Tools to Evaluate Outdoor Lighting
A global movement is on to replace conventional outdoor lighting with LEDs. LEDs potentially can save energy and provide better “visual efficacy” than other light sources, such as high-pressure sodium, because their color properties can be selected to maximize the spectral sensitivity of the human visual system (typically “cooler” or bluish lighting).
Nevertheless, questions abound on how to choose the best outdoor lighting for streets, parking lots and other areas. Can LEDs meet standard lighting requirements and provide light levels and distribution similar to conventional outdoor lighting? Will they last as long or longer? Will they save energy? How does the life-cycle cost compare? Some LED systems are not realistically able to meet the requirements of good outdoor lighting, and no simple method has existed to evaluate and compare the performance of outdoor lighting systems before selection and installation.
This need led the LRC and ASSIST, beginning in 2009, to develop two tools for evaluating and selecting both LED and conventional outdoor luminaires: a new metric rooted in the concept of application efficacy and a free online calculator based on this metric. The metric, called Luminaire System Application Efficacy (LSAE), calculates efficacy by considering only the luminous flux reaching the application area (e.g., the parking lot ground) that has an illuminance level and uniformity falling within IES recommendations. Evaluation methods were developed for both parking lot luminaires and street and roadway luminaires.
Along with this metric, LRC researchers in 2009 developed an alternative method to evaluate the “visual efficacy” of outdoor lighting. The maximum spectral sensitivity of the human visual system and how the eye sees under mesopic conditions are considered in this system for choosing among commercially available light sources to deliver the same unified, rather than photopic, photometric quantity. This method integrates a new, unified system of photometry that more accurately characterizes different light sources at any light level, facilitating the specification of effective lighting systems for different applications, including those used outdoors at night.
The LRC, on behalf of ASSIST, also investigated in 2010 claims of “blue spectrum" outdoor lighting and its potential impact on the human circadian system. LRC researchers found the ability of outdoor lighting to stimulate the human circadian system under practical exposure scenarios to be limited.
In 2011, a calculation method for estimating discomfort glare from exterior lighting was published based on the existing De Boer (1967) discomfort glare rating scale and a published discomfort glare model.
In 2012, LRC research was conducted on whether improved illuminance uniformity in parking lots could be used to lower overall average light levels. The results were used to inform the ASSIST LSAE metric.
ASSIST recommends...Outdoor Lighting
ASSIST recommends...Parking Lot Lighting
ASSIST recommends...Street and Roadway Lighting
ASSIST recommends...Discomfort Glare from Exterior Lighting
Parking Lot Luminaire Online Calculator
Parking Lot Lighting with Improved Uniformity
Potential of Outdoor Lighting for Stimulating the Human Circadian System
Technical Reports and Publications
ASSIST. 2011. ASSIST recommends...A Method for Estimating Discomfort Glare from Exterior Lighting Systems. Vol. 9, Iss. 1. Troy, N.Y.: Lighting Research Center.
ASSIST. 2011. ASSIST recommends…Recommendations for Evaluating Street and Roadway Luminaires. Vol. 10, Iss. 1. Troy, N.Y.: Lighting Research Center
ASSIST. 2009, 2010. ASSIST recommends…Recommendations for Evaluating Parking Lot Luminaires. Vol. 7, Iss. 3. Troy, N.Y.: Lighting Research Center.
ASSIST. 2009. ASSIST recommends…Outdoor Lighting: A Short Guide to Applications, Objectives and Considerations. Vol. 6, Iss. 1. Troy, N.Y.: Lighting Research Center.
ASSIST. 2009. ASSIST recommends…Outdoor Lighting: Visual Efficacy. Vol. 6, Iss. 2. Troy, N.Y.: Lighting Research Center.
Narendran, N., J.P. Freyssinier, and Y. Zhu. In press. Energy and user acceptability benefits from improved illuminance uniformity of parking lot illumination. Lighting Research and Technology, first published on June 4, 2015 as doi:10.1177/1477153515587959.
Rea, M.S., A. Smith, A. Bierman, and M.G. Figueiro. 2010. The potential of outdoor lighting for stimulating the human circadian system. Report prepared for the Alliance for Solid-State Illumination Systems and Technologies.
Project Summary Sheets
Does outdoor lighting affect the human circadian system? (2010)
ASSIST recommends… Metric for Evaluating Outdoor Luminaires (2009)