Calculations and Measurements - Road Lighting: Fundamentals, Technology and Application - page 216

Fig. 14.13 Commercial
photometer with rotating
mirror and fixed luminaire
position

near-field photometry requiring only a limited laboratory space, has become feasible.
In near-field photometry, the luminaire is not considered as a point source but as
a combination of bright surfaces, each with its own photometric properties that
can be characterized by their luminances in many different directions. Near-field
goniophotometers map the luminance distribution of these light-emitting surface
areas using a luminance meter with CCD detectors.

14.2.3.2 Light Output

As has been mentioned in the Section about the measurement of luminous flux, the
total luminous flux of a lamp or luminaire can be obtained from the calculation of the
solid angle weighted average of all luminous intensities. In fact, using high-quality
goniophotometers for obtaining these luminous intensities offers the most accurate
method for determining the luminous flux or light output of a luminaire. Since here
absolute values are required, calibration against a light source with known luminous
flux is needed.

14.2.4 Measuring Road Surfaces

It has been shown in Chap. 12 that the reflection properties of a road surface can, for
the purpose of luminance calculations, be characterized by a reflection table contain-
ing 396 reduced luminance coefficients. These road surface reflection properties can