Lighting device with liquid crystal film, and corresponding light-emitting method

Abstract

The present invention relates to a vehicle lighting device (1), comprising: - at least one photon emitter (3); - a control unit (2) for controlling the photon emitter (3), the control unit (2) capable of applying a voltage pulse to bias the photon emitter (3) at a first frequency; - a liquid crystal film (4) capable of transmitting or blocking light emitted by the photon emitter (3); and - an AC voltage (V) applied to the film (4) at a second frequency. AC The lighting device (1) is equipped with a control means (5) capable of applying an AC voltage (V) applied to the film (4). AC The present invention relates to a vehicle lighting device (1) characterized by comprising means for synchronizing a photon emitter (3) with a voltage pulse applied to the photon emitter (3).

Description

[Technical Field]

[0001] The present invention relates to the fields of electronics and automobiles, and more particularly to a vehicle lighting device that uses a liquid crystal film, for example, a liquid crystal film comprising liquid crystal dispersed in a polymer, also known as a polymer-dispersed liquid crystal (PDLC) film. Liquid crystal films are used in automobiles, in particular, to provide smart glazing, to display content especially on the sunroof, or to modify the appearance of lighting elements to produce various luminescence effects, including signaling or active light concealment. [Background technology]

[0002] Applying an electric field to such a film makes it possible to orient the liquid crystals contained in the film so that light arriving on the film can pass through, in which case the film has a transparent or semi-transparent appearance. On the other hand, in the absence of such an electric field, the molecules do not have a consistent orientation, resulting in numerous reflections in multiple directions within the film, thereby producing an opaque effect, or at least an effect of scattering light that could have passed through the film.

[0003] Liquid crystal films can be likened to capacitive loads and must be supplied with an AC voltage with an average voltage of zero. This is because applying a DC voltage to the film will ultimately damage it.

[0004] Figure 1 shows the AC voltage V applied to the PDLC film as a function of time, in volts (V). AC , and this AC voltage V AC A current in milliamperes (mA) flows through the film that has been subjected to this treatment. A This shows the AC voltage V. AC It has a frequency of 100 Hz (Hertz), that is, an electrical period of 10 ms (milliseconds). Current I A is AC voltage V ACis zero outside the phase where the polarity changes, and within that phase, the current I flowing through the film A is the AC voltage V AC reaches a negative amplitude peak when it decreases, or reaches a positive amplitude peak when the AC voltage V AC increases. It can be understood that this is the case.

[0005] The last line in Fig. 1 shows, as a function of time and as a percentage, the transmittance T of the light beam passing through the PDLC film that has received the AC voltage V AC This transmittance T of the PDLC film T is fixed at around 70% when the AC voltage V T is at its maximum absolute value. On the other hand, this transmittance T AC decreases until it reaches 50% when the AC voltage V T is at zero value at the center of such a phase where the polarity of the AC voltage V AC changes. Note that the average transmittance of the PDLC film is only 68% due to the decrease in the transmittance T AC during the phase where the polarity of the AC voltage V AC changes. Similarly, the transmittance of other types of liquid crystal films also decreases during the polarity change phase, while the AC voltage has an absolute value smaller than the threshold voltage. T during the phase where the polarity of the AC voltage V

[0006] Fig. 2 shows, as a function of time, the relative value φ AC of the incident light beam arriving on the PDLC film that has received the AC voltage V LR This value is dimensionless as it is the ratio between the value of the light beam in candela units and the peak value of this light beam in candela units. This relative value φ LR is 1 here, and the incident light beam is generated by a light-emitting diode supplied with a DC voltage. The transmittance T LR of the PDLC film, reproduced below the line of the relative value φ of the light beam T is the same as that shown in Fig. 1. Therefore, the average transmittance of the light beam emitted by the light-emitting diode is 68%.

[0007] The inventors envision using PDLC film technology to conceal vehicle lighting or signaling means, particularly when the vehicle is stationary or when certain functions (such as daytime running lights) are not in use, by, for example, placing such PDLC films opposite the closing outer lenses of each headlamp of the vehicle, and therefore across the light beams that are easily emitted by the lighting or signaling means, or across the daylight arriving on these lighting or signaling means. In this case, it is necessary to adjust the supply voltage to the light-emitting diodes (LEDs) that perform the vehicle lighting or signaling function so that the LEDs provide the same light intensity through the PDLC film as before, in order to meet regulatory constraints related to these functions. However, with the aforementioned average transmittance of 68%, the supply voltage to the diodes must be significantly increased, which consumes energy. Furthermore, depending on the lighting or signaling function performed by the light-emitting diodes, their supply voltages may fluctuate, potentially generating flickering. This flickering, coupled with the AC voltage applied to the film, can increase discomfort for road users, whether they are vehicle drivers or others.

