Interior Lighting for Designers

between the reflected screen images of the
luminaire and ceiling.
With a well-designed indirect system,
the light received on the ceiling plane exhib-
its an even luminance, yielding minimal
brightness contrast in the VDT screen. The
underside of the indirect luminaires must be
approximately the same luminance as the
ceiling plane. When the luminance seen
across the VDT screen is uniform, minimal
interference occurs.

Paper-based tasks
Almost all office work involves paper-based
tasks. Paper documents are referenced for
word processing, order entry, information
retrieval, and computer-aided design. In
addition to the lighting requirements for VDT
tasks, lighting for paper-based visual tasks
must also be considered.

Ambient Lighting

Ambient lighting is provided by two basic
methods: (1) downlighting (direct), where
overhead luminaires provide a downward

light distribution, and (2) uplighting (indi-

rect), where pendant luminaires provide

upward light that is then reflected from the

ceiling.

Downlighting (Direct)

With downlighting (direct lighting), luminaires

are arranged according to the ambient light-

ing requirements for either uniform or nonuni-

form distribution over the horizontal work-

plane.

For direct ambient lighting, thespacing

criterion (SC), orspacing-to-mounting-height

(S/MH) ratio, provided by the luminaire man-

ufacturer, gives the maximum recommended

spacing between luminaires to achieve uni-

form, ambient lighting.

To quickly assess the potential of a

downlight luminaire to provide uniform illumi-

nation of the horizontal plane, SC is the

center-to-center distance betweenluminaires

(spacing) based on their mounting height

above the workplane.

S = MH × SC

INTERIOR LIGHTING FOR DESIGNERS

Figure 13.14A large area of the ceiling is within the field of view when viewing a VDT.