Illuminating Engineering Society of North America (IESNA) - Light Levels

Acknowledgement and appreciation go to Lithonia Lighting Company, manufacturers of Holophaneä systems for much of the following taken from their "INDUSTRY UPDATE," entitled Some "Myths" about Outdoor Lighting; also to Walter O. Mauldin, Director of University Security, University of Rochester for providing considerable insight into campus lighting. Information from other sources is also credited.

Effective outdoor lighting requires careful consideration of a variety of issues. Some of the primary considerations that are evaluated during the design process include:

• Providing good visibility
• Choosing luminaires that address the aesthetic needs of the application
• Controlling light emitted into the night sky that can cause sky glow or light pollution
• Creating a safe a secure area
• Reducing discomfort and disability glare
• Minimizing light trespass onto adjacent properties
• Selecting an energy effective system maintaining the institution

In many applications the desire is for a luminaire with the aesthetic characteristics that complement the area. There are a variety of decorative products that significantly reduce the upcasted light and flux at high angles as compared to older luminaire designs. Optically designed refractors and translucent decorative shielding can also provide a good alternative to smooth transparent enclosures.

The challenge for outdoor lighting design is understanding the interaction of these variables and determining the appropriate balance among them. For example, designing a system that reduces sky glow may compromise the safety and security of the campus if not properly designed.

A key element of the lighting design is selecting the proper luminaire for the application. In the past, there have been some common beliefs that are not as reliable as they once were because of new technology in luminaire optics and lighting research.

Sky glow is created by light directed into the sky. Full cutoff luminaires do not emit any light above 90 degrees and are often a very good choice in areas where sky glow is a concern. However, in some applications, if the pole height does not allow for a reasonable spread of light, the result might be bright spots near the pole and dark areas in between or at the perimeter of the campus. The bright areas reflect light into the sky and contribute to sky glow. In addition, non-uniform lighting levels can cause visibility problems as one drives through a given area forcing the vehicle operator's eyes to adapt to different light levels. Some solutions are to:

• Select the pole height and lamp wattage that maximizes the distribution of light from the luminaire
• Design the lighting layout so that it provides good visibility for horizontal surfaces (ground, sidewalk, etc.) and vertical surfaces (cars, building facades, people)
• Utilize a luminaire that minimizes uplight

According to Walter O. Mauldin, Director of University security, the University of Rochester (NY), "as a simple rule of thumb, two 250 watt HPS fixtures on a 28 ft. pole should be spaced about 60 ft. apart to achieve the desired target. The height of the pole can affect readings. Another approach is to place pole bases at twice the length intervals of the pole height. So, a 25 ft light on a pole would be spaced about 50 ft apart from the next pole." As Walter states, "no rocket science but a good thumbnail estimate." He advises that if tall poles are a design requirement, it may be better to select a luminaire with a small amount of upcasted light in order to avoid reflected light into the sky and improve visibility, safety, and security.

According to Lithonia Lighting, the amount of light required for an outdoor area should be based on a variety of design criteria. Adding more luminaires or increasing the wattage of the lamps to be used may increase glare or reduce uniformity. One reason owners of retail applications may want their property brighter than adjacent properties is to make individuals feel safe. However, when someone leaves a bright mini-mart/gas station such as the one on the corner of University Boulevard and Reservoir Street and drives onto a dark highway, the adaptation time required for their eyes to adjust to significantly lower light levels may create a momentary unsafe driving situation.

The Illuminating Engineering Society of North America (IESNA) has published recommendations for a variety of sites (IESNA Handbook). It is a very useful source for determining the proper illuminance level for a given outdoor application, including parking lots. The range for parking lots is one to five foot candles. However, that does not tell the whole story.

Again Walter Mauldin, "Lights lose approximately 30% of their luminance during the course of their service life. Secondly, the collection of dust and bugs in the light housing can affect the effectiveness of fixtures, particularly if there is not a regular preventive maintenance schedule. Also, the 1 to 5 foot candle (fc) range is intended to suggest choices that take into account surrounding terrain and structures. Vertical structures (trees, building walls, etc.) of dark color may absorb light. The fixtures should not cause what is sometimes referred to as 'horizontal plane glare.' One way to tell is when one can see the lamp appears similar to mis-aligned vehicle headlights."

"There should not be a variance of more than 4:1 between the brightest spot and the least illuminated spot nearby. This is referred to as the "differential". A greater disparity creates visual hot spots and is counter-productive in assisting patrons to readily observe conditions."

"What form of measurement is recommended? The traditional method uses the foot candle reading from a point one foot (1 ft.) above the horizontal surface (i.e. paving). However, many practitioners view a measurement at about 28-30 inches (waist high) to be more critical, as that's where most people perform more precise movements with keys and so on. On a vertical surface, such as a parking or building wall, the measurement is taken at six feet above the floor."

"Two to three foot candles is within the target design parameters for parking lot lights. If the photometry projections from engineers suggest that a particular area might be, say 1.7 fc, do not be concerned as long as the general areas nearby are in the 2 to 3 fc range and there are no light differentials projected at more than a 4:1 ratio."

"High pressure sodium (HPS) or metal halide lights are recommended for parking lots. Both are energy efficient and have a very long service life, HPS being the most efficient. Most people prefer metal halide due to the more natural color rendition. It too is energy efficient, but its service life is about half that of HPS. However, that is seen by some to be offset by the use of a pure white light (for truer color renditions). The HPS light gives a slightly muted (orange) look to all colors, and can play tricks on discerning image colors accurately."

