Greenhouse system may comprise an illumination, a sensor, and a controller. The illumination and controller are arranged to vary the intensity and the spectral distribution of the light emitted by the illumination. The emitted light may be pulsed light, the pulse characteristics being variable by the controller in dependency of the output of the sensor. The controller is arranged to interpret the relevant variables measured by the sensor and to assess the actual and/or expected growth of the relevant plants, and to control the intensity and/or the spectral distribution of the light emitted by the illumination. Some sensors may be provided for measuring the intensity and/or spectral distribution of the actual light in the greenhouse, other sensors for measuring plant dimensions of the relevant plants or plant groups. The illumination may comprise a heat collector which can be connected to heating or air conditioning inside or outside the greenhouse.