Produced by: Light Modifiers Rental
Written by: DP: Camrin Petramale & Gaffer: Neil Adamson
Part 3: Falloff
We are taught that light behaves a certain way, and that falloff is calculated by the Inverse-Square Law. While the Law is scientifically sound in theory, how we practically use and manipulate light on set changes falloff outcome. Understanding that Illumination drops as the distance from a light source increases, and Illumination increases as the light is moved closer, many of us were taught that there is a fixed rate of change that can be used to approximate this relationship between distance and illumination on set. The inverse-square law explains this falloff rate according to the following equation:
The easiest way to understand the Inverse-Square Law is usually to apply the rule that if you double the distance, you take ¼ of the original intensity. Similarly, if you triple the distance, you would take 1/9 of the original intensity. This is where the name of the law comes from (inverse - taking the reciprocal of the distance - 2 = ½ square - squaring that distance - ½2). However, while this law is absolutely true, the variables at play will often produce results that prove problematic when trying to use this formula on set.
Energy at new distance = original energy / new distance2
Figure 1 - Standard depiction of the Inverse-square law at work..