The radiance increases as the square of the frequency, illustrating the ultraviolet catastrophe. In the limit of high frequencies (i.e. small wavelengths) Planck's law tends to the Wien approximation : B ν ν ( T ) ≈ ≈ 2 h ν ν 3 c 2 e − − h ν ν k B T or B λ λ ( T ) ≈ ≈ 2 h c 2 λ λ 5 e − − h c λ λ k B T .