Fiber optic sensors primarily use LEDs as their light source, which emit light that is transmitted through the optical fiber to detect objects or measure physical quantities.

Fiber optic sensors rely on a light source to generate the optical signal that travels through the fiber. Most commonly, LEDs (Light Emitting Diodes) are used because they provide stable, fast, and reliable light suitable for sensing applications . The light emitted from LEDs is typically unpolarized, meaning it oscillates in multiple directions, but it can be converted to polarized light using optical filters when required for specific sensing functions . The light from the LED is coupled into the core of the optical fiber, which guides it via total internal reflection along the fiber to the sensing region . Depending on the sensor type, the light may be reflected back from a target (reflective sensors) or detected by a separate receiver (through-beam sensors). The fiber itself can be made of plastic or glass, with plastic fibers being flexible and cost-effective, while glass fibers allow high-temperature operation . In addition to LEDs, some fiber optic sensors may use laser diodes for applications requiring higher intensity, longer range, or more precise beam control, though LEDs remain the most common choice due to their simplicity and durability . The light source is integrated into the fiber-optic amplifier unit, which also contains the detector and processing electronics, ensuring that the light can be transmitted, modulated, and analyzed effectively . Overall, the LED light source is central to the operation of fiber optic sensors, enabling non-contact detection, high-speed response, and immunity to electromagnetic interference, making these sensors suitable for harsh or confined environments .