Method and apparatus for measuring illumination characteristics of a luminaire
A method and associated apparatus are disclosed for measuring illumination characteristics of a luminaire having unknown characteristics. The method includes steps of providing an array of calibrated photodetectors in known locations in proximity to a mounting location, and then illuminating the array with a luminaire having unknown illumination properties. The resulting data is used to calculate the luminous intensity vs. angle from the luminaire and the luminous flux of the luminaire. Methods of calibrating the measurement with a known luminaire are presented along with methods of determining the angular position of the detectors in the array. Color-sensitive detectors can be used to determine the angular distribution and average value of the luminaire's correlated color temperature.
1. A method for measuring illumination characteristics of a first luminaire comprising:
providing a luminaire mounting location and a surface upon which an array of photodetectors is disposed, each photodetector in the array having a known position, the surface being oriented to allow a first luminaire at the luminaire mounting location to illuminate the array of photodetectors;
determining, by a processor of a computer, responsiveness of the photodetectors in the array of photodetectors to illumination characteristics of the first luminaire, to thereby provide measured illumination data;
using, by the processor of the computer, calibration constants for each photodetector to calculate a luminous intensity at a horizontal angle and a vertical angle of each photodetector;
mounting a second luminaire having known illumination characteristics at the luminaire mounting location;
determining, by the processor of the computer, responsiveness of the photodetectors in the array of photodetectors to the known illumination characteristics of the second luminaire, to thereby provide a calibration illumination data set;
calculating, by the processor of the computer, calibration factors of each photodetector from the calibration illumination data set based on the known illumination characteristics of the second luminaire; and
storing, by the processor of the computer, results of a comparison of measured output data in a computer system memory to thereby provide a set of scaling factors for each of the photodetectors.
2. The method of claim 1 , wherein the method further comprises:
interpolating the luminous intensity at intermediate angles between the photodetectors; and
integrating the luminous intensity to obtain a luminous flux of the luminaire.
3. The method of claim 1 , wherein the known position of each photodetector in the array is determined by:
mounting alight source at the luminaire mounting location, the light source providing a beam of light of a known orientation;
scanning the beam of light over the array of photodetectors, the photodetectors being responsive to being illuminated and providing an output signal in response thereto; and
saving, by the processor of the computer, information which correlates the known orientation of the beam of light with the output signals from the photodetectors to thereby obtain the position of the photodetectors with respect to the luminaire mounting location.
4. The method of claim 1 , wherein the photodetectors measure total luminous intensity and color coordinates versus horizontal and vertical angles relative to the luminaire, and the computer uses the measured color coordinates to calculate a correlated color temperature of the luminaire.