The characteristics of hot cathode fluorescent lamps in low current regions (10∼40mA) were investigated by experiments and numerical analysis. A quantitative correlation between the cathode fall voltage and the lifetime was obtained. If the cathode fall voltage is less than or equal to 14V, arc discharge can be maintained stably during the lifetime, and hence, the life reliability of lamps can be improved. In order to reduce the cathode fall voltage for a given lamp current, it is effective to increase Ar gas pressure, and to decrease the surface area of the coils. The cold spot temperature is not effective to reduce the cathode fall voltage in the range of 10 to 60°C. The relation between the lamp design parameters and the cathode fall voltage was analyzed numerically on the basis of a modified theoretical model. The calculated results support the experimental results.

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Although originally developed for aircraft use, head-up displays (HUDs) have found application in automobiles recently. A system for evaluating automotive HUDs has been developed which is based on the double task method and takes into account driving conditions. Seven kinds of correct response rates (CRRs) are defined as the evaluation standards. Using various kinds of HUDs, evaluations are made focussing on the relationship between the fineness of the image and the distance from the driver’s eyes to the image. It can be concluded that the task of reading the HUD image has little effect on recognition of the forward view and is closely related to peripheral vision. This paper also discusses a new merit index derived from the CRRs, which can be used as a measure of HUD performance. The results suggest there is an optimal image fineness and distance to the HUD image.

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A formula for luminance distribution on the clear cloudless sky and a formula for total horizontal illuminance from that sky are proposed based on a scattering theory. The clear sky light consists of the scattered light of the direct sunlight and that of the reflected light from the ground surface. And the main scattered light in the clear sky is the 1st-order scattered light of the direct sunlight, but its higher order scattered light than or equal to the 2nd-order and the scattered light of the reflected light from the ground surface are considerably included in the clear sky light and they have effect on the variation of clear sky light, respectively. In the proposed formulas, these effects are estimated from the result of a theoretical analysis. In the conventional formulas for the clear sky luminance distribution which are derived based on observation, however, these effects are not done because of difficulties of the estimation by means of measurements. Therefore the luminance distributions from the proposed formula approximate more closely to measured data under the clear sky than the conventional formulas. And the proposed formula for total horizontal illuminance from the clear sky is applicable not only to the clear sky but to the overcast sky because the scattering characteristics of the overcast sky is equivalent to those of the clear sky where aerosole is included quite densely.

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Adaptation for uniform fields and for non-uniform fields is compared. Experimentally, the luminance difference thresholds for the Foveal Adaptation Luminance (Lf), the Background Luminance (Lb) and the Equivalent Veiling Luminance (Leq) are separately investigated. On the basis of the results, a method to derive the necessary luminance of an object or of the background against which the object in the non-uniform field is seen is explained.

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