Abstract: A lighting device (1) comprises a plurality of LEDs (11-14) producing light (21-24) of mutually different colors. The LEDs are driven in switching cycles (63) with a duty cycle controlled supply current of constant magnitude. In each switching cycle, each LED is first switched ON (61) and then switched OFF (62). In a measuring mode, during one switching cycle (63B), all ON phases of all LEDs are briefly interrupted, except for one LED (11), so that a light sensor (70) measures the light from this one LED. This measurement can be used to adapt the duty cycle of this one LED. In the next switching cycle (63C), the interruption of the ON phases is compensated by extending the ON phases of all LEDs except said one LED, the extension having a duration equal to the duration (?D) of the interruption.

Abstract: Light source having a plurality of light elements (207) and a control system for controlling the light elements. The control system comprises a plurality of light element controllers (213), each connected to a respective light element (207), and arranged to obtain light element data; and a bus interface (203), which is connected to the light element controllers (213) via a light source bus (209). The bus interface (203) provides the light element controllers (213) with a general command, and the light element controllers generate light element drive signals on basis of the general command and the light element data.

Abstract: A lighting device (10) comprises a LED (4), a driver (3), and a controller (2) which regularly switches from a drive state to a measuring state and back. In the measuring state, the controller controls the driver such that the driver does not generate any LED current. The LED produces a measuring signal (Sm) indicating a measured light level. The controller processes the measuring signal received from the LED, and makes a decision on the desired light output of the LED. In the drive state, the controller controls the driver such that the average light output produced by the LED corresponds to the desired light output as determined in the measuring state. In a possible embodiment, the driver generates a nominal LED current INOM, and sets the duration (? 1) of the drive state on the basis of the desired light output of the LED as determined in the measuring state.

Abstract: A lamp driver circuit (400) comprises a feedback circuit for controlling stable operation of a discharge lamp (La), e.g. an inductively coupled discharge lamp such as a molecular radiation lamp, and for controlling a light output level of the discharge lamp (La). In particular, if the discharge lamp (La) is operated at a dimmed light output level, the light output is sensitive to changes in the lamp voltage (VLa), possibly resulting in flickering. In order to control stable lamp operation and prevent flickering, a high-sp feedback circuit is provided for controlling an operating frequency. In order to provide a relatively large dimming range for controlling the light output level, a low-speed feedback circuit is provided for controlling a DC supply voltage level (VDC).

Abstract: A drive circuit for driving a fluorescent tube lamp comprises a variable frequency oscillator generating a lamp drive frequency, a resonant drive circuit driving the lamp with the lamp drive frequency, and a control unit for driving the variable frequency of the latter under control of a synchronization signal. When a pre-heating frequency is generated by the variable frequency oscillator, the lamp is pre-heated while when an illumination drive frequency is generated, the lamp ignites and operates in its illuminated state. The control unit comprises a transition controller for at an ignition of the lamp limiting the drive frequency to an ultimate ignition frequency, and only enabling transition from the ultimate ignition frequency to the illumination drive frequency after an ignition delay time.

Abstract: A method for dimming an illumination system (20) capable of emitting light (L) with a variable color is described. The illumination system (20) comprises three dimmable light sources (21, 22, 23) generating respective lights (L1, L2, L3) having respective, mutually different colors (C1, C2, C3). The method comprises the step of reducing the light intensities (I1, I2, I3) of the three dimmable light sources (21, 22, 23) while maintaining the color point until one of said light sources (21) reaches a lower dim limit (IMIN)—The method further comprises the step of maintaining the light intensity (I1) of said one light source (21) at its lower dim limit (IMIN) and reducing the light intensities (I2, I3) of the two other dimmable light sources (22, 23) in such a manner that the hue is maintained.

Abstract: The present inventions relates to a method for adjusting the light setting for a multi-color light source, which method comprises receiving input from a user related to at least one of white color, hue, and chroma, and adjusting white color, hue, and chroma of the light source in accordance with the user input. The method is characterized in the step of automatically changing a current hue and chroma level when the user input is received. This automatic change makes possible to render the subsequent adjustment in setting perceivable for the user, which facilitates the adjustment of the light source. The present invention also relates to a corresponding system and computer program product.

Abstract: A drive circuit for driving a fluorescent tube lamp comprises a variable frequency oscillator generating a lamp drive frequency, a resonant drive circuit driving the lamp with the lamp drive frequency, and a control unit for driving the variable frequency of the latter under control of a synchronization signal. When a pre-heating frequency is generated by the variable frequency oscillator, the lamp is pre-heated while when an illumination drive frequency is generated, the lamp ignites and operates in its illuminated state. The control unit comprises a transition controller for at an ignition of the lamp limiting the drive frequency to an ultimate ignition frequency, and only enabling transition from the ultimate ignition frequency to the illumination drive frequency after an ignition delay time.

Abstract: A back light emitter (4) of a display apparatus is supplied with alternating current (AC) bursts. An emitted light representing signal is generated from the AC bursts as supplied to the light emitter (4). The emitted light representing signal is compared with a reference signal REF to provide an error signal. A duration of the AC bursts is adjusted dependent on the error signal, such as to minimize the error signal.

Abstract: A fluorescent lamp (2), in particular a backlight lamp of a display device, is supplied with an alternating voltage, a frequency and an amplitude of which being greater during ignition than during normal operation of the lamp. The voltage (V) across the lamp and the current (I) through the lamp are measured to provide a measured voltage value and a measured real lamp current value. From the alternating voltage there is derived a voltage (V2). The measured voltage value is multiplied by the sum of the measured real lamp current value and the derived voltage. The multiplication result (P=V*(I+V2)) is compared with a reference value (Ref), which results in a difference or error value. The error value is used to control the frequency and the amplitude of the alternating voltage (V), such that the error value is minimized.

Abstract: The lamp life of a gas discharge lamp (6) depends inter alia on the deterioration of an electrode of the lamp during operation. The deterioration depends on an operating temperature of the electrode. A method according to the present invention for controlling the lamp life includes controlling the electrode temperature during operation by generating a temperature signal (12) representing the electrode temperature and providing said signal to a lamp driver circuit (4) operating said lamp. The lamp driver circuit controls an operating signal (10) supplied to the lamp (6) in order to control the electrode temperature to lie within a predetermined temperature range, thereby minimizing damage to the electrode during operation.

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 an electronic ballast equipped with a high-frequency bridge circuit, a microprocessor for controlling lamp operation and a stop circuit for interrupting the operation of the ballast in case of a fault condition, the stop circuit interrupts both the operation of the bridge circuit and the operation of the microprocessor. Unstable operation of the ballast caused by the fault condition is prevented thereby.

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: 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 an electronic ballast equipped with a high-frequency bridge circuit, a microprocessor for controlling lamp operation and a stop circuit for interrupting the operation of the ballast in case of a fault condition, the stop circuit interrupts both the operation of the bridge circuit and the operation of the microprocessor. Unstable operation of the ballast caused by the fault condition is prevented thereby.

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 lamp is operated using a DC-AC converter provided with switches and a control circuit for controlling the switches and generating a high-frequency AC lamp current. In each half period of the control signal generated by the control circuit, each of the switching elements is rendered conductive during successive time intervals. The lamp can be dimmed without instabilities by adjusting the second time interval in each half period of the control signal.

Abstract: A lamp is operated using a DC-AC converter provided with switches and a control circuit for controlling the switches and generating a high-frequency AC lamp current. In each half period of the control signal generated by the control circuit, each of the switching elements is rendered conductive during successive time intervals. The lamp can be dimmed without instabilities by adjusting the second time interval in each half period of the control signal.