HK1111856B - Lightning apparatus and method - Google Patents

Description

Lighting device and method

Technical Field

The present invention relates to improvements in lighting systems, and in particular to lighting systems having variable colour temperature.

Background

Lighting systems with variable color temperature are well known in the art to improve the comfort of office and home environments, typically incandescent lamps used at night have a lower color temperature and fluorescent lamps used at daytime with a higher color temperature. The Solux Lamp (www.soluxtli.com) is a 'cold' light Lamp made with a special coating that can emit light with a color temperature of about 4700K. However, at low light intensities, such light sources appear too blue when dimmed, and a multiple light source approach is preferred for improved effectiveness and comfort of treatment.

Background of the prior art can be found in WO 96/28956, JP 05-121176, JP 04-206391, DE 3526590, JP 03-226903, EP 0545474, DE 3916997, US 3180978, FR 2151121, and WO 85/01566. However, a problem with prior art systems is that they require new control wiring, additional mounting of light sources of different color temperatures, and special control means, such as light sensors mounted outdoors. Typically, prior art systems require at least two separate lighting circuits for controlling light sources having different color temperatures, thereby making them incompatible with standard home lighting fixtures and increasing the cost of providing a manual lighting fixture with a variable color temperature.

It would be advantageous to provide a variable color temperature capable lighting system that can be used in standard office and home lighting circuits, including standard dimmers. In particular, it would be advantageous to provide a plug-in device that can replace existing light bulbs and that incorporates a variable color temperature device for use in conjunction with existing dimmer circuits.

Disclosure of Invention

According to one aspect of the present invention, there is provided an apparatus for controlling two light sources using an input voltage of a power dimmer, the light sources comprising: a first light source configured to emit light having a first color temperature and a second light source configured to emit light having a second color temperature, wherein the second color temperature is higher than the first color temperature, the apparatus comprising: an input connection for receiving an input voltage from a power dimmer; a sensor for detecting a voltage value of an input voltage; a driving device for driving the light source; and a controller for controlling the driving device in response to the detection.

The voltage output waveform of the power dimmer may vary depending on the design of the dimmer. One method for determining the power level set on the dimmer is to determine the rms voltage of the dimmer, as this can provide a level of power delivered to a purely resistive load. The sensor may directly detect the average voltage or it may measure the instantaneous voltage at the power supply input at various intervals over a period of time and determine the average voltage. As another alternative, it may detect the average voltage indirectly, for example, by detecting a duty cycle (duty cycle) of the waveform.

The device may control the light sources such that the brightness of the first light source increases when the average voltage of the power dimmer increases from zero to a reference voltage (between 1/2 and 1/3 supply voltages, e.g., the 1/2 supply voltage). When the average voltage is further increased from the reference voltage to the maximum voltage (e.g. 230V in UK and most european countries and 115V in USA), the brightness of the second light source may be increased while the brightness of the first light source is decreased, so that the overall brightness of the two light sources to the observer is substantially constant. Since the two light sources emit light with different color temperatures, the overall color temperature of the emitted light may increase from the first color temperature to the second color temperature when the average voltage is increased from the reference voltage to the maximum voltage.

The drive levels of the two light sources may be obtained from a look-up table which may be configured to take into account different light source types and different transfer curves. Alternatively, the first light source may be controlled in proportion to the average voltage minus the reference voltage, so that between zero voltage and the reference voltage, the first light source is off; and between the reference voltage and the maximum voltage the first light source is switched on. The second light source may be controlled in proportion to a difference between the average voltage and the reference voltage so that the second light source has a maximum intensity at the reference voltage, and the intensity of the second light source is decreased when the average voltage is changed to be greater than or less than the reference voltage.

According to another aspect of the present invention, there is provided a light source configured to provide light of variable colour temperature, the light source comprising: a power input for receiving an input power source, a first illumination source, a second illumination source, and a controller coupled to the power input and coupling the first and second illumination sources, wherein the controller is configured to provide a variable drive level to the first and second illumination sources that is dependent on the input power source to provide the variable color temperature light.

