In January, the Alliance for Solid-State Illumination Systems and Technologies (ASSIST) published a new volume in its ASSIST recommends series about parking lot lighting, a rapidly growing market for the LED lighting industry. The issue “Recommendations for Evaluating Parking Lot Luminaires,” describes a new metric for evaluating parking lot luminaires based upon how well they cater to the application’s requirements, rather than their luminous efficacy. The metric was developed through previous research by the LRC and builds upon the concept of application efficacy.
Now an online calculator is available based on ASSIST’s recommendation to estimate the performance of parking lot luminaires for all light source technologies. The calculator uses the luminaire's IES distribution file and other inputs to:
- Estimate how well a luminaire caters to the application’s need;
- Estimate and correct light levels based on visual sensitivity changes at nighttime light levels;
- Compare and identify the optimum luminaire for a specific parking lot application; and
- Estimate life-cycle cost of a parking lot luminaire.
ASSIST’s metric and the calculator incorporate existing standards for outdoor light levels and uniformity. While the calculator considers only one luminaire per pole, analyses show that the rank order for performance remains the same—regardless of the number of luminaires per pole—when comparing several products of the same distribution type.
“Manufacturers of LED-based outdoor luminaires often claim significant energy savings and life-cycle cost reductions compared to traditional luminaires; however, some of these LED systems are not realistically able to meet the requirements of good outdoor lighting,” says N. Narendran, Ph.D., director of research at the LRC, which organizes ASSIST. “ASSIST provides a method to evaluate and compare the performance of outdoor lighting systems before selection and installation, and now that method is available in an easy-to-use online calculator.”
The Parking Lot Luminaire Calculator and the January 2009 publication can be accessed from the ASSIST Web site.
Calculating System Application Efficacy
ASSIST's recommendation to determine the System Application Efficacy of luminaires for parking lot applications is based on the premise that luminaires should meet the target photometric criteria for parking lots with minimum energy usage.
The two main design criteria for parking lots are a minimum light level and a certain uniformity ratio. Because luminaires are designed to meet the needs of different parking lot geometries, manufacturers assign distribution types that describe the extent to which the luminaires are intended. Thus, the System Application Efficacy is based on a calculation area corresponding to the intended coverage for a given luminaire's distribution. The calculation method accounts for the light (in lumens) that falls inside this target area, but only if the illuminance and uniformity criteria are met.
More information on the evaluation method can be found in the recently published, “Recommendations for Evaluating Parking Lot Luminaires,” available for free download from the ASSIST Web site.