For the spectral measureme n t of the global radiation, we designed an instrument using an interference filter, a multiplier phototube and a diffuser. Since the diffuser plays a very important role in maintaining the directional cosine law, we constructed it taking the utmost precaution. As the results of the experimental tests, it was shown that the integrating sphere attached to the opaque plastic plate at the exit hole of the light, represents the best charactetistics of the diffusibility. The deviation of the characteristic curve from the cosine curve is less that 5% at the incident angles from 0 to 70 deg.
We picked out five narro w wave length intervals from near-ultra violet and visible regions. As detectors, five photomultipliers were used and their output photocurrents are recorded simultaneously.
The response of the instrument is very sensitive to the variation of the high tension power supply and even a small fluctuation is able to cause a significant error in the recorder.
Calibration was carried out by means of the standard lamp several times a day.
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