First radiation constant = 3.741 771 852... × 10⁻¹⁶ W·m²

Name: First radiation constant — CODATA 2022 value
Creator: NIST

Value: 3.741 771 852... × 10⁻¹⁶
Unit: W·m²
Uncertainty: exact (by definition)
Copy-ready: 3.741771852e-16

The first radiation constant c₁ = 2πhc², the prefactor of Planck's law for spectral exitance.

Used in radiometry and pyrometry to compute the power a black body radiates at each wavelength.

The same quantity, other ways NIST lists it

Quantity (NIST name)	Value	Unit	Uncertainty
First radiation constant for spectral radiance	1.191 042 972... × 10⁻¹⁶	W·m²·sr⁻¹	exact

NIST, Fundamental Physical Constants — Complete Listing (2022 CODATA adjustment), retrieved 2026-07-26.

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The same quantity, other ways NIST lists it

Electrical, thermal and X-ray constants

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All physical constants