[0008] Therefore, for aesthetic reasons, there is a need for shielding vehicle lighting or signaling means that conserve energy and do not pose a risk of causing visual discomfort. This is particularly relevant when it comes to homogenizing the style of the vehicles. [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The present invention aims to at least partially overcome the shortcomings of the prior art by providing a vehicle lighting device comprising a liquid crystal film that limits energy consumption and flicker compared to the prior art, an optical unit comprising such a lighting device, and a light-emitting method implemented by such a lighting device or such optical unit. [Means for solving the problem]

[0010] For this purpose, the present invention provides a lighting device for vehicles, - At least one photonic emitter, - A control unit for controlling a photonic emitter, which is capable of applying a voltage pulse to the photonic emitter to impart polarity to the photonic emitter so that the photonic emitter emits light, - A liquid crystal film capable of transmitting or blocking at least a portion of the light emitted by a photonic emitter, - Control means capable of applying an AC voltage to the film and Equipped with, The lighting device is characterized by comprising a synchronization means for synchronizing the AC voltage applied to the film with the voltage pulse applied to the photonic emitter. We propose a lighting device for vehicles.

[0011] The photonic emitter is, for example, a light-emitting diode. Preferably, the lighting device comprises a matrix of multiple photonic emitters, such as light-emitting diodes, capable of generating a regulatory beam through a liquid crystal film. This is, for example, a PDLC film, but of course other types of liquid crystal films may be used.

[0012] It should be noted that since liquid crystal films can block light that may be emitted by photonic emitters, they can also block daylight arriving on photonic emitters, and therefore perform the function of shielding these illuminating or signaling elements when they are not in use.

[0013] The control unit and / or control means are configured to use synchronization means so that none of the voltage pulses are applied during a change in the polarity of the AC voltage. The voltage pulses and AC voltage may not have a specific frequency. Nevertheless, the synchronization means allows the control means to suppress light emission during a decrease in the transmittance of the film, or allows the control means to change the polarity application of the AC voltage between the two voltage pulses.

[0014] In one embodiment of the present invention, the control unit is capable of applying a voltage pulse at a first frequency, and the control means is capable of applying an AC voltage to the film at a second frequency.

[0015] The control unit comprises a voltage pulse source, wherein the voltage is, for example, in the form of a square wave, and analog means for changing a first frequency of these square waves. Such a voltage pulse source is, for example, a pulse width-modulated source, used to avoid excessive temperature rise of the diode, to adapt the intensity of light emitted onto the same output surface to perform various illumination or signaling functions using the same diode, and / or to adapt the light emission if the vehicle's light-emitting module is segmented.

[0016] The control means comprises an AC voltage source, the electrical period of which preferably comprises a first phase in which the voltage is constant and positive, a second polarity change phase thereafter, and a third phase in which the voltage is constant and has a value opposite to the voltage value in the first phase.

[0017] The present invention provides a lighting device comprising synchronization means for synchronizing a voltage pulse applied to a photonic emitter with an AC voltage applied to a film, thereby enabling the matching of a second frequency to a first frequency, or vice versa, to avoid the troublesome flickering phenomenon. This phenomenon occurs particularly when the extinction phase of the photonic emitter shifts with respect to a phase in which the polarity of the AC voltage changes, during which the transmittance of the film decreases. This synchronization can, in addition, enable energy savings compared to conventional lighting devices with the same transmittance, since the period during which the photonic emitter is not powered corresponds to a phase in which the film has low transmittance.

[0018] According to one optional feature of the present invention, the synchronization means comprises a transmitting means for transmitting a synchronization signal to a control unit. In this case, the control unit can, for example, generate a voltage pulse based on the synchronization signal, whose first frequency is equal to a second frequency or an integer multiple of the second frequency. These transmitting means may be, for example, the control means. The first frequency is preferably selected to be twice or more the second frequency. In particular, when a photonic emitter emits a signaling beam, the intensity emitted by the photonic emitter is lower than in the case of an illumination beam, so the first frequency is much higher than the second frequency, for example, equal to four times the second frequency.

