First radiation constant for spectral radiance
Physico-chemicalExact
= 1.191 042 972… × 10−16 W m2 sr−1
- Value
- 1.191 042 972… × 10−16 W m2 sr−1
- 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: 1.191 042 972 397 188 414 079 4892 × 10−16…
Use in a calculation
# first radiation constant for spectral radiance, CODATA 2022 (NIST)
first_radiation_constant_for_spectral_ra = 1.1910429723971884140794892e-16 # W m^2 sr^-1, exact
# SciPy: scipy.constants.physical_constants['first radiation constant for spectral radiance']What it is
The first radiation constant when Planck's law is written for spectral radiance (power per area per solid angle per wavelength): 2hc², which is c₁/π.
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.
In other units
| Unit | Value | |
|---|---|---|
| CGS (cm4 g s−3) | 1.191 042 972 × 10−5 | exact |
Converted with ConstantID's unit table; digits are rounded to the precision of the value, and a long exact value is rounded only for display.
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 | 1.191 042 972… × 10−16 | exact | exact |
| 2018 | 1.191 042 972… × 10−16 | exact | +1.3 σ of 2014 |
| 2014 | 1.191 042 953(15) × 10−16 | 1.3 × 10−8 | +1.6 σ of 2010 |
| 2010 | 1.191 042 869(53) × 10−16 | 4.4 × 10−8 | +1.9 σ of 2006 |
| 2006 | 1.191 042 759(59) × 10−16 | 5.0 × 10−8 | −0.3 σ of 2002 |
| 2002 | 1.191 042 82(20) × 10−16 | 1.7 × 10−7 | +1.1 σ of 1998 |
| 1998 | 1.191 042 722(93) × 10−16 | 7.8 × 10−8 |
“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).