Equations · equation

Planck's Law

Radiation · 1900

Equation: B(λ,T) = (2hc²/λ⁵) / (e^(hc/λkT) − 1)
Field: Radiation
Named After: Max Planck
Year: 1900

Symbols

B spectral radiance — brightness at each wavelength · λ wavelength · T temperature · h Planck constant · c speed of light · k Boltzmann constant

Significance

The full glow curve of a hot body, exact at every wavelength — and to get it Planck had to assume light is emitted in discrete lumps of hν, an 'act of desperation' that founded quantum theory. Both Wien's peak and the Stefan–Boltzmann total are buried inside it; the CMB matches it to a part in ten thousand, the most perfect black body ever measured.

Minerals

Timeline

Photon Decoupling — the CMB Reionization Black Holes Evaporate

Celestial Objects

Sun

Theories

Black Hole Thermodynamics Quantum Hypothesis

Related

Stefan–Boltzmann Law Planck–Einstein Relation Boltzmann Distribution Einstein A and B Coefficients Equipartition Theorem Cosmological Redshift Wien's Displacement Law Saha Ionization Equation Cosmological Equation of State

Instruments

Planck Satellite Atacama Large Millimeter/submillimeter Array (ALMA)James Webb Space Telescope (JWST)

Constants

CMB temperature Boltzmann constant Planck constant Speed of light in vacuum

Spectral Types

Y-type Stars (Y Dwarfs)T-type Stars (T Dwarfs)M-type StarsG-type StarsL-type Stars (L Dwarfs)O-type Stars

Required By

Stefan–Boltzmann Law

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From the Equations database in Notion, last edited 2026-08-15. This page is the row, rendered by the build; nothing on it is written by hand.