[0019] According to one optional feature of the present invention, the lighting device according to the present invention comprises, for example, a detection means for detecting when the absolute value of the gradient of an AC voltage exceeds a minimum gradient threshold, and capable of forming a synchronization signal, wherein a control unit is capable of forming a falling edge of one of the voltage pulses upon receiving a pattern of the synchronization signal corresponding to the exceedance. Thus, each change in the sign of the AC voltage occurs between two voltage pulses, i.e., when one or more photonic emitters are not polarized. Therefore, during the phase in which the polarity of the AC voltage changes, corresponding to a lower transmittance of the film, one or more photonic emitters do not emit light, thereby making it possible to achieve an average transmittance of 70% instead of 68% using the same film used in connection with Figures 1 and 2. In other words, this makes it possible to save the energy used to power the photonic emitters for the same transmittance.

[0020] It should be noted that the transmittance of the film depends on the relaxation time of the liquid crystal. In some applications, such as displays, a higher polarity change rate may be advantageous. In this case, the transmission gain provided by the present invention becomes even better.

[0021] According to one optional feature, in one alternative embodiment of the present invention, the synchronization means comprises a transmission means for sending a synchronization signal to a control means. In this case, the control means can, for example, make the second frequency of the AC voltage equal to the first frequency, or an integer submultiple of the first frequency. In this case, these transmission means are, for example, located in a control unit, and the control means comprises an analog means for changing the second frequency of the AC voltage applied to the film. The second frequency is selected to be, for example, half of the first frequency, or even a smaller fraction, particularly when one or more photonic emitters emit a signaling beam, or more generally, when pulse width modulation is used to power the photonic emitters.

[0022] According to one optional feature of the present invention, in this alternative embodiment of the invention, the control means is capable of setting each sign change of the AC voltage between the falling edge and rising edge of two consecutive pulses of the voltage pulses, based on a synchronization signal. This allows each sign change of the AC voltage to occur between the two voltage pulses, thereby saving energy used to power the photonic emitter for the same transmittance.

[0023] According to one optional feature of the present invention, the control unit comprises determination means for determining the peak voltage value of a voltage pulse depending on the duration of the phase in which the polarity of the AC voltage changes, and / or a second frequency, and / or the response time of the film. These determination means enable compensation for the loss of brightness due to the extinction of the photonic emitter during the phase in which the polarity of the AC voltage changes. Thus, for example, when the illumination function is performed by an illumination device that normally requires a continuous supply of power to the photonic emitter, the peak voltage value is increased to emit the same amount of light as in the DC supply mode on average over one period of the power supply signal to the photonic emitter, compared to this initially required DC supply mode, and this amount of light is emitted only over the phase in which the voltage applied to the film is constant. The duration of the polarity change phase depends in particular on the response time of the film and the frequency of the film, and therefore, when these characteristics can vary, it is beneficial to use a map.

[0024] The present invention also relates to a left front or right front optical unit for a vehicle, comprising an illumination device according to the present invention and capable of performing an illumination or signaling function, wherein the optical unit comprises a closed outer lens, and a film is positioned between the control unit, control means, and photonic emitter on one side and the closed outer lens on the other side, so as to shield the control unit, control means, and photonic emitter when the illumination or signaling function is not activated.

[0025] The present invention also provides a method of light emission carried out by a lighting device according to the present invention or by an optical unit according to the present invention, namely, - The control means includes the step of applying an AC voltage to the film at a second frequency, - The control unit receives a synchronization signal, - A step in which a control unit applies a voltage pulse to a photonic emitter at a first frequency, wherein the voltage pulse is synchronized with an AC voltage by the control unit. The present invention relates to a light-emitting method comprising [the same equipment].

[0026] The present invention also provides a method of light emission carried out by a lighting device according to the present invention or by an optical unit according to the present invention, namely, - The control unit applies a voltage pulse to the photonic emitter at a first frequency, - The control means receives a synchronization signal, - A step in which a control means applies an AC voltage to a film at a second frequency, wherein the AC voltage is synchronized with a voltage pulse by the control means. The present invention relates to a light-emitting method comprising [the same equipment].

[0027] According to one optional feature of the present invention, in the light emission method according to the present invention, each change in the sign of the AC voltage occurs between the falling edge and the rising edge of two consecutive pulses of the voltage pulse.

[0028] According to one optional feature of the present invention, the light emission method according to the present invention may include the step of determining the peak voltage value of a voltage pulse depending on the duration of the phase in which the polarity of the AC voltage changes, and / or a second frequency, and / or the response time of the film.

[0029] The optical unit and light-emitting method according to the present invention have advantages similar to those of the lighting device according to the present invention.

