Lower energy use. Increase visibility, safety and security.
"More is better" doesn't apply to exterior lighting design. Over-lighting can increase glare, decrease visibility and waste energy. When you're thinking about your exterior lighting needs, consider these facts:
- Parking lot light levels - Call a lighting designer to have your light levels tested. Or, if you're already working on a project with an architect or engineer, consult with them about testing your light levels. The minimum maintained horizontal illuminance should not be below 0.2 footcandles (fc) and the maximum-to-minimum uniformity ratio should not exceed 20:1. This ratio would keep the maximum illuminance to 4.0 fc.
- Visibility - To determine how much light you need for maximum visibility without glare, consult the guidelines recommended by the Illuminating Engineering Society of North America, at www.iesna.org.
- Glare - In addition to eliminating excessively bright fixtures, be sure that lights are aimed well. You'll increase visibility and safety for both pedestrians and drivers on your exterior property.
- Color - The color cast by a lamp has a significant impact on how well you can accurately see illuminated objects after dark. Metal halide lamps, for example, produce an icy-white color light, similar to moonlight. These lamps have a higher color rendering index (CRI 75) than the yellow-orange light from high pressure sodium lamps. The optimal choice for accuracy, therefore, is the metal halide.
- Skyglow - This refers to the glow that is visible in the night sky above developed areas. This is considered light pollution because it blocks the view of the stars. Here's how you can reduce skyglow:
- Only use as much light as you need
- Use full cut-off fixtures
- Minimize uplighting on building facades and signs
- Only use as much light as you need
Guidelines for Exterior Parking Area & Security Lighting Fact Sheet (PDF)
