Blackbody Spectrum Generator

Enter a temperature and watch the blackbody spectrum draw itself in real time — Planck's law, Wien's law, Stefan–Boltzmann flux, and the object's true apparent color, computed live.

Blackbody spectrum generator

K
visible10.0 nm100.0 nm1.00 µm10.0 µm100.0 µm

Spectral radiance, normalized to peak

Apparent color#FDEFE8
Peak wavelength (Wien)
501.5 nm
Total flux (Stefan–Boltzmann)
63.20 MW/m²

Any object emits a continuous spread of electromagnetic radiation determined almost entirely by one number, its temperature. An idealized perfect emitter is called a blackbody, and the curve it traces out — how much light it puts out at every wavelength — is one of the most useful shapes in all of physics. It’s what tells you a star’s color from its temperature.

The physics

Three laws describe the whole curve. First, Planck’s law itself — the spectral radiance emitted at wavelength λ by a blackbody at temperature T:

B(λ,T)=2hc2λ5⋅1ehc/(λkBT)−1B(\lambda, T) = \frac{2hc^2}{\lambda^5} \cdot \frac{1}{e^{hc/(\lambda k_B T)} - 1}

Second, Wien’s displacement law — where the peak of that curve sits:

λmax⁡=bT,b≈2.898×10−3 m⋅K\lambda_{\max} = \frac{b}{T}, \qquad b \approx 2.898 \times 10^{-3}\ \text{m·K}

Hotter objects peak at shorter wavelengths — bluer light. Third, the Stefan–Boltzmann law — the total power radiated per unit area, integrated across all wavelengths:

j⋆=σT4,σ≈5.670×10−8 W/m2K4j^{\star} = \sigma T^4, \qquad \sigma \approx 5.670 \times 10^{-8}\ \text{W/m}^2\text{K}^4

That fourth-power dependence is why small temperature changes matter so much: double an object’s temperature and it radiates sixteen times more power per unit area. The generator above computes all three live as you move the slider, alongside the full curve.