Lighting device comprising liquid crystal film, and corresponding light emission method

Abstract

The 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 being able to apply a voltage pulse which polarizes the photon emitter (3) at a first frequency; a liquid crystal film (4) capable of transmitting or blocking the light emitted by the photon emitter (3); and-control means (5) capable of applying an AC voltage (VAC) to the film (4) at a second frequency, the lighting device (1) being characterized in that it comprises means for synchronizing the AC voltage (VAC) applied to the film (4) with the voltage pulses applied to the photon emitter (3).

Description

[0001] This invention relates to the fields of electronic devices and motor vehicles, and more particularly to a lighting device for vehicles that uses a liquid crystal film, such as 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 suitable for use in motor vehicles, particularly for producing smart embedded glass, especially for displaying content on sunroofs, or for modifying the appearance of lighting elements to produce various luminous effects (including signaling or active light concealment).

[0002] Applying an electric field to such a film allows the liquid crystal contained in the film to be oriented so that light reaching the film can pass through, and the film then has a transparent or semi-transparent appearance. In the absence of such an electric field, the molecules do not have a coherent orientation and produce a large amount of reflection in multiple directions within the film, thereby producing an opaque effect at the output or at least the effect of scattering the light that has managed to pass through the film.

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

[0004] Figure 1 The AC voltage V applied to the PDLC film as a function of time is shown. AC (in volts (V)) and the voltage V flowing through this AC voltage. AC The membrane current I A (In milliamperes (mA)). AC voltage V AC This has a frequency of 100 Hz (Hertz), which means an electrical cycle of 10 ms (milliseconds). It can be seen that at AC voltage V... AC Outside of the polarity change phase, current I A The current I flowing through the membrane is zero during these stages. A At AC voltage V AC When the amplitude decreases, it reaches the negative amplitude peak, or at AC voltage V. AC When the amplitude increases, it reaches the peak value of the positive amplitude.

[0005] Figure 1 The last curve shows the change over time and is expressed as a percentage through the AC voltage V. AC The transmittance T of the PDLC film T It should be noted that when the AC voltage V AC When the absolute value is at its maximum, the transmittance T of the PDLC film is... T It is fixed and approximately 70%, while the AC voltage V AC During the polarity change phase, this transmittance T T Decrease until the AC voltage VAC This phase reaches 50% when it reaches zero in the middle. This is because the AC voltage V... AC Transmittance T during the polarity change phase T The reduction in AC voltage results in an average transmittance of only 68% for the PDLC film. Similarly, the transmittance of other types of liquid crystal films decreases during the polarity change phase, during which the AC voltage has an absolute value less than the threshold voltage.

[0006] Figure 2 This shows the arrival time under AC voltage V as a function of time. AC The relative value of incident light flux of the PDLC film This value is dimensionless because it is the ratio between the value of the luminous flux (in candela) and the peak value of this flux (in candela). This relative value Here, the value is 1, and the incident luminous flux is generated by a light-emitting diode supplied with a DC voltage. In the relative value of luminous flux... The transmittance T of the PDLC film reproduced under the curve T and Figure 1 The transmittance shown is the same. Therefore, the average transmittance of the luminous flux emitted by the light-emitting diode is 68%.

[0007] The inventors have envisioned using PDLC film technology to conceal vehicle lighting or signaling devices, particularly when the vehicle is stationary or when certain functions (such as daytime running lights) are not in use, for example, by placing such a PDLC film as a closed outer lens facing each headlight of the vehicle and thus across beams of light easily emitted by the lighting or signaling devices, or across sunlight reaching these devices. It is then necessary to adapt the supply voltage of the LEDs performing the vehicle lighting or signaling functions so that they provide the same luminous intensity without the use of this film as they would with the PDLC film, in order to meet the regulatory constraints associated with these functions. However, with the aforementioned average transmittance of 68%, the supply voltage of the diodes must be significantly increased, which consumes energy. Furthermore, depending on the lighting or signaling function performed by the LEDs, their supply voltage may be variable and produce flicker, and the coupling of flicker with the AC voltage applied to the film may increase discomfort for road users (whether the vehicle's driver or others).

[0008] Therefore, for aesthetic reasons, it is necessary to conceal vehicle lighting or signaling devices, which saves energy and avoids the risk of causing visual discomfort. This specifically involves unifying the styling of vehicles.

[0009] The present invention aims to overcome, at least in part, the disadvantages of the prior art that limit energy consumption and flicker compared to the prior art by providing a lighting device for a vehicle equipped with a liquid crystal film, an optical unit including such a lighting device, and a light emission method implemented by such a lighting device or such optical unit.

