Interior Lighting for Designers

For example, if theSC= 1.5, then for an
8-ft ceiling height,

MH= 8 ft 0 in – 2 ft 6 in to the workplane

= 5 ft 6 in AFF

S = 5.5 ft × 1.5 = 8.25 ft

The center-to-center maximum spacing from
the center of one luminaire to the center of
the next is thus 8.25 ft (figure 13.15).
For rectilinear luminaires,SCis expressed
as parallel or perpendicular, indicating the
spacing-to-mounting-height ratio in either the
direction parallel to or perpendicular to the
orientation of the lamps within the luminaire.
To maintain uniformity of light intensity
over a large work area, avoid exceeding the
manufacturer’s recommended maximum
SC. Because of wall surface absorption,
maximum distance from the last row of
luminaires to the wall is usually one-half to
one-third the spacing in the room to prevent
a falloff in illuminance near the walls (figures
13.16 to 13.18).

Even with this reduced spacing, work

surface illuminance near the walls is often

only half that measured in the center of the

room. In critical seeing areas, supplemen-

tary luminaires are added near the wall

(figure 13.19).

Office partitions block some overhead

light from a direct system, preventing it from

reaching work surfaces. Depending on the

location of the downlights, some areas will

be left in shadow (figure 13.20). Well-

designed uplighting, because it produces

even illuminance overhead, softens and

reduces this shadowing.

Uplighting (Indirect)

The primary use of uplighting (indirect light-

ing) is to create evenly luminous ceilings that

reduce VDT screen reflections. For uplighting

to be successful, luminance differences on

the ceiling plane must be minimal. If bright

patches of higher luminance occur, they are

reflected in the VDT screen, causing a dis-

tracting background.

DESIGN

Figure 13.15Spacing-to-mounting-height ratio.