We report measurements of the absolute spectral intensity due to galvanomagnetic luminescence of intrinsic InSb at room temperature. Together with a calculation of carrier and photon transport, these measurements form the basis for a new technique for the determination of carrier lifetimes and diffusion lengths. The excess carrier lifetime for InSb is found to be 6 ns, and the ambipolar diffusion length at 1.9 T is 3 μm. The spectrally integrated luminescence has a bilinear form in terms of the exciting current density j and magnetic field B: ΔF=GB j, where ΔF is the change in the total emitted radiant energy flux from the thermal equilibrium value ( j=0). In particular ΔF can be negative. The new thermodynamic transport coefficient G has the value 1.8 μW A−1 T−1 at 33 °C and decreases with increasing temperature.