Construction of Two-Axis Goniophotometer for Measurement of Spatial Distribution of a Light Source and Calculation of Luminous Flux

A two-axis goniophotometer is constructed at National Metrology Institute of Turkey (TUBITAK UME) for characterizing photometric properties of compact light sources. With the new device, total luminous flux emitted by a light source at both cap-up or cap-down mounting positions is calculated from the integration of the illuminance values E(theta, phi) measured on the goniometric spherical surface. The internal calibration of the system is performed by means of two calibrated light sources with known luminous flux values. The constructed system is also capable of measuring the luminous intensity distribution values I(theta, phi) of compact light sources. The uncertainty analyses of the luminous flux measurements as well as the internal calibration of the instrument are also presented herein.