According to the U.S. Department of Energy, commercial lighting can account for 15% to 50% (median of 35%) of a building’s annual energy consumption. Outdoor lighting is included in that statistic and retrofits in conjunction with interior lighting retrofits can reduce that annual energy consumption by as much as 85%. Outdoor lighting retrofits can be more expensive with a longer payback than interior lighting , but have a more predictable payback since they are typically on for 4200 hours a year and usually on a set schedule from sundown to sun up with little to no human intervention. Outdoor lighting can include retrofitting existing lighting controls, existing lighting fixtures or replacing with new fixtures. For the purpose of this post, outdoor lighting consists of pole mounted site lighting and wall mounted fixtures. Other exterior fixtures I will not be discussing, for now, and that you may encounter are landscaping, monument signs and billboard lighting.
The easiest way to save energy on outdoor lighting is to not have them on at all, but that is not very practical. Since we can’t control when the sun is out and the fact that we need outdoor lighting at our buildings at night for security and safety we must look at what we can control. Controlling how much light and when it is on can result in the fastest return on investment and can often times utilize the existing lighting layout and fixtures. Lighting controls consists of astronomical time clocks, photocells, motion sensors, lighting contractors and lighting control panels. With the advent of LED and dimming HID technologies motion and photocells can now be tied together to dim the output and reduce energy costs even more. For example as the sun goes down in the evening the outdoor lighting can turn on at a set level of say 25% and increase in brightness as the sun goes down until 100% lighting levels are achieved and then be dimmed down to 50% during non-business hours until a motion sensor detects movement and increases the lighting levels then returns them back to 50% after the motion is not detected. A system such as this could save 40% to 60% of energy costs but may not work with existing lighting. Which control system is the right choice depends on the lighting technology used and the use facility.
Outdoor fixtures are subject to extreme environmental conditions such as vibration, wind, sun, extreme temperature swings and physical abuse and therefore any decision about retrofitting the lamp in an existing fixture must take into account the robustness of the lamp source and the fixture housing. For example, a retrofit with a compact fluorescent lamp (CFL) that prefers warmer operating temperatures in a fixture originally designed for a HID source such as mercury vapor or metal halide might not be the best choice if the fixture is installed in an area that sees temperatures below 0 degrees F for more than a few days. Most CFLs are not rated to start below this temperature and light output can be reduced by as much as 50%. Another consideration is lamp compatibility with the existing fixture. The existing lamp base (medium or mogul), operating voltage (120, 208, 240, 277, 347, 480 VAC, etc.), physical size limits and the type of distribution pattern provided with the fixture can reduce retrofit options or make it impossible to do. In my experience, the most successful retrofit that I have performed are 175 watt mercury vapor HID fixtures which requires the use of now outlawed ballasts in the United States that can consume approximately 205 watts per fixture. These can be retrofitted by removing the ballast, wiring line voltage directly to the socket and installing a 60 – 80 watt hi-lumen CFL rated for the appropriate voltage.
As mentioned in regards to controls, existing high pressure sodium, low pressure sodium, metal halide, mercury vapor or Compact fluorescent fixtures can be replaced with new fixtures employing the latest lighting technologies such as LED and dimming controls for improved energy savings. The retrofit can often reuse the existing mounting hardware, circuiting and in some case can reduce the number of fixtures required for the same amount of light. With the right fixture choice and lighting design energy consumption can be reduced by 50% or more depending over the original fixture.