Impact Of LED Color Temperatures And Visibility On Lighting In Tunnel Interior Zone

The paper is based on the National Natural Science Foundation of China,"the Applicability of LED Light Source Spectrum/Color temperature to Tunnel Lighting".Tunnel safety is becoming more and more important in the development of highway.LEDs are widely used in highway tunnels because of their long service life,relatively low light attenuation,high luminous efficiency.When the illumination of each section of the tunnel is different,the corresponding human eyes experience the luminance and the corresponding visual response is also different.The vision of the human eye can be divided into scotopic vision,mesopic vision and photopic vision according to different luminance.The luminance of the tunnel interior determined according to the tunnel lighting illumination specification is within the mesopic vision range of the human eye.However,the existing optical measuring instruments are all measured and corrected based on the light visual efficiency of the photopic vision spectrum,so the illumination of the tunnel interior does not truly reflect the actual perceived luminance of the driver's eyes.Therefore,it is necessary to research the factors that affect the lighting of the tunnel interior to ensure the driving safety.The correlated color temperature can cover a common range of 2500K-8000K.The correlated color temperature of the LED light source is different,and the spectral composition of the light source is also different.LED light sources with different spectral will have different effects on human eyes' perceived luminance.Because of its special semi-closed tubular structure,the tunnel interior is greatly affected by automobile exhaust and floating particles.As a result,the light emitted by the light source in the tunnel interior has a larger attenuation range,and the low light transmittance has poor visibility.The selection of lighting in tunnel interior section should take into account the two aspects:color temperatures and visibility.A calculation model of human eye perception luminance considering mesopic vision and visibility is proposed.The light transmittance of nine monochromatic LED light sources wasobtained through experiments.The spectral composition of seven light sources with different color temperatures was measured using a spectroradiometer without smoke.Finally,the effect of different color temperature light sources on the perceived luminance of human eyes under different visibility and luminance is calculated and analyzed.In order to verify the theoretical calculations,an experiment was conducted to measure the visual clarity of the human eye.Visual clarity can indirectly represent the effect of different color temperature LED light sources on the perceived luminance of the human eye under different luminance and visibility conditions.Experimental observers tested the visual clarity under different color temperature LED lamps in an experimental system with adjustable visibility and light source luminance.The experiment was conducted in a light-tight sealed glass box with a length of 3 meters,a width of 1.5 meters,and a height of 2 meters.Four kinds of lighting luminance,five kinds of visibility conditions,seven different color temperatures,and 50 observers conducted the experiment.Both experimental results and theoretical analysis indicate that the main factors affecting visual clarity are the luminance and visibility of the light source.Higher brightness of the light source or lower visibility can provide the driver with a higher luminance perceived by the human eye.Although increasing the brightness of the LED light source in an environment with low visibility can improve the visual clarity of the observer,the effect of increasing the brightness as the visibility decreases becomes more limited.Under this condition,the LED light source with higher color temperature can provide better luminance for human eyes.Therefore,it is recommended to use the LED light source with,high color temperature in the lighting of the tunnel interior to ensure the traffic safety of the tunnel.