The Blackbody Spectrum

A surface at temperature T radiates with a spectrum fixed by that temperature alone. The blue curve is M_lam, the power leaving one square metre per nanometre of wavelength; the gold region is the slice between the two band edges, and the share readout is how much of the whole output that slice is. Drag the temperature and watch the share climb to a maximum near 7042 K and then fall again. The vertical axis rescales with every temperature — the number at the top of the frame is the only thing that says by how much, so compare the shapes of two curves and never their heights.

M_lam at the probe8.0849e+4 W/m²/nm
Photon energy at the probe2.2543 eV
Photon energy at lam13.0996 eV
Photon energy at lam21.7712 eV
Share below lam112.18 %
Share above lam251.18 %
M_lam at the peak8.2434e+4 W/m²/nm
Top of the vertical axis8.24e+4 W/m²/nm

The frameThe top of the frame is 8.24e+4 W/m²/nm and the axis runs to 2000 nm. Both are set by this temperature, so compare the shapes of two curves and not their heights.

Share of the power inside the band  F
36.64 %
Peak wavelength  lam_peak = b/T
502.0 nm
Total exitance  sigma T^4
62.94 MW/m²
Power inside the band  F sigma T^4
23.06 MW/m²
Surface temperature T5772 K
Lower band edge lam1400 nm
Upper band edge lam2700 nm
Probe wavelength550 nm
Planck's law for an ideal blackbody · sigma = 5.6704e-8 W/m2/K4 · Wien b = 2.8978e-3 m K
The band edges are a convention, not a constant — widen 400–700 to 380–750 and the Sun's share goes from 36.64 % to 43.77 %. lam_peak is the per-wavelength peak; the per-frequency curve peaks elsewhere. Real surfaces are not blackbodies.