BUG Ratings for Outdoor Light Fixtures

Having proper outdoor light fixtures guarantees minimal light pollution. For humans, light pollution can cause light trespass into homes, messing up sleep schedules. For wildlife animals, light pollution can affect migrating and hunting, and be distruptive for nocturnal animals. Light pollution increases our carbon footprint and electricity waste. Installing fixtures with a low BUG Rating can help prevent this. 

BUG Ratings

BUG Ratings were established by the Illuminating Engineering Society (IES) and DarkSky International in 2009 as an update to the original outdated cutoff system. BUG stands for Backlight, Uplight, and Glare. Backlight (light trespass) measures the amount of light spread behind a fixture, displaying unwanted light into private residences. Uplight (skyglow) is caused by fixture's spreading light upwards, reducing the visibility of the night sky. This is especially harmful for wildlife using the moon and stars for navigation. Glare (also light trespass) refers to when fixtures emit intense light, creating excessive brightness. This can cause eye strain and create a safety risk.

How Are BUG Ratings Calculated?

Each of the categories is broken down into its own subzones. 

• Backlight Subzones: Backlight Very High (BVH), Backlight High (BH), Backlight Mid (BM), Backlight Low (BL)

• Uplight Subzones: Uplight High (UH), Uplight Low (UL)

• Glare Subzones: Forward Light Very High (FVH), Forward Light High (FH), Backlight Very High (BVH), Backlight High (BH) 

Note: When doing the calculations, the BH subzone will be used for both backlight and glare, but BVH will only be used for glare. Forward light mid (FM) and forward light low (FL) shouldn’t be used in the calculations since their light distribution is only 0-60° from the ground and is considered beneficial light. 

Lumen Requirements

The rating for each fixture category is based on the lumens emitted in each subzone. You will base the rating on the highest amount of lumens. 

To understand the graphics below, use the light fixtures' photometric data. This data provides you with the lumen value for each subcategory. Take the lumen value and find the closest rating that doesn’t exceed the max lumens. For example, if you're calculating the Uplight rating, a UH subzone with 35 lumens would have a U2 rating.

Calculate the remaining subcategory ratings for each category. The highest subcategory rating will be overall rating. For example, in the previous example the UH subzone had a U2 rating. If the UL zone had 8 lumens, giving it a U1 rating, the overall Uplight rating would still be U2. 

Refer to the graphics below for the exact lumen threshold for each rating. However, we typically include our BUG rating in the product specification table, specification sheet, or photometric data sheet so you won't have to calculate it manually. 

Light Zones

If you’re unsure if you need a fixture with a higher BUG rating, consider the Lighting Zone of the area. Areas with a lower zone should prioritize low BUG ratings and minimal light pollution.

Product Showcase

We carry various outdoor light fixtures with a low BUG rating.

Shop Now

Choosing the correct outdoor light fixtures is the best way to reduce light pollution and protect wildlife. For assistance choosing the right outdoor light fixture or for additional questions, reach out to our team of product support specialists at 866-590-3533 or by completing this contact form.