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Evaluating Your Parking Lot Lighting
If your facility was constructed more than ten years ago, chances are good that your outdoor security lighting is inadequate. For many years, lighting in parking lots and other outdoor areas was a low priority for lighting designers. In many cases, the purpose of outdoor lighting was to enhance the architectural appearance of the facility rather than to provide lighting for safety and security.
It is recommended that every security manager conduct an evaluation of the exterior lighting at the facilities for which he or she is responsible. The adequacy of outdoor lighting is an important factor in maintaining good security in parking lots and other outdoor areas. The inadequacy of exterior lighting has been the basis of many lawsuits alleging that the facility owner was negligent in providing a proper level of security.
The design of lighting systems is a highly technical science that can take years of training to learn. While it is unlikely that most security managers will ever become lighting experts, there are a few fundamentals of lighting design that are important for every security manager to know. Knowing these fundamentals will allow the security manager to accurately assess the lighting system in use at his or her facility
There are five basic considerations when evaluating a lighting system:
Conducting A Lighting Survey
The first step in evaluating an existing lighting system is to determine the types of lamps that are presently being used. Determining this will answer many questions concerning the lighting system. There are five types of lamps commonly used in outdoor parking lot lighting systems:
The types of lamps being used at your facility can usually be determined by asking the maintenance person or the lighting contractor that services your lighting system.
The second step in evaluating an existing lighting system is to survey the area being illuminated to determine the light levels present. Light levels are measured in foot candles (fc), or its metric equivalent, the lux (lx).
To measure light levels accurately requires the use of a light-level meter. A suitable light level meter will have a range of at least .1 fc to 25 fc. Light level meters can be purchased relatively inexpensively (for less than $500 US) or borrowed. (Please note that most light level meters designed for photographic use are usually not suitable for lighting system evaluation - they give inaccurate readings at the lower light levels.)
Before beginning the light level survey, obtain or draw an accurate map of the area being surveyed. For ease of use, the map should be drawn at a standard architectural or engineering scale. If not already shown on the map, draw in the locations of all existing light poles and fixtures and any other significant features in the area.
Begin the lighting survey at one end of the area. Hold the light meter in front of you and be sure that it is not being blocked by any part of your body. Take the reading and write it down on the place on the map that indicates where you are standing. Continue to take readings at approximately ten to twenty foot intervals throughout the entire area that you are surveying. Also, be sure to take readings at all pathways and walkways that lead between the surveyed area and adjacent building entrances.
Evaluating Your Results
There is much debate as to what constitutes "adequate" lighting in a parking lot or other outdoor area. Published standards show that acceptable light levels in parking lots can range from a minimum of .5 fc (in low activity areas) to a high of 5 fc (for high activity areas where pedestrian security is a concern.)
For parking lot areas, Silva Consultants recommends an absolute minimum light level of 1 fc throughout the entire area, with 2 to 4 fc being more desirable.
Equally important is the uniformity of lighting throughout the area. Uniformity of lighting is expressed as a ratio between the lowest light level reading and the average light level reading taken throughout the area. For example, if the average light level reading that you took was 5 fc, and the lowest light level reading that you took was 1 fc, the uniformity ratio would be 5:1. Silva Consultants recommends a maximum uniformity ratio of 3:1 for most outdoor parking lot applications.
Many parking lots that we have surveyed fall far short of the recommended light level standards. Average light levels of .3 fc or less are not uncommon at many parking facilities. More significantly, the uniformity of lighting found in many parking lots is very poor.
It is not uncommon to see uniformity ratios as high as 200:1! Typically, high light levels (20 to 30 fc) will be found directly under light fixtures. As you walk way from the light fixture light levels diminish, and at the midpoint between fixtures, it is not uncommon to see light levels of .1 fc or less. This lack of uniformity is usually caused by light fixtures that are spaced too far apart. The situation is complicated when trees or other types of landscaping are located between light fixtures.
Making Lighting Improvements
If your survey revealed inadequate light levels or lack of uniformity in light levels, you should consider making improvements in your parking lot lighting. Silva Consultants recommends that you contact a qualified lighting engineer to assist you in determining which specific improvements should be made.
Here are a few additional things to consider:
Have additional questions about parking lot lighting? Please contact us.
Also see related article: Use of LED Lighting for Security Purposes
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