Mauldin continues, "If that is the problem, one route is to go with HPS lights for parking lots, metal halide for campus walkways and for entrances to buildings. This is one way to better designate such routes or destinations - and - it also gives us a truer lighting picture in situations where close contact w/other persons may often occur. Walkway poles should be 15 to 20 feet tall. Use of 70 watt to around 150 watt bulbs is recommended, depending on the type of fixture and local conditions."

Again Lithonia Lighting, "Various studies show that at low light levels the human eye is more sensitive to blue-green light than yellow or orange. In fact, one study shows that high Pressure Sodium (HPS) requires four times more lumens to produce the same reaction time as Metal Halide on well-lit highways. Low Pressure Sodium (LPS) requires five times more lumens for the equivalent reaction time. For roadways that have lower illuminance levels, these rations increase significantly. Therefore, HPS and LPS are not as efficacious when considering visibility of tasks. Furthermore, energy is a function of power (watts) and time."

If the luminaires are incorporated with time of day controls, they can be dimmed or switched off late at night and various times of the campus year when activity levels within a given area are very low. The energy savings achieved by incorporating lighting controls can be much more effective in saving energy than the selection of the light source. Again, HPS and LPS will compromise accurate color identification. Some effective design techniques for outdoor lighting include:

• Use full cutoff luminaires on appropriate height pole to reduce sky glow. Insure the design results in good uniformity to improve visibility of horizontal and vertical tasks and minimize reflected light into the sky. Avoid tilting cutoff luminaires whenever possible.
• Confine light within the borders of the campus to avoid complaints from neighboring communities. Type IV (forward throw) reflectors can be used at the edge of campus to minimize the spill of light behind the pole into adjacent residential areas.
• Use IESNA illuminance recommendations to determine appropriate lighting levels.
• Consider the use of lighting controls. Control systems enhance the flexibility of the design by providing the right amount of light at the right time. Turning lights off in non-critical areas will eliminate nuisance light on adjacent residential areas at night. Controls can adjust lighting levels based on the level of activity at different times during the evening and can result in significant energy savings.

If using CCTV cameras to watch a number of parking areas and walkways, most modern systems can be set to adjust for color correction for morning, midday, late afternoon and night lighting conditions. In summary, it involves the camera focusing on a large white placard (poster board) then having a trained and knowledgeable technician/operator make adjustments until the monitor image of the placard appears as close to "white" as the actual sample. Some systems make these adjustments automatically, but one can fine-tune them if needed for individual situations (like cameras that catch light from the setting sun or nearby light poles at night).

New optical techniques have resulted in improved luminaire performance that can incorporate internal or external shields to minimize glare and up casted light. Cutoff wall-paks are very effective in providing light for walkways adjacent to buildings while minimizing "uplight." Floodlights are often used to light large areas where pole locations are limited. With the proper application analysis, floodlights can be tilted without creating glare. Internal or external shields are used to minimize light trespass onto neighboring properties.

Mauldin picks up here, "In 1997 the International Association of Campus Law Enforcement Administrators (IACLEA) issued recommended crime prevention guidelines. The lighting section proposed a minimum of five foot candles - for some of the reasons cited above. Many practitioners objected to that target, arguing that the substantial increased cost for installations would not be justified by the potential increased luminance. Five fc minimum may be TOO HIGH. In fact, when one projects costs out for a few projects with this target lighting level and estimates may nearly double."

"The one to five fc range, with a desired target of two to three foot candles average lighting are the acceptable parameters. Some "midpoint" between two poles, or a point to the side might be around 1.7 fc. That is acceptable, but the campus lighting engineer should not let it slip down to below 1.3 fc. A corner, particularly if its near a bush or building or other light absorbing site, might be a place for a little higher light level. Defining the perimeter well is consistent with a technique often referred to as "taking away the night". If one can see what's at the periphery of the campus area, a more reassuring sense of what's out there, or what is between that peripheral area and one's own location, is assured."

Livonia: "Effective outdoor lighting is rarely the lowest cost solution. By understanding the interaction of various design criteria, plant engineers and public safety officials can work with campus constituencies to educate them on issues critical to the design. Operating costs, including energy and maintenance are also a critical element to the cost evaluation."

There are a number of resources available to assist one with outdoor lighting needs. The Illuminating Engineering Society of North America (IESNA) publishes outdoor lighting design information in their Handbook as well as a number of application Recommended Practices (RPs) for exterior environments, parking facilities, roadway, and sports lighting. More information about IESNA is available at...

The National Electrical Manufacturers Association (NEMA) has published a white paper on outdoor lighting code issues at...

Credit should go to:

• David A. Mars, James Madison University Electrical Engineer, for providing much of this information through pertinent literature. Mr. Mars can be contacted by...
  Voice Telephone (540)568-6580
  FAX (540)568-6026
  E-Mail:marsda@jmu.edu
  
  
• Illuminating Engineering Society of North America, "The IESNA Handbook - Ninth Edition"
  
  
• "Road Scholar" by Ian Lewin - LD+A, March 1999, concerns level of lumens and the ratio to reaction time by vehicle operators on the highway
  
  
• "Roadway Lighting Designs for Optimization of UPD, STV and Uplight" by D. Keith - Journal of the Illuminating Engineering Society, Summer 2000
  
  
• Walter O. Mauldin, Director of University Security, University of Rochester for providing much of this recommended information. For close to twenty years he has recommended over $1 million in lighting enhancements for buildings and lots on Rochester's campus. Members of his staff are graduates of National Crime Prevention Institute (NCPI). One has taught CPTED courses there. Walter and that staff member teach the New York State Crime Prevention Course section on security lighting when it is held in the Rochester area. Mr. Mauldin can be contacted by...
  Voice Telephone (716)275-3340
  Fax (716)275-0334
  E-Mail:walter@security.rochester.edu