f_{λ}(λ) = ergs/cm^{2}/s/Angstrom

N = ∫ \frac{f_{λ}(λ) T (λ)}{hc/λ}dλ photons/cm^{2}/s

N(z) = ∫ \frac{f_{λ}(\frac{λ}{1+z}) T (λ)}{hc/λ}dλ photons/cm^{2}/s