Exterior Lighting Q & A

Release Date: 
December 21, 2016 - 09:45

Q: Is exterior lighting any different from interior lighting?
A: Yes.

One of the main differences of exterior lighting is that it’s not usually contained by walls or a ceiling. This can lead to two issues that are different, but related. One is Light Trespass, wherein the light leaves one property and goes onto another. The other is Light Pollution, where light goes upward into the sky (sometimes called Sky Glow). These issues are a concern for at least two reasons:

  1. they are a nuisance because they can cause glare and/or unwanted light in areas that don’t require lighting, and in some instances may be a violation of local ordinances.
  2. light trespass and light pollution are wasteful, and represent lighting energy that is directed into unnecessary places.

One important element in any lighting design strategy is putting light where it’s needed (whether task, ambient or accent). This idea cuts to the heart of light trespass and light pollution. Having proper fixtures installed in the correct location is key to minimizing complaints about unwanted light, and lowering operational costs of a lighting system. Some fixtures are designed to shine light mostly or totally downward. These are informally called “cutoff” or “full cutoff” fixtures.
Cutoff Image Blog Dec2016.png
Using them will minimize sky glow. Additionally, some fixtures have an optical pattern that shines most of the light forward and to the sides. Imagine these on poles at the edge of a parking lot or even a traffic lane facing inward; the light will tend to stay on the site and not go onto adjacent properties. Even well designed decorative fixtures can have these optical properties. In areas like industrial parks and corporate campuses this is not usually a problem, but on properties adjacent to residences, poor optics can become a big problem. Above all of this, excess energy is being expended to light unintended areas. One of the great aspects of LED luminaires is that they have high lumens per watt (high efficacy) and the potential for excellent optics, where light can be delivered uniformly onto a precise location. Not all LED luminaries do this, but if they are well-engineered, the optics can help minimize energy use.

Q: If I analyze exterior lighting it must be done at night, right?
A: For the most part, yes.

But, walking around the facility during the day can reveal problems with the lighting system that may not be apparent at night.

The primary reason to patrol the area during the day is to identify “day burners”, e.g., lights on during daylight hours. Usually the photocell has failed, most often in the ON position. But there are other causes, such as debris on the sensor or problems with the wiring. If you only look when it’s dark, all you will see are lights that are out, not ones in constant ON mode and burning all day without purpose. Correcting these problem fixtures can save a lot of energy and maintenance costs. Something else to look for are fixtures that are particularly dirty and have yellowed or cracked lenses. It can be very difficult to see these things in a dark environment.