Exterior Lighting Guidelines
Lower your 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:
- 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. For parking areas, 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.
- 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. LED and metal halide fixtures, for example, typically produce an icy-white color light, similar to moonlight. These technologies have a higher color rendering index (approximately 75) than the yellow-orange light from high-pressure fixtures.
- Skyglow - Artificial nighttime light that shines into the atmosphere, either directly or indirectly through reflection, produces an effect called skyglow. The following steps can help reduce skyglow:
- Only use as much light as you need.
- Use fixtures that emit no “uplight”, sometimes referred to as full cut-off fixtures.
- Minimize uplighting on building facades and signs.
- Controls - All exterior lighting systems require a control mechanism for operation. Since control systems are used on a daily basis, automatic control methods are more reliable and cost-effective. In addition, automatic controls save energy by turning lighting systems off or reducing light output when they are least needed. Control systems might include:
- Photo (daylight) sensors
- Time clocks
- Motion sensors
- Bi-level stepping/dimming
- A combination of the above options, such as a photo sensor and motion sensor, is recommended for maximum energy savings.
- LED technology - LED fixtures can deliver exterior lighting more efficiently and in a more uniform illumination pattern, while using less light, compared to traditional exterior lighting equipment. Significant energy savings are possible due to the more efficient LED light source and the need for less light. LED fixtures also tend to produce less skyglow and are much more easily integrated with any of the control options identified above.
Additional Resources