Objects illuminated by the fixture on the left are clearer and more visible than those illuminated by the fixture on the right. Contrast is greatly reduced. Photos: Architectural Area Lighting
As climate changes continue, using efficient and effective lighting equipment can be the first step to reduce total energy consumed, thus reducing greenhouse gas emissions.
Energy efficacy, the ratio of how much light is produced per the amount of wattage, is simply lumens of light out per watt of electricity in. Lumens per watt (LPW) can be compared to the EPA mpg fuel-efficiency rating. LPW is the rating given to the lamp or light source itself.
Efficiency, on the other hand, applies to the entire system. Numerous energy-efficient sources are available commercially today, including metal halide, high-pressure sodium, compact fluorescent, induction, and LEDs, with source efficacies in the 90 LPW range. The most recommended are the white light sources, such as metal halide, compact fluorescent, induction lamp systems, and LEDs with a balanced color spectrum. Even the most efficient sources, however, can be energy hogs if they distribute the light to where it is unneeded or unwanted. The light produced must also be energy effective.
Effectiveness relates to the luminaires' performance. Light disbursed at all angles creates light pollution, either as skyglow (light directed upward) or light trespass (light falling into unwanted space), for example, street or parking lot light falling into a bedroom. The International Dark Sky Association (IDA) estimates that 30% of all outdoor lighting is directed skyward and wasting $1.5 billion/year in the United States alone. Effective lighting design means putting light where it is wanted and needed and eliminating light where it is not wanted or needed.SAFETY AND AMBIENCE
Effective lighting is critical when it comes to illuminating a park setting. Parks are an important asset for any city by providing an escape from the grind of day-to-day living and can provide a place for social gathering as well as individual reflection. As such, the lighting within parks must provide not only safety and security for visitors, but also an appropriate atmosphere.
Determining appropriate light levels for parks within urban areas can be challenging. It is important that the lighting not overwhelm the natural environment, but it must be bright enough to avoid giving the appearance of an unsafe or undesirable location. Lighting for pathways should be uniform and provide even illumination.
Uniformity is the ratio between the minimum and maximum foot-candle levels in the environment. Since our eyes perceive the minimum-maximum levels, a low ratio is important. Uniformity allows better sight at night because your eyes do not have to adjust constantly between bright and dimly illuminated areas.
Those luminaires with focused optical systems allow you to precisely aim the light, resulting in smooth, even illumination of the environment. The uneven pools of light common with other fixtures are eliminated. Objects in the environment are easier to identify because the perceived lighting level between the fixtures does not vary.
Another consideration for parks is the sustainability of the luminaire itself. Those luminaires that feature vandal-resistant hardware and options such as rock guards will help prolong the life of the product. Proper mounting heights also should be considered. The luminaire must be at a level that provides easy access for maintenance but is out of the reach of vandals. A recommended mounting height is about 14 feet. Other products would include inground landscape lighting as well as pathway bollards. Both provide lighting at a lower level, providing safe and easy passage through the park at night.LIGHT POLLUTION
Finally, it is important to consider the night sky when choosing lighting for parks. A luminaire's cutoff classification describes the control of vertical light distribution above maximum intensity. The higher the angle of light, the greater the chance of disability and discomfort glare as well as night-sky light pollution.
The IDA has four classifications for determining the potential for light trespass and light pollution: non-cutoff, semi-cutoff, cutoff, and full cutoff. This type of distribution helps to minimize light trespass and pollution and may reduce glare. To be classified as full cutoff, zero-emitted light occurs at or greater than an angle of 90 degrees above nadir (opposite the zenith and directly below the observer). This is usually the most desirable for a park setting, however, local codes and lighting zoning ordinances should be consulted before deciding on any luminaire.
High-performance optics feature segmented, high-reflectance, aluminum mirrors that put light where it is needed and minimize light trespass, sky glow, and other forms of light pollution. These optical systems are engineered for highly controlled, and thereby effective, light distribution. Site and area luminaires that feature high-performance optics effectively light walking areas without excessive glare and present minimal adverse environmental effects.
Making the right lighting choices is one step that we all can take to ensure a greener planet in the future. Lighting specifications for luminaires should be carefully written to avoid the substitution of inferior products that might sacrifice energy savings. A good specification will ensure the style, quality, and energy-efficiency of the site lighting.
— Greene is the marketing manager for Architectural Area Lighting.