Wien's Displacement Law Calculator
Peak wavelength or temperature of a black body from Wien’s law — colour and spectral region, peak frequency, and comparisons with the Sun, a light bulb and the cosmic microwave background.
How it works
λ_max · T = 2.898 × 10⁻³ m·K; ν_max = 5.879 × 10¹⁰ Hz/K × T (the frequency peak is not c/λ_max)
Hotter objects radiate at shorter wavelengths: the peak slides from the far infrared for room-temperature objects, through red and orange for embers and filaments, to the blue-green where the Sun’s spectrum tops out. Wien’s constant makes the conversion trivial and is how astronomers read a star’s surface temperature from its colour. Note the two peaks: the maximum per unit wavelength and per unit frequency fall at different places because the two spectral densities are different functions.
Worked example
The Sun at 5,778 K peaks at 2.898 × 10⁻³ ÷ 5,778 = 502 nm — green, though the broad spectrum looks white; a 2,700 K incandescent filament peaks at 1.07 µm, wasting most of its energy as infrared.
Frequently asked questions
Why does the Sun not look green?
Its spectrum is broad and nearly flat across the visible; our eyes integrate it to white.
Why are hotter stars blue but not violet?
A 30,000 K star peaks in the far UV; across the visible band its spectrum is still falling from blue to red, so blue dominates.
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This calculator is for educational purposes. Double-check important results before acting on them.