens, the beauty of the night’s celestial sphere will once again be visible to everyone, everywhere.

Some IDA Approved Lighting Fixtures

There are scores of luminaires that have been given IDA’s Fixture Seal of Approval and are certified as dark sky friendly. Don’t be fooled by imitations. See their website at for details about these products.

To submit a fixture or apply to the Fixture Seal of Approval (FSA) Program, please download the FSA Application at (Adobe Reader Required). You may also call 1 (520) 293-3198.

A full cut-off fixture. Here it is used for a major shopping center parking lot. No glare, no light trespass to bother neighbors, no wasted light. The poles are high, so light gets between cars. A safe, effective, efficient, good design. Everyone wins.
Photos courtesy of International Dark-Sky Association

Antique (or period lighting) fixture, full cut-off. Looks nice in the day, and at night too. Good control of the light output. No glare

The new lighting at an installation with much better lighting control, more effective for the task, no neighbor complaints, and happy astronomers.

Good wall packs, full cut-off, good light distribution on the ground too.

Sports lighting can be good. Here is it using full cut-off lighting. Very good design.

A full cut-off LPS street lighting fixture. They give excellent light output control, there is no glare, and no confusion of the yellow LPS with the yellow traffic signals.

An example of a full cut-off low pressure sodium fixture. Excellent light control is possible with these type fixtures.

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October 20, 2019, 5:57 pm PDT

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