Week Two: Lighting Quantity Criteria

LIGHTING QUANTITY CRITERIA
I. LIGHT IS MEASURED IN UNITS
A. Units are Foot Candles (US, or lux for countries using metric)

o Units are generally measured at a plane 30” from floor (desk height)

B. Decisions should be based on energy codes and IESNA recommendations

II. ILLUMINATION ENGINEER SOCIETY OF NORTH AMERICA MAKES RECOMMENDATIONS
IESNA recommendations for some visual tasks:
A. PUBLIC SPACES: 3 FC
B. BASIC ORIENTATION: 5 FC
C. SIMPLE VISUAL TASKS: 10 FC
D. TASKS OF HIGH CONTRAST AND LARGE SIZE: 30 FC
E. TASKS OF HIGH CONTRAST AND SMALL SIZE: 50 FC
F. TASKS OF LOW CONTRAST AND SMALL SIZE: 100 FC
G. VISUAL TASKS NEAR THRESHOLD: UP TO 1000 FC
H. MOST OFFICE TASKS: CATEGORY D
I. ACCOUNTING OR MAP READING: E OR F

III. CODE REQUIREMENTS MAY SUPERSEDE THESE RECOMMENDATIONS
A. ENERGY CODES (T-24 FOR EXAMPLE) MAY REQUIRE LOWER LEVELS IN SOME AREAS
B. HEALTH AND SAFETY REGULATIONS MAY HAVE HIGHER REQUIREMENTS (such as NFPA 101 requiring 1 FC average along a path of emergency egress)

IV. DESIGN FOR THE POPULATION USING THE SPACE
A. OLDER USERS NEED MORE LIGHT
B. TASKS THAT ARE SMALL OR HAVE LOW CONTRAST NEED MORE LIGHT
C. THESE GUIDELINES ARE AVERAGES

V. OVERALL UNIFORMITY IS NOT GENERALLY NEEDED
A. GRADUAL DIFFERENCE BETWEEN AREAS REDUCES EYE STRAIN
B. INTERIOR TASK PROPER AREA: 67-133% OF CRITERION VALUE
C. TASK IMMEDIATE SURROUND: 33-100% OF CRITERION VALUE
D. SURROUND: 10-100% OF CRITERION VALUE