How to Build Your Own Direct/Diffuse Radiation Sensor

The measurement of the direct and diffuse components of solar radiation is of interest to plant physiologists and solar energy practitioners. Unfortunately, the cost of currently available direct/diffuse sensors often limits their deployment. We describe a simple shadow-band apparatus that can be constructed in any shop with commonly available parts for a fraction of the cost of commercial instruments, with equal or superior performance. Further, we demonstrate its use in measuring the direct and diffuse PAR components above and below a corn canopy with line quantum sensors.