Weighting Factors to be in Selecting Specific illuminance within Ranges of Values for Each Categories

a.  For illuminance categories. A through C

Room and occupant characteristics

Weighting factor

-1

0

+1

Occupant ages

Under 40

40-55

Over 55

Room surface reflectance’s*

Greater than 70 percent

30 to 70 percent

Less than 30 percent

b.  For illuminance categories  D  through I

Task and worker characteristics

Weighting factor

-1

0

+1

Worker's ages

Under 40

40-55

Over 55

Speed and/or accuracy 1

Not important

Important

Critical

Reflectance of task background 2

Greater than 70 percent

30 to 70 percent

Less  than 30 percent

 *Average weighted surface reflectance’s, including wall, floor and ceiling reflectance’s, if they encompass a large portion of the task area or visual surround. For instance, in an elevator lobby, where the ceiling height is 7.6 meters (25 feet), neither the task nor the visual surround encompass the ceiling, so only the floor and wall reflectance’s would be considered.

1 In determining whether speed and /or accuracy are not important, important or critical, the following questions need to be answered: What are the time limitations?  How important is it to perform the task rapidly? Will errors produce an unsafe condition or product?  Will errors reduce productivity and be costly? For example, in reading for leisure there are no time limitations, and it is not important to read rapidly.  Errors will not be costly and will not be related to safety. Thus, speed and/or accuracy is not important.  If however, a worker is involved in exacting work, accuracy is critical because of the close tolerances, and time is important because of production demands.

2 The task background are that portion of the task upon which the meaningful visual display is exhibited. For example, on this page the meaningful visual display includes each letter, which combines with other letters to form words and phrases. The display medium, or task background, is the paper, which has a reflectance of approximately 85 percent.