First radiation constant
Physico-chemicalExact
= 3.741 771 852… × 10−16 W m2
- Value
- 3.741 771 852… × 10−16 W m2
- 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: 3.741 771 852 192 758 011 367 155 555 93 × 10−16…
Use in a calculation
# first radiation constant, CODATA 2022 (NIST)
first_radiation_constant = 3.7417718521927580113671555559299851e-16 # W m^2, exact
# SciPy: scipy.constants.physical_constants['first radiation constant']What it is
One of the two constants in Planck's law for black-body radiation, written for spectral exitance (power per area per wavelength).
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
In other units
| Unit | Value | |
|---|---|---|
| CGS (cm4 g s−3) | 3.741 771 852 × 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 | 3.741 771 852… × 10−16 | exact | exact |
| 2018 | 3.741 771 852… × 10−16 | exact | +1.3 σ of 2014 |
| 2014 | 3.741 771 790(46) × 10−16 | 1.2 × 10−8 | +1.5 σ of 2010 |
| 2010 | 3.741 771 53(17) × 10−16 | 4.5 × 10−8 | +1.8 σ of 2006 |
| 2006 | 3.741 771 18(19) × 10−16 | 5.1 × 10−8 | −0.3 σ of 2002 |
| 2002 | 3.741 771 38(64) × 10−16 | 1.7 × 10−7 | +1.1 σ of 1998 |
| 1998 | 3.741 771 07(29) × 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).