Model Lighting Ordinances – Dark Sky Impacts

Light Pollution and Lighting Codes

An Analysis of the Light Pollution Control Effectiveness of the IDA-IES Model Lighting Ordinance and the IDA Pattern Outdoor Lighting Code


From the Executive Summary:


The POLC is found to provide substantial improvements over unregulated outdoor lighting practice in all evaluated light pollution impacts. In the “brightest” POLC LZ 3, the total lighting amount for commercial sites is reduced on average to about one-half or less of the amount used on unregulated sites; in POLC LZ2 they are reduced to one-quarter and less. The amount of sky glow expected is reduced nearly a factor of 100 compared to average unregulated outdoor lighting practice.

Under MLO standards, outside of MLO LZ 0 and 1, the total lumen allowances, direct uplight allowances, and amount of sky glow are notably greater than expected under POLC standards; in MLO LZ 3 and 4 they are dramatically greater. In LZ 2 and above sky glow impacts are greater than what can be expected even when lighting is unregulated.

The MLO approach to fixture shielding and “limits to off site impacts” is ineffective in limiting sky glow, light trespass and glare. The MLO allows any (including no) fixture shielding, permitting the installation of the most egregious types of lighting fixtures. Compared to POLC lighting codes with “fully shielded” standards, even the (optional) MLO Luminaire Classification System “BUG” shielding standards and “off-site impact” limits offer weaker control of glare and uplight than the POLC.

The POLC requires the use of yellow (LPS, HPS, amber LED) or warm-white LED (CCT<3500K) for general area lighting, which accounts for 80% to 90% of outdoor lighting, thus reducing many aspects of light pollution such as visible sky glow, glare, human circadian impacts, and impacts on many biological systems. MLO does not address lamp spectrum, and thus leaves this crucial aspect of light pollution unaddressed.

In general, the POLC is shown to be far more effective than the MLO in curbing the detrimental aspects of outdoor lighting. The analysis of the various MLO regulatory options shows that the Performance Method Option B provides notably poor control of both direct uplight (and therefore skyglow) glare, and light trespass.

We conclude that a substantial reduction in light pollution is attainable to communities that adopt lighting codes following POLC standards. Adoption of a code based on the IDA-IES MLO cannot realistically be expected to produce improvement. Certainly for the medium-sized and small communities and rural areas that most frequently seek to reduce light pollution and protect the natural night environment, the MLO represents a significant step backward in light pollution limitation and control compared to the older IDA POLC model.

Read the full report:

Light Pollution and Lighting Codes

Light Pollution and Lighting Codes – Appendix A

Light Pollution and Lighting Codes – Appendix B

To celebrate, promote, and protect the glorious dark skies of Flagstaff and northern Arizona.