Exterior Lighting: Onwards and Upwards

December 12, 2011 / no comments

Approaching a lighting design project is always a balancing act of multiple goals towards a single end: a beautifully lighted project that enhances the perception of the place, meets the budget, and satisfies code requirements. But as discussions of dark-sky compliance and reduced power consumption to meet stringent new requirements have come to the forefront of exterior lighting design, the quality of the lighted nighttime environment has come under siege. Are we moving forward into a world of lighted pavement, mitigated only by the siren glow of illuminated commercial signage?

Lighting of exterior environments not only provides for safe navigation during hours of darkness, but can reveal design elements, both built and natural, that are lost in daylight, returning delight to the hours without sun. With all of our energy focused on lighting the ground, the importance of vertical illumination is getting lost in the darkness.

Silver Spring Lam Partners

Early versions of LEED SS Credit 8 (Light Pollution Reduction), with stringent requirements to limit all light above the horizontal plane with the exception of very low-brightness fixtures, was an effort to push dark-sky agendas forward without acknowledging what a well-lighted exterior environment actually requires, or what it contributes to the urban environment. Downlight with sufficient uniformity can facilitate movement across plazas and walkways, but where are people headed? Lighted pavement alone can provide orientation only without end or destination.

While obscuration of the heavens through urban sky glow is one of the most unfortunate results of the urbanization and industrialization of our planet, the metrics for nocturnal illumination cannot be based upon the assumption that the primary task of humans in an urban environment is to go and gaze at stars. Even when these standards are met, the results can still have a negative impact: a modestly lighted parking lot with light-colored concrete pavement lit to the minimum IES recommendations, using only cut-off fixtures, can substantially degrade a dark residential environment if that pavement is within view of residences – and the reflected light from the pavement is going into the sky, even though the fixture itself does not emit light above horizontal. (This is a great opportunity to advocate for tree cover – not only does it provide parking lots with cooling shade during the summer and soften their appearance during the day, but it blocks reflected light from trespassing upwards! That’s not accounted for in the requirements).

Walmart Store Parking Lot

The Lighting Research Center at Rensselaer Polytechnic Institute has developed a metric for evaluating and designing exterior lighted environments, known as Outdoor Site-Lighting Performance (OSP), that accurately documents the effect of electric illumination on a project. OSP acknowledges that glare, light trespass beyond the physical limits of the site, and sky glow are all important factors that warrant consideration. However, by using modeling tools that measure the amount of uplight trespassing off the site – not only light emitted by fixtures, but also the reflected light off of surfaces such as the parking lot mentioned above – a more realistic picture of the lighting effect can be examined. Similarly, current and future versions of LEED SS Credit 8 do allow for some amount of uplight in the urban environment.

What about projects where reliance on cut-off downlight fixtures is not a good fit architecturally? Can they still meet the intent of a sensitively lighted nighttime environment? Lam Partners’ Hermann Park Lake Plaza project avoides pole-mounted fixtures, equipment that is, in effect, prescribed by LEED and other dark-sky guidelines. Determined not to use pole-mounted lighting along the water’s edge to avoid distracting reflections in the water, the designers devised a fully integrated approach. One-watt LED button steplights illuminate and guide, tracing the arc of steps around the lake; ground-recessed ceramic metal halide tree uplights create a welcoming border.

Hermann Park Lam Partners

The graceful composition remains uncluttered by hardware, focusing solely on form and line. The arrangement is serene and contemplative in early evening, then emerges dazzling and energetic as night descends. Because awakening the appearance of surfaces and landscape forms was critical to attracting visitors after dark while fostering safety and security, tree trunks and wall surfaces are boldly illuminated.

Hermann Park Lam Partners

The team deliberately relinquished the LEED light pollution credit (although the project did achieve LEED status), and yet, the uplit trees are magical during nighttime strolls. As darkness conceals architectural stonework, the wooded procession comes to life through light. From across the lake, the trees form an illuminated horizon, and indirectly lighted walls form the edges of this exterior room.

Photo Credits: Anton Grassl / Esto (1), Walmart Stores (2), Overland Partners (3, 4)

Why Light It?