[0030] Other features and advantages of the present invention will become more apparent, on the one hand, from the following description and on the other hand from several exemplary embodiments given as indicators, not limitations, with reference to the accompanying schematic diagrams. [Brief explanation of the drawing]

[0031] [Figure 1] This figure shows the AC voltage applied to a PDLC film, the current flowing through the PDLC film, and the associated transmittance of the PDLC film as a function of time, as previously mentioned in relation to the prior art. [Figure 2] Also, as previously mentioned in relation to the prior art, this figure shows the relative value of the incident light beam arriving on the PDLC film to which the AC voltage is applied, and the associated transmittance of the PDLC film, as a function of time. [Figure 3] This figure schematically shows the elements of a lighting device according to the present invention in one embodiment of the present invention. [Figure 4] This figure shows the steps of the light emission method according to the present invention, as performed by the lighting device shown in Figure 3. [Figure 5] This figure shows the relative values ​​of the incident light beam arriving on the PDLC film as an AC voltage is applied according to the light emission method shown in Figure 4, and the associated transmittance of the PDLC film, as a function of time. [Figure 6] This figure shows the relative values ​​of the incident light beam arriving on the PDLC film and the associated light beam ratio, determined according to the light emission method shown in Figure 4, as a function of the response time of the PDLC film. [Figure 7] This figure shows the relative values ​​of the incident light flux arriving on the PDLC film and the associated light flux ratio, determined according to the light emission method shown in Figure 4, as a function of the frequency of the AC voltage applied to the PDLC film. [Figure 8]This figure shows the relative values ​​of the incident light flux arriving on the PDLC film as a function of time, when an AC voltage is applied according to the light emission method in Figure 4, in the case of using the illumination device in Figure 3 corresponding to the emission of a signaling beam, and the associated transmittance of the PDLC film. [Figure 9] This figure shows the steps of another light emission method according to the present invention, in another embodiment of the present invention. [Modes for carrying out the invention]

[0032] According to one embodiment of the present invention shown in Figure 3, a lighting device 1 according to the present invention, intended to be mounted on a vehicle, comprises one or more photonic emitters 3, in particular light-emitting diodes, and the supply of power to them, and therefore their brightness, is controlled by a control unit 2.

[0033] The control unit 2 comprises a voltage pulse source, wherein the voltage is in the form of a rectangular wave, and a means for changing the frequency of these voltage rectangular waves, which is referred to in this application as the first frequency. The voltage pulse source supplies voltage rectangular waves to the light-emitting diode 3, i.e., a non-zero voltage value V that takes the value zero between two voltage rectangular waves and is greater than or equal to the bias voltage of the light-emitting diode 3 on each voltage rectangular wave. L Alternatively, a voltage signal is supplied that takes the peak value. As a result, between the two voltage square waves, the light-emitting diode 3 does not emit light, and they do not emit light from the voltage of the voltage square wave V L When they receive the light, they become luminous flux φ L1The light-emitting diode 3 emits light. To modulate the intensity of the light emitted by the light-emitting diode 3, the duration T1 of the voltage square wave (referenced in Figure 5) can be selected to be more or less shorter than the zero-voltage duration T0 (referenced in Figure 5) between two consecutive voltage square waves. The control unit 2 includes modification means for changing each of these durations, and thus modulation means for modulating the intensity of the light emitted by the light-emitting diode 3 in response to a control signal for activating an illumination beam, low beam, signaling beam, or daytime running lights (DRL). In fact, in this embodiment of the present invention, the light-emitting diode 3 is capable of performing different illumination or signaling functions depending on the time. The beam of light φ emitted by the light-emitting diode 3 L1 is AC voltage V AC An AC voltage is applied by the control means 5 and sent toward the closed outer lens so as to pass through a liquid crystal film 4, called a PDLC film, which has liquid crystals dispersed in a polymer, and this AC voltage has a frequency called the second frequency.

[0034] The control means 5 includes an AC voltage source, the electrical period of which, as in the prior art, comprises a first phase in which the voltage is constant and positive, followed by a second polarity change phase corresponding to a falling voltage gradient, then a third phase in which the voltage is constant and opposite to the voltage value in the first phase, and finally a fourth polarity change phase corresponding to a rising voltage gradient.

[0035] According to the present invention, the lighting device 1 uses an AC voltage V AC The system includes a synchronization means 10 for synchronizing the voltage pulse emitted by the control unit 2 with the AC voltage V. In this embodiment of the present invention, the synchronization means 10 includes a transmission means for sending a synchronization signal h to the control unit 2, and the transmission means is incorporated into the control means 5. The control unit 2 then synchronizes the voltage pulse with the AC voltage V, as will be described below in relation to Figure 4. AC This synchronization signal h is used to synchronize it with the other signals.

