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This study was designed to investigate how the spectral power distribution (SPD) of LED headlamps (including correlated color temperature, CCT) affects both objective driving performance and subjective responses of drivers. The results of this study are not intended to be the only considerations used in choosing SPD, but rather to be used along with results on how SPD affects other considerations, including visibility and glare. Twenty-five subjects each drove 5 different headlamps on each of 5 experimental vehicles. Subjects included both males and females, in older (64 to 85) and younger (20 to 32) groups. The 5 headlamps included current tungsten-halogen (TH) and high-intensity discharge (HID) lamps, along with three experimental LED lamps, with CCTs of approximately 4500, 5500, and 6500 K. Driving was done at night on public roads, over a 21.5-km route that was selected to include a variety of road types.

In the near future, the LED headlamps will be available in the market by improvement of the technique. There are some methods that can produce white light using LEDs. Probably, we think most generally method is using blue LED and yellow phosphor. But, spectral power distribution (SPD) of this type of white LED is much different from traditional white light that is produced by halogen or HID. This type of the white LED has poor spectral power in long wavelength region and much spectral power in short wavelength region. So, the white light by LED might have color-rendering problem. On the assumption that automotive head lamps with white LED and halogen, the human color perception and recognition under wide range of illuminance conditions from photopic to mesopic was measured, using categorical color naming method and elemental color scaling method. As the result of this measurement, stability of categorical color naming was lower under lower illuminance level with both light sources.

Growing preferences for high-velocity motor vehicles lead a strong demand for headlamps with higher brightness and visibility. The low beam of conventional two-lamp system headlamps provides drivers poor visibility, since they are equipped with bulbs which have low-beam filament with relatively small power (35-45W) and luminous flux, compared to the high-power filament (65W) used for high-beam, in order to restrain the glare to on-coming drivers. The new halogen bulb with C-8/C-8 filament structure has such high power as 65/55W and when used in combination with a multi-focus reflector to compose a new 2-lamp system headlamp, it significantly increases the brightness of low-beam without causing much glare to the on-coming vehicles. At the same time, this new 2-lamp system headlamp is able to illuminate a broad area including the zone just in front of the vehicle without sacrificing the visibility of farthest area.

Incandescent bulbs have been mostly used in the field of conventional light source for display and automotive lamp. However, recent increasing requirements for compact structure, color display, high display quality and improvement of total car design by means of color coordination, can only he satisfied with more natural color light sources. These requirements have led us to develop miniature halogen bulb without exhaust tube which was common in conventional halogen bulb. This new bulb gives compactness in its structure, high efficiency whiter light, and good luminous flux retaining characteristics. In this paper, we report the details of the developed bulb and its applications.

Stanley introduced during the SAE congress '87 a LED HMSL, for the first time in the world, which fully conformed to FMVSS 108, and which was ready to be installed on actual vehicles. In the following year, utilizing the accumulated technology through LED HMSL and the superiority of LED, we presented a paper on the development of LED rear combination lamp which has multi-function features, such as sequential turn signal, character and/or pattern displays in addition to conventional stop & tail function and which is thin in its shape and long life (maintenance free). This year, we have successfully developed a LED rear combination lamp with a built-in optical proximity sensor function fully integrating all the accumulated design technology and application technology of optical semiconductors for automotive LED lighting through the above developments.

Along with the tendency to esteem fuel economy, driving security and aerodynamic excellence, the voice to demand technical improvement of headlamps is getting higher and higher every day. With the expectation to meet such common and strong demand of world's automotive industry, retractable headlamps and slanting headlamps (headlamps of which front lenses are slanted) have been put to practical use so far. However, retractable headlamps have a disadvantage that once lighted, they lose their aerodynamic efficacy. Moreover, the mechanism of retractable headlamp system is rather complicated and causes cost increase. On the other hand, in slanting headlamps, light emission inefficiency that increases in proportion to the lens slant angle settles certain limitation on the popularity of this system.

Many types of low profile headlamps have been developed to meet the great demand to improve both aerodynamics and styling. However, none have resolved the principal subject, “the compatibility of light-efficiency and styling”. Our innovative development is the super -low profile headlamp system, which contains totally unique reflectors. The special combination of reflectors is designed to generate beam pattern. To achieve this innovation, the precise light control technology and the research for optimal headlamp beam pattern were essential. The head-lamp performance was examined by our original computer simulation system. As a result, this headlamp is only 30mm high and it has extremely high light efficiency. It also provides excellent headlamp performance, in regards to the bright foreground illumination, long distance visibility and accurate glare control.

LEDs offer great advantages such as low power consumption and compact size. In addition to the physical benefits, however, they also boast 1.2times the feeling of brightness compared with halogen bulbs, as shown in previous research, and the colors of LED sources have been shown to stand out better than other sources (halogen and HID) used for traffic signs, offering superior perceived Clarity and sharpness. As well as traffic signs, it is essential to be able to see pavement markings clearly when driving an automobile. In this study, tests were carried out on public roadways using automobiles installed with halogen, HID and LED-based headlamps. It was found that the LED sources were found to provide the clearest illumination of the white lines. White lines on an actual road surface were also illuminated with halogen, HID and LED lamps in order to compare the effects of these sources on the visibility of the white lines by static evaluation.