Patent ID: 8823945

Claim:
A measuring device for determining a vegetation index value of plants, comprising a plurality of light emitting elements each of which emits substantially monochromatic light of a predetermined wavelength, a light receiving element which receives the light of the light emitting elements reflected by the plants and generates a signal indicating the respective intensity of the received light, and comprising a control means which successively drives the light emitting elements in a cyclical sequence, determines the respective intensity of the reflected light based on the output signal of the light receiving element, and calculates the vegetation index value, based on the determined intensities of the overall measuring cycle, characterized in that the light receiving element is a light frequency converter; the light emitting elements include four light-emitting diodes each emitting a respective wavelength of 670 nm, 700 nm, 740 nm or 780 nm, wherein the half-width of the emitted light preferably is between 20 and 30 nm; and the control means calculates the red edge inflection point (REIP) as a vegetation index value in according with the following formula: REIP =λ 2 +(λ 3 −λ 2 )(( P 1 +P 4 )/2 −P 2 )/( P 3 −P 2 ) wherein the values P 1 to P 4 designate a respective measured intensity of the reflected light of the respective light-emitting diode, and λ 2 and λ 3 designate a respective wavelength of the respective light-emitting diode.