September 28, 2009 / no comments

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Light pollution and light trespass are hot exterior lighting topics, and they both relate directly to the broader topic of energy conservation. Simple logic tells us that shooting light into the night sky, either directly or inadvertently, is basically a waste of light and energy. The light that escapes above the horizon hits nothing but air, water, and smog. Some of that light is reflected back down as light pollution, that eerie yellow glow that obscures the stars, but none of it is useful – it’s an unutilized byproduct of the artificially illuminated environment.

That’s not a good thing! Sky glow and light trespass have been linked to problems like sleep disorders, migratory bird death, and obstruction of the night sky. Small problems that may seem insignificant? Well, think of it this way: sky glow exposes how much energy and money we pump into the air, and guess who pays for all that extra light – you, the taxpayer! Millions and millions a year, and most of it is powered by fossil fuels.

Can we simply turn off all the exterior lights then? No, unfortunately, the lighting was probably installed in the first place to serve a purpose: the lighting of streets, buildings, parks, and other places that people navigate to at night.

Could we reduce the amount of exterior lighting, though? We can already discern that a lot of lighting is wasted in the sky. Could it also be possible that we’ve intentionally lit that which should not or need not be lit to begin with – that the purpose served was not a legitimate, well-conceived purpose? Absolutely!

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Since the invention of the light bulb, we’ve been putting electric lighting EVERYWHERE. We did it because we needed it and wanted it, to see where we were walking and driving (street lighting), to see where we were going (sign lighting), because it looked nice (decorative lighting), to show off our accomplishments (building and bridge lighting), to illuminate nature (tree uplighting), and for security and safety (the former as a police control measure and the latter as a matter of perceived personal well-being).

Now some designers are taking another look at the “why” of design, questioning whether or not we really need all that lighting. Do we need to light a stretch of rural highway when we have headlights on our cars? Do we need to light city centers to 50 lux (5 footcandles for you Imperialists) when 20 will do? It’s not just a question of yes or no, but also of how much.

To take a few of these examples, here are some issues that we should think twice about:

  • Street lighting – do we need to light roadways so much that we can do without headlights entirely? (I’ve seen it – no headlights! Insane!) Perhaps we can use the task-ambient approach here: ambient from very low-level street-based systems, and task from headlights. We’ll still need to pay attention to the vehicular-pedestrian intersections but all that lighting in between could possibly be reduced.
  • Sign lighting – do you really need to light your signs all night long, from the bottom shining up? What if you turned the sign off after midnight, and lit it from above?
  • What about building lighting? Many developers, architects, and designers want to see their projects as the beacon of the neighborhood. Uplights graze the columns, floodlights slam into concrete walls, and twinkly lights adorn the penthouse. Should every building do this, though? Are they entitled to? What if the desire to be the best on the block simply precipitates escalation of building lighting – where does it end? Everyone needs to ask themselves “Should I even light the outside of this building?” That goes for public monuments, too; maybe we should take public money used for lighting public monuments and put it somewhere more useful, like healthcare. How about focusing on the entry and letting the rest go dark at night?
  • How about landscape lighting – why? We light the trees and shrubs only because we can. Yes, it does look pretty, but at what expense? The amount of light the canopy of any particular tree can catch in comparison to what shoots straight into the sky is very little.
  • And finally, lighting for security and safety. This is a very sensitive issue. Police officers, emergency response professionals, and the general public would prefer more light as opposed to less. The popular opinion is that more lighting equals less crime and, while more light will certainly help the police in identifying perpetrators, it doesn’t necessarily create safe environments. There are very well-lit alleys in which all sorts of crimes happen. The statistics have too many variables to pin down an unquestionable correlation. Maybe we should concentrate on good quality lighting that serves these purposes without increasing light levels. Better lighting, not more!

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All of these applications are only marginally effective, which supports the position that we simply do not need as much lighting as we have. If a total of three people drive by a building at 3:00 a.m. and see it lit up, is keeping it illuminated all night long worth the collective fifteen seconds of viewing?

Every developer, architect, or designer should question if it’s really worth it. But then, it’s a hard question to ask – who’s to say what qualifies and what doesn’t? Who will speak up and tell someone “no”?

Photo Credits: Liber (1), Ian Plumb (2), Clav (3)