[0036] The lighting device 1 is incorporated into the left front or right front optical unit of the vehicle, capable of performing lighting or signaling functions. The PDLC film 4 is placed opposite the closed outer lens of the optical unit and, for example, is bonded to the lens on its inside. This allows the PDLC film 4 to shield the control unit 2, control means 5 and light-emitting diode 3 when the lighting or signaling function is not activated and the PDLC film is in an opaque or nearly opaque mode.

[0037] Figure 4 shows the steps of the light emission method 100 performed by the lighting device 1.

[0038] The first step 110 is that the control means 5 applies an AC voltage V to the PDLC film 4 at a second frequency, for example, 100 Hz. AC This is the step of applying the AC voltage V. In this step, the detection means, which is incorporated into the control means 5 and forms part of the synchronization means 10, detects the AC voltage V. AC The system detects the start of a phase in which the polarity changes, and emits a voltage pulse each time the polarity change phase begins, thereby forming a synchronization signal h that is sent to the control unit 2.

[0039] These detection means, for example, more specifically, AC voltage V AC Fluctuations in AC voltage V AC A non-zero gradient is detected, and for this variation or gradient to trigger detection, its absolute value must be greater than or equal to a predetermined minimum threshold.

[0040] These detection means also include AC voltage V AC The end of a phase in which the polarity changes can be detected, and a voltage pulse can be emitted when such a polarity change phase has ended. In this case, the synchronization signal h comprises two pulses for each polarity change phase, one indicating the start of such a phase and the other indicating the end of such a phase.

[0041] The next step 120 is for the control unit 2 to receive the synchronization signal h.

[0042] The next step 130 is for control unit 2 to operate with AC voltage V AC Depending on the duration of the phase change in polarity, the square wave voltage value V to be applied to the light-emitting diode 3 should be determined. L This is the step to determine the phase, which in some cases depends on the second frequency of the PDLC film and / or the response time of the PDLC film. This duration is determined by the AC voltage V AC Along with the second frequency, the second frequency is determined by the control unit 2, for example, using a synchronization signal h, where the synchronization signal h indicates the start and end of each polarity change period. In a variant form, this duration and this second frequency are predetermined.

[0043] In step 130, the control unit 2 also sets an initial zero voltage duration T between two voltage square waves, along with a first frequency which is an integer multiple of the second frequency, for example, equal to twice the second frequency, depending on the desired brightness for performing the illumination or signaling function provided by the illumination device 1. i Determine the initial zero voltage duration T. i The initial zero voltage duration T between the two voltage square waves depends on the initial DC supply voltage to the light-emitting diode 3. i By dividing this initial DC supply voltage into a voltage rectangular wave having the following properties, the luminous flux emitted by the light-emitting diode 3 through the PDLC film 4 is determined to provide the desired brightness.

[0044] Initial zero voltage duration T i However, if it is shorter than the duration of the polarity change phase, the control unit 2 determines the zero voltage duration T0 value to be equal to the duration of the polarity change phase; otherwise, the control unit 2 determines the initial zero voltage duration T i The zero voltage duration T0 value is determined by equality.

[0045] Initial zero voltage duration T iHowever, when the initial zero voltage duration T0 value is shorter than the zero voltage duration T0 value determined in this way, the control unit 2 would have been able to perform the desired illumination or signaling function through the PDLC film 4 without optimizing the average transmittance of the PDLC film 4. i In order to compensate for the loss of brightness due to the increase in the zero-voltage duration T0, in this step 130, the square wave voltage value V L This can be adjusted. This square wave voltage value V compensates for the loss of brightness due to the extended extinction of the light-emitting diode 3. L The determination of this is, for example, the initial zero voltage duration T. i When is zero, the square wave voltage value V that should be applied depends on the duration of the polarity change phase. L A map that provides this can be used.

[0046] In a modified embodiment of step 130, when the synchronization signal h contains only an indication of the start of the phase, the control unit 2 then infers a second frequency, and then, for example using a map, determines the duration of the polarity change period according to the second frequency, and / or, according to the second frequency, a square wave voltage value V to be applied to compensate for the loss of brightness due to the extinction of the light-emitting diode during this polarity change period. L This determines the peak value V depending on the type of PDLC film used. L It is used by control unit 2 to adapt to the requirements.

[0047] In the next step 140, the control unit 2 sets a predetermined square wave voltage V at a first frequency which is said to be an integer multiple of the second frequency determined in the previous step. L And a synchronization signal h is used to construct a voltage square wave signal with a predetermined zero-voltage duration T0.

