Automotive head-up displays (HUDs) are superior to conventional console displays in permitting recognition of the forward view and the displayed images. To test the superiority of HUD in visual optics, we have proposed the hypothesis that the peripheral field of vision plays an important role in allowing the driver to recognize displayed images while watching objects outside the vehicle. Using an experimental setup which can position HUD images three-dimensionally in space, we can verify the validity of this hypothesis based on a visual optical model.
One experimental result is that drivers can recognize some amount of information from the HUD in the peripheral field of vision. Another result is that the HUD being out of focus in the peripheral visual field can affect recognizability of HUD images. These results support the hypothesis. The model predicts that the recognizability of the HUD image will depend on depression angle. This is also confirmed qualitatively.

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The performance characteristics of a lead peaked ballast is analyzed using the equivalent circuit model and the discharge voltage-current model. The operating temperature of the lamp is 40°C or 0°C. The obtained results are as follows:
1) The discharge current consists of the currents flowing through the leakage inductance and the saturated inductance based on the splined-gap in the secondary iron core. The discharge current waveform can be controlled by adjusting the ratio of the two current components and the phase difference between them.
2) The crest factor of the discharge current takes a minimum at a certain N₂/N₁ ratio when the peak of the output voltage under a no-load codition is kept constant, where N₂/N₁ is the ratio of the secondary and the primary winding numbers.
3) The crest factor of the discharge current decreases with increasing the width of the splined-gap, when the output wattage is kept constant by adjusting the other circuit parameters.
4) The off-time is produced at the reignition phase when the reignition voltage of the lamp overcomes the applied voltage supplied through the circuit.
5) When the operating temperature of the lamp is low, the applied voltage through the circuit decreases, while the reignition voltage of the lamp increases.
6) The crest factor of the discharge current decreases while the applied voltage increases, when both of the splined-gap width and the capacitance increase.

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LaPO_4: Tb, Ce phosphors have been used for the green component of three-band emission type fluorescent lamps.
We have confirmed that emission intensity of Tb³⁺ under 254nm excitation is greatly enhanced by the energy transfer from Ce to Tb in the case of the Ce co-doping, and the fluorescent intensity-temperature characteristics were also improved by substituting borate for a small part of phosphate, or by additive doping with thoriun.
In order to apply this phosphors to high pressure mercury lamps which operate at higher wall temperature and loading than low pressure mercury lamps, some characteristics of this phosphors under 365nm excitation were investigated. However, the green emission intensity under 365nm excitation was rather decreased by doping with cerium. The reason for this phenomena could possibly be caused to energy transfer from Tb³⁺ to Ce³⁺, as excitation spectra of Tb³⁺ and emission spectra of Ce³⁺ overlap each other.
Time-resolved spectra have been also observed under 365nm dye laser excitation. The ⁵D₃→⁷F_j emissions were found in highly Tb-doped LaPO₄: Tb, Ce phosphors, and new line emissions around 600nm were found in (La, Ce, Th) (PO₄, BO₃): Tb phosphors under 365nm pulse excitation which are considered to be originated to Ce²⁺.

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If HID lamps are operated on sinusoidal high frequency power (above 1kHz-), acoustic resonances occur in the discharge tube and arc instabilities are observed. For this reason, high frequency electronic ballasts have not been widely used. If it were possible to operate HID lamps on high frequency power without arc instabilities, one could expect a reduction in weight, size and wattage losses of the ballast. Such electronic ballasts would lead to the wider application of HID lamps. In order to find new methods for the stable operation of HID lamps at high frequency, the authors have first analyzed the instability phenomenon theoretically. They then classified the stable operating methods which had been reported in the past. They then devised a new stable operating method which consisted in changing wavelength in the discharge tube from a progressive wave to a reflected wave. This method can suppress the formation of a standing wave and has not been reported.
norder to find new methods for the stable operation of HID lamps at high frequency, the authors have first analyzed the instability phenomenon theoretically. They then classified the stable operating methods which had been reported in the past. They then devised a new stable operating method which consisted in changing wavelength in the discharge tube from a progressive wave to a reflected wave. This method can suppress the formation of a standing wave and has not been reported.
Next, the authors analyzed and simulated the new stable operating method theoretically and found the best operating condition. By the simulation, it was found that HID lamps can be operated stably at high frequency by changing the wavelength in the ratio of 1.0: 0.4 every cycle. Finally, in a practical experiment, HID lamps were operated under the conditions that had been simulated. The new method permitted operation without acoustic resonances and with greater stability then normal sine wave operation.

