illustration by James Provost

In 2004, the International Dark-Sky Association (IDA) and the Illuminating Engineering Society (IES) were each developing their own model lighting ordinance. The intent of each was to provide municipalities across the country with a framework that they could use to write or update their local lighting ordinances. (The IDA's mission is to preserve the night sky; the IES is the technical society for illuminating engineering, which writes outdoor-lighting guidelines and recommendations for those involved with illuminating engineering and lighting design.)

The common goal for both associations was to produce a defensible ordinance that allows quality lighting while greatly reducing light pollution and light trespass. But it became apparent that two model ordinances would lead to confusion and inconsistencies. So in November 2005, the two organizations agreed to form a joint committee, the Model Lighting Ordinance Joint Task Force (MLOJTF), which was charged with developing an industry-wide Model Lighting Ordinance (MLO). Committee meetings commenced in early 2006.

The overall goals were for the MLOJTF to develop an ordinance that could be applied to any small or large municipality; easy to understand for city planners, enforcement officers, and applicants; comprehensive enough to address all outdoor lighting; technically sound; and sure to reduce light trespass and light pollution.

DEVELOPING AN ORDINANCE FROM SCRATCH The initial MLO pulled from several sources. It combined existing outdoor lighting codes, California's Title 24 energy code, and substantial revisions that included revising energy budgets to maximum lumen allowances; addressing luminaire backlight, glare, and uplight; reducing light during curfew hours including Lighting Zone Zero for areas with no continuous outdoor lighting; and adding a performance method for complex lighting projects.

As work continued, it became clear that simply patching together existing codes would not really address the concerns and goals that had prompted the decision to create such a document in the first place. While a significant amount of previous work was incorporated and was very valuable, the MLOJTF had to create a substantial amount of new material. None of the existing ordinances were comprehensive enough to incorporate all of the goals, especially a method for dealing with complex lighting projects. Prior to the MLO draft, ordinances would typically categorize these projects as “special review,” but not provide any means for the planning staff to hold a review.

DISCOVERING WEAKNESSES IN CURRENT RECOMMENDATIONS One drawback to the initial version of the MLO was with the IES uplight-outdoor-luminaire classification system. This system classified luminaires as full-cutoff, cutoff, semi-cutoff, and non-cutoff depending on the percentage of uplight emitted from the fixture. It did not address how much uplight would be acceptable, nor did it address glare and backlight potential. For example, a 1,000W luminaire may be classified as full-cutoff yet have a higher glare potential than a 5W incandescent lamp non-cutoff luminaire.

Designing a new luminaire classification system that addressed the absolute amount of light for backlight, uplight, and glare appeared to be necessary for the MLO. As a result, the IES created and issued a technical memorandum, TM-15, in 2007. Commonly called the “BUG” (backlight, uplight, and glare) rating, it is incorporated into the MLO text, and the MLO User's Guide explains how it works.

HOW THE PROCESS WORKED First Public Review (Feb. 9–Apr. 10, 2009): The MLOJTF took almost three years to develop the first document for public review. The comments received from across the lighting industry were extremely helpful, and the task force realized that major revisions were required. First, the MLO had to be simpler. The Complete Site Method was too complex as a prescriptive method, so it was changed to fall under the performance method. A user's guide was added to help explain the details of the MLO and provide examples. The second major revision did include street lighting as an optional ordinance for municipalities that want to have a simple street lighting ordinance.

Second Public Review (June 24–Aug. 23, 2010): The major suggestion from the MLO's second public review was to use initial luminaire lumens instead of initial lamp lumens. This was adopted and it puts all luminaires on an equal basis and encourages quality designs. Using this measurement also means that absolute versus relative photometry is no longer an issue.

Many commenters were also confused about the uplight values and why a substantial amount of uplight was being allowed in Lighting Zones 3 and 4. Since the uplight value was linked with a glare zone that is at a higher angle, this value permitted more uplight in LZ3 and LZ4. As a result of this feedback, uplight will be decoupled from these glare zones, which requires a modification to TM-15. (The next revision of TM-15 is presently under way.)

Comments varied when it came to the performance method Lumen Allowance Values, but the majority of respondents felt that the values were still too high to reduce light-trespass and light-pollution goals. Independent reviews showed that if an applicant applied every single layer allowance, then lighting levels would far exceed IES recommended values. The lumen allowances and the number of extra allowances are being reviewed to address this issue.

LZ4 allows for higher lighting levels, which may be only appropriate for areas that have continuous nighttime pedestrian use. Stronger caution statements were inserted emphasizing that LZ4 is not a default lighting zone.