[0048] For example, each time the control unit 2 receives a voltage pulse of the synchronization signal h indicating the start of the polarity change phase, it forms a voltage falling edge, and then, after a time interval equal to the zero voltage duration T0 determined in step 130, it forms a rising edge. The control unit 2 then sends the voltage square wave thus formed to the light-emitting diode 3.

[0049] Figure 5 shows that the light-emitting diode 3 is supplied with a voltage square wave signal constructed according to step 140 of the light-emitting method 100, and the square wave voltage value V L However, in order to compensate for the loss of brightness due to the extinction of the diode during the polarity change phase, when not adjusted in step 130, the luminous flux φ emitted by the light-emitting diode 3 L1 The evolution of the luminous flux φ is illustrated. The corresponding voltage curve as a function of time is the luminous flux φ whose maximum value is set to 1. L1 The thick line in Figure 5 represents the relative luminous flux φ, which corresponds to this. LR1 This is the line. In this exemplary application of the light emission method 100, the first frequency is selected to be equal to twice the second frequency, thereby allowing no power to be supplied to the light-emitting diode 3 during each polarity change phase.

[0050] Figure 5 also shows the AC voltage V AC Transmittance T of PDLC film 4 after receiving T This reproduces the changes over time.

[0051] Relative luminous flux φ LR1 The zero relative luminous flux φ between the two square waves LR1 The corresponding extinction duration of each light-emitting diode 3 is in the region 41 with low light flux transmittance, i.e., AC voltage V AC It can be seen that the polarity of corresponds to the phase in which it changes. As a result, when the light-emitting diode 3 emits light, the light passes through the PDLC film 4 and, in this embodiment of the present invention, benefits from the better transmittance of the PDLC film 4, which is 70%. Thus, the luminous flux φ L1The average transmittance of the treated PDLC film becomes 70%, compared to 68% in the conventional technology. Of course, other types of PDLC films with transmittances that may differ from 70% can be used; for example, its transmittance is 80% during a constant voltage supply phase.

[0052] Another line is supplied with a voltage square wave signal constructed by the light-emitting diode 3 according to step 140 of the light-emitting method 100, with a square wave voltage value V L However, when adjusted in step 130 to compensate for the loss of brightness due to the extinction of the diode during the polarity change phase, the luminous flux φ emitted by the light-emitting diode 3 is L2 This shows the progression. The corresponding voltage line as a function of time is the relative luminous flux φ of the thin line in Figure 5. LR2 It is a line of light, and the luminous flux φ L2 The value of the luminous flux φ L1 This corresponds to the result of dividing by the value of [the variable].

[0053] Figure 6 shows the relative luminous flux φ corresponding to the second frequency. L2 This shows the change in the value of and the corresponding luminous flux φ L2 To compensate for the loss of brightness due to the polarity change phase, its rectangular wave voltage value V L A voltage square wave signal, adjusted according to a second frequency, is emitted by the light-emitting diode 3 supplied with it. On the one hand, the light beam φ is transmitted through the film, as shown by line L2. L2 * T T On the other hand, the ratio of the initial DC supply voltage to the beam of light that will be emitted by the supplied light-emitting diode 3 is kept constant at 70%, and therefore at the maximum transmittance of the PDLC film 4, regardless of the value of the second frequency. To obtain this result, the relative luminous flux φ LR2 The value of, and therefore the square wave voltage V adjusted in step 130. L The value of increases as the second frequency increases.

[0054] Figure 6 shows the luminous beam φ L1 The value of the square wave voltage V supplied to the light-emitting diode 3 to generate it Lis not adjusted to compensate for the loss of luminance due to the polarity change phase, so the relative light beam φ LR1 shows that the value of does not vary according to the second frequency. Thus, as indicated by line L1, on the one hand, the light beam φ L1 * T T transmitted by the film, and on the other hand, the ratio with the light beam that would be emitted by the light-emitting diode 3 supplied with the initial DC supply voltage decreases significantly according to the second frequency.

[0055] Line L represents, on the one hand, the light beam φ L * T T transmitted by the film in the prior art, and on the other hand, the ratio with the light beam that would be emitted by the light-emitting diode 3 supplied with the initial DC supply voltage. This ratio decreases with the second frequency but still provides a luminance higher than that of the light beam φ L1 .

