You can use an optical thermometer or spectrometer to measure the filament temperature, find the peak wavelength, and then calculate the temperature according to Wien's theorem. Method of measuring filament temperature: measure the spectral intensity of filament with optical thermometer or spectrometer, find out the peak wavelength, and then calculate the temperature with optical thermometer and spectrometer according to Wien theorem. The editor of Wien Theorem found the law of thermal radiation-Wien displacement, established Wien formula of blackbody radiation, and won the1864 ~19165438 Nobel Prize in physics. At the end of 19, people have realized that both thermal radiation and optical radiation are electromagnetic waves, and there have been in-depth theoretical and experimental studies on the distribution of radiation energy in different frequency bands, especially blackbody radiation. Wayne and Lamel invented the first practical blackbody cavity emitter, which provided them with the "complete radiation" needed for experimental research. Wayne put forward the displacement law of ideal blackbody radiation in 1893: lmaxT= constant. The law points out that with the increase of temperature, the wavelength corresponding to the maximum radiation energy density moves to the short wave direction. Because the ratio of radiation flux density to radiation energy density is c/4, after measuring the maximum radiation flux density, the temperature of the radiator can be determined according to Wien displacement lmax. Optical thermometers are made according to this principle. Then, Wayne studied the distribution of blackbody radiation energy by wavelength. Based on the thermodynamic theory, after analyzing the experimental data, he got a semi-empirical formula: u = b (λ -5) (e -a/λT) (where λ -5 and e -a/λT represent the -5th power of λ and the -a/λT power of E, respectively). U represents the function of energy distribution, λ is the wavelength, T is the absolute temperature, and A and B are constants. Of course, here is just to show you what this formula looks like. Friends who have no research on mathematics and physics can look at it without considering its specific meaning. Wayne formula. Where E 1 is the radiation energy per unit wavelength interval at the wavelength l; C 1 and C2 are two empirical parameters, which are determined by fitting experimental curves. T is the temperature at equilibrium. Wien's formula is in good agreement with the experiment in short wave band, but obviously deviates from the experiment in long wave band. Later, in the process of further exploring a better radiation formula, Planck established a radiation quantum theory consistent with all experiments. However, when using optical pyrometer to measure temperature, people still often use Wien formula because it is simple and accurate enough.