Good sustainable design meets the needs of the present without compromising the needs of the future. It is no longer sufficient to simply comply with state and federal regulations; it is necessary for organizations, governments, and individuals to take environmental responsibility one step further.
Sustainability as it applies to a manufactured product has many facets. It is important to look for manufacturers whose products provide sustainable advantages in their use through the most efficient use of energy. The less energy consumed in the manufacturing process, the less the energy that must be generated through fossil fuel combustion or nuclear facilities.
The environmental impacts and suspected global warming caused by carbon emissions have escalated the need for more carbon-responsible business practices. As such, many organizations have taken the lead to reduce, and ultimately eliminate, their CO2 emissions.
To become carbon neutral, an organization must calculate its total climate-damaging carbon emissions, reduce them where possible, and balance the remaining emissions. This can be accomplished by using alternative energy sources and/or fuels, contributing to research funding in the field of energy, purchasing carbon credits to offset emissions, or investing in reforestation and the resulting carbon sequestration process.
The need for environmental responsibility has never been greater. According to the United States Green Building Council (USGBC),1 38 percent of all CO2 emissions in the United States are attributed to buildings, and over the next 25 years, CO2 emissions are projected to grow faster than any other sector, with emissions from commercial buildings projected to grow the fastest, at 1.8 percent a year through 2030. Building green is one of the best strategies for meeting the challenge of climate change because the technology to make substantial reductions in energy and CO2 emissions already exists.
Using efficient and effective lighting equipment can be the first step to reduce the total energy consumed, thus reducing greenhouse gas emissions.
Efficient, Effective Lighting
Energy efficiency is a simple matter of lumens of light out per watt of electricity in. Lumens per watt (LPW) can be compared to the EPA miles per gallon fuel-efficiency rating. LPW, or efficacy, is the rating given to the lamp or light source itself. Efficiency, on the other hand, applies to the entire system, lamp plus fixture. There are numerous energy-efficient lighting sources commercially available today, including metal halide, high-pressure sodium, compact fluorescent, induction, and LEDs, with efficacies in the 90-LPW range. The most recommended of these are the white light sources, such as metal halide, compact fluorescent, induction lamps, and LEDs with a balanced color spectrum.
Even the most efficient sources, however, can also be energy hogs if they distribute light to places where it is unnecessary or unwanted. The light produced must be "energy effective." Effectiveness relates to the luminaire's performance. Light that is disbursed in all angles creates light pollution, either as skyglow, which is light directed upward, or light trespass, which is light falling into unwanted spaces such as street or parking lot light falling into a bedroom. The International Dark-Sky Association (IDA) estimates that 30 percent of all outdoor lighting is directed skyward and is wasting $1.5 billion per 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.
Many lighting quality issues, such as glare, light pollution, and light trespass are related to where the light is directed and where it is minimized. For example, a billboard is more visible and easier to read when it's brightly lighted; however, most of the light is being directed upwards and being wasted. Another example would be a brightly lighted gas station. This may seem more open and attractive to customers, but if the light is spilling into the bedroom window of the neighbor's house next door and keeping them up at night, the wrong luminaire, or too many luminaires, were chosen for the project. Both of these situations could have been greatly improved by a more careful and thoughtful selection of luminaires.
Oftentimes, controlling the distribution of light may seem to reduce a luminaire's efficiency. Lenses, reflectors, and house side shields may reduce a lamp and ballast system's overall efficiency especially when compared to a bare lamp. For example, a bare acorn luminaire may have an efficiency of approximately 95 percent but a luminaire with a precision optical system may have an efficiency of only 77 percent. Is the loss in efficiency worthwhile? When you remember that roughly half of the acorn's light is directed skyward instead of to the application you want illuminated, it is clear that the effectiveness/performance more than offsets the apparent efficiency loss. Furthermore, acorn-style luminaires are extremely bright compared to the objects around them, making visibility at night difficult. Figure 1 demonstrates this phenomenon. Notice the difference in the "visibility" or clarity of nearby objects illuminated by the fixture on the left. Disability glare or "veiling luminance" (the contrast ratio between the brightness of the luminaire and surrounding objects) is greatly reduced.
A luminaire's energy effectiveness/performance should not be judged on its efficiency alone, or even the light source's efficacy. The best and most effective luminaires are those that deliver the light only where it is needed, and do so efficiently.
Getting the light to the surface where it's needed is more critical than selecting a luminaire with a higher percentage of total efficiency. For example, a decorative site light that has an efficiency of 95 percent — of which 25 percent of that light is emitted into the sky, contributing to light pollution — is neither energy effective nor a desirable product. A site light that is only 77 percent efficient but directs those lumens downward in the desired pattern is a better product.
Another key element for a luminaire to be effective is uniformity. Uniformity is the ratio between the minimum to maximum footcandle levels in the environment. Our eyes perceive the minimum and maximum levels, which is why a low minimum-to-maximum ratio is important. Good uniformity allows you to "see" better at night because your eyes are not constantly adjusting 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.
