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.

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).

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.

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.

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)

The old adage of measuring twice and cutting once applies just as well to design as to construction, and especially to the design of our lighted environment. Lighting can certainly be judged quantitatively, and it often needs to be, but it is also always qualitative and very subjective. The perception of brightness, the balance of light and dark, shade and shadow, and the appropriate contrast to enhance a sense of dimensionality without visual clutter, all play a role in the quality of lighting.

Sometimes numbers aren’t enough, or they don’t show the whole picture; sometimes seeing really is believing. In the case of a recent high-rise tower project, the penthouse screen wall was backlighted to create a glowing crown within the nighttime skyline. This started as a computer model to study the relative output needed, along with the general patterning of the screen wall structure. Then, during the glass selection process with the architect, a series of full-scale mockups were done on the rooftop of the existing building to evaluate the appropriate brightness.

Numerous glass samples were explored and tested, during the day and backlighted at night. Various frit patterns and interlayer films behaved differently at night, lighted from one side, than they did during the day when daylight illuminated both sides.

Care was taken to accurately simulate the structure supporting the screen wall, in order to represent realistic shadowing; however, the primary purpose of the full-scale mockups was to determine with the client the preferred brightness of the backlighted glass. There was no right answer in this case.

If the process had stopped there though, we still would have missed the mark, because brightness was only one piece of the composition. The next step went back to small-scale modeling. A 1/4”-scale physical model was constructed of one entire façade, with all of the structure and fixtures accurately represented. This allowed the overall pattern of the wall, with all of its potential shadows, to be scrutinized and explored.

The interplay of shadows from vertical and horizontal structural elements, in relation to standard fixture lengths, created a depth to the lighted wall that, at this grand scale and from normal street-level vantage points, became a positive quality that the entire design team, along with the client, preferred over a relatively uniform and flat appearance. The distinction between texture and visual clutter can be a very fine line, and neither the computer model nor the full-scale mockup really told the full story.

Sometimes the answer is quick and right in front of you, and other times, especially when perception and subjective qualities are in question, multiple methods need to be explored to make sure that the right measurement was made. A single measurement would have cut this design too short.

Photo Credits: D Sharon Pruitt (1), Lam Partners (2-5)

Many people would argue that the healthiest lighting at night is no lighting at all. Studies are revealing that biological rhythms are offset, sleep patterns are disrupted, even breast and prostate cancers are more likely with disrupted circadian rhythms, due in part to improper lighting at improper times of the day.

The human race evolved under both light and dark. The light-and-dark cycle sets our circadian rhythms and is responsible for our good physical and mental health. Relying on the sun, moon, and stars has for centuries provided us with high-quality, healthy lighting. That’s why there is such an interest in daylighting our buildings, not only to save energy, but to put us in touch with a natural light spectrum that changes throughout the day and provides us with healthy lighting. However, we sometime need to augment this cycle at times when tasks must be performed and there is no available “natural” light.

Exterior lighting provides useful illumination at night mostly through electric means, and there are a plethora of electric light sources available to light our cities, towns, and campuses at night. What’s the best choice? Unfortunately, that question is far too many times answered by “what’s the cheapest?” – cheapest to purchase, operate, and maintain. “What’s the most energy-efficient?” is another, more admirable, question.

Both metrics are easily quantifiable and, as a result, are used almost exclusively in decisions about what light source to use. But since we are primarily lighting for humans, we should be asking “what’s the healthiest lighting to provide at night?” This is a more difficult question to answer. We may find that the healthiest lighting at night is no lighting. But, if we determine that some sort of illumination should be provided for some given task, what kind of light is best?

Most of America’s highways, streets, and pathways are illuminated with high-pressure sodium lamps, a yellow, monochromatic source. Many lighting designers, though, prefer metal halide over sodium vapor due to its “whiter” color and superior color-rendering properties. However, designers have had a tough time justifying this qualitative aspect when compared to the efficiency and long life of sodium.

