  Starting from a fully quantized Hamiltonian for an ensemble of identical
emitters coupled to the modes of an optical cavity, we determine analytically
regimes of thermal, collective anti-bunching and laser emission that depend
explicitly on the number of emitters. The lasing regime is reached for a number
of emitters above a critical number (which depends on the light-matter
coupling, detuning and the dissipation rates) via a universal transition from
thermal emission to collective anti-bunching to lasing as the pump increases.
Cases where the second order intensity correlation fails to predict laser
action are also presented.
