Vertical Surface Illumination
Wall lighting is sometimes a substitute for
indirect ceiling lighting: it lightens shadow and
reduces excessive contrast. It works espe-
cially well when the walls are high in relation
to the size of the room. Another substitute is
direct downlights in combination with a light-
colored floor: the floor reflects light back to
the ceiling as though indirect lighting were
being used. The floor must be kept clean for
this technique to be successful.
The ideal lighting arrangement is often a
combination of direct and indirect light,
where the direct light takes the place of the
sun, casting shadows and modeling shapes,
and the indirect light softens the shadows,
acting as a blue sky or a photographer’s fill
light. Direct/indirect lighting designs are pro-
duced either with separate systems for
downward and upward light or with one
system that provides both downward and
upward distribution.
Surface Finishes and Reflectances
What is perceived as brightness is not the
incident light on a surface, but the light that is
reflectedfrom that surface toward the eyes.
Brightness results from the intensity of light
that initially strikes a surfaceandthe reflect-
ing or transmitting properties of that surface.
Whether it is of high or low intensity,
some amount of incident light from lumi-
naires or from interreflection falls on all room
surfaces. The relative size of these surfaces
and the intensity of light reflected from them
determine their visual prominence in an inte-
rior composition.
Reflected light is usually diffuse and
multidirectional, causing interreflection
between all surfaces and objects. This
interreflection fills in shadows, reduces con-
trast, and yields more uniform brightness.
The overall brightness results from the
distribution of reflected light, which, in turn,
depends on the reflectance properties of the
surfaces in the space. Dark-colored, low-
reflectance finishes absorb much of the light
that strikes them, reflecting only a small
amount toward the eye. This gives an
impression of a dark, high-contrast space
regardless of the amount of illuminance (fig-
ures 3.17 and 3.18).
Light-colored and high-reflectance fin-
ishes reflect much more of the incident light,
contributing to a higher brightness and a
greater diffusion of light (figures 3.19 and
3.20). This interreflection is independent of
the initial distribution of light, whether that
distribution is concentrated or diffuse.
The choice of surface finishes augments
or negates the initial distribution of light from
luminaires. This influence of reflected light
must be accounted for: understanding the
relationship between lighting equipment and
room surfaces is critical to successful light-
ing design.Secondary Light Sources
Any object or surface that reflects or trans-
mits light becomes a secondary light source.
The moon is an example: it is incapable of
producing light. The moonlight we see is pro-
duced by a primary source—the sun—which
is reflected by the moon’s surface.
Similarly, a lighted wall or ceiling
becomes a secondary light source that illu-
minates a room through reflection. The
result is then dependent on the reflected
light from the lighted surface, rather than on
the initial distribution of light from the
luminaires (see color plate 5).Three-Dimensional Form
In addition to altering our perception of
space, the direction and distribution of light
affect the perception of surfaces and objects
in a room.
All three-dimensional form is seen as a
pattern of brightness contrasts, often con-BRIGHTNESS