excessive contrast is created in a different
way. Even when uniform ceiling luminance is
achieved, the diffuse reflected light may
have a “washing out” effect that reduces the
visibility of the screen. Moreover, because all
of the light in the space is diffuse, indirect
systems also create a bland interior.
It is thevariationin room luminance that
is extremely critical, however. All surfaces
and objects reflected by the VDT screen into
the worker’s normal line of sight—especially
room surface finishes such as system divider
panels, vertical surfaces of filing cabinets,
and the ceiling plane—must be of more or
less equal luminance if distracting images
are to be prevented.
Many high-quality VDTs are now fur-
nished with integral low-reflectance screens;
newer, flat-screen monitors have liquid crys-
tal displays (LCDs), which reflect very little
light from all directions except perpendicular
to the screen. In time, VDTs may cease to be
a lighting challenge.
Sparkle
The principal difference between glare and
sparkle is the relationship between the area
and magnitude of luminance in the field of
view. Large areas of luminance are distract-
ing and disconcerting; relatively small areas
of similar or higher intensity are points of
sparkle and highlight that contribute to emo-
tional excitement and visual interest.- Direct sparkle. Examples include Christ-
mas tree lights; small, exposed, clear fila-
ment lamps; and perforated shielding
materials (see color plate 6). - Reflected sparkle. Examples include
textured metal and pebbled surface finishes
(see color plate 7). - Transmitted sparkle. Examples include
crystal chandeliers and sandblasted- or
etched-glass (frosted)diffusersaround clear
filament lamps. Clear filament lamps com-
bined with crystal glass, particularly when
that glass is faceted, introduce subtle color
BRIGHTNESSFigure 3.36Proper desk lighting.