The light output properties are described for a microcavity laser having dimensions on the order of the emitted wavelength. Analytic resolution of rate equation for the nonradiative depopulation not equal to zero is derived for the first times. The results show that increasing the coupling of spontaneous emission into the cavity mode causes the lasing properties becoming quite different from those of the conventional laser having cavity dimensions much larger than the lasing wavelength. In the closed microcavity of an ideal four-level laser system, when nonradiative depopulation is zero, the light output property of the microcavity laser is linearly. When nonradiative depopulation is not zero (in fact it is usually true), it is not linearly even for an ideal four-level laser system in the closed microcavity.