An infrared light source 620 and detectors 520 are arranged on a seed tube 142 to measure light transmitted across a sectional plane 610 of the tube. The ray paths subdivide the plane into sectors (figure 7A) and there is at least one detector which receives light from at least two sectors, permitting identification of the simultaneous passage of two or more seeds. Signals from the detectors are conditioned, including by amplification, and a controller generates a seed count based on the conditioned signals. The processing system (figure 5) may include a preamplifier, and a plurality of conditioning channels targeted at different sizes of seed, each channel having a selected gain, bandwidth and filter. Preferably, the seed tube has four sides, with an array of LEDs 625 mounted behind an emitter window 615 on one side and arrays of detectors 630 mounted behind receiver windows on the other three, defining multiple sectors (figure 7B).
