When working with small light sources, the proximity to the subject significantly impacts the lighting intensity. Halving the distance between the light source and the subject results in lighting that is four times brighter. This occurs because the light becomes concentrated over a smaller area, specifically one-quarter the original size.
For instance, when using a small flashlight or studio lamp to illuminate a portrait, reducing its distance to the subject by half increases the light intensity by four times. Conversely, doubling the distance reduces the light intensity to one-quarter of its original brightness. This principle, known as the inverse square law, also applies to print exposures when adjusting the magnifier height for close-up shots.
In practice, this law necessitates careful consideration when lighting multiple objects at varying distances in a compact studio setting. A compact, hard light source can create challenges in achieving consistent lighting for elements at different distances with a single exposure setting.
One solution is to position the light source further away, thereby reducing the ratio of light intensity between the nearest and furthest objects. Alternatively, using multiple light sources or diffusers can mitigate the “fallout” effect of uneven lighting.
In outdoor settings, direct sunlight does not present this issue. The sun is so distant that the difference in distance between two locations on Earth, such as a seaside and a mountain peak, is negligible. Variations in luminosity in landscape photography are influenced by local atmospheric conditions rather than the sun’s distance.
Indoors, however, sunlight entering through a small window acts as a compact light source. The intensity of this light will vary with distance similarly to a lamp placed in the same position.
