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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.

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.

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.

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.

In 1987 SAE Congress, Stanley Electric Co., Ltd. reported a successful development for the first time in the world of LED HMSL which conforms to FMVSS No. 108 and which can practically be mounted on cars. Since then, we have developed LED rear combination lamp with multi display function making the best use of our technology accumulated during development of LED HMSL and the superiority of LED, which outstrips the conventional rear combination lamp with incandescent bulb. By utilising LED as a light source, rear combination lamp with capability of free pattern display of letters and symbols, which is impossible for conventional lamps, was realized. Here we report the development, since we believe that LED will play an important role in and widely contribute to automotive industry and general public as a light source.

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.