recommended illuminance values may be
misleading because a dull or gloomy envi-
ronment will be unsatisfactory.
True illuminance requirements vary with
the visual difficulty of the work task, the age
and eyes of the worker, and the importance
of speed and accuracy in the completion of
the task. Typical illuminance values are
shown in table 15 in the Appendix. At best,
these values provide aguideto the quantity
of illuminance needed on the work surface
for accurate and comfortable seeing.
In itsLighting Handbook, ninth edition,
the IESNA publishes an illuminance selec-
tion procedure with horizontal illuminance
recommendations for specific applications.
It is supplemented by a “Design Guide” that
attempts to account for other factors that
influence perception: including the appear-
ance of the interior, color appearance and
color contrast, daylighting integration, glare,
vertical illuminance, surface finishes and
textures, brightness contrast, facial model-
ing, and the presence of sparkle.
A consolidated listing of the IESNA hori-
zontal illuminance recommendations appears
in table 16 in the Appendix. It covers illuminance
values for seven categories and a variety of
tasks.
Categories A, B, and C include casual
activities that take place over the entire area
of a space. For example, in a circulation
space such as a hotel lobby or office building
corridor, the visual task of circulation is a
constant throughout the space, and an
illuminance value of 5 fc is recommended.
Categories D, E, and F refer to common
tasks that remain fixed at one or more partic-
ular locations; these values are to be applied
only to the appropriate task area, recognizing
that several different kinds of tasks may occur
in the same room. The IESNA recommends a
value of 20 fc as the minimum illuminance on
the horizontal work surface for the “non-task”
parts of the room where less demanding
visual work is performed.
Category G is for special, visually difficult
tasks. The lighting system for these tasks
requires careful analysis. Recommended
illuminance values are achieved with supple-
mental task lighting, and range from 300 to
1,000 fc.Age
IESNA illuminance recommendations do not
account for the age of the occupants. The
visual requirements of older persons differPHOTOMETRICSFigure 10.3Rectilinear luminous intensity distribution curve of a 60PAR38/HIR spot lamp (left) and a 60PAR38/HIR flood
lamp (right).