This paper describes a fast daylight model suitable or embedded daylight controllers. For a given room geometry (including position and tilt of venetian blinds, and the sun's position), the indoor illuminances are modeled as a linear combination of outdoor global and diffuse irradiances. A controller can implememnt this model by continuously recording simultaneous measurements of illuminance, blinds' model has beend validated against a RADIANCE model of an office room, and a "toy" controller thant uses this model has been shown capable of keeping the horizontal work plane illuminance close to a given setpoint.