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Introduction to MLO: A crucial tool for the future of lighting design

The Early Days of MLO

Let’s go down memory lane – in the 1970s when light pollution first emerged as a problem. The astronomers discovered that the night sky was deteriorating due to the increased lighting associated with development and growth and termed it light pollution.

Light pollution knows no bounds; the effects of polluting light can be felt up to 200 kilometers (120 miles) away from the source. The discovery of more environmental impacts of lighting led to the emergence of an international “dark sky” association advocating for a precautionary approach to outdoor lighting design.

Then, the International Dark-Sky Association (IDA) and the Illuminating Engineering Society of North America (IES) developed a Model Lighting Ordinance (MLO) to address the need for outdoor lighting regulation in North America.

MLO Explained

The MLO enables communities to significantly reduce light pollution, glare, and excessive light levels. MLO includes adopting five different lighting zones (LZ0, LZ1, LZ2, LZ3, and LZ4), allowing each governing body to modify the stringency of lighting restrictions based on the area’s sensitivity while also accommodating community intent. Therefore, communities can fine-tune the MLO’s impact without having to customize it.

The MLO also includes a Backlight-Uplight Glare (BUG) rating system for luminaires, allowing better control of unwanted light. Today, many cities and towns have passed the Anti-Light Pollution Legislation and MLOs.

Approach and Purpose

The MLO introduces several novel approaches to outdoor lighting regulation, including:

- The use of five lighting zones to classify land use and assign appropriate lighting levels to each class of land use. For instance, LZ0 zones are designed for pristine natural environments with limited outdoor lighting, while LZ4 zones are intended for limited application in areas of extensive development in the largest cities.

- Placing limits on the amount of light that can be used for each property.

- The use of the IES’s TM-15-11 “BUG” (Backlight, Uplight, and Glare) style to classify outdoor lighting fixtures, ensuring that only well-shielded fixtures are used. In addition, no uplight for an area or street lighting is permitted in any zone.

The purpos