During past decade phosphors for fluorescent lamps have extensively been developed. Emission characteristics of important phosphors for. fluorescent lamps, together with a general review of the phosphors developed recently by numerous workers, are described. All the phosphors used in this investigation, except some phosphors such as calcium and magnesium tungstate which are used as standard samples, were prepared by the present authors. Spectral energy distribution curves of these phosphors are given and they allow us to compare the relative intensity of emission in the visible or ultraviolet region of the spectrum.

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Noctovision is a device to see things in complete darkness under near-infrared illumination. The essential element of the device consists of a vacuum tube, called an image converter tube, which is sensitive to radiation of the wave-length ranging from 0.4 to 1.2 micron. When it is used in combination with an infrared filter, which transmits radiation of the wavelength of 0.8 micron or longer, the equipment can be made to be sensitive only to the near-infrared range. One of the most interesting aspects of such a noctovision equipment is that whether or not it can be used under conditions of low visibility such as the case of seeing through rainy, foggy, hazy or smoky atmosphere.
This paper is concerned with an experimental investigation of the atmospheric transmission in the near-infrared and visible portions of the light spectrum.
The field tests were performed during the period of April through December 1957, at and near the Kenzaki Light-House in Kanagawa Prefecture, the span being approximately 280 meters round trip. Light from an incandescent lamp was separated in two parts by means of an optical fi lter, one being the near-infrared radiation of 0.8-1.2 micron, while the other being the visible light of 0.4-0.7 micron. These twe portions of the light, after being transmitted through the atmosphere to be investigated, are received by two independent light receivers, thereby enabling one to record the behavior of the change of the amount of light attenuation through the same atmosphere.
Laboratory experiments were also conducted for the purpose of measuring light transmission through artificial fog or through many types of smoke produced under different conditions.
The artificial fog were tried to simulate natural fog as much as possible, whose particle diameter usually ranging between 5 and 20 microns. It is produced by cooling warm air using dry ice. Many different types of noctovision equipments explained previously were tentatively manufactured and they were used under diversified conditions in order to compare the results with those of direct vision by human eyes.
As the results of experiments, it has been made clear that the atmosphere in question has a fairly good transparency of near-infrared as compared with visible light when the atmosphere contains relatively small particles, i. e. haze or smoke. However, in the case of rain or fog whose particle size is larger than that of haze or smoke, the transmission of the near-infrared becomes worse in exactly the same manner as in the case of the visible light. It was experimentally made clear that this statement also holds in the case of the field experiments of the noctovision equipment. In fact, one can see through smoke or haze fairly well by means of the noctovision equipment just as effectively as in the case of infrared photography. According to the authors' experience, the details of the surfaces of distant mountains or of distant beach could be seen through the noctovision equipments clearly and distinctly through smoky or hazy atmosphere in many instances.

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