To minimize triggering by sunlight, photoelectric sensors typically use which type of light?

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To avoid false triggers from sunlight, photoelectric sensors use a wavelength that is easy to isolate from ambient light. Infrared light is the common choice because the system can be built to respond only to a specific infrared wavelength and often to a modulated signal at a set frequency. This modulation lets the receiver distinguish the sensor’s beam from the constant, broad ambient light found in sunlight. Infrared LEDs and detectors are also inexpensive and compact, and optical filters can be tuned to pass only the chosen IR wavelength while blocking most visible light. The result is a robust beam that remains quiet in daylight.

Other options would mix more readily with daylight: visible light is abundant in sunlight and would cause more false triggers; ultraviolet is less practical for reliable detection and safety/hardware reasons; microwave is a different sensing method altogether and not the typical light-based photoelectric approach.