The controller may be configured such that the overall brightness of the light source remains substantially constant to an observer over a portion of the variable color temperature range. The controller may be configured such that the sum of the luminous flux (measured in lumens) output by the first illumination source and the luminous flux output by the second illumination source is substantially constant. Alternatively, the controller may be configured such that the sum of the illuminance (measured in lux) output by the first illumination source over a certain distance and the illuminance output by the second illumination source over the same distance is substantially constant.

According to another aspect of the present invention, there is provided a light bulb having a plurality of light sources, the light sources comprising: a first light source configured to emit light having a first color temperature and a second light source configured to emit light having a second color temperature, wherein the second color temperature is higher than the first color temperature.

The light bulb is preferably a plug-in device that can replace conventional incandescent, fluorescent, or other light sources.

The first light source and the second light source may be different types of light sources. For example, one light source may comprise a plurality of LEDs, while another light source may comprise a filament-type light source. Alternatively, either or both light sources may comprise fluorescent tube light sources. Under predetermined conditions, e.g. drive voltage and/or drive current, the first light source emits light with a lower color temperature and the second light source emits light with a higher color temperature. These conditions may be different for the two light sources, in particular they are different types of light sources. For example, a filament-type light source may have a higher voltage rating than an LED. The color temperature of the light emitted from the second light source is higher than the color temperature of the light emitted from the first light source when they are operated under the respective rated driving conditions.

Preferably, the first color temperature is less than 3000K and the second color temperature is greater than 5000K. For example, the first color temperature may be 2700K (which may be referred to as a 'warm' light source), and the second color temperature may be 5500K (which may be referred to as a 'cold' light source).

The light bulb may contain circuitry for controlling the light source using the input voltage of the power dimmer. This may be useful when the light bulb comprises an insertion means of a common light bulb, wherein the color temperature of the light emitted by the light bulb and the intensity of the light can be adjusted separately.

According to another aspect of the invention, there is provided a circuit for controlling a plurality of light sources using an input voltage of a dimmer, the circuit comprising: an input connection for receiving a power control signal from a dimmer; a voltage sensor for detecting the power control signal; a driving device for driving the plurality of light sources; and a controller for controlling the driving device in response to the detection.

Preferably, the circuit provides light of variable color temperature. Preferably, the light source includes: a first light source having a first color temperature and a second light source having a second color temperature, the second color temperature being higher than the first color temperature. Preferably, the controller provides variable drive levels to the first and second light sources, which depend on an average of said input voltage, to provide light of a variable color temperature. Here, the average value includes the RMS voltage value, for example, in the case where the dimmer varies the duty cycle ratio of the power supplied.

The circuit may be connected to a dimmer and two light sources, one of which emits light of a higher color temperature and the other of which emits light of a lower color temperature. It is also possible to use light sources arranged to emit light with an intermediate color temperature in order to improve the color temperature variation between the two extremes. Preferably, the dimmer is a mains dimmer, i.e. a dimmer that can dim mains lighting (as described below, such a dimmer may provide a variable low voltage control signal rather than variable mains power).

According to another aspect of the present invention, there is provided a method for controlling a plurality of light sources using a common input voltage to provide light of variable color temperature, the light sources comprising: a first light source configured to emit light having a first color temperature and a second light source configured to emit light having a second color temperature, wherein the second color temperature is higher than the first color temperature, the method comprising the steps of: the value of the input voltage is detected and in response to said detection both light sources are controlled to provide variable drive levels to said first and second light sources, which depend on said average value to provide a first portion of a control range in which the color temperature of the light is varied while the observed luminance is substantially constant.

Controlling the two light sources may also provide a second portion of the control range in which the observed luminance varies, while the color temperature may remain constant, or may vary substantially with luminance.

One method for detecting the average voltage is to measure the instantaneous voltage at various intervals over a period of time and to determine the average voltage from these measurements. Another method is to detect the duty cycle of the mains voltage waveform and determine the average voltage from this duty cycle.

The present invention may be embodied as computer program code. In another aspect, therefore, the present invention provides such code on a carrier medium, e.g., a floppy disk, configured to carry out the method described above. The invention also provides an integrated circuit, e.g. a microprocessor or a memory, carrying such code.

