Investigation of LED light attenuation in fog

Abstract

In fog, visibility reduces and the illuminance levels of street surface and objects that are in the observer's field of view alter. In order to establish the technical characteristics of intelligent street lighting with the effect of fog taken into account, the peculiarities of light propagation and luminance of objects in fog are to be known. In this work, a fog chamber that allowed for the experimental investigation of the transmittance and luminance attenuation for white and coloured LEDs in fog with variable density was developed. The obtained dependences of transmittance and relative luminance on relative fog density were described by exponential regression functions. The dependence of the illuminance and luminance attenuation coefficients on light colour (dominant wavelength) was investigated. Light of shorter wavelengths (blue and green) was found to be scattered by about 1.5 times weaker than that of longer wavelengths (yellow and red). When additional foreground light was applied, a high fog density resulted in that the main contribution to luminance in the field view was due to the luminance of the foreground light scattered in fog rather than due to the luminance of the object itself. An increase of the correlated colour temperature of the white LED was observed due to the dependence of light scattering on wavelength. Ill. 7, bibl. 5, tabl. 4 (in English; abstracts in English and Lithuanian).