Method of controlling a lighting device

Abstract

According to an aspect of the invention, a method of controlling a lighting device is provided. The method comprises receiving an input from a dimmer, the input being representative of a desired light output level for the lighting device. A control voltage for operating a driver unit comprised in the lighting device is computed based on the input and a calibrated relationship between power consumption and control voltage for the lighting device.

Claims

1. A method of controlling a lighting device having a commissioning and operating phase, comprising: receiving, during the commissioning phase, an input from a dimmer, said input being representative of desired light output level for said lighting device, and computing, during the commissioning phase, a control voltage for a driver unit comprised in said lighting device, for thereby operating a light source used in said lighting device based on said input so as to provide said desired light output level, wherein said computing is at least partly based on an earlier established calibrated relationship between power consumption and control voltage for said lighting device by measuring power consumption values obtained from applying various control voltage values; whereby light output levels are determined that correspond to said various control voltage values and the control voltage is available during the operating phase.

2. A method according to claim 1, wherein said calibrated relationship is represented by a lookup table.

3. A method according to claim 1, wherein said calibrated relationship is represented by a dim curve.

4. A method according to claim 1, comprising storing said measured power consumption values and said various control voltage values of said calibrated relationship.

5. A method according to claim 4, further comprising analyzing said measured power consumption values as a function of said various control voltage values to establish a dim curve.

6. A method according to claim 5, further comprising analyzing said measured power consumption values to determine a type of said light source.

7. A method according to claim 1, further comprising analyzing said measured power consumption values to determine a warm-up time and/or a life expectancy of said light source.

8. A method according to claim 1, wherein said light source is selected from the group consisting of LED and fluorescent light sources.

9. A method according to claim 1, wherein said control voltage is in a range of 0 to 10 V or in a range of 1 to 10 V.

10. A control unit for a lighting device, said control unit being configured, in a commissioning phase of operation, to receive an input from a dimmer, said input being representative of a desired light output level for said lighting device, and to compute a control voltage for a driver unit comprised in said lighting device, for thereby operating, in an operation phase, a light source used in said lighting device based on said input so as to provide said desired light output level, wherein said computing is at least partly based on an earlier established calibrated relationship between power consumption and control voltage for said lighting device by measuring power consumption values obtained from applying various control voltage values; whereby light output levels are determined that correspond to said various control voltage values.

11. A lighting device comprising a control unit according to claim 10, wherein the driver unit is configured to convert the control voltage into a drive signal for said light source so as to provide said desired light output level, and wherein the lighting device further comprises a power measurement unit configured to measure power consumed by at least one of said light source and said driver unit during operation of the lighting device.

12. A lighting device according to claim 10, with said control unit furthermore being configured to analyze said measured power consumption values as a function of said various control voltage values to establish a dim curve.

13. A lighting device according to claim 10, said lighting device being part of an indoor or outdoor lighting system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiments of the invention.

(2) FIG. 1 is a schematic representation of an embodiment of a lighting device according to the invention.

(3) FIG. 2 is a graphic representation showing an (exemplary) actual driver dim curve and an (exemplary) linearly approximated dim curve.

(4) FIG. 3 is an outline of a method of controlling a lighting device according to an embodiment of the present invention.

(5) The figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the invention, wherein other parts may be omitted or merely suggested.

DETAILED DESCRIPTION OF EMBODIMENTS

(6) With reference to FIGS. 1-3, a lighting device according to an embodiment of the present invention will be described.

(7) FIG. 1 schematically represents a lighting device 100 according to an embodiment of the present invention. The lighting device 100 comprises a dimmer 120, a control unit 130, a driver unit 140, a light source 150 such as a lamp, and a power measurement unit 160. It is here to be understood that in other embodiments the dimmer 120 need not be comprised in the lighting device 100, and instead may be comprised in a separate controller responsible for controlling a plurality of lighting devices (not shown).

(8) Control unit 130 receives at step 310 (of FIG. 3) an input representative of a desired light output level from dimmer 120. The input may be in terms of % light level of a maximum light level. The control unit 130 is for example an Outdoor Luminaire Controller (OLC). Based on a calibrated relationship, which will be described in further detail below, the control unit 130 determines at step 320 the control voltage corresponding to the input, generally representing a desired light output level. The computed control voltage is applied to a driver unit 140, such as an electronic 0-10 V or 1-10 V dimming driver. The driver unit converts the control voltage into a drive signal for the lamp 150 in order to adjust the light intensity to the desired light output level. Power measurement unit 160 measures the power consumed by the lamp 150 and/or the power consumed by the driver unit 140 and provides the resulting measured values to the control unit 130.

(9) In the graphic representation that is FIG. 2, exemplary dim curves are shown. The linear curve denoted “b” represents a linear approximation of light output (y axis) as a function of control voltage (x axis), which is common in prior art control units. The linear approximation is based on dimming characteristics comprised in a lamp type file which has to be distributed to the control unit. The dimming characteristics of the lamp type file typically define a minimum dimming level and a maximum control voltage.

(10) Even if the linear approximation resulting from the interpolation between e.g. a minimum value and a maximum value is defined in order to match the actual driver dim curve as closely as possible, there is frequently a discrepancy at certain points. In this example, the actual driver dim curve denoted “a” (black squares) differs from the linear curve denoted “b” e.g. at 2 V and at 6 V. Further, the control voltage saturates at 9 V. This means that when the light input level is e.g. 60%, the control unit's task is to provide a control voltage corresponding to this desired light level. To accomplish this, a prior art control unit utilizes the linear dim curve denoted “b” resulting in a required control voltage of 6 V. A control voltage of 6 V will, however, based on the actual dim curve of the driver, result in a dimming level of 70% instead of the correct level of 60%.

(11) In the present embodiment, a control voltage for operating the lighting device is computed based on the input and a calibrated relationship between power consumption and control voltage for the lighting device such that the computed control voltage corresponds to the input. An exemplary method of defining a calibrated relationship between power consumption and control voltage is described below.

(12) During e.g. installation (commissioning phase) of a lighting device, a control unit performs a series of power consumption measurements (absolute or relative) for various control voltages. An exemplary output of such measurements is given in the table below.

(13) TABLE-US-00001 TABLE 1 Exemplary output of power measurements Control Voltage [V] 1 2 3 4 5 6 7 8 9 10 Power value [%] 60 60 65 70 75 80 85 100 100 100

(14) In this example, power consumption is measured for each control voltage integer between 1 and 10 V. Depending on the protocol of the dimming driver, power measurements may be performed for other ranges of control voltages. The number of power measurements performed within the control voltage range moreover influences dimming resolution. In practice, power measurements may be performed at every 1 V or at every 0.5 V.

(15) Based on the measured power consumption presented in Table 1, the control unit determines the minimum dimming level (in this case 60%) and generates a dimming table, i.e. a lookup table. In this particular case such a table would be as follows:

(16) TABLE-US-00002 TABLE 2 Lookup table Power value [%] (or Light level [%]) 10 20 30 40 50 60 70 80 90 100 Control voltage [V] — — — — — 2 4 6 7.5 8

(17) In the lookup table, power consumption values or, according to embodiments of the invention, light levels may be presented for various control voltages.

(18) Once the calibrated relationship is established, dimming can be controlled by providing e.g. a required light output level percentage. The actual control voltage is determined using the dimming table. In order to fine tune the relationship between light output level and control voltage, linear interpolation can be used between sampled levels.

(19) The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention and that those skilled in the art will be able to design alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be constructed as limiting the claim. The word “comprising” does not exclude the presence of elements or steps not listed in a claim. The word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. No specific sequence of acts is intended to be required unless specifically indicated.