LEED AP Building Design and Construction (BD+C) Practice Exam

What is the primary cause of skyglow?

1. Unshielded light sources and atmospheric particles

2. Overhead street lighting activation

3. Natural night sky conditions

4. Cloud cover and humidity levels

The correct answer is: Unshielded light sources and atmospheric particles

The primary cause of skyglow is unshielded light sources and atmospheric particles. Skyglow refers to the brightening of the night sky over populated areas due to artificial lighting. When light is emitted from unshielded fixtures, it disperses in multiple directions, some of which end up being directed into the atmosphere. This light interacts with atmospheric particles, including dust, water droplets, and gas molecules, resulting in a scattering effect that increases the brightness of the night sky. The impact of unshielded light sources is particularly significant in urban areas where the concentration of artificial lighting is high. Such lighting can come from streetlights, signage, buildings, and other urban fixtures. The result is a sky that appears less dark and can interfere with astronomical observations as well as disrupt nocturnal wildlife. While other factors, such as overhead street lighting activation and natural night sky conditions, can influence the perception of skyglow, they are not the primary cause. Additionally, cloud cover and humidity levels can sometimes amplify skyglow due to reflection and scattering, but these are secondary effects rather than the fundamental source. Therefore, unshielded light sources combined with atmospheric particles are clearly the main contributors to the phenomenon of skyglow.