[0056] Similarly, FIG. 7 shows the transition of the value of the relative light beam φ LR2 according to the response time of the PDLC film used, and the light beam φ L2 is emitted by the light-emitting diode 3 supplied with a voltage rectangular wave signal, the rectangular wave voltage value V L of which is adjusted according to this response time to compensate for the loss of luminance due to the polarity change phase. As indicated by line L20, on the one hand, the light beam φ L2 * T T transmitted by the film, and on the other hand, the ratio with the light beam that would be emitted by the light-emitting diode 3 supplied with the initial DC supply voltage is kept constant at 70%, thus at the maximum transmittance of the PDLC film 4, regardless of the value of the response time of the PDLC film. To obtain this result, the value of the relative light beam φ LR2 , and thus the value of the rectangular wave voltage V L adjusted in step 130, increases as the response time of the PDLC film is longer.

[0057] FIG. 7 shows the light beam φL1 The value V of the rectangular wave voltage supplied to the light-emitting diode 3 to generate L is not adjusted to compensate for the loss of luminance due to the polarity change phase, so the relative light beam φ LR1 shows that the value of does not vary according to the response time of the PDLC film. Thus, as indicated by line L10, on the one hand, the light beam φ L1 * T T transmitted by the film, and on the other hand, the ratio to the light beam that would be emitted by the light-emitting diode 3 supplied with the initial DC supply voltage decreases significantly according to the response time of the PDLC film.

[0058] Line L0 represents, on the one hand, the light beam φ L * T T transmitted by the film in the prior art, and on the other hand, the ratio to the light beam that would be emitted by the light-emitting diode 3 supplied with the initial DC supply voltage. This ratio decreases with the response time of the PDLC film, but still provides a higher luminance than the light beam φ L1 .

[0059] FIG. 8 shows the light beam φ L emitted by the light-emitting diode 3 when the light-emitting diode 3 is supplied with a voltage rectangular wave signal constructed according to step 140 of the light-emitting method 100, and the rectangular wave voltage value V L1 is not adjusted in step 130 to compensate for the loss of luminance due to the extinction of the diode during the polarity change phase, and the first frequency is assumed to be equal to 8 times the second frequency. The zero voltage duration T0 is longer than the duration of the polarity change phase, so such adjustment is not necessary here to generate the desired luminance. Thus, the line of the corresponding relative light beam φ LR1 forms a very small rectangular wave that extensively surrounds each region 41 of low light beam transmissivity. In this exemplary application of the light-emitting method 100, the lighting device 1 generates daytime running lights that require little luminance.

[0060] Finally, Figure 9 shows the steps of another light-emitting method 200 according to the present invention, which is carried out by the lighting device 1.

[0061] The first step 210 is the step in which the control unit 2 determines a first frequency of a voltage square wave signal to be applied to the light-emitting diode 3 in order to generate a desired brightness through the PDLC film 4, depending on the lighting or signaling function to be performed by the lighting device 1, and the zero voltage duration T0 between the square waves.

[0062] The second step 220 is a step in which the control unit 2 applies a voltage square wave signal to the light-emitting diode 3 at a first frequency determined in the previous step, the signal having a predetermined voltage duration T0 during the square wave. In this step 220, the control unit 2 duplicates the square wave voltage signal and sends it to the control means 5, and the square wave voltage signal constitutes a synchronization signal h.

[0063] The third step 230 is the step in which the control means 5 receives a synchronization signal h.

[0064] Finally, the fourth step 240 is the step in which the control means 5 determines a second frequency based on the first frequency and applies an AC voltage at the second frequency to the PDLC film, synchronized with the voltage pulses sent to the light-emitting diode 3. The second frequency is selected to be a divisor of the first frequency, for example, half of the first frequency. Synchronization is performed by the control means 5 to cause a change in the sign of the AC voltage between the falling edge and rising edge of two consecutive pulses of the voltage square wave signal applied to the light-emitting diode 3.

[0065] In this other light-emitting method 200 according to the present invention, the AC voltage V ACThe phase at which the polarity changes may be shorter than the zero-voltage duration T0 between the two voltage square waves supplied to the light-emitting diode 3, equal to the zero-voltage duration T0, or longer than the zero-voltage duration T0. Nevertheless, this alternative light-emitting method 200 makes it possible to improve the average transmittance of the PDLC film compared to the prior art.

[0066] Of course, the present invention is not limited to the examples described above, and numerous modifications can be made to these examples without departing from the scope of the invention. In particular, the features of the various modified embodiments of the invention envisioned in this application can be combined to carry out the invention, provided that these modifications do not contradict each other.

