F( λ )=ΦE 1 Δλ in SI units
in SI units: F(λ) is the spectral irradiance in Wm-2μm-1; Φ is the photon flux in # photons m-2sec-1; E and λ are the energy and wavelength of the photon in joules and meters respectively
F( λ )=Φ q 1.24 λ(μm) 1 Δλ(μm)
