Black-body radiation

Change temperature and watch the Planck spectrum brighten and shift. Explore the laws that connect heat, colour, peak wavelength and total radiated power.

Warm whitePeak: infrared

Temperature5,778 K

Peak wavelength502 nm

Emitted power63.2 MW/m²

Peak regionVisible

Wien: λ_max = b/TStefan–Boltzmann: P/A = εσT⁴Planck: B_λ(T)

Planck’s breakthrough

Planck’s law replaced the classical ultraviolet catastrophe by treating energy exchange as discrete quanta. The curve gives spectral radiance at every wavelength.

Hotter means bluer

Wien’s law shows that the peak moves to shorter wavelengths as temperature rises. Cooler everyday objects still radiate, mainly in the infrared.

Power rises rapidly

The Stefan–Boltzmann law makes total emission proportional to T⁴. Doubling temperature increases emitted power sixteenfold for the same emissivity.

Model note: An ideal black body has emissivity 1. Real materials are grey or selective emitters. Screen colour is an approximate visual mapping and cannot display ultraviolet or infrared radiation.