The spectral power distribution of a blackbody radiator is a function of wavelength *λ* (in meters) and temperature *T* (in kelvin).
This function is described by Planck's formula:

where:

$$c_1 = 2 \pi h c^2 \text{, W m}^2$$ $$c_2 = h c / k \text{, mK}$$ $$c = 2.99792458 \times 10^8 \text{, m/s (velocity of light)}$$ $$h = 6.626176 \times 10^{-34} \text{, Js (Planck constant)}$$ $$k = 1.380662 \times 10^{-23} \text{, J/K (Boltzmann constant)}$$**Implementation Notes:**

- This equation is often used in a
*relative*form, normalizing so that $M_e (\lambda = 560 \text{nm})$ is either 100 or 1.0.