There are several methods to measure how much light is intercepted by a canopy in order to determine if water loss is from evaporation or transpiration. There's the hard way. There's the expensive way. And then there's the smart way: the LP-80.
The optimal method for measuring fractional PAR (photosynthetically active radiation) is with the LP-80 Ceptometer. It's a highly accurate way to determine canopy growth and canopy light interception, along with calculating fractional interception and crop coefficient. And because the methodology is automated, it spares you from intensive hand labor, saving you time. The LP-80's low cost also saves your entire budget from evaporating.
Backed by 35 years of research, the LP-80 is one of the most trusted and relied upon instruments among crop scientists, ecologists, and foresters. Why? One of the main reasons is because it uses precise sun angle calculations to accurately and automatically calculate leaf area index (LAI) in real time, so you can be confident your data is right while in the field.
Another reason for the LP-80's popularity is an included external PAR sensor which can be used to make simultaneous above- and below- canopy PAR measurements as a reference for intercepted light in clear, partly cloudy, or even overcast sky conditions. No wonder it's relied on for publishable measurements year after year.