Don’t BUG me! Preventing Unwanted Light and Creating a Bird-Safe Building

By Joshua Baker

Our LAMP program partner, Michael Reunert of Conserve Energy, answers your lighting questions in our new lighting blog series:

Customers often ask:

My current lighting setup sends unwanted light onto adjoining properties and shines in the eyes of pedestrians and traffic. I’ve also heard that sending light up into the night sky is harmful to birds. Can a LED lighting retrofit avoid these problems but still provide enough light on my property?

Yes, switching to LED lighting is a smart choice to save energy and thankfully, with a wide range of color, intensity, and good directionality, can make it easy to pick quality lighting that is safe for birds (and better for people too!)

When specifying outdoor lighting fixtures, it is important to select fixtures that will deliver light where you need it, but don’t send unwanted light onto neighboring properties, directly into the eyes of pedestrians, drivers, or up into the night sky. Lighting choices are particularly important to keeping birds safe as exterior lighting can confuse birds, and many get lost and die from exhaustion. Others smash into windows when interior lighting is left on at night and visible through a window

Fortunately, the Illuminating Engineering Society and the International Dark Sky Association have developed the “BUG” rating system to compare fixtures based on the amount of light escaping in unwanted directions.BUG stands for Backlight, Uplight, and Glare.   

Backlight is light that shines behind and below the fixture.

Uplight is light shining up, into the sky.

Glare is light that shines from the front of a fixture at angles known to cause glare.

Commercial outdoor fixtures are rated for each attribute on a scale of 0 to 5.  A rating of 0 designates little or no light being emitted and 5 means a large amount of light being emitted.  A typical pole fixture might have a rating like B-1, U-0, G-2.  This fixture has a minimal backlight, almost zero uplight, and some glare, although not excessive.

On some fixtures, you might find ratings like full-cutoff, or partial cut-off.  This was an older classification system that looked only at uplight.  Full-cutoff would be equivalent to U-0, zero uplight, in the new system.

Understanding the BUG rating is important when selecting appropriate exterior fixtures for different locations on a property. Pole fixtures on the edge of a property should face in, towards the property, and should have little or no backlight to prevent “light trespass” onto neighboring properties. Many jurisdictions have stringent requirements for light trespass, and if fixtures with high backlight are installed, the project may fail inspection and have to be redone. Similarly, many building codes require outdoor fixtures to be rated at U-0, or the older full-cutoff, to prevent skyglow which is wasted light and can disorient migrating birds. Glare is unpleasant and will detract for the appearance of a property. In extreme cases, fixtures with a lot of glare could blind drivers or pedestrians resulting in safety issues.

In older fixtures, the light source was typically a lamp that gives off light in all directions. To control the light, fixtures were designed with reflectors and shields to direct light in the desired output pattern. LED fixtures contain multiple chips that give off directional light. Fixture manufacturers carefully design the LED chip layout within a fixture and may add lenses for individual LED chips, so that light output can be much more precisely controlled in newer LED fixtures. Many manufactures also offer optional shields for area fixtures that can take backlight down to almost zero.

Using lighting design software, designers can determine the best fixture for each location on a property and perform photometric analysis which will accurately estimate the light levels at any point before any lighting is installed.   They can also assure that any light trespass will be minimal and will comply with local codes.

Want help to select exterior fixtures that don’t “Bug” your customers, tenants, neighbors, and birds? Contact the Lloyd EcoDistrict’s LED Advantage Member (LAMP) team.