Which scientific law relates blackbody radiation wavelength to temperature?

Wien’s displacement law relates the peak wavelength of blackbody radiation to the object’s absolute temperature. In its common wavelength form, λmaxT = b, where b is Wien’s displacement constant, approximately 2.898 × 10⁻³ meter-kelvin.

The law says that hotter blackbodies emit their peak radiation at shorter wavelengths, while cooler blackbodies peak at longer wavelengths. This explains why heated metal progresses from dull red toward orange, yellow, and eventually whiter or bluer light as its temperature rises. Objects at ordinary temperatures still radiate strongly, but their peak emission is usually in the infrared rather than the visible spectrum.

German physicist Wilhelm Wien derived the law in 1893, before Max Planck developed the more complete quantum theory of blackbody radiation. Planck’s law describes the entire emission spectrum; Wien’s law identifies how its peak shifts with temperature.

A subtle point is that the peak depends on whether radiation is plotted per unit wavelength or per unit frequency. The numerical peak differs between those representations, but the inverse relationship between wavelength and temperature remains the standard meaning of Wien’s displacement law.