A safety light curtain operates on the through-beam principle: a transmitter unit sends a tightly focused, synchronized array of infrared light beams to a receiver unit.

Ambient Light Rejection (FWHM)

• The FWHM (bandwidth) must be very narrow band to achieve high Out-of-Band Blocking.
• This narrow passband is essential because safety light curtains are often used in brightly lit factory environments or near windows where sunlight (which contains significant NIR energy) could saturate the detector and cause a false "clear" signal, bypassing the safety function.