Wien wavelength displacement law constant
Physico-chemicalExact
= 2.897 771 955… × 10−3 m K
- Value
- 2.897 771 955… × 10−3 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: 0.002 897 771 955 185 172 661 478 605 448 09…
Use in a calculation
# Wien wavelength displacement law constant, CODATA 2022 (NIST)
b_Wien = 2.8977719551851726614786054480928847e-3 # m K, exact
# SciPy: scipy.constants.physical_constants['Wien wavelength displacement law constant']What it is
The wavelength at which a black body radiates most strongly is b/T. For the Sun's surface, about 5772 K, that gives 502 nm, green-blue light; for a body at room temperature, 293 K, it gives 9.9 µm, in the infrared.
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
- Wien's displacement law
- in terms of h, c and k
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 | 2.897 771 955… × 10−3 | exact | exact |
| 2018 | 2.897 771 955… × 10−3 | exact | −0.6 σ of 2014 |
| 2014 | 2.897 7729(17) × 10−3 | 5.9 × 10−7 | +0.3 σ of 2010 |
| 2010 | 2.897 7721(26) × 10−3 | 9.0 × 10−7 | +0.7 σ of 2006 |
| 2006 | 2.897 7685(51) × 10−3 | 1.8 × 10−6 | −0.0 σ of 2002 |
| 2002 | 2.897 7686(51) × 10−3 | 1.8 × 10−6 | +0.0 σ of 1998 |
| 1998 | 2.897 7686(51) × 10−3 | 1.8 × 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).