We present an original implementation of the absolute-sphere method recently proposed by Ohno. The luminous-flux unit, the lumen, is realized by means of an integrating sphere with an opening calibrated by a luminous-intensity standard placed outside. The adapted experimental setup permits one to measure luminous-flux values between 5 and 2500 lm with a significant improvement with respect to the simulated performances reported in the literature. Traditionally, the luminous-flux unit, the lumen, is realized by goniophotometric techniques in which the luminous-intensity distribution is measured and integrated over the whole solid angle. Thus sphere results are compared with those obtained with the Istituto Elettrotecnico Nazionale goniophotometer. In particular, a set of standards, characterized by luminous-flux values of ~2000 lm, has been calibrated with both techniques. We highlight some of the problems encountered. Experimental results show that the agreement between the two methods is within the estimated uncertainty and suggest promising areas for future research.
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D1 and D2 denote diaphragms of aperture diameters of 0.1798 and 0.1734 m, respectively.
Table 5
Conversion Factor f1 for Different Average Luminous Fluxes
inside the Sphere from the External Lamps
(lm)
f1 (lm A−1)
7.68 ± 0.39
21.57 ± 0.32
38.4 ± 1.8
21.47 ± 0.65
72.0 ± 0.58
21.58 ± 0.04
104.4 ± 0.67
21.62 ± 0.02
Table 6
Luminous Fluxes of Three Lamps in the 100–400-lm Range Measured by the Absolute Sphere and by a Traditional Ulbricht Sphere Calibrated with Respect to the IEN Goniophotometer
Ratio between the luminous flux measured by the absolute sphere and the value measured with the Ulbricht sphere.
Mean value of this ratio and its standard deviation.
Table 7
Luminous Fluxes of Six Standard Lamps Measured by the Absolute Sphere and the Goniophotometer
Ratio between the luminous flux measured by the sphere and the value measured by the goniophotometer.
Mean value of this ratio and its standard deviation.
Tables (7)
Table 1
Uncertainty Budget for the Luminous-Flux Measurement with the Absolute Sphere
D1 and D2 denote diaphragms of aperture diameters of 0.1798 and 0.1734 m, respectively.
Table 5
Conversion Factor f1 for Different Average Luminous Fluxes
inside the Sphere from the External Lamps
(lm)
f1 (lm A−1)
7.68 ± 0.39
21.57 ± 0.32
38.4 ± 1.8
21.47 ± 0.65
72.0 ± 0.58
21.58 ± 0.04
104.4 ± 0.67
21.62 ± 0.02
Table 6
Luminous Fluxes of Three Lamps in the 100–400-lm Range Measured by the Absolute Sphere and by a Traditional Ulbricht Sphere Calibrated with Respect to the IEN Goniophotometer
Ratio between the luminous flux measured by the absolute sphere and the value measured with the Ulbricht sphere.
Mean value of this ratio and its standard deviation.
Table 7
Luminous Fluxes of Six Standard Lamps Measured by the Absolute Sphere and the Goniophotometer
Ratio between the luminous flux measured by the sphere and the value measured by the goniophotometer.
Mean value of this ratio and its standard deviation.