good lighting

Energy efficient outdoor lighting = Astronomer-friendly lighting

by Bob Parks, Virginia Outdoor Lighting Taskforce (

There are three main factors that can significantly reduce energy consumption. The use of full cut-off fixtures ensures that all of the energy used is directed to the task of lighting the ground beneath the fixture. This means that a lower wattage lamp can be used to achieve the same level of illumination compared to the wattage of lamp in a non or partial cut-off fixture. Typical energy savings of 20 to 30%.

The second factor is to design lighting to meet the minimum level of illumination needed. Overlighting wastes energy by making the area brighter than it needs to be for the required task. You see this in gas stations and parking lots where the illumination levels are sometimes 5 to 10 times higher that those recommended by IESNA. The mentality seems to be is that if a little light is good, than a lot of light must be great. There is also an economic factor at work. There is some proof that consumers will choose to patronize the brighter establishment because they have been taught to believe that bright equals safe. So some stores have decided to have lighting wars, where the brightest lit wins.

The third factor to be considered is whether lighting is actually required for a given task. This is where the most energy is wasted. You can see this in every major shopping center. After closing, empty parking lots are lit for no reason. There should be a curfew provision that requires that parking lot lighting be reduced to 25% or less within 2 hours of closing.

You also see this in roadway lighting. There are no studies that show any reduction in accidents by lighting entire roads. The only conclusive studies that show a reduction in accidents are in what are called "conflict zones". These are intersections and ramps. However over the last 30 years power companies have been very successful lobbying state and local governments to light entire roads. They have sold this practice to the governments as an matter of providing increased safety, but no scientific studies have ever supported this claim. Some studies have actually concluded that lighting roads may contribute to an increase in accidents because drivers feel "safer". Feeling safer they tend to drive faster than they would normally drive and can't stop in time to avoid obstacles that are beyond their limited range of vision at night.