When the great landscape architects, Frederick Law Olmstead and Cavert Vaux designed New York?EUR??,,????'???s Central Park in the 1870?EUR??,,????'???s, the issue of lighting never really arose. In that pre-electric era, the glories of such Park features as Bethesada Fountain and the Rambles were daylight vistas by force of nature. Only in 1910 did the dim glow of the early, crude incandescent lamps first pierce the gloom of night across the acreage of that world-class example of landscape architecture.

Nowadays, Central Park is lit by modern high-output lamps enclosed in classically beautiful luminaries which, though of recent design, are actually sophisticated recreations of the best park and street lighting of the era of the early days of electric light, the first dozen or so years of the turn of the twentieth century. Yet, evocative as they are of that bygone time, these modern lighting units are many times brighter and far more energy efficient than the crude incandescent lamps of that earlier era. The result is a park lighting system notable for its beauty, efficiency and durability.

The Central Park story illustrates an important insight, namely that contemporary landscape architects have available to them advantages that their colleagues of decades ago did not have. They can employ outdoor lighting specialists who are equipped with analytic methods and a fund of knowledge that enable them not only to bypass mistakes, but also to expand their range of landscape design versatility?EUR??,,????'??+both technically and aesthetically. The following paragraphs present aspects of the methods used by these specialists.

Defining Lighting Goals

The first question the specialist must answer is: what must the lighting accomplish? Is the goal primarily colorful special effects? Or is it the raising of the general light level across an entire area for general illumination or, perhaps, only as a matter of security? Each of these goals suggests a distinct direction in terms of hardware and placement.

The most usual goal is to produce an acceptably high ambient light level throughout the landscaped grounds of a park, garden, plaza, campus, housing development, office park, resort, hospital or other institutional facility or other outdoor environment. This class of assignment has several dimensions. For example, there may be limitations on trespass or spill light that is light that shines well beyond the site to be lighted and onto other adjacent properties. Glare both on and off the site to be lighted can also be a consideration.

The question of the appearance of the lighting equipment?EUR??,,????'??+the luminaires and the poles?EUR??,,????'??+in daylight raises issues of style, suitability, and architectural harmony. Yet another issue is whether the electrical wiring is to be installed entirely underground or in above-ground facilities.

Once all of these issues are decided, others arise. For example, what foot-candle level of light intensity is to be achieved. And, finally, what quality and color of light is required. Different types of lamps emit very different kinds of light.

All of these issues, among others, must be approached and solved by the lighting specialist in the course of designing a lighting system for a park or other landscaped site. Each will be dealt with briefly here.

Architectural Style

Fortunately there is a very wide variety of architectural styles of lighting fixtures from which to choose. From a simple lantern, derived from the ancient colonial village street lamp (or the hanging lantern of the stage coach) to the ornately sculptured Florentine pole that suspends a “bishop’s crook” luminaire, fixtures are now available representing many styles, periods, and aesthetic schools.

The luminaire used in New York’s Central Park, referred to above, is an unusual case. It was designed in 1982 by two architect designers, Gerald Allen and Kent Bloomer, for the Central Park Conservancy, a citizen’s group organized to maintain and improve the Park. Artistically, it was conceived as an aesthetic mate to the original cast iron posts still standing since their installation back in 1910. As such, it reflects the popularity of botanical sculptural bas-relief detailing that was immensely popular on buildings, park and street furniture, and even on interiors during the nineteenth century.

Other examples of such high-styled luminaires are to be found throughout the industry, as for example, luminaires that suggest the Art Deco styles of the 1920’s and 1930’s, or French Beaux Arts, or Munich Bauhaus, or the Italian Renaissance, or the Victorian or Georgian historical periods, among others. Recently the City of Indianapolis commissioned an original design luminaire for a new downtown multi-use landscaped project. That luminaire has unique lines best described as neo-art deco, lines that integrate well with a variety of settings.

Durability

Related closely to the design of the luminaire is the ruggedness of its construction. This obviously has a direct bearing on its durability, not only in terms of normal, expected service life, but also with regard to human depredation, or vandalism, a problem on every urban scene.

The best luminaires offer such construction features as structural parts made of cast or heavily dimensioned spun aluminum; a heavy cast base, deep within which are situated the electrical components, including ballast and wiring; and a lens or globe made of adequately thick, high grade, tempered glass or polycarbonate, the toughest plastic available today.

A good criterion for judging the durability of a luminaire is whether it meets the specifications of a major city. New York, for example, sets stringent requirements on the materials and construction and design of the luminaires permitted to be installed on its streets and parks, requiring them to meet certain performance standards in tests for electrical safety, resistance to weather, and assaults by vandals. Other large cities establish similar requirements.

Posts, Poles, and Standards

The posts and standards that support these luminaires are also available in a variety of styles that integrate well with the styles of the luminaires.

