From luminous efficacy models, illuminance can be estimated if irradiance is known or can be estimated. In the present paper, Muneer's models for the luminous efficacy of global and diffuse radiation, useful for illumination engineers, are statistically assessed using data obtained at Madrid during a seven-year period. Several other models inspired on the simple approach proposed by Muneer are developed and statistically assessed. Some of those model the luminous efficacy of global or diffuse solar radiation, while others directly model the global or the diffuse illuminance. It is shown that for diffuse illuminance estimation the ratio of diffuse to extraterrestrial irradiance is to be preferred as independent variable to the ratio of global to extraterrestrial irradiance proposed by Muneer. Some models that estimate global illuminance from global irradiance and solar elevation, or diffuse illuminance from diffuse irradiance and solar elevation, perform practically on a par with the corresponding luminous efficacy models. It is also concluded that the striking difference between global luminous efficacy between the United Kingdom and Japan observed by Muneer is not due to a latitude effect.