Photosynthesis Light Sensor and Meter

An improved light sensor with a spectral response based on photon absorption between 400 and 700 nm was developed for both field and environmental chamber use. The indicated sensor response was selected because it approximates the photosynthetic response of plants for which data are available. A silicon photo cell with high response in the visible range was used as a sensor. The spectral response was controlled by use of a Kodak Gelatin Wratten Filter. A visible bandpass interference filter produced a sharp cutoff at 700 nm. Heat—absorbing glass eliminated transmission beyond 1,000 nm, and a diffusing plastic and filters were mounted in a miniaturized cosine—corrected head that was fitted with a collimating system to eliminate spectral shifts which arise when light enters the interference filter at oblique angles. Error calculations indicate that under sun—and—sky radiation and various artificial light sources the errors are smaller than those associated with available standard calibration lamps. The device also includes a battery—operated meter circuit suitable for making measurements over a wide range of intensities.