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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.


Basic Considerations


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:

  • Intensity of the lighting: how bright is the light?

  • Uniformity of lighting: how consistent is the light level from place to place throughout the lighted area?


  • Color of lighting: how accurately does the lighting render colors?


  • Efficiency of lighting: how much light per watt of electricity does the lighting system deliver?


  • Lamp life: How long do lamps last before they must be replaced?


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:


Mercury Vapor

Commonly used at facilities constructed in the 60's and 70's. Poor color rendition; gives off a blue-green light. Excellent lamp life, although light levels diminish significantly as lamp ages. Least efficient of all types of lamps in terms of energy usage.


Low Pressure Sodium

Poor color-rendition; gives off orange-yellow light. Relatively short lamp life, but with little light level depreciation as lamp ages. Most efficient type of lamp in terms of energy usage.


High Pressure Sodium

Most commonly used type of lamp in 80's and 90's. Poor color rendition; gives off a yellow-amber light. Longest lamp life with minimal reduction in light level as lamp ages. Very efficient in terms of energy usage.


Metal Halide

Excellent color rendition; gives off nearly a white light. Moderate lamp life. More efficient than mercury vapor but less efficient than low pressure sodium or high pressure sodium in terms of energy usage.

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 $250 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:

  • If your facility is presently using either mercury vapor or low pressure sodium lamps, you should consider replacing them with either high pressure sodium or metal halide lamps. In many circumstances, the costs of replacing these older lamps can be regained quickly through ongoing savings in lamp replacement or reduced energy costs.

  • The metal halide lamp is the best lamp to use for security purposes. This is because the metal halide produces a nearly white light that allows colors to be clearly distinguished, making it easier to correctly identify people and vehicles. The white light produced by the metal halide appears more natural and, in our opinion, has more of a deterrent effect than lighting produced by other types of lamps.


  • Outdoor lighting plays a crucial role in how well closed-circuit television (CCTV) systems will work in the outdoor environment. While most modern CCTV cameras will work at relatively low light levels, uniformity of lighting is extremely important. If the lighting uniformity ratio is too high (greater than 5:1), then the image viewed by the camera will be of poor quality, having both "hot spots" (bright areas of glare) and "cool spots"(areas of darkness where details cannot be seen). If color cameras are used outdoors, then the color of the lighting is also important. Using a lamp other than the metal halide type may cause colors seen by the camera to appear incorrectly.


  • The type of light fixture/luminare used largely determines how the light from each fixture will be distributed. Many older types of luminares used for parking lot lighting are very inefficient, projecting much of their light horizontally and upward rather than downwards towards the surface of the parking lot. Replacing luminares with a more modern type or adding a "skycap"(light shield) to existing fixtures can greatly improve light levels and fixture efficiency.


  • Many cities and towns have enacted ordinances concerning "light pollution". These ordinances often set limits on the amount and type of light that can be used for outdoor parking lot lighting. Be sure to consult the authorities having jurisdiction in your area before making any changes in your lighting system.


  • Outdoor lighting fixtures require regular maintenance. Lamps tend to produce less light as they age. Replace lamps at scheduled intervals - not just when they burn out. Dirty light fixtures also produce less light. Arrange to have fixtures cleaned both inside and outside on a regular basis.


  • The growth of trees and other types of landscaping can have a significant effect on outdoor lighting. Often times, a well-designed lighting system becomes ineffective as trees grow to a point where they block out large portions of the light. Arrange to have trees and landscaping regularly trimmed so that the lighting system is not adversely effected.


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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