The quality of the tomato fruit at harvest time is extremely important for maximum storage after harvest and shelf life. A device to measure the slow induction of chlorophyll fluorescence has been developed. The system contains a unit of measure, a controller, an electronic unit, and major additional units. The device consisting of a radiation source (photodiode) emitting in the blue region of the spectrum with a radiation maximum λ= 470 nm, and a radiation receiver in the red region of the spectrum. The device relates to agricultural machinery and can be used for sorting tomatoes in harvesting machines and at post-harvest processing points.