To better understand kinetic solvent effects on chemical reactions, experiments aim to measure reaction rates in a variety of solvents. Experimentally determining reaction rates for radical reactions in solution can be difficult due to the short-lived nature of some radicals; however, some methods have been developed over the last century and are commonly used for measuring these kinetics. In an early method pioneered by Briers and Chapman known as rotating sector, or the intermittent-illumination method (IIM), a sample is exposed to a constant intensity of light for intermittent periods of time, such that the amount of time spent in light and in the dark remains constant . The average reaction rate, W M , can be calculated by: