Experimental Research On The Fog Penetrability And Photometric Characteristic Of LED In Mesopic Vision

LED lamps will replace the current light sources of road lighting and vehicle signalswith its unique advantages such as energy saving. The difference in the fog penetrability ofdifferent kinds of light sources will influence the safety of road traffic directly along withthe increasing environmental pollution and bad weather such as fog.The spectral of LED Lamp and current light sources like tungsten filament lamp, MetalHalide Lamp(MH),High Pressure Sodium Lamp(HPS) in different fog densities aremeasured with a spectrometer in a black box to study the fog penetrability. The difference inthe fog penetrability and the optics characteristics with the change of spectral luminousefficiency are further analyzed based on the MES2model in mesopic vision.This experiment has three core aspects. Firstly, the bias of fog penetrability producedby the change of spectral luminous efficiency is avoided by measuring the spectral with aspectrometer and calculated based on MES2model which makes the results objective andreproducible. Secondly, this essay studies not only the fog penetrability, but also studies thecolor shift in fog which makes the consequence more practical while studying the fogpenetrability of different colors of vehicle signals. Thirdly, this essay also studies the changein transmittance through glass with wavelength, which offers theoretical foundation forlamp design.The main conclusions are as follows:1. For all of the four lights, the variation of the transmittance with various brightnessare less than5%. The transmittance of tungsten filament lamp is the best while that of LEDis the worst. When the fog is thick, MH is better than HPS, and on the contrary HPS isbetter than MH. The illumination of LED, tungsten filament lamp and MH increase whilethat of HPS decrease with brightness reduce because of the difference in spectral powerdistribution.2. The variation of the transmittance through fog of all vehicle signals are less than2%and the illumination decrease with brightness reduce. The color coordinate of all vehiclesignals in fog shift along a straight line with the slope of-1.3. Lights with same frequency, despite their luminescent mechanism, have the sametransmittance through glass. When penetrating through optics glass, the transmittance with wavelength does not vary, but penetrating through ordinary glass, and the transmittance getshigher then lower with wavelength increasing.This research is very important for the design and test of road lighting and vehiclesignals, which also provides the theoretical and practical value to the promotion of safedriving.