Calculable is the ratio of the populations of the two states at room temperature (T ≈ 300 K) for an energy difference Δ E that corresponds to light of a frequency corresponding to visible light (ν ≈ 5 × 10 Hz). In this case Δ E = E 2 − E 1 ≈ 2.07 eV, and kT ≈ 0.026 eV. Since E 2 − E 1 ≫ kT, it follows that the argument of the exponential in the equation above is a large negative number, and as such N 2 / N 1 is vanishingly small; i.e., there are almost no atoms in the excited state. When in thermal equilibrium, then, it is seen that the lower energy state is more populated than the higher energy state, and this is the normal state of the system. As T increases, the number of electrons in the high-energy state (N 2) increases, but N 2 never exceeds N 1 for a system at thermal equilibrium; rather, at infinite temperature, the populations N 2 and N 1 become equal. In other words, a population inversion (N 2 / N 1 > 1) can never exist for a system at thermal equilibrium. To achieve population inversion therefore requires pushing the system into a non-equilibrated state.