Modern aluminum alloy posts are strong, virtually immune to corrosion when properly pre-finished, therefore need no periodic painting or other maintenance, and compare very favorably in price, especially as against cast iron. The light weight of aluminum is another important factor. A post that weighs 80 pounds in aluminum weighs 500 pounds in cast iron. The consequent savings in shipping, handling, and installation labor time are correspondingly great.

Character of the Light

The most evident aspect of the character of the light transmitted to the immediate surroundings is the color of the light generated by the lamp installed inside the luminaire.

The days of the simple incandescent “bulb’’ or lamp for serious outdoor lighting are long gone?EUR??,,????'??+for some forty years now, at least. Though still utilized widely for indoor lighting, the incandescent lamp has long since been replaced by a class of lamp technically labeled high-intensity discharge, or HID. Nor does the fluorescent lamp, commonly used for indoor lighting, occupy any place of importance in outdoor lighting. Fluorescent lamps function badly at temperatures under 50 degrees F. And their very large dimensions, typically four to eight feet, make them prone to ready damage from natural and man-made causes in outdoor applications.

One of the oldest forms of HID lighting is the mercury vapor lamp. When introduced well before World War 11, mercury represented a major advance in energy efficiency and service life over the then widely used incandescent. Mercury vapor light is characterized, however, by a purplish cast that is hardly flattering to human complexions, though its high green content does tend to render visible foliage, trees, and flowers.

Currently the most efficient and long-lived HID lamp is the high-pressure sodium, or HPS, which, for its quality of light, offers the highest lumen (light intensity) level per watt of electrical power expended, as well as a service life of more than 24,000 hours. HPS lamps are popular for these reasons, but are often rejected for critical landscape lighting applications for another reason. People object to their ?EUR??,,????'??golden-white” colored light, which creates color shifts that distort our conceptions of what we think things should look like. The human complexion, especially lips and eyes, are color-shifted by HPS, as are foliage and flowers. For that reason, HPS is often used in less critical locales, settings where attention to aesthetics can give way to sheer utility without offending anyone.

(For the sake of completeness, we should also mention low-pressure sodium lamps, or LPS, which, though even higher in efficiency, are usually confined to such aesthetically innocuous applications as roadways and tunnels because their output is intensely monochromatic. They render everything within their reach as it would look in a black and yellow movie?EUR??,,????'??+not a very flattering rendition of anyone or anything, especially where the objective of the landscape architect is to create an uncompromisingly beautiful environment at night as well as by day.

Next in efficiency and service life is metal halide, which is favored over HPS in many landscape lighting circumstances because of its intensely “white” light, which is actually the presence of a broad spectrum of visible wave lengths of light. People, trees, walls, flowers, leaves, cars, sculpture, structures, all look about as we remember them from daylight when lighted by metal halide lamps. Because it meets this important “seeability” criterion, metal halide, as you would expect, was selected for installation in the Central Park luminaires mentioned earlier. And subsequent critiques and evaluations of the Park’s lighting system have borne out the wisdom of that choice.

Lighting Level

Among the answers provided by such a computer program are the recommended placement of fixtures, type and wattage, height above ground, and resulting footcandle levels to be expected. What is especially important is that these results are optimized to the site. Moreover, the program allows the specialist to test for further optimums simply varying one or more parameters at a time. And it enables him to anticipate, deal with, or eliminate potential problems such as dark spots, spill, or glare, in advance, well before anyone has made an investment in equipment, materials, or labor.

Controls

One of the main sources of energy conservation is careful control of lighting so as to confine it only to the hours of need. Clearly, manual switching is too haphazard, too subject to the memory or forgetfulness or conscientiousness of the people in charge of the lighted facility.

Time controls are probably the simplest means for minimizing waste of energy. They offer fairly sophisticated means, such as week-at-a-time programming, automatic adjustment for change with season of hours of dusk and dawn, and even spring-wound mechanisms or battery packs that maintain lighting schedules in the event of power failures.

Photocells built into the domes of post-top luminaires are another well-tested way to turn lighting on and off with automatic regularity. The more sophisticated of these devices now have a time-delay feature that prevents undue cycling when clouds obscure the sun.

A combination of luminaire-mounted photocells and scheduling and environmentally attuned controls often presents the most effective approach to the control of lighting systems. More and more, such controls are incorporated into the existing centralized building control systems that handle other functions as well, including lighting, HVAC, and security.

Affordability

One of the advantages of the contemporary computer approach to the design of lighting systems for landscaped sites is the precision with which the costs of every aspect of the installation can be developed in advance.

Such costs include design of the system; prices of lighting fixtures (luminaires and poles); costs of installation; costs of relamping, replacement of ballasts, cleaning of lamps and lenses, and other periodic maintenance; and a less tangible aspect, namely the cost of higher or lower foot-candle level. This last factor has a specific implication: though it may well be less in first cost to design in a lower level of illuminance, the cost of night patrols to sustain a higher degree of security in a more dimly lit area will nearly always exceed the cost of a higher level of light.

All told, illuminating your landscape need not be a cut-and-try attempt, not if you employ a qualified lighting specialist.