The exact quantum yield of the O (1D) formation from the ozone photolysis in the UV range 295--320 nm is important for aeronomic calculations, since O (1D) is the primary source for OH radicals in the troposphere. Recent O (1D) quantum yield determinations at 230, 268, 298 and 320 K are summarized and an analytical expression is derived which relates the quantum yield of O (1D) formation as a function of wavelength and temperature.