In the above-described apparatus, circuits and systems, the dimmer may be of the type that provides a dc control voltage, which is used in conjunction with a (usually separate) power supply. In this case, for example, the circuit may provide a variable drive level output for controlling a pair of fluorescent lamp ballast units, which may drive a respective pair of fluorescent lamps having different color temperatures. The ballast unit may be of the type having mains power as an input and a control signal of 0-10V and providing a fluorescent lamp drive output in dependence on the control signal, for example, Huco Limited 09-7570. The input voltage sensitive to the device/circuit may be a dc control signal of this type.

Generally, we have referred to above as driving two light sources having different color temperatures, however, the skilled person will appreciate that three or more light sources may be employed, some of which may have the same or overlapping color temperatures.

Drawings

These and other features of the present invention are described below, by way of example only, with reference to the following drawings, in which:

fig. 1 shows a block diagram of an apparatus for variable color temperature control.

Fig. 2 shows a flow chart of a method used in the controller of the block diagram shown in fig. 1.

Fig. 3 shows an example of a driving voltage scheme providing variable color temperature control.

Detailed Description

The block diagram in fig. 1 shows a device suitable for inclusion in a light bulb, which may be connected to a power source via a conventional dimmer. There are several different dimmer designs on the market, for example, leading edge dimmers, trailing edge dimmers, Pulse Width Modulation (PWM) dimmers, and resistive dimmers. Preferably, the device can be adapted to any type of dimmer circuit.

A voltage sensor (101) is connected to the power supply input (102) and is arranged to detect an average voltage, e.g. root mean square voltage, of the input, thereby providing an output indicative of a set power level at the dimmer. Alternatively, a duty cycle sensor may be used which can determine the power level set on the dimmer by detecting the portion of the power cycle (mains cycle) when the power is on. This is particularly suitable for leading edge and trailing edge type dimmers. A controller (104) is connected to the output of the voltage sensor and to the inputs of the at least two light source drivers (106 and 107). A simple power supply circuit (103), for example a circuit employing zener diodes, may be connected to the power supply input to provide a stable voltage output to the light source driver. However, the power supply circuit is not essential to the controller, and the light source driver may be configured to receive power directly from the power supply input or through a full-wave or half-wave rectifier. The device can be used in combination with low voltage light sources, e.g. LEDs, and therefore can have a large voltage range.

The function of the control circuit is to provide signals of different drive levels to the first light source and the second light source, so that when the power level set on the mains dimmer increases from zero, the intensity of the first light source increases to a maximum value, while the intensity of the second light source remains substantially zero, and with further increase of the power level of the mains dimmer, the intensity of the first light source may be reduced, while the intensity of the second light source increases from zero to a maximum value.

The first light source may comprise a low color temperature light source (also referred to as a 'warm' light source), such as an LED, fluorescent lamp or incandescent lamp, having a color temperature of about 3000K under normal operating conditions, preferably 2700K. The second light source is a higher color temperature light source (also referred to as a 'cold' light source) which may also include: LEDs, fluorescent or incandescent lamps, which have a color temperature of about 5000K, preferably 5500K. When the setting on the dimmer is increased from zero, the brightness of the first light source is increased. The first light source has a maximum brightness when the average voltage on the power supply input reaches a predetermined reference voltage (e.g., a fraction of the power supply voltage, e.g., 1/2). For power level settings above this level, the overall brightness of the bulb may remain substantially constant, while the color temperature may increase, as the brightness of the second light source increases and the brightness of the first light source decreases.

Note that the 'power level setting' on the mains dimmer refers to the power supplied to a normal light bulb or a purely resistive load. The power supplied to this circuit may actually increase, remain substantially constant, or decrease when the average voltage is increased from the reference voltage to the maximum supply voltage. This depends in part on the ratio of the first light source to the second light source and the amount of output light produced by each light source. If the second light source is more efficient than the first light source, the power required for the circuit to operate at the maximum voltage may be less than the power required to operate at the reference voltage.

