Interior Lighting for Designers

Brightnessis what we perceive. It is a
subjective attribute perceived in varying
degrees of intensity. Reflected light was for-
merly measured in footlamberts (fL).
Because brightness changes with viewing
angle, the term footlamberts has been dep-
recated by the Illuminating Engineering Soci-

ety of North America (IESNA). Perceived

luminance is now measured by exitance.

It is only meaningful to measure

exitance, however, if this quantity remains

constant (or nearly so) for a wide range of

viewing angles. Diffuse surfaces, called

Lambertian for the German physicist and

INTERIOR LIGHTING FOR DESIGNERS

Figure 10.1Polar luminous intensity distribution curve.