Interior Lighting for Designers

CRIs of different lamps are valid only if they
have similar correlated color temperatures.
Therefore, it is inappropriate to compare two
light sources unless their color temperature
is similar—within 100 K to 300 K.
For example, a 3000 K RE-70 fluores-
cent lamp and a 6500 K “daylight” fluores-
cent lamp render objects differently, despite
the fact that they both have a CRI of 75. This
occurs because the CRI for the 3000 K lamp
was compared to a blackbody radiator and
the CRI for the 6500 K lamp was based on
comparison to actual daylight.
Rais an average of the color rendering
ability of eight test colors; better performance
at some wavelengths is concealed when
averaged with poorer performance at other
wavelengths. As a consequence, two lamps
that have the same color temperature and
CRI may have different spectral distributions
and may render colored materials differently.
Some typical CRIs appear in table 1 in
the appendix.
The color properties of the light source
significantly alter the appearance of people.
Because incandescent sources are rich in
red wavelengths, they complement and flat-
ter complexions, imparting a healthy, ruddy,
or tanned quality to the skin. Cool fluores-
cent and HID sources that emphasize the
yellow or blue range produce a sallow or pale
appearance.

Subjective Impressions

The color of light has a profound effect on
subjective impressions of the environment.
The Amenity Curve indicates that warmer
light is desirable for low luminance values
(figure 4.2). It also shows that a room uni-
formly lighted to 20 footcandles (fc) will be
unpleasant with either kerosene lamps
(about 2000 K) or lamps that simulate day-
light (about 5000 K).
With the warm-toned kerosene source,
the quantity will seem too high and the

space too greatly lighted. With the simulated

daylight source, the same quantity of light

will seem dark and dingy. Both warm fluores-

cent (2700 K or 3000 K) and standard

incandescent lamps (2600 K to 3100 K) fall

within the acceptable range on the chart.

In addition, a warm atmosphere sug-

gests friendliness or coziness. A cool atmo-

sphere implies efficiency and neatness.

Flynn evaluated subjective responses to

colors of white light that are produced by

electric light sources in interior spaces at

intermediate illuminance values.

Flynn’s subjects categorized their impres-

sions of visually warm versus visually cool

space as follows: cool colors (4100 K) stim-

ulate impressions of visual clarity; warm

colors (3000 K) reinforce impressions of

pleasantness, particularly when a feeling of

relaxation is desirable.

Flynn found that diffuse light plus warm

(orange-red) hues intensify impressions of

tension and anxiety. Diffuse light plus cool

(violet-blue) hues reinforce impressions of

somberness; at low luminance values, they

create an impression of gloom.

He also found that patterns of sparkle

plus saturated warm (orange-red) hues

strengthen impressions of playfulness and

merriment; this is particularly strong with

random patterns of light and color. Patterns

of sparkle plus saturated cool (violet-blue)

hues reinforce impressions of enchantment;

this is particularly strong with rhythmic or

regimented patterns of light and color.

Surface Finishes and Color of Light

To reiterate: light does not have color, and

objects do not have color. Color resides in

the eye/brain system.

The relationship between the spectral

distribution of light and the colors of fabrics,

walls, and other elements in the interior is,

therefore, pivotal. Some objects appear to

INTERIOR LIGHTING FOR DESIGNERS