Visual perception of color LED light in dense fog

At some point in our lives most of us will be affected by reduced visibility from fog. Fog is defined as the visible portion of small water droplets suspended in the atmosphere on or near the earth's surface, Visibility can be measured by several methods although all are partially limited to some degree. The most common and readily available methods are by: trained human visual observers, transmissometers and forward scatter / back scatter meters. The method used to determine night time visibility is based on the contrast between a bright point light source against a dark or black background. Contrast reduction law does not hold in fog because the target apparent luminance depends on the droplet size. By measuring human spectral sensitivity with LED light brightness inside of fog, it is understood that short wavelengths are scattered much more strongly than long wavelengths. However, in human vision RB and RY color that can be easily seen in foggy conditions, despite the fact that the color wavelength is not as long as red color.