def Planck_wavelength(l, T):
u = hPlanck*c_light/l/kBoltzmann/T<EOL>return <NUM_LIT:2>*kBoltzmann**<NUM_LIT:5>*T**<NUM_LIT:5>/hPlanck**<NUM_LIT:4>/c_light**<NUM_LIT:3>*u**<NUM_LIT:5>/(exp(u)-<NUM_LIT:1>)<EOL>
The Planck function (flux density for blackbody radiation)
    in wavelength space
    l is wavelength in meters
    T is temperature in Kelvin

    Formula (3.3) from Raymond Pierrehumbert, "Principles of Planetary Climate"