Abstract: An illumination system (1) comprises: —at least one light source (2); —a control system (3) for controlling the light sources, the control system comprising a sensor system (4) with at least one light sensor (5) for sensing ambient light (L1) and for generating a sensor output signal (M) representing the sensed light level, wherein the control system is designed for controlling the light sources in relation to the sensor output signal. The control system automatically calibrates the sensor system. The control system measures the ambient illumination level (MMIN) at a moment of calibration and stores this measured ambient illumination level into a memory (7). The control system, preferably with the light sources in an OFF condition, monitors the ambient illumination level and compares this with the stored value, and automatically performs a calibration procedure when the ambient illumination level reaches a new minimum value lower than the stored value.

Abstract: A ballast circuit for operating a discharge lamp equipped with a control loop for controlling the power consumed by the lamp. A first circuit part is coupled to the discharge lamp and to input terminals for connection to a source of supply voltage for the ballast circuit. The first circuit part is coupled to the input terminals to supply lamp current from the supply voltage. The control loop includes a second circuit part coupled to the first circuit to generate a first signal that represents a desired value of lamp power. A third circuit part is coupled to the input terminals for generating a second signal that depends on the amplitude of the supply voltage. A fourth circuit part has an input coupled to the third circuit part and an output coupled to an input of the second circuit part for adjusting the value of the first signal dependent upon the second signal. The power consumed by the lamp is decreased when the amplitude of the supply voltage decreases.

Abstract: An electronic ballast for supplying a lamp comprises a control loop for controlling the rms value of an operational parameter so as to be constant. In the control loop, the actual rms value of the parameter is generated as a linear combination of its average value and its peak value.

Abstract: In a ballast circuit for operating a lamp equipped with a control loop for controlling the power consumed by the lamp, this power consumed by the lamp is decreased when the amplitude of the supply voltage decreases. Too high currents in the ballast circuit are thereby prevented.

Abstract: A ballast circuit comprises an inverter formed by a bridge circuit. The power consumed by a lamp connected to the ballast circuit is controlled by controlling the duty cycles of control signals that drive the bridge switches. The duty cycle is proportional to digital signals generated by a pulse duration modulator included in a microprocessor. To increase the number of settings to which the lamp power can be set, the digital signals are modulated.

Abstract: An electronic ballast for supplying a lamp comprises a control loop for controlling the rms value of an operational parameter so as to be constant. In the control loop, the actual rms value of the parameter is generated as a linear combination of its average value and its peak value.

Abstract: A ballast circuit comprises an inverter formed by a bridge circuit. The power consumed by a lamp connected to the ballast circuit is controlled by controlling the duty cycles of control signals that drive the bridge switches. The duty cycle is proportional to digital signals generated by a pulse duration modulator comprised in a microprocessor. To increase the number of settings to which the lamp power can be set, the digital signals are modulated.

Abstract: In a ballast circuit for operating a lamp, which comprises a bridge circuit and a control circuit for controlling the bridge switches, the control circuit comprises a microprocessor. The control signal for controlling the switches is generated by a separate circuit comprising a signal generator, a timer, two comparators and two reference signal generators. The microprocessor is used only to set the reference signals to the desired values, thereby dimming the lamp.

Abstract: A circuit arrangement for operating a lamp has two power feedback loops, and a transformer is incorporated in one of the feedback loops. The transformer is used to adapt the amount of power fed back to the amplitude of the mains supply voltage for different lamp voltages.

Abstract: In a circuit arrangement for operating at least one lamp, and comprising two power feedback loops, a transformer with two primary windings and one secondary winding is included in the load circuit. The voltage present at a common terminal of the two primary windings is fed back by one of the feedback loops. The circuit arrangement can operate lamps with a lamp voltage that is much higher than the rms voltage of the mains supply generating only a limited amount of total harmonic distortion.

Abstract: In a ballast circuit for operating a discharge lamp, two different lamp power levels are adjustable. The ballast circuit is equipped with a switch to optimize the amount of power feedback for the lamp power level. This enables total harmonic distortion and power balance to be optimized for more than one power level.

Abstract: In a ballast circuit for operating a lamp, which comprises a bridge circuit and a control circuit for controlling the bridge switches, the control circuit comprises a microprocessor. The control signal for controlling the switches is generated by a separate circuit comprising a signal generator, a timer, two comparators and two reference signal generators. The microprocessor is used only to set the reference signals to the desired values, thereby dimming the lamp.