How can lighting designers make sure they achieve the results they want when they try to reduce the light pollution affecting local communities, towns and villages?
The Lighting Research Center (LRC) reports that, although one would expect that limiting outdoor luminaires or choosing suitable ones would have a positive effect in this direction, quantitative analyses indicate that the result is not significant.
To “heal” this gap, the LRC, working with a group of outdoor lighting manufacturers from North America and Europe, has developed the so-called “Outdoor Site (Lighting) Performance” (OSP) metric, a model for quantifying the light pollution caused by outdoor lighting equipment.
The manufacturers working with the LRC on OSP are Acuity Brands, Lumec, R-Tech/Schreder and Philips.
The OSP model is the first comprehensive, quantified system for calculating light pollution. It rests on the logical premise that site owners should be able to meet the goals of their design while also complying with any light pollution regulations that may exist in their local communities (we are referring to America here; in Greece, such regulations probably do not yet exist).
The OSP model uses a calculation framework based on the property “boundaries” and the surface under study. According to the LRC, using property lines is considered the most logical approach, as it provides a “natural” separation between private land and public spaces.
As a calculation framework, OSP uses calculation surfaces that can be created in any commercial lighting software capable of calculating light reflections. Specifically, OSP calculates the light that “crosses” the surfaces under examination in every direction and provides practical information on the characteristics of the light emanating from each property.
The OSP model takes the following 3 factors into account:
• Glow, that is, the average luminous flux across the whole calculation grid of the area under examination, which is taken as an indication of the potential to cause skyglow
• Trespass, that is, the maximum luminous flux observed on any vertical calculation surface, which indicates the potential to “disturb” neighbouring properties
• Glare, the degree to which the luminous flux of the luminaires becomes bothersome to observers.
By using real lighting equipment, OSP provides a realistic and accurate basis for developing limits on glow and trespass (as defined above). In addition, the LRC carried out experiments indoors and outdoors to develop reasonable criteria for limiting discomfort glare.
The specific limits for glow, trespass and glare are being discussed by a number of stakeholders. LRC researchers have presented related information at several industry meetings and conferences.
Jennifer Brons, a leading researcher at the LRC, reports that many representatives of the lighting industry point to OSP as a promising practical tool for curbing the spread of light pollution and its negative effects.
The LRC is also inviting engineers to take part in building a database from which it can develop a statistical basis for the OSP model.
The results of the related work on the OSP model were published in October 2007 in “The Lighting Journal” by the U.K.’s Institution of Lighting Engineers (ILE).
You can find more information on the OSP model in the Outdoor Lighting section of the LRC website.
