Measuring minimum illumination at construction sites

May 8, 1991

Ms. Madelynn R. Kirkpatrick
Assistant Office Manager
Cameron Construction Incorporated
[Recipient address omitted]
Dear Ms. Kirkpatrick:

Thank you for your letter of April 4, concerning the Occupational Safety and Health Administration (OSHA) standard at 29 CFR 1926.56, related to the requirements for minimum illumination at construction sites.

In your letter you state, "It would be most helpful, if you could provide me with a simple definition of how much illumination a single foot-candle provides." You further state that "While 'foot-candle' is an international and commonly used measurement of illumination levels, it is also without specific reference for those people it is intended to safeguard."

The computation of illumination intensity at work level can be an extremely complex procedure. Many variables are involved such as: the specific light source, intensity, distance, atmospherics (air purity), floor, wall and ceiling color, and the respective surface sheens, to name a few. Therefore, the existing illumination level at any work surface within a work site is best measured with a light meter reading in lumens per square foot which are equal to foot-candles. You may obtain a light meter at any convenient photographic store or supply source.

The required illumination specified by the OSHA standard was derived from the specifications provided in the American National Standards Institute (ANSI) standard ANSI A11.1-1965, R1970. A copy of that standard is available from:

American National Standards Institute, Inc.
1430 Broadway
New York, New York 10018

It is understandable that the use of foot-candles as a unit of measurement for illumination may be some what confusing. However, it is the only absolute means for defining illumination levels. Incidently, one foot-candle illumination is the light level at a distance of one foot away from a standard unit candle.

Additional information and assistance should be available from:

Illumination Engineering Society of North America
345 East 47th Street
New York, New York 10017

If we may be of further assistance, please contact us.

Sincerely,
Patricia K. Clark, Director
Directorate of Compliance Programs