This lecture covers the principles and applications of optical sensors, focusing on topics such as Doppler velocimetry, optical current sensors based on the Faraday effect, and optical pyrometry for non-contact temperature measurement. It also discusses optical gyrometers based on the Sagnac effect and the use of monochromatic and two-color pyrometers for emissivity measurements. The lecture delves into the theory behind these sensors and provides examples of their practical applications in various fields.