DESIGN OF A SIMPLE INSTRUMENT FOR THE MEASUREMENT OF RED FAR-RED RATIOS

An apparatus was designed for outdoor measurement of the ratio of two wavelength bands, particularly red and far-red. A sensor, containing optical and electronic components, is connected to a signal processing unit displaying the red to far-red ratio and signals proportional to the irradiance at each waveband. Calibration procedures and technical performance are given. The low cost of components for the apparatus and the build-in voltage divider make the apparatus suitable for ecological studies where measurements under different conditions and sometimes continuous recordings are necessary. Examples of contrasting values of the red to far-red ratio and of their biological effects are given.