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During the daytime we are accustomed to natural surroundings, even in densely populated urban areas. The sky, clouds, trees, and ground cover provide a comfortable backdrop to our daily lives. High levels of illumination make possible the perception of vivid color from reflected light. At the same time, contrast levels between the brightest and dimmest objects in our field of view are moderate.
Nighttime is a different story. Our natural backdrop, the stars, planets, and moon, are hidden behind an artificial urban haze. Illumination levels are low, and color perception from reflective sources is muted or nonexistent. The only color we perceive generally is from lighting sources themselves. Contrast ratios between lighting sources and the background is many times that during daytime. Even trained architects and engineers have difficulty in dealing with the nighttime, manmade environment.
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