Grasslands Observatory - Essays - Recommended Lighting Levels for Exterior Lighting

Recommended Lighting Levels for Exterior Lighting

by Tim Hunter

The Illuminating Engineering Society of North America (IES or IESNA, 120 Wall Street, 17th Floor, New York, NY 10005) is the main professional organization for lighting engineers in this country. The IES publishes many information books for lighting professionals and has established sets of recommended lighting levels for various applications. For nighttime sports activities, these recommended levels may be quite high, but for security lighting in a rural area with little activity, they will be quite low. The IES recommended lighting levels are not the absolute answer for every lighting situation or need, but they are a good start for most occasions requiring a reasonable amount of nighttime lighting. In general, it is a good idea for a lighting application not to exceed IES recommendations; otherwise, there may be considerable wasted energy, possible light pollution, light trespass, and glare.

The International Dark-Sky Association, Inc. (IDA) is a sustaining member of the IES and believes very strongly in the professional approach the IES takes toward lighting applications. Most of the individual members of the IES make their living designing indoor and outdoor lighting systems, and many of them are familiar with IDA. Most professional outdoor lighting engineers who are members of the IES are supportive of IDA's goals.

Below are simple summaries of some of the IES recommendations. This information is taken from IDA Information Sheet Number 77 (October 1993) by David Crawford, IDA's Executive Director. These tables are simplifications of IES recommendations, and some of the recommendations may still be under discussion or change in the near future. These are recommendations NOT standards. Federal, state, county, and municipal governments set standards for their various lighting needs. These standards may make no sense whatsoever, or they may be closely linked to the IES recommendations. The key to outdoor lighting is that it should be carefully designed for all relevant factors, including preservation of the night sky. Other significant factors are the minimizing of glare, estimating light system depreciation, calculating appropriate mounting heights and pole spacing, judging access control, and planning for a mix of commercial, industrial, residential, and rural needs.

The lighting illuminance levels are given in foot-candles, which is the most common unit used in the United States. Lux is the preferred international unit, and it is the unit recommended by the IES. Ten lux is approximately one foot-candle.