Then, a number of years ago, studies started to show that cool or bluish light (white light with relatively high color temperatures, 5000K to 6000K) improved visual acuity in off-axis seeing tasks. There was even discussion about measuring this benefit for exterior lighting applications, since off-axis tasks were very important for good nighttime vision, (scotopic) driving, and walking. Finally, designers had a scientific reason for recommending metal halide over sodium for ‘people-centric’ tasks.

On the other side of the coin is the research saying that blue light at night is bad. Studies are starting to reveal that exposure to light with higher concentrations in the blue spectrum at night may actually be bad for our health. Apparently, it is especially harmful to people prone to macular degeneration. Cool blue light in the morning and during the day, at high levels of illumination, is crucial in setting our circadian rhythms by producing serotonin in the body.

Conversely, warm-colored light at night does not suppress melatonin, which is needed for proper sleep cycles. This is why some claim that night lights should be amber or red so as not to disturb sleep patterns through the night, or that people should stop working on their computers or watching TV at least an hour before going to bed, because of blue-rich light emanating from the visual displays.

And then there is the psychological side. Most people prefer a warm tone for low levels of illumination. It feels more natural. The sun gets warmer closer to sunset. Firelight has a nice warm glow. Dimming an incandescent lamp warms its color temperature. Kruithof’s amenity curve reinforces the notion of relating color temperature to the illuminance level.

Just to complicate matters, many exterior applications are beginning to embrace the burgeoning technology of the LED. It seems to make sense from a maintenance standpoint, since LEDs have a very long lamp life. However in order for these diodes to be very efficacious, they must be in the very cool or blue end of the spectrum, about 6000K. When this color temperature is used for outdoor applications of 10lux or less, the resultant lighting system looks very unnatural, not to mention what it does to skin tones.

On the Boston Common, like in many communities across the nation, there is a mock-up of several different styles and manufacturers of LED pedestrian lanterns. One evening, as we were observing the differences between the luminaires, we received an unsolicited opinion from a passer-by who commented on how the warm-white LED lantern looked the best. I tend to agree. The blue light at night simply looks unnatural. I often wonder why induction lighting is not more common for exterior lighting applications – the color temperature and rendering properties are superb, and it is rated at twice the life of most LED systems.

Ultimately it comes down to good lighting design:

1. Identify what needs to be illuminated and what can remain dark, in order to create useful contrast and manage energy usage wisely.

2. Highlight features to reinforce a hierarchy of events and provide orientation for the user.

3. Arrange light sources in clear, understandable patterns to create optical guidance for wayfinding.

A comprehensive nighttime visual environment must provide safety, foster a sense of security, be convenient for performing tasks, and appear aesthetically pleasing. When it comes to choosing the source, it should have a high color-rendering index and a nice warm color somewhere in the 2700K range. And, remember the rule of “everything in moderation”! Providing low levels of well-considered lighting will reveal the environment to the user much more effectively than flooding an area with high levels of potentially glary light, and chances are we’ll all be healthier for it. We won’t be breathing air that is polluted by power plants used to produce electricity to power exterior lighting, and we won’t be subjected to luminous energy that disrupts our biological rhythms. A win-win situation for everyone!

Photo Credits: longhorndave (1), *melody* (2), kevindooley (3), Lam Partners Inc (4)

Integrated LED steplights create a processional approach to the plaza and reinforce the bridge’s architectural rhythm.

What happens when a heavily worn piece of an urban park gets a little well-deserved attention? And what role does lighting play in all of this?

Newly renovated Lake Plaza is the crown jewel in Houston’s popular Hermann Park. Run by the Hermann Park Conservancy, a non-profit citizens’ organization, in partnership with the City, this project has attained LEED certification through energy efficiency and sensitive restoration of landscape, as well as comprehensive site water management.

New train, new station, open for business.

A new main station for the park’s miniature train railroad, a gift shop, pedestrian bridge, pedal-boat rental, café, and service buildings all support recreation and rejuvenation in the heart of the city. While the plaza is used often during the day as a staging area for school groups attending the zoo, until the renovation, it had languished at night, despite the plaza’s proximity to the Miller Outdoor Theatre and its quarter of a million annual visitors.

The existing train pavilion prior to renovation.

