An optical pyrometer measures temperature by identifying what characteristic?

An optical pyrometer measures temperature based on the color of the light emitted by a hot object, which is directly related to its temperature. As an object heats up, it emits light in different wavelengths; this phenomenon is known as blackbody radiation. The specific color or wavelength of light emitted can provide a precise indication of the object's temperature.

This method utilizes the principle that different temperatures correspond to different colors due to blackbody radiation—the color changes from red to orange to white as the temperature increases. Therefore, measuring the color of light allows for accurate temperature readings without the need for direct contact with the object.

In contrast, the other options do not accurately relate to how optical pyrometers function. For example, pressure of the gas is relevant to gas behavior but not temperature measurement via emitted light. The amount of heat radiated may contribute to the understanding of an object's thermal characteristics, but it does not encompass the spectral color analysis central to the optical pyrometer's function. Lastly, conductivity pertains to how well a material conducts electricity and is not a method used by optical pyrometers to ascertain temperature. By focusing on the color of the light, the optical pyrometer effectively measures temperature in a non-invasive manner.