Wien's Displacement Law

Wien's displacement law says that a hotter blackbody radiates most strongly at shorter wavelengths, so the peak of its spectrum moves left as temperature rises. It comes from the shape of Planck's blackbody radiation curve: when you find the wavelength where that curve is maximal, the product of the peak wavelength and temperature is constant, with b set by fundamental constants. This is why an iron rod glows red first and then shifts toward orange-white as it gets hotter.

Use this formula when you know the temperature of a near-blackbody and want to estimate the wavelength where its thermal emission is strongest. It is common in astrophysics, thermal imaging, furnace physics, and any problem involving the color or spectrum of hot objects.

• Using degrees Celsius instead of kelvin for T
• Treating the formula as giving the average wavelength rather than the peak wavelength
• Forgetting that b has units of m·K, so the result must be a length