Abstract: An apparatus and method for determining the photosynthetic activity of a plant by determining the chlorophyll fluorescence of the plant is provided. The apparatus includes a light impermeable housing, a light to illuminate the housing, a light intensity in the housing and to adjust the light intensity controller. The light intensity may be between zero and 700 micromoles of photons per square meter per second. The monitor may be a photodiode protected by light filters which permit only light of wavelengths corresponding to plant fluorescence emission to pass to the photodiode. A computer analysis of the data obtained, corrects for Dark and Straylight signals in the housing and normalizes the data by correcting for the Fo fluorescence.

Abstract: Apparatus for detecting and measuring fluorescence emission comprising a fluorometer probe including a light emitting means for illuminating the object under study, a red cut-off filter, a light sensitive detector for obtaining the fluorscence signal from the object, and a preamplifier connected to the phototransistor for amplifying the said signal to a first level, and power and control unit including electronic indicating means. In the preferred embodiment the sensor and emitter are a light emitting diode (LED) and a phototransistor arranged in piggy-back relation with the LED having an epoxy body acting as a fluorescence light guide from the object to the phototransistor.