Quantitatively V.. aa. it is characterized by V.'s coefficient. aa. σ = ivt/ip, where - ivt the current formed by secondary electrons, ip - current of primary electrons, coefficient of elastic r = ir/ip and inelastic η = iη/i of reflection of electrons, and also coefficient of issue of truly secondary electrons δ = iδ/i (ir, iη, iδ - the currents corresponding is elastic reflected, it is not elastic to the reflected and truly secondary electrons, ivt = ir + iδ + iδ).
But current increases not indefinitely, since some tension of U how many not to increase tension on the anode, current size in a lamp remains to constants, there is a saturation current. This results from the fact that under existing conditions the cathode (+) allocates approximately identical quantity of electrons, and all of them move to the anode (-).