Experiments are described in which low‐pressure mercury, mercury‐argon, and mercury‐krypton discharges were irradiated with a dye laser pulse at 405 nm, thus exciting mercury atoms from the metastable 63P0level to the 73S1level. The 73S1level decays radiatively to the 63Plevels. By recording the time dependence of the 63P1level density at the 254‐nm fluorescence signal, the effective radiative lifetime of this level was determined. These measurements were performed for a wide range of mercury vapor densities. From the effective radiative lifetime and the 63P1level density, the 254‐nm output can be calculated. Reasonable agreement is found for two discharges of which the 254‐nm output had been measured directly.