Thus, blue light gets more diffused than yellow light, which gets more diffused than red light. This phenomenon repeats itself as light travels over long distances in the atmosphere. The result is that light progressively loses its blue component and retains a greater proportion of red. This explains why the sky appears blue during the day and red at sunset. This also explains why blue light is more disruptive for star gazing.
At night, yellow light is much better perceived by the human eye than blue light, and so a weak yellow light can assure good nocturnal vision. Due to the moderate diffusion of yellow light, weak bulbs of this colour represent the ideal compromise between being able to see and performing astronomical observations.