Second radiation constant
Physico-chemicalExact
= 1.438 776 877… × 10−2 m K
- Value
- 1.438 776 877… × 10−2 m K
- Standard uncertainty
- exact
- Relative uncertainty
- exact
- Status
- Exact since the 2019 SI redefinition
- Symbol
- Source
- CODATA 2022 via NIST · NIST entry
NIST prints this exact value cut to 10 digits. ConstantID recomputes it from the defining constants: 0.014 387 768 775 039 338 021 466 716 0154…
Use in a calculation
# second radiation constant, CODATA 2022 (NIST)
second_radiation_constant = 1.4387768775039338021466716015439116e-2 # m K, exact
# SciPy: scipy.constants.physical_constants['second radiation constant']What it is
The constant in the exponent of Planck's law. It sets where the black-body spectrum peaks for a given temperature.
It is built only from constants that have exact values since 20 May 2019, so it is exact too; CODATA 2018 was the first adjustment to list it that way.
Equations
- definition
- Planck's law
How the value changed, 1998–2022
Each point is one CODATA adjustment, plotted as its difference from the 2022 value; the bars show one standard uncertainty (an arrowhead means the bar runs off the chart). Diamonds mark adjustments in which the value was exact.
Relative uncertainty
| CODATA | Value (uncertainty) | Relative uncertainty | Change from previous |
|---|---|---|---|
| 2022 | 1.438 776 877… × 10−2 | exact | exact |
| 2018 | 1.438 776 877… × 10−2 | exact | −0.6 σ of 2014 |
| 2014 | 1.438 777 36(83) × 10−2 | 5.8 × 10−7 | +0.3 σ of 2010 |
| 2010 | 1.438 7770(13) × 10−2 | 9.0 × 10−7 | +0.7 σ of 2006 |
| 2006 | 1.438 7752(25) × 10−2 | 1.7 × 10−6 | +0.0 σ of 2002 |
| 2002 | 1.438 7752(25) × 10−2 | 1.7 × 10−6 | +0.0 σ of 1998 |
| 1998 | 1.438 7752(25) × 10−2 | 1.7 × 10−6 |
“Change from previous” is the shift in the value divided by the standard uncertainty of the previous adjustment. Earlier values are converted into the current unit where NIST changed it (for example J s to J Hz⁻¹).