The optical power meter must be set to the proper range (usually dBm, but sometimes mW) and the proper wavelength when measuring power. TIA standard test FOTP-95 covers the measurement of optical power. Other general purpose light power measuring devices are usually called radiometers, photometers, laser power. Keysight optical power meters measure optical signal strength, providing multi-channel measurement processing and system control while offering rapid response times, wide dynamic range, and simple integration into automated test setups. The output is a voltage linearly proportional to the input power. Generally speaking, when measuring the fiber loss of multimode fiber, you need to use 850/1300nm LED light source, and when measuring the fiber loss of single mode fiber, you need to use 1310/1550nm laser.