Light Responsibly

The Model Lighting Ordinance (MLO), produced jointly by the Illuminating Engineering Society (IES) and the International Dark-Sky Association (IDA), provides a template for municipalities seeking to develop standards for responsible outdoor lighting.

Specifically, the MLO addresses skyglow (light emitted up into the sky that obscures nighttime viewing of stars), light trespass (light emitted onto neighboring property), and glare (excessive brightness that impairs or disables vision).

There are approximately 10,000 lighting ordinances in effect in the United States. Many are easy to understand but difficult to comply with because they often are not written by lighting designers. And, ordinances may vary considerably.

IES and IDA teamed up in 2004 to produce a standard municipal ordinance to regulate outdoor lighting on private property. After a lengthy review and revision process that involved development of a new outdoor lighting fixture classification system, the document became available for use in June 2011, including code-ready text, supporting tables and a user’s guide complete with examples.

The MLO covers all types of outdoor lighting with some exceptions, such as temporary lighting, emergency lighting, and public monument and statuary lighting. Its rules do not supersede applicable electrical, building and energy codes.

As a core principle of the document, the guidelines should be customizable based on land use. The MLO begins with a list of five zones labeled LZ0 through LZ4, identifying areas of no ambient lighting to high ambient lighting. A LZ1 area might include parks and reserves, for example, while LZ4 includes dense urban areas.

The MLO distinguishes nonresidential and residential lighting and then provides multiple compliance paths designed to limit the amount of light and offensive distribution the lighting system produces. It also covers lighting controls.

Regarding controls, the MLO requires lighting to be turned off during the day, using a photosensor, astronomical time switch or equivalent functions in a programmable controller. With some exceptions, curfews should be established following close of business in which light output is reduced by at least 30 percent or turned off at nighttime. The jurisdiction should create the curfew times and conditions based on local values and norms.

For nonresidential and multifamily (with common areas) applications, the designer may choose between two compliance paths: prescriptive and performance.

The simpler, prescriptive method imposes a cap on total initial fixture lumens produced by all of the outdoor lighting. It is, in turn, is based on a lumens-per-parking-space or lumens-per-square-foot (hardscape area) method. Using the hardscape-area method, additional allowances are permissible for sales and service facilities, such as outdoor sales lots and service stations.

The prescriptive method further regulates light distribution by indicating maximum backlight (B), uplight (U) and glare (G), or BUG, ratings for the selected lighting fixtures, again depending on lighting zone and other factors, such as setback from the property line in the case of backlight. Many manufacturers publish BUG ratings (based on IES TM-15-11) for their products, allowing detailed analysis of the light emission (see “Sorry to BUG You,” February 2011, at Emitted uplight, for example, is not allowed for area lighting in any zone.

The performance method, oriented to design professionals, is suited to more complex projects. The total installed initial fixture lumens cannot exceed prescribed values, again based on lighting zone, and with additional lumen allowances for unique site conditions. The designer must further demonstrate the proposed design will not produce off-site impacts by either specifying fixtures rated and installed with appropriate BUG ratings or producing computer lighting calculations, demonstrating compliance with a maximum vertical light level at any point in the plane of the property line.

For residential lighting, including multi-family properties lacking common areas, with some exceptions, the designer must select outdoor lighting fixtures that are fully shielded and do not exceed certain lumen values based on type of fixture and lighting zone. Landscape lighting cannot be aimed onto neighboring properties.

The document concludes with requirements for lighting authorized by special permit, including high-intensity and special-purpose lighting, complex and nonconforming uses, and existing lighting systems.
As the MLO is adopted and tested by community standards and the electrical industry, it will be further vetted and potentially improved. In the meantime, this is a significant document—the result of years of expertise and hard work—that promises to deliver several benefits: a single standard, written by lighting experts and satisfying the IDA folks, that can be customized based on land use, outdoor lighting application and complexity of project; promotion of good design that avoids overlighting, glare and wasteful stray light; specification of outdoor lighting products with a thorough understanding of how they emit light; and reduced skyglow, energy costs and carbon emissions.

The IES/IDA MLO-2011 is available for free download at

DILOUIE, L.C., a lighting industry journalist, analyst and marketing consultant, is principal of ZING Communications. He can be reached at

About the Author

Craig DiLouie

Lighting Columnist
Craig DiLouie, L.C., is a journalist and educator specializing in the lighting industry. Learn more at and .​

Stay Informed Join our Newsletter

Having trouble finding time to sit down with the latest issue of
ELECTRICAL CONTRACTOR? Don't worry, we'll come to you.