Associate Safety Professional Practice Exam

How does the inverse square law apply to illumination?

1. Light intensity is directly proportional to the distance

2. Light intensity is unaffected by distance

3. Light intensity varies inversely with the square of the distance

4. Light intensity increases with the square of the distance

The correct answer is: Light intensity varies inversely with the square of the distance

The inverse square law describes how the intensity of illumination from a point light source decreases as the distance from that source increases. According to this law, the intensity of light is inversely proportional to the square of the distance from the source. This means that if you double the distance from the light source, the intensity of the light is reduced to one-fourth of its original value. This relationship arises because light spreads out over an area that increases with the square of the distance—specifically, the area of a sphere (which is relevant for point sources of light) is proportional to the square of its radius. For example, if you have a light source and you measure its intensity at 1 meter, moving to 2 meters away will result in a significant decrease in light intensity because the same amount of light is now spread over a larger area. This principle is crucial in fields such as lighting design, illumination engineering, and safety assessment, as it helps professionals understand how far light travels and how much it diminishes over distance, allowing them to make informed decisions regarding lighting installations and safety measures.