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Skin color appearance in an important factor in various fields of illumination, cosmetic, television and printing. Studies have been reported on the appearance of skin color under many kinds of lamps. In many papers, the observers of the experiments evaluated their own faces in the mirror.In practice, however, we are seen by others in a variety of places. From the point of view of female skin types, there are natural skin and make-up skin, but the difference in appearance between the two types has not been sufficiently discussed.
We evaluated experimentally the difference in appearances between natural skin and make-up skin under six lamps. Evaluations were made by six female objects and by 17 other observers.
In this paper, we examine the following items,
(1) The observers' evaluation of natural and make-up skin.
(2) The difference in skin color appearance under six lamps.
(3) The difference in natural skin and make-up skin appearances.
(4) The difference between the observers' and the objects' evaluation.

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The brightness perception of a light with non-uniform luminance distribution is not clearly understood, especially at suprathreshold levels. Two experiments were done to clalify this mode of brightness perception. In the first experiment, subjects made brightness matches between a test stimulus with non-uniform luminance distribution and a matching stimulus with uniform luminance distribution. Matches were made as function of background luminance. In the second experiment, brightness matches were made between a multiple-point stimulus and a one-point stimulus as a function of the point and separation.
With respect to the variables of stimulus size and background luminance, the results show that the brightness perception of the non-uniform stimulus and the multiple point stimulus is similar to that of the uniform stimulus. The brightness of the non-uniform stimulus may be obtained with an element-contribution function derived from circular stimuli with uniform luminance distribution. The brightness of the multiple-point stimulus also agrees with the from the elementcontribution model at a background luminance of 0 cd/m², but does not agree at a background luminance of 10 cd/m².

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Because of several distinct advantages, inverter circuits are widely used to operate discharge lamps. One of the issues in the development of inverter circuits is to reduce the weight and size of the inverter. It is therefore necessary to reduce the size of the electronic components, especially the inductors.
In this paper, a non-linear magnetic model developed by Potter is used to simulate the characteristics of inductors. The model shows good approximation for the magnetic characteristics of thin ribbon and ferrite materials. The model is adapted for the resonance inductors used in the inverter circuits for fluorescent lamps, and the filter chokes for HID lamps. The wave-forms in inverter circuits obtained by the simulation agree well with those of the experimental results.

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Reduction of reflected glare on visual tasks such as printed papers in an office, is one of the most important factors of office lighting designs.
In this paper, experimental studies have been carried out to apply the latest lighting technology to office lighting designs for reduction of reflected glare.
The authors studied the permissible luminance limits of the reflected light source by subjective appraisal, and developed rules for the relationship among various lighting factors. The factors are: permissible luminance of the light source, illuminance on paper, luminance contrast between a character and its background.
The results are as follows:
(1) Luminance contrast between a character and its background without reflected glare gives a large influence on the necessary value of luminance contrast with reflected glare. A higher luminance contrast without reflected glare needs a larger amount of luminance contrast with reflected glare under the same condition of the background luminance.
(2) Accordingly, if the luminance contrast without reflected glare is different, each character with reflected glare on paper does not have the same visibility, even though both background luminance and luminance contrast are the same.

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An intercomparison of relative spectral responsivities of silicon photodiodes was carried out among four laboratories, ETL (Electrotechnical Laboratory), Saitama University, Hamamatsu Photonics Co., Ltd. and Matsushita Electric Industrial Co., Ltd.
The photodiodes were calibrated in the 250-800nm range using each laboratory's spectral responsivity standards. As a result, the relative spectral responsivities of the photodiodes calibrated by each laboratory agreed within 1.1% standard deviation in the 400-800nm, 2.2% in 315-400nm, 3.9% in 280-315nm and 4.1% in 250-280nm. Therefore, it is confirmed that the 4 laboratories have sufficient accuracy for calibration of the relative spectral responsivity of the detector in the ultraviolet and visible wavelength region.

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