 The resulting current density "J"c through the collector (per unit of collector area) is again given by Richardson's Law, except now
where "A" is a Richardson-type constant that depends on the collector material but may also depend on the emitter material, and the diode geometry.In this case, the dependence of "J"c on "T"e, or on "ΔV"ce, can be fitted to yield "W"c.

This retarding potential method is one of the simplest and oldest methods of measuring work functions, and is advantageous since the measured material (collector) is not required to survive high temperatures.The photoelectric work function is the minimum photon energy required to liberate an electron from a substance, in the photoelectric effect.