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ABSTRACT:
1 Introduction
Night-time driving takes place under changing mesopic conditions. Vehicle headlamps illuminate a small (mainly para-foveal) part of the visual field, street lighting produces a more or less even background luminance, and the headlamps of approaching vehicles modulate the state of adaptation of the driver continuously in a very unpredictable way, as well as causing glare for the driver. In recent years car headlamps underwent a major change, when the traditional incandescent lamp and later the halogen incandescent lamp became replaced by high pressure gas discharge lamps, first called Xenon lamp and at present known as the High Intensity Discharge (HID) lamp. Nowadays manufacturers already equip their concept cars (see e.g. [
]) with LED headlamps. While in case of tungsten halogen lamps and HID lamps manufacturers had no much choice in selecting spectral power distribution delivering best visibility and minimal glare, the spectrum of LEDs can be still trimmed within a reasonable range.
Night time driving is under mesopic visibility conditions. It is generally known that the spectral sensitivity of the human eye changes as lighting levels drop below 10 cd/m2, but there is still no generally accepted mesopic photometric system available. Recently several groups, both in the USA and Europe addressed the question of mesopic photometry for night time driving situations [ , ], taking into consideration both reaction time of observing a coloured light and of achromatic threshold experiments [ ]. Experiments have shown – as could have been expected – that with lowering the luminance level the spectral sensitivity of the human visual system shifts towards shorter wavelengths.
At the same time discomfort glare experiments have shown that the human spectral responsivity to glare peaks in the bluish part of the spectrum, leading to speculations that discomfort glare might be mediated by the blue cone response or the rod response [ , ].
Earlier experiments were, however, not convincing enough to draw a glare sensitivity spectrum. Therefore we started simultaneous visibility and glare experiments.
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STATISTICS
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