Internal Traceability between Luminous Flux and Illuminance Standards

Two methods for the measurement of the luminous flux are presented: the first is based on an integrating sphere and a luminous flux standard lamp, the second utilizes an accurate goniometer and an accurate illuminance meter. A comparison between the two methods is carried on for two different light sources: an LED and a halogen source, presenting different luminous fluxes. The measuring procedure and an evaluation of the measurement uncertainties are described for both the methods. The comparison shows a good agreement between the two measuring processes: both of them allow the identification of the luminous fluxes with relative uncertainties of about 1.5%, covering the differences between the luminous flux values. The comparison is considered a valid possibility of verifying the calibration constancy of the laboratory luminous flux and illuminance standards.