Not too long ago, we designed outdoor lighting for nighttime safety and visibility, and also used it to reveal the beauty and character of the architecture and landscape. Lighted billboards promoted products and destinations, auto dealers glorified their new automobiles with lumens and sparkle, and cities erected lighting for sportsfields galore. We worried little about the energy used, the light spilling onto neighboring properties, or the glare that sometimes accompanied the lighting installation. We measured our success in footcandles and uniformity of light on the lighted surfaces.
Those were the good ol' days. We know better now. Here are reasons why we need to be judicious about the use of nighttime lighting:
- Electric power use is expensive, especially at the critical hours of the late afternoon when homes and businesses are using electric power and the utilities are struggling to turn on inefficient power plants to keep up with the demand.
- Electric power use contributes to air, water, and land pollution - not to mention global climate change due to greenhouse gases.
- Nighttime lighting use contributes to skyglow (the smear of light over populated areas that obscures the view of the glorious night sky).
- Light at night disrupts the habitats and natural cycles of animals, from hatching turtles lured by resort and street lighting away from the safety of the ocean to migrating birds that circle lighted city skyscrapers at night until falling, exhausted, to their deaths on the pavement below.
- Unintended glare from exterior lighting may distract drivers and shift their light adaptation level such that they can no longer see details on the roadway or pedestrians crossing the road.
- Exposure to light at night may even contribute to some human health problems. (Until we know more, we should be cautious about stray light that enters bedroom windows.)
- More and more communities are enacting legislation and ordinances against excessive outdoor lighting because people are annoyed by overly bright LED signs or soccer fields that remain brightly lighted until 1 a.m., or lights from a gas station that shine into residential windows, or bank ATM lighting that causes a glare hazard to drivers. So, it’s now a legal concern for the lighting designer/engineer.
How do we respond to these issues, while still providing the benefits of outdoor lighting?
- Use only as much light as is needed to provide visibility. Not every location needs high security light levels. After all, if lighting eliminated crime, there would be no crime during the daytime. Think about ways to enhance visibility with less light: redesign landscaping, parking lots, walkways, and building service areas to reduce areas where “bad guys” can hide or pedestrians are difficult to see. Locate luminaires where they don’t cast spooky shadows.
- Don’t use easy, conservative design. Use the lowest-wattage lamp you can, and target lower average illuminances and slightly higher max:min ratios. Specify sealed luminaires that STAY CLEAN (i.e. lower Light Loss Factors so that you don’t have to overlight the area when the fixtures and lamps are new). Specify high-efficiency luminaires based on the light distribution that’s needed, recognizing that a fixture that eliminates backlight and uplight and glare often has an efficiency of well below 50 percent.
- Specify fixtures that limit light emitted in glare zones (80 to 90 degrees from straight down).
- Specify fixtures that limit light emitted horizontally (80 to 100 degrees from straight down) because these are the worst angles for producing skyglow.
- Specify fixtures that limit light emitted toward bedroom windows, neighboring properties, nature habitats, and the sky. Use luminaires that eliminate (or limit to less than 2 percent) upward light except in urban areas with high pedestrian traffic where seeing faces or seeing building façades is especially important.
- Reduce light levels after principal business hours, or when vehicle/pedestrian conflict levels drop. For example, if an industrial plant has a day shift, a reduced swing shift, and a nighttime shift for maintenance only, consider a lighting layout like the one pictured at the top of the page. Design the parking lot with poles with two fixtures each. Circuit the parking lot so that you can shut off the lights far from the building entrance altogether after the first shift has gone home. Circuit the two-headed poles with two switch groups. Then, after the swing shift has left, your control system can automatically shut the lighting down to half level for the rest of the night, keeping the building’s entrance lighting on. In many areas, lighting can be completely extinguished during late night hours.
- Use control systems with astronomical time clock capabilities, because they can automatically switch lighting on at dusk, reduce lighting levels after curfew hours, or switch lights on automatically early in the morning in time for users who arrive before dawn. These systems are less expensive and easier to operate than ever before.
What does it mean to “limit” lighting in the “glare” zone? Wouldn’t a 100-watt floodlight used in a national park look a lot more glaring than one used in urban Chicago? You betcha. The Illuminating Engineering Society has established five “Lighting Zones” that can be adopted by communities. Here are some very brief descriptions:
- LZ0 (no ambient lighting) is for parks or natural habitats where lighting interferes with the environment and should be minimized.
- LZ1 (low ambient lighting) describes a rural or small community where outdoor lighting is unwanted and/or unneeded, and lighting should be well shielded, low in wattage, and used only at intersections, for example.
- LZ2 (moderate ambient lighting) is a designation for more densely populated areas, where lighting is used for safety and convenience, but is not expected to becontinuous.
- LZ3 (moderately high ambient lighting) can apply to commercial and urban areas, where lighting is expected to be more continuous and uniform along streets and in parking lots.
- LZ4 (high ambient lighting) usually applies to high-density urban areas where users are adapted to high light levels. Lighting is considered necessary for safety and security, and lighting is usually more continuous and uniform.
How do you know how to “limit” light in light trespass, uplight, or glare zones?
The Illuminating Engineering Society has introduced the Luminaire Classification System (LCS) that quantifies how much light is emitted at angles that are most likely to cause light trespass (“Backlight”), skyglow (“Uplight”), and “Glare”. Using this “BUG” system, a standard IES photometric file can be run through a piece of software that reports whether the luminaire is suitable for use in Lighting Zones 0, 1, 2, 3, or 4. A 250W metal halide Type IV distribution “shoebox” fixture may have a rating of B1 U1 G2, where the maximum number indicates the lowest Lighting Zone in which it's suitable. It can be used in Lighting Zone 2. If you want to use this same fixture in Lighting Zone 1, you can, but you have to drop the wattage to get there. The 100-watt version of the fixture has a BUG rating of B1 U1 G1, so it's suitable in Zone 1.
Yes, outdoor lighting is more difficult than it has been in the past, but with some planning and careful specification of equipment, you can help people see clearly and enjoy nighttime activities, and enhance the beauty of spaces without causing long-lasting harm to the environment.
Naomi Miller is principal at Troy, NY-based Naomi Miller Lighting Design.