Approximating the probability-density function of optical irradiance fluctuations in the turbulent atmosphere under all propagation conditions requires a model with at least two parameters. Two phenomenological two-parameter models that have been proposed, the IK and the log-normally modulated Rician probability-density functions, are compared with measured probability-density functions of the irradiance of laser light in a turbulent atmosphere under a variety of propagation conditions. The parameters for each model are obtained from measured second and third moments. It is concluded that the log-normally modulated Rician model is the better approximation to the data. However, the effects of the intermittency of turbulence must be included in the model for short propagation paths.