Lighting for Safety and Security
LED capabilities require adjusted lighting calculations and design
LED light fixtures have the capacity to achieve very wide light distribution, which makes it easy to meet Illuminating Engineering Society North America (IESNA) guidelines – in Publication RP-20-98, “Lighting for Parking Facilities” – for a minimum illuminance of 1-footcandle anywhere on the floor. However, the average illuminance can be as low as 2- to 3-footcandles.
Previous editions of RP-20 (1985) recommended an average illuminance of 5-footcandles or greater on the floor. While the eye does not see average illuminance, it is a gauge as to the brightness of the space, as well as making patrons feel more comfortable and secure. IESNA Publication G-1-03, “Guideline for Security Lighting for People, Property and Public Spaces,” recommends an average illuminance of 6-footcandles or greater “where security is a concern.”
The issue as to “where security is a concern” is subject to wide speculation and varied interpretations. The proper approach to this determination is to evaluate the incidents of criminal activity in the vicinity of the parking facility project.
One such service is CAP Index (www.capindex.com), which provides a report of various types of criminal activity within a 1- to 6-mile radius of the site and compares the local level of criminal activity to county, state and national averages for those types of incidents. Its database includes crime statistics per census track reported for homicide, rape, robbery, aggravated assault, burglary, larceny and motor vehicle theft. If the level of criminal activity exceeds the national average, then security is a concern.
It’s my experience that just about any medium-sized metropolitan area or larger will exhibit criminal activity that exceeds the national average.
Since parking structures are not common in smaller cities and rural areas, virtually any parking structure will have a security concern, particularly if it is open 24/7. Therefore, virtually all parking structure lighting systems should meet an average of 6-footcandles or more on the covered levels and an average of 3-footcandles or more on the roof level, as required by IESNA Publication G-1-03.
Another concern is the proper evaluation of the “lumen depreciation factor” used in the lighting calculation. All light sources lose light output with age. Traditional lamps such as high-pressure-sodium, metal-halide and fluorescent will eventually burn out and need to be replaced. The lumen depreciation immediately before the end of rated life is then used in the lighting calculation. However, LED chips do not burn out.
The industry standard for LED light sources is to use a rated life at the point in time when the light output is at 70% of the initial output. The rated life can be 100,000 hours or more. Owners should periodically measure the illuminance directly under the LED fixture and replace the LED module when the light output depreciates to 70% of initial output.
There are many instances where LED light fixture representatives are using higher lumen depreciation factors. This practice requires replacing the LED module when the light output depreciates to the lumen deprecation factor used in the calculation, which will be much less than the rated life of the LED fixture.
Maintenance costs will be much higher in that instance, or owners will be at risk for damages in the event of a personal injury lawsuit that alleges poor lighting was a contributing factor and the illuminance falls below lighting industry standards due to lack of maintenance.
LED light fixtures are extremely energy efficient and have significant benefits in terms of low maintenance and good lighting uniformity. However, owners need to be sure the lighting calculations and lighting design are performed properly and meet current parking facility lighting industry standards for safety and security.
Don Monahan. P.E., is a Vice President at Walker Parking Consultants. Contact him at firstname.lastname@example.org