Investigation of LED Light Attenuation in Fog

K Otas,A Vaskys,P Vaskys,V J Pakenas

doi:10.5755/j01.eee.121.5.1651

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).DOI: http://dx.doi.org/10.5755/j01.eee.121.5.1651

Highlights

Solid-state lighting technology based on lightemitting diodes (LEDs) allows for the development of intelligent street lighting systems with the dynamic changing of the photometric characteristics of luminaires and the luminance of the road surface, depending on traffic and weather conditions [1]
The dependences of relative luminance measured in the field of view of the luminance meter on the relative fog density are shown in Fig. 5 for two types of LEDs used for foreground illumination
The output of such a detector can be used in intelligent street lighting systems

Summary

Introduction

Solid-state lighting technology based on lightemitting diodes (LEDs) allows for the development of intelligent street lighting systems with the dynamic changing of the photometric characteristics of luminaires and the luminance of the road surface, depending on traffic and weather conditions [1]. When light propagates through fog, the electromagnetic waves interact with water droplets suspended in the air Because of this interaction, the light is attenuated. Intelligent street lighting systems can be based on various solid-state sources of light, such as phosphor conversion LEDs, as well as clusters of coloured LEDs. In order to develop intelligent street lighting systems that adapt to fog conditions, the propagation of light of different spectral composition and the peculiarities of the formation of luminance patterns of objects in fog of different density are to be known. Some models described in the literature [3,4] can be used for this purpose These models lack experimental data on light propagation and object luminance for different LEDs under fog conditions. We present an experimental investigation of the characteristics of the propagation of light emitted by solid-state sources of various colours in artificial fog with varying density

Materials and methods

Conclusions