The inverse square law is by far one of the most fundamental and important concepts that every photographer working with artificial light should understand. If that is something you struggle with a bit or you have not heard of it before, this fantastic video will get you up and running in no time at all.
Coming to you from Matt Granger, this great video tutorial will show you how the inverse square law works. The issue is that humans are generally pretty bad at estimating things that do not behave linearly, and if you are not aware of how light deviates from linear (and thus intuitive) behavior, it can be a bit confusing when you are learning how to use strobes. In essence, the inverse square law says that light intensity decreases as the square of distance; in other words, if you double the distance, the intensity drops to a quarter strength. If you triple the distance, it drops to a ninth the original strength. Once you get the hang of it, it is pretty easy to work with and will help you better light your subjects. Check out the video above for the full rundown from Granger.
If you would like to continue learning about lighting, be sure to check out "Illuminating The Face: Lighting for Headshots and Portraits With Peter Hurley!"