The controller may be designed using a microprocessor or may be designed using analog circuitry, such as transistors and operational amplifiers. FIG. 2 illustrates a methodology suitable for use in microprocessor controller design. In a first step (201), the power level setting of the power dimmer is read out from the voltage sensor and determined. As different mains dimmer designs output various voltage waveforms, the microprocessor may execute program code to calculate the power level setting of the dimmer, e.g., over a period of several mains cycles, to avoid instantaneous voltage level changes due to clipping of the mains voltage waveform.

In a second step (202), the microcontroller may utilize a look-up table to derive drive levels for the first and second light sources. A suitable length for the look-up table may be 256 entries (suitable for an 8-bit digital-to-analog converter in a voltage sensor). The look-up table is configured to first increase the intensity of the first light source in response to an increased mains dimmer power, and then increase the intensity of the second light source while decreasing the intensity of the first light source.

Finally, in a third step (203), the drive level of the light source is output to the light source driver. The two light sources may operate at different voltage levels, current levels or overall power levels. This may be implemented in the light source driver or in a look-up table of the controller. In a first example, the same look-up table may be used for different light sources, wherein the appropriate light source driver is matched for the particular light source used. In a second example, the same light source driver may be used for all light sources, with the look-up table being changed to suit the particular combination of light sources used in the design. Thus, if the light source is changed, the same light source driver can be used for the new light source, and only the ROM of the look-up table needs to be updated.

In another embodiment, the controller of FIG. 1 may be formed of analog components, such as operational amplifiers and transistors. The controller is designed to function as if it were a microprocessor, but is hardwired. One advantage of using a microprocessor is that the program code (optionally including look-up tables) can be changed for different light sources or different reference voltages and maximum voltages, while a hard-wired design is only applicable for one embodiment. In particular, the look-up table may also be varied for different light intensity and color temperature curves and for different dimmer power level curves. Leading and trailing edge dimmers may produce different power level transfer curves than PWM dimmers, while some light sources may have a more linear relationship between intensity variation and drive voltage. Some or all of these effects may be taken into account when compiling the look-up table. The non-linear circuit may also simulate the exponential transfer curve using analog electronics, for example, using diodes.

Fig. 3 shows two example average voltage settings for the power supply input in the dimmer. At 301, the dimmer is set to slightly less than the reference voltage, approximately 80V. In this example, the first light source is at about 80% intensity, while the second light source is off. At 302, the dimmer is set between the reference voltage and the maximum supply voltage, approximately 190V. The first light source is at about 30% intensity and the second light source is at about 70% intensity. The drive voltage may vary linearly between two reference values on the graph (k1 being the full light intensity of the first light source and k2 being the full light intensity of the second light source), or the drive voltage may vary non-linearly in order to take into account the non-linearity of the voltage-intensity curve of the light sources and/or the curve of the power level of the dimmer versus the position of the dimmer. The following represents a typical equation for the linear relationship between two reference voltages on figure 3.

0≤V_AVERAGE≤V_REF

DV2＝0

V_REF≤V_AVERAGE≤V_MAINS

For example, V_REFMay be 100V. The driving voltage may be arranged such that the sum of the luminous flux output by the first light source and the luminous flux output by the second light source is constant between the reference voltage and the maximum supply voltage.

Lumens(S1)+Lumens(S2)＝consl

No doubt many other effective solutions can be envisaged by the skilled person. It will be understood that the invention is not limited to the embodiments described above and may include various modifications well known to those skilled in the art, which modifications are within the spirit and scope of the present invention as defined in the appended claims.

Claims (17)

1. A device for controlling two light sources, wherein an input voltage from a mains dimmer is used, the light sources comprising: a first light source configured to emit light having a first color temperature and a second light source configured to emit light having a second color temperature, wherein the second color temperature is higher than the first color temperature, the apparatus comprising:

an input connection for receiving the input voltage from a power dimmer;

a sensor for detecting a value of the input voltage;

a driving device for driving the light source; and

a controller for controlling the driving device in response to the detection,

wherein the controller is configured to control the driving means such that, at least over part of the average voltage range, the overall brightness of the two light sources is substantially constant for a human observer, despite a change in the color temperature of the light from the combined light source.

