# First Radiation Constant

Use First Radiation in Calcul.io. See what this built-in constant represents, enter it in an editable calculation, and review related values and units.

## firstRadiation

First radiation constant

Try it yourself:

```calculio
firstRadiation
```

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## First Radiation Constant

**firstRadiation** is a radiation constant used in Planck-law and blackbody spectral formulas.

## Thermal radiation

Use it with [secondRadiation](https://calcul.io/constants/secondRadiation/index.md), [planckConstant](https://calcul.io/constants/planckConstant/index.md), and [boltzmann](https://calcul.io/constants/boltzmann/index.md). Wavelength, frequency, and temperature units must match the chosen Planck-law form.

[All constants](https://calcul.io/constants/index.md)