Lighting guides and invites movement, making visual and architectural connections. Existing pathway lighting in Hermann Park relied upon historic “acorn” metal halide post-top lanterns. While well-designed historic lanterns can work well, many of the park’s fixtures had been installed in a piecemeal fashion, and they’d been over-lamped in a well-intended attempt to increase the sense of security. The layout of the lanterns did not provide the necessary visual connection from the Miller Theatre to the plaza, and existing lanterns in the plaza were overly bright, dominating the landscape (the eye always goes to the brightest thing in the line of view). It actually created the perception of less light because distracting glare constricted visitors’ pupils.

The gift shop by day: an airy structure that relates nicely with the wooded surroundings.

The design team chose to rework the plaza without the existing lanterns, and relocated them along the winding paths, where trees could mitigate their brightness, restoring the visual connection of the pathways to the rest of the park.

At night, the illuminated pavilions take on a different character and anchor the park’s destination points.

Illuminated, not by lanterns, but by the landscape and buildings surrounding it, the plaza beckons. Transformed at night into a composition of glowing pavilions, these structures create a welcoming destination and backdrop for evening strolls. Exactingly integrated compact fluorescent uplight sconces give the structures a fixtureless appearance, revealing finely crafted architectural details that are shaded during the day.

Tree uplights highlight rhythm and textures, while LED steplights reinforce the stepped form of the water’s edge.

Photo Credits: Overland Partners, except #3 by Lam Partners

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!

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!

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)

Custom House after lighting restoration

In the Fall of 2008, Boston’s oldest skyscraper was showing its age. Originally completed in 1849, the twenty-year-old façade lighting on the 1915 tower addition was in disrepair. The building maintenance budget could not keep up with the required frequency of re-lamping in such precarious locations, and only a few of the lights were still operating, as seen below.

Lighting in disrepair before restoration

Motivated by the lighting festival, IlluminaleBoston 08, and the promise of reduced building maintenance costs, the design team and building ownership endeavored to restore the landmark’s night image to prominence in the Boston skyline – but more than a few obstacles stood in our way, and chief among them were budget and time. Though planning for the event began in February 2008, design for the Custom House site did not begin until May. This left less than five months to complete the site analysis, design documentation, and installation. The majority of project funding would come from donations and sponsorship, so the budget was both modest and unpredictable.

To maximize the impact of the project, the team focused available resources on the top of the tower, which is visible all over the city. The main shaft of the tower, up through the 16th floor, was softly illuminated from below with ceramic metal halide floodlights to keep the tower grounded. Narrow-beam LED spotlights with clear lenses uplight the colonnade above from the sides of each column, spilling light onto the entablature above and revealing the granite dentils that confirm its precedent in classical architecture. Two additional fixtures highlight each corner to complete the tower’s form.

Custom House after completed renovation

Linear LED wall-grazers are concealed to wash the balcony-level façade below the clock, and adjustable LED spotlights extended on rotating outriggers light the sculpted eagles and highlight the corners of the clock tower. The outriggers swing over to the accessible balcony for maintenance.

The clock face retained its original lighting. A low pressure sodium lamp in each number provides an orange glow, and blue compact fluorescent backlights the minute marks. At the observation deck above, the columns are silhouetted with LED spotlights behind the base of each column to add depth to the façade and hide the fixtures from visitors’ view. Additional outriggers are located at the corners to accentuate entablature ornaments.

Lighting at the peak was restricted by FAA requirements, but LED floodlights with frosted lenses were concealed at the base of the crown to graze the towers’ cap and expose the pyramid of dormer windows. These fixtures are accessible from the windows at the base of the pyramid.

The completed project has successfully restored the Custom House Tower to its rightful place as one of the crown jewels of the Boston skyline, while drastically reducing the lighting energy consumption and maintenance costs. The building is expected to save 19,000 kWh annually, and to use only 30% of the energy consumed by the previous design over its expected 20-year lifespan.

Location: Boston, Massachusetts

Project size: 496 feet, overall height of tower

Project cost: $75,000 labor and installation / $160,000 donated lighting equipment

Photo Credits: Brad Koerner / Lam Partners Inc (1, 4, 5), Lam Partners (2), Brandon Miller (3)