Law

Wien's displacement law

λ_{m a x} T = b (b = 2.898 \times 1 0^{- 3} m K)

Statement

The wavelength of peak emission is inversely proportional to absolute temperature.

Symbols and units

$λ_{m a x}$	peak emission wavelength	m
$T$	absolute temperature	K
$b$	Wien's displacement constant	2.898×10⁻³ m·K

When it applies

An idealized blackbody (perfect absorber and emitter) in thermal equilibrium.

Don't use when

Assumes an idealized blackbody (perfect absorber and emitter) in thermal equilibrium — a real object's emission spectrum deviates from the ideal blackbody curve.

Derivation

An empirical relation between a blackbody's peak emission wavelength and its temperature, later reproduced by Planck's full radiation law.

λ_{m a x} T = b

Watch out for

As temperature increases, the peak wavelength DECREASES — hotter objects glow bluer or whiter, cooler ones redder, the inverse of what 'more heat, more red' intuition suggests.