Claims

1. A lighting device (1) for a vehicle, - At least one photonic emitter (3), - A control unit (2) for controlling the photonic emitter (3), which is capable of applying a voltage pulse to the photonic emitter (3) to impart polarity to the photonic emitter (3) so that the photonic emitter emits light, - A liquid crystal film (4), particularly a PDLC, capable of transmitting or blocking at least a portion of the light emitted by the photonic emitter (3), - Apply an AC voltage (V) to the film (4). ＡＣ Control means (5) capable of applying ) Equipped with, The lighting device (1) applies the AC voltage (V) to the film (4). ＡＣ The system is characterized by comprising a synchronization means (10) for synchronizing the photonic emitter (3) with the voltage pulse applied to the photonic emitter (3), A lighting device for vehicles (1).

2. The control unit (2) and / or the control means (5) control the AC voltage (V) if any of the voltage pulses are ＡＣ A vehicle lighting device (1) according to claim 1, configured to use the synchronization means (10) so as not to be applied during a change in the polarity of the )

3. The control unit (2) is capable of applying the voltage pulse at a first frequency, and the control means (5) applies the AC voltage (V) to the film (4) at a second frequency. ＡＣ A vehicle lighting device (1) according to claim 1 or 2, which is capable of applying )

4. The vehicle lighting device (1) according to any one of claims 1 to 3, wherein the synchronization means (10) comprises a transmission means for sending a synchronization signal (h) to the control unit (2).

5. The vehicle lighting device (1) according to claims 3 and 4, wherein the control unit (2) is capable of generating a voltage pulse from the synchronization signal (h) wherein the first frequency thereof is equal to or an integer multiple of the second frequency.

6. The vehicle lighting device (1) according to any one of claims 1 to 3, wherein the synchronization means comprises a transmission means for sending a synchronization signal to the control means (5).

7. Based on the synchronization signal, the control means (5) applies the AC voltage (V) between the falling edge and rising edge of two consecutive pulses among the voltage pulses. ＡＣ The vehicle lighting device (1) according to claim 6, wherein it is possible to set each change in the sign of ).

8. The control means (5) controls the AC voltage (V ＡＣ The vehicle lighting device (1) according to claim 3 and claim 6 or 7, wherein the second frequency of the device can be set to the first frequency or to an integer fraction of the first frequency.

9. The control unit (2) controls the AC voltage (V ＡＣ Depending on the duration of the phase in which the polarity of the voltage changes, and / or the second frequency, and / or the response time of the film (4), the peak voltage value (V) of the voltage pulse is determined. Ｌ A vehicle lighting device (1) according to any one of claims 3 to 8, comprising a determination means for determining ).

10. A left-front or right-front optical unit for a vehicle, comprising an illumination device (1) according to any one of claims 1 to 9, and capable of performing an illumination or signaling function, wherein the optical unit comprises a closed outer lens, and the film (4) is positioned between the control unit (2), the control means (5), and the photonic emitter (3) on one side and the closed outer lens on the other side, so as to shield the control unit (2), the control means (5), and the photonic emitter (3) when the illumination or signaling function is not activated.

11. A method of emitting light carried out by an illumination device (1) according to claim 3 and claim 4 or 5, or by an optical unit according to claim 10 as referenced from claim 3 and claim 4 or 5, namely, - The control means (5) applies the AC voltage (V ＡＣ ) to the film (4) at the second frequency, and - The control unit (2) receives the synchronization signal (h), - The control unit (2) applies a voltage pulse to the photonic emitter (3) at the first frequency, wherein the voltage pulse is controlled by the control unit (2) to the AC voltage (V ＡＣ ) is synchronized with the steps and A method of emitting light, comprising the following features.

12. A method of emitting light carried out by an illumination device (1) according to any one of claims 3 and 6 to 8, or by an optical unit according to claim 10 as a reference to any one of claims 3 and 6 to 8, namely, - The control unit (2) applies a voltage pulse to the photonic emitter (3) at the first frequency, - The control means (5) receives the synchronization signal, - The control means (5) applies the AC voltage (V) to the film (4) at the second frequency. ＡＣ A step of applying the AC voltage (V ＡＣ ) is synchronized with the voltage pulse by the control means (5) in steps and A method of emitting light, comprising the following features.

13. The aforementioned AC voltage (V ＡＣ The light-emitting method according to claim 11 or 12, wherein each change in the sign of ) occurs between the falling edge and the rising edge of two consecutive pulses of the voltage pulse.

14. The aforementioned AC voltage (V ＡＣ Depending on the duration of the phase in which the polarity of the voltage changes, and / or the second frequency, and / or the response time of the film (4), the peak voltage value (V) of the voltage pulse is determined. Ｌ The light emission method according to claim 13, further comprising the step of determining ).

Images