The results of the study on the threshold value of visual perception of Landolt’s Ring visual targets within the visual field in a visual environment having uniform background luminance has already been reported. In the present paper are described the results of an experiment concerning the effect of a highly luminant object such as a light source or window existing in the visual field on the threshold value of visual perception. In the experiment, an apparatus as shown in Fig. 1 and a target consisting of a sheet of unglossed printing paper with its one half printed in black were used, and the observers were told to adjust the position at which the boundary of the white and black parts of the target become imperceptible as the target was brought near to the light source. Considering that at that point the contrast of the target and the background luminance were changed to the threshould value of visual perception by the veiling light produced by the highly luminant light source, the quantity of the veiling light was calculated. The results of the calculation obtained are summarized as follows:
(1) The veiling light radically decreases in the inverse proportion to the light source deflection angle from the position at which the glare light source does not enter directly into the fovea centralis of the eye.
(2) The quantity of the veiling light occurring in the human visual system increases approximately in direct proportion to the increase of the luminance of the glare light source.
(3) When the size of the glare light source is increased, the quantity of the equivalent veiling luminance increases approximately in the direct proportion to the increased size.
(4) For the quantity of the equivalent veiling light when the size of a light source is large, the large glare light source should be divided by the solid angle of 1° visual angle and the quantities of the equivalent veiling light generated by the respective units of the divided light source should be summed up, and thus the background luminance and the contrast can be obtained.

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Color matching properties of Japanese observers were examined by using a new trichromator equipped with numerical control devices. The additivity law of the color matching equation was confirmed to hold good for both of the 2° and 10° fields, but it was suggested that the color matching functions might be affected by the chromatic adaptation to the color stimulus pre-exposed in the visual field. Two sets of the 10° color matching functions were obtained by ten Japanese observers. One of them was determined by the method of constant stimuli and the other by the method of adjustment. There were no appreciable differences between the two sets of the ETL 10° color matching functions, but both of them differred a little from the data of the CIE 1964 supplementary standard colorimetric observer in the region of long wavelengths.

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Complex vapor compounds of the form MLnl₄, where M is an alkali metal ion and Ln is a lanthanide or another trivalent ion, play an important role in metal halide arc lamps. Such compounds may be the dominant species in the vaporization process and increase the density of desired radiative species in discharge medium. Data are reported from a number of such systems obtained by mass spectroscopic, optical adsorption, vapor transport and lamp characteristic measurements.

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The study of the new High Pressure Sodium Lamp with the improved color rendition is reported. This type of lamp has the high efficacy of 120lm/W and the improved color rendering index of Ra 60. Furthermore, it can be operated on the conventional mercury lamp ballast. Effect of filling Xenon gas, the new sealing glass and the new type of electrodes were useful to realize this new type of lamp.

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Recent investigations about electron emission materials for HID lamps are reviewed. In high pressure mercury and high pressure sodium lamps, new emission materials like Ba_1.8Sr_0.2CaWO₆ have been developed and resulted in a significant improvement of lamp performance. In the case of metal halide lamps, rare-earth oxides have been used because of their higher stability in lamp performance. However, the performance of metal halide lamps is still poor, and thus much work on the improvement is continued.

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