What this calculator does
Blackbody Radiation works out spectral radiance a hot object emits at one wavelength, from Planck's law. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaBλ = 2hc²/λ⁵ × 1/(e^(hc/λkBT) − 1)
The inputs explained
| Field | What to enter |
|---|---|
| Wavelength (λ) (nm) | A number, measured in nm. Starts at 500. |
| Temperature (T) (K) | A number, measured in K. Starts at 5778. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with wavelength (λ)
Every other input is held at the calculator’s starting values while wavelength (λ) varies. Select any row to load that scenario into the calculator.
How the answer changes with wavelength (λ)
| Wavelength (λ) (nm) | Spectral radiance at this wavelength | Spectral radiance | hc/(λ·kB·T) |
|---|---|---|---|
| 250 | 5.7612e+3 W/(sr·m²·nm) | 5.7612e+12 W/(sr·m³) | 9.960 |
| 375 | 2.1014e+4 W/(sr·m²·nm) | 2.1014e+13 W/(sr·m³) | 6.640 |
| 500 | 2.6376e+4 W/(sr·m²·nm) | 2.6376e+13 W/(sr·m³) | 4.980 |
| 750 | 1.8823e+4 W/(sr·m²·nm) | 1.8823e+13 W/(sr·m³) | 3.320 |
| 1,000 | 1.0767e+4 W/(sr·m²·nm) | 1.0767e+13 W/(sr·m³) | 2.490 |
| 1,500 | 3.6821e+3 W/(sr·m²·nm) | 3.6821e+12 W/(sr·m³) | 1.660 |