2. The apparatus of claim 1, wherein the sensor comprises a voltage sensor and the value sensed by the sensor comprises an average voltage of the input voltage.

3. The apparatus of claim 1, wherein the sensor comprises a duty cycle sensor.

4. Apparatus according to any one of claims 1 to 3, wherein the sensor is configured to determine the root mean square voltage of the input voltage.

5. The apparatus of claim 4, wherein the controller comprises:

consulting means for consulting the first control voltage and the second control voltage in response to the detection; and

and the output device is used for outputting the first control voltage and the second control voltage to the driving device.

6. The apparatus of claim 5, wherein the controller comprises:

means for controlling the first light source in proportion to the average voltage minus the reference voltage; and

means for controlling the second light source in proportion to a difference between the average voltage and the reference voltage.

7. A light source configured to provide light of variable color temperature, the light source comprising:

a power input for receiving an input power source;

a first illumination light source;

a second illumination light source; and

a controller coupled to the power input and to the first and second illumination sources; and

wherein said controller is configured to provide a variable drive level to said first and second illumination sources, the variable drive level being dependent on said input power supply so as to provide said variable color temperature light, and wherein said controller is configured to control said two illumination sources such that the overall brightness of said two illumination sources remains substantially constant to a viewer over at least part of said variable color temperature of said light.

8. A light bulb having two light sources, the light sources comprising: a first light source configured to emit light having a first color temperature and a second light source configured to emit light having a second color temperature, wherein the second color temperature is higher than the first color temperature, the bulb further comprising: a circuit for controlling a light source, wherein an input voltage from a mains dimmer is used, the circuit comprising:

an input connection for receiving power from a mains dimmer;

a sensor for detecting an average voltage of an input voltage;

a driving device for driving the light source; and

a controller for controlling the driving device in response to the detection.

9. The bulb according to claim 8, wherein the first color temperature is less than 3000K and the second color temperature is greater than 5000K.

10. A circuit for controlling two light sources using an input voltage from a power dimmer to provide light of variable color temperature, the light sources comprising: a first light source configured to emit light having a first color temperature and a second light source configured to emit light having a second color temperature, wherein the second color temperature is higher than the first color temperature, the circuit comprising:

an input connection for receiving an input voltage from a power dimmer;

a sensor coupled to an input connection for detecting the input voltage;

a driving means coupled to input connections connected to the plurality of light sources for driving the light sources; and

a controller for controlling the driving means in response to said detection to provide a variable drive level to said first and second light sources, the variable drive level being dependent on an average of said input voltage to provide said light of variable color temperature.

11. The circuit according to claim 10, wherein said input connection is configured to receive mains power for said light source.

12. The circuit according to claim 11, wherein the sensor is configured to detect a level of said received power supply or to detect an average voltage value of said power supply.

13. A method of controlling two light sources using a common input voltage to provide light of variable color temperature, the light sources comprising: a first light source configured to emit light having a first color temperature and a second light source configured to emit light having a second color temperature, wherein the second color temperature is higher than the first color temperature, the method comprising:

detecting the value of the input voltage; and

controlling both light sources in response to said detection to provide a variable drive level to said first and second light sources, the variable drive level being dependent on the average value to provide a control range in which the color temperature of the light is varied while the observed luminance is substantially constant.

14. The method of claim 13, wherein said detecting comprises: the average value is measured, or the root mean square voltage of the input voltage is measured.

15. The method of claim 13, wherein said detecting comprises: the duty cycle of the input voltage is measured.

16. The method according to any one of claims 13 to 15, wherein said controlling comprises:

referring to the first control voltage and the second control voltage corresponding to the average voltage in the look-up table; and

outputting a first control voltage to the first light source and a second control voltage to the second light source.

17. The method according to any one of claims 13 to 15, wherein said controlling comprises:

controlling the first light source in proportion to the average voltage minus the reference voltage; and

the second light source is controlled in proportion to a difference between the average voltage and the reference voltage.