[0010] Therefore, the present invention provides a lighting device for a vehicle, the lighting device comprising: -At least one photon emitter - Control unit, which controls the photon emitter and can apply voltage pulses to polarize the photon emitter, causing it to emit light. - A liquid crystal film capable of transmitting or blocking at least a portion of the light emitted by a photon emitter, and - A control device capable of applying an AC voltage to the membrane. The lighting device is characterized in that it includes a synchronization device for synchronizing the AC voltage applied to the membrane with the voltage pulse applied to the photon emitter.

[0011] For example, the photon emitter is a light-emitting diode (LED). Preferably, the lighting device includes a matrix of multiple photon emitters, such as LEDs, capable of generating a modulated light beam that passes through the liquid crystal film. For example, this is a PDLC film, but other types of liquid crystal films can certainly be used.

[0012] It should be noted that since the liquid crystal film can block light that can be emitted by the photon emitter, it can also block sunlight that reaches the photon emitter, and thus can perform the function of masking these lighting or signaling elements when they are not used.

[0013] The control unit and / or control device are configured to use a synchronization device such that no voltage pulse is applied during a change in the polarity of the AC voltage. The voltage pulse and AC voltage may not have a specific frequency. However, the synchronization device allows the control device to suppress light emission during a decrease in the film's transmittance, or allows the control device to change the polarization of the AC voltage between two voltage pulses.

[0014] In one embodiment of the invention, the control unit is capable of applying voltage pulses at a first frequency, and the control device is capable of applying AC voltage to the membrane at a second frequency.

[0015] The control unit includes a voltage pulse source (the voltage being, for example, in the form of a square wave) and an analog device for modifying a first frequency of these square waves. This voltage pulse source is, for example, a pulse width modulation source, used to prevent excessive temperature rise of the diodes and also to adapt the light intensity emitted on the same output surface so as to perform various lighting or signaling functions with the same diodes, and / or to adapt light emission when the vehicle's light-emitting modules are segmented.

[0016] The control device includes an AC voltage source, the electrical cycle of which preferably includes a first phase during which the voltage is constant and positive, followed by a second polarity-changing phase and a third phase during which the voltage is constant and has a value opposite to that during the first phase.

[0017] According to the present invention, the lighting device includes a synchronization device for synchronizing the voltage pulses applied to the photon emitter with the AC voltage applied to the membrane, thereby allowing a second frequency to be adapted to the first frequency or vice versa, in order to avoid annoying flickering. This phenomenon occurs particularly when the photon emitter's off-state phase is shifted relative to the phase of AC voltage polarity change, during which the membrane's transmittance decreases. Compared to prior art lighting devices with the same transmittance, this synchronization can further save energy because the periods during which the photon emitter is not powered correspond to phases when the membrane has low transmittance.

[0018] According to an optional feature of the invention, the synchronization device includes a transmitting device for sending a synchronization signal to a control unit. In this case, the control unit is, for example, capable of generating voltage pulses based on the synchronization signal, the voltage pulses having a first frequency equal to or an integer multiple of a second frequency. These transmitting devices may, for example, be integrated into the control device. The first frequency is preferably selected to be two or more times the second frequency. In particular, when the photon emitter emits a signal beam, the first frequency is much higher than the second frequency, for example, four times the second frequency, because the intensity emitted by the photon emitter is lower than that of an illumination beam.

[0019] According to an optional feature of the invention, the lighting device according to the invention includes, for example, a detection device for detecting when the absolute value of the slope of the AC voltage exceeds a minimum slope threshold to enable the formation of a synchronization signal, and a control unit is capable of generating a falling edge of a voltage pulse in the voltage pulses upon receiving a pattern corresponding to the passing synchronization signal. Therefore, each sign change of the AC voltage occurs between two voltage pulses, that is, when the one or more photon emitters are not polarized. Thus, during the phase of the AC voltage polarity change, corresponding to the lower transmittance of the film, the one or more photon emitters do not emit light, thereby enabling the use of [the device] with respect to [other aspects]. Figure 1 and Figure 2 The same film achieves an average transmittance of 70% instead of 68%. In other words, this allows for energy savings in powering the photon emitter for the same transmittance.

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

[0021] According to an optional feature, in an alternative embodiment of the invention, the synchronization device includes a transmitting device for sending a synchronization signal to a control device. In this case, the control device is, for example, capable of making a second frequency of the AC voltage equal to or equal to an integer divisor of the first frequency. These transmitting devices are then, for example, in a control unit, and the control device includes an analog device for modifying the second frequency of the AC voltage applied to the membrane. The second frequency is selected, for example, as half of the first frequency, or even a smaller fraction, particularly when the one or more photon emitters emit signal beams, or more generally when powering the photon emitters using pulse-width modulation.

[0022] According to an optional feature of the invention, in this alternative embodiment, the control device is capable of setting each sign change of the AC voltage between the falling and rising edges of two consecutive pulses in the voltage pulse based on a synchronization signal. Therefore, each sign change of the AC voltage