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The objective of light is to generally provide sufficient lighting that one can see well enough for a certain application, right? Of course, lighting can be used to enhance design and architectural features, wow folks with shows and awe such as in Las Vegas, light up cities for show as well as safety, or to provide safe lighting at parking lots. However, light also has taken away a precious commodity: seeing the vast and beautiful universe in which our planet resides.
If anyone has had the pleasure of visiting rural America, camping out in the Rocky Mountains, being able to see the glory of the universe is a sight to behold. The good news is that today the technology is getting so that proper lighting can be accomplished without totally inhibiting the night sky.
"The goal is not about no light, but the most sensible light," explains Peter Strasser, senior technical advisor, International Dark Sky Association, a non-for-profit group committed to achieving darker skies so we and the astronomers can see and appreciate the universe and local dark skies.
"Light that shines up is wasted. The purpose of street lighting or parking lot lighting, for instance, is to shine down where it's of greater use — not up," Strasser adds. "Why spend the money for lighting that is not effective?"
According to studies by the IDA, an estimated 30 percent of all U.S. outdoor lighting is wasted because it is directed skyward. A study conducted for the Building Design Leaders Collaborating on Carbon-Neutral Buildings by the U.S. Green Buildings Council (USGBC), the average LEED-certified building uses 32 percent less electricity and saves 350 metric tons of CO2 emissions annually. Strasser claims about $10 billion a year is wasted in lighting costs. Better and more efficient lighting can lower monetary losses while improving light.
Lighting technology
Technology is available that is dark-sky friendly. One is photometrically "full cutoff," in which less than 1 percent of the light from the fixture is directed towards the sky. Strasser says full cutoff luminaire lighting achieves the greatest lumens of light to the ground.
Another technology is flat glass lens assembly. Kim Lighting employs this technology, which restricts light in the uplight planes. It also achieves full cut-off designation.
Segmented optical systems is another. According to Architectural Area Lighting, these lights feature a die cast back-housing with segmented, high reflectance, aluminum mirrors in a precision optical system. It puts light where it's needed and minimizes light trespass, sky glow and other light pollution.
These technologies enable the opportunity to attain darker skies at night. But they provide other benefits too. "By directing all usable light downward to the pedestrian plane, versus a globe fixture where light is directed in all directions, the user can theoretically cut wattage in half. In addition, with optimized reflectors, the user is able to achieve the same performance with half the energy," notes MJ Paul, director of marketing, Kim Lighting, a division of Hubbell Lighting Inc.
"Non-uniform lighting is now the recommended form of lighting," Strasser adds.
Mark Lien, director, Lighting Solutions Center, Hubbell Lighting Inc., says lighting efficiency sometimes suffered when the full cutoff fixtures were mandated. If the distribution of light is narrow and focused only downward it can require additional fixtures to maintain acceptable uniformity ratios.
"If outdoor levels are not acceptably uniform our eyes cannot adapt quickly enough and this can cause safety and security issues. In some applications the additional fixtures needed to achieve acceptable uniformity use more electricity which wastes energy and contributes to the environmental issues stemming from power generation," Lien notes. He adds that focusing all of the light downward can reflect more light up, defeating the original intent.
"The increased design flexibility allowed by the new "BUG" rating addresses the total upward light on a project but allows the lighting designer to mix fixture types as long as they maintain skyglow control. This flexibility should allow for wider distribution fixtures to be used providing a balanced approach," Lien says.
"BUG" stands for Backlight, Uplight and Glare. The impetus behind BUG and upcoming legislation is to define an acceptable fixture performance standard when using dark sky jurisdictions.
Lien adds that exterior lighting can look brighter without using additional energy by using a "white" light source like metal halide rather than high pressure sodium which gives off a yellowish light. In very bright light, our eyes are most sensitive to the warm or yellow light sources but at low or night light levels our eyes perceive that cooler color temperatures like metal halide appear brighter.
He says empirical studies show the footcandle measurement of metal halide light often appears twice as bright as high pressure sodium at night. Research has shown that we have increased depth of field with the white light sources, which means that objects appear clearer at a distance that increases our perception of brightness.
On the horizon
IDA and other groups are pushing for legislation that will help attain dark skies. IDA and the Illuminating Engineering Society of North America Joint Task Force is developing a Model Lighting Ordinance (MLO) to address the need for strong, consistent outdoor lighting regulation.
The MLO seeks to attain:
- Recommendations based on light use.
- Light measured in phototopic lumens; corresponding wattages will be provided.
- Luminaires classified by high angle output and uplight through the Luminaire Classification System (LCS).
- Zones identified by five Lighting Zones (LZs), LZ-0 through LZ-4.
- Two lighting design methods to be recommended, which are:
- The prescriptive method to provide minimum requirements, based on allowed lumens per square foot, for each lighting zone; this method shall be intended for most lighting projects.
- The performance method should require compliance with a special review process, based on the LCS, for certain special applications; this method is intended for complex lighting projects.
- Limits on lighting installed for public benefit should not be imposed; however, communities should evaluate and improve their public lighting systems based on MLO recommendations.
author: By John Dyslin, editor - Electrical Contracting Products