In order to convert the corresponding forms so that they express the same quantity in the same units we multiply by the spectral increment. Then, for a particular spectral increment, the particular physical energy increment may be written B λ λ ( λ λ , T ) d λ λ = − − B ν ν ( ν ν ( λ λ ) , T ) d ν ν , which leads to B λ λ ( λ λ , T ) = − − d ν ν d λ λ B ν ν ( ν ν ( λ λ ) , T ) .