Choose luminaires that distribute light only where it is needed and wanted.
Site and Area Lighting
The changing needs of society have required architects and developers to expand services and develop all-inclusive locations to meet client demands. This results in a mixture of retail stores, office buildings, restaurants, apartments, and homes in close proximity.
Lighting solutions should address the lighting performance and aesthetic needs for such diverse environments. In addition, light trespass and light pollution issues should be addressed. In a mixed-use environment, it is imperative that appropriate directional elements are used to meet the lighting needs of retailers and wayfinding for shoppers while providing privacy and security for residential tenants and homeowners. Selecting the appropriate fixture to meet these goals becomes paramount.
Precision Optical Systems
When determining lighting performance elements, two things should be considered: distribution type and dark-sky-friendly options. 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.
High-performance optics are those that 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. As shown in Figure 2, the fixture on the left, without a precision optical system, has a significant amount of up light, as illustrated with the red, while the image on the right, with a precision optical system, has no up light, meaning it is the most energy efficient. This is energy-effective use of lighting equipment.
Typical distribution types for site and area lighting include type II, type III, type IV, and type V. The term "distribution type" refers to the pattern of light emitted from the luminaire. Figure 3 provides an illustration of the four distribution patterns.
Type II distribution is ideal for long and narrow pathways and should be placed near the pathway at approximately 1.75 mounting heights in width.2
Type III distribution is perfect for roadway applications, is one of the most requested distribution patterns, and should be placed near the side of the location, approximately 2.75 mounting heights in width.3
Type IV distribution is perfect for wall mountings as they have a distinctive forward throw. Ideally, the luminaires should be used near the side of the area with more than 2.75 mounting heights in width.4
Type V distribution is used primarily for general-area lighting applications. Along with Type III, Type V distribution is one of the most requested patterns. Type V distribution produces a circular distribution and should be located near the center of the intended area. The candlepower is distributed somewhat evenly at all lateral angles.5
The International Dark-Sky Association (IDA) "works collaboratively worldwide — with the public, industry, and government — to halt the adverse environmental impact of light pollution on the nighttime environment by educating everyone about the value and effectiveness of quality nighttime lighting, conducting research, and engaging in outreach activities." (See www.darksky.org.)
To accomplish this goal, IDA has developed a set of guidelines that classify various levels of cutoff for outdoor luminaires.
The most common classifications used when determining light trespass or light pollution potential are as follows:
- A non-cutoff luminaire distributes light in any direction or may be completely uncontrolled.6
- A semi-cutoff luminaire provides some optical control but still distributes a considerable amount of light above the horizontal. For this classification, the light emitted does not exceed 5 percent at or above an angle of 90 degrees above nadir (the starting point of a radius of degrees in a vertical rotation around a fixture).7
- A cutoff luminaire sends most of its light below the horizontal but could still have high-angle light that could cause glare. It has a light distribution in which light emitted does not exceed 2.5 percent at or above an angle of 90 degrees above nadir.8
- A full cutoff luminaire guarantees that its light is emitted below the horizontal. 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 above an angle of 90 degrees above nadir.9
Site and area luminaires that feature high-performance optics effectively light walking areas without excessive glare and present minimal adverse environmental effects, according to IDA.
To define "photometric," we must look at the individual components. "Photo" means light while "metric" means measurement. Therefore, photometric data describes the direction and intensity of light that is emitted by a luminaire (the light distribution). This information is the basis for the evaluation of the luminaire performance.
When using photometric reports, it is always best to use those that are either from an independent laboratory or a laboratory that is accredited by the National Voluntary Laboratory Accreditation Program (NVLAP), which is administered by the National Institute of Standards and Technology (NIST). It is also important to look for photometric reports that have been run from 0 to 180 degrees and not just from 0 to 90 degrees.
Typical photometric reports will provide a description of the luminaire, including the manufacturer's catalog number and the lamp type and ballast used in the testing. From the photometric reports, oftentimes manufacturers will create isofootcandle templates, providing architects and designers a tool to help them specify the most appropriate fixtures for their application. An example is shown in Figure 4.
The values listed in the isofootcandle templates are based on a single pole location at various mounting heights and wattages. The curve shown is at a 1.00 value and is based on the wattage/mounting height combination for that particular curve. These templates are scalable, as conversion factors are provided for other wattages and mounting heights. Figure 4 is based on a 150-watt metal halide at 14 feet. These templates are a powerful tool and can easily be used for comparing various luminaires.
Protecting the environment is everyone's responsibility. 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 can ensure the style, quality, and energy efficiency of the site lighting.
Kathy Greene (firstname.lastname@example.org) is the marketing manager for Architectural Area Lighting and has been in marketing management for more than 10 years.REFERENCES:
IES Lighting Handbook, 8th Edition
- IES Lighting Handbook, 8th Edition
- IES Lighting Handbook, 8th Edition
IES Lighting Handbook, 8th Edition
- www.lrc.rpi.edu - Glossary | Light Pollution | Lighting Answers