Limitations of Pyrometer Technology in the Ultraviolet and Visible Spectral Bands According to Planck's Law on the Real Body

This article investigates the limitations of pyrometric technology in the visible and ultraviolet spectral bands. These studies rely on a theoretical analysis of thermal radiation, Planck's fundamental laws, and multispectral processing methods based on nonlinear models. Accurate high-temperature measurement is a major challenge in many scientific and industrial fields, including thermal processes, metallurgy, energy, and fundamental research. Uncertainty in emissivity is the main source of error in conventional pyrometric measurements. To reduce the influence of emissivity and improve measurement reliability, several approaches have been developed, including monochromatic, bichromatic, and multispectral pyrometry based on Planck's law. The chromatic luminance characteristics in the visible and ultraviolet bands, obtained from a temperature range across both spectral domains, highlight the high potential of pyrometry for measuring high temperatures in complex environments. These characteristics will be applied with different wavelengths in each visible and ultraviolet spectral band. Comparative studies of the results will be able to highlight the limitations for each band. Compared to traditional approaches, this pyrometry technology offers a small advantage for detecting very high temperatures despite variations in emissivity and environmental uncertainties. The luminance for these two spectral bands exhibits a very low flux almost at temperatures below 1900K.