Yutaka Kurioka

Method for Selecting a Photomultiplier Suitable for Accurate Measurement of Spectro-Radiometric Standard in Ultra-Violet Region and its Photometric

The present paper describes the method selecting for a photomultiplier with good performance, especially suitable for making the measurement with high precision and accuracy at very weak light levels, such as the ultra-violet radiation from a black body standard radiator.The following four characteristics were studied:(1) photocathode sensitivity, (2) anode sensitivity and signal to noise ratio, (3) stability or fatigue, and(4) linearity of the electrical output to the light input.The relations among the above four characteristics were also investigated using two kinds of measuring methods, which were D. C. method and photoelectron counting method. The former is the most conventional method for measuring average photoelectric D. C. current from a photomultiplier and the latter is a recently developed method for counting the photoelectron pulses from a photomultiplier.Based on these studies, some notable remarks in selecting photomultipliers were revealed as follows;(1) Although the photocathode sensitivity is the most important characteristic, there are large variations among the sensitivities of photomultipliers.are large variations among the sensitivities of photomultipliers. photoelectron counting method, and it is independent of the photomultiplier gain in the D. C. method.(3) Even the photomultiplier, which has the fatigue of several percent in a few hours in the D. C. method, shows better stability in the photoelectron counting method.(4) In the linearity, there is no significant difference between the two methods.

Studies on Color Rendering and Illuminant Metamerism (Part 3)

Based on the spectral power distributions of actual fluorescent lamps (about 6, 500 K in color temperature), the amounts of line spectra were pre-assigned as 80.0 to 405 nm, 200.0 to 436 nm, 100.0 to 546 nm and 30.0 to 578 nm, respectively.The existence of the spectral power distributions of the test illuminants with these amounts of line spectra, which fulfil the following requiremnts further was examined.(1) With respect to any of the reference illuminatnts, the test illuminants have the same chromaticity coordinates and the general color-rendering index of Ra=100, provided that the spectral power distributions of the reference illuminants are normalized as 100 or near 100 at the wavelength of 560 nm.(2) In addition to the requirement 1), the minimum value of the sum of squares is expected with respected to the difference in spectral power distributions between the reference and the test illuminantsThese conditions are reduced to solving the linear homogeneous equations derived by applying the Lagrange multiplier method. The spectral power distributions Jt (λ) of the test illuminant was obtained with respect to the CIE standard illuminant C as the reference, which also satisfied the above two requirements.However, the computed results give an imaginary spectral power distribution which corresponds to negative radiations in some of the visible spectra. This might suggest the impossibility to realize the general color rendering index of Ra=100 with a fluorescent lamp having the pre-assigned amounts of line spectra shown above.

Some Problems on the Power Source and measuring Circuit for the Photometry of Fluorescent Lamps

Although in the precise measurements, a fluorescent lamp should be controled at a rated lamp wattage, it has also some advantages to control it at a rated lamp current in the practical measurements.The authors compared these methods on the following factors:1. Measuring instruments to be used, 2. difficulties of the measurments, 3, effects of the impedance drop at the rated lamp current, and of the material and saturation characteristics of the used choke coil, 4. effects of the frequency and the voltage wave form of the power source, 5. the relation between the percent variation of the luminous flux and that of the lamp wattage or amp current.From these experiments the authors recommend to control the lamp combined with a proper choke coil at a rated lamp current for the practical measurments, and propose a specification on the power source and conditions for the measuring circuit, in order to obtain the unified luminous flux and electrical pararneters on fluorescent lamps among the industrial laboratories. Deformation of the wave form in each parlf of the measuring circuit due to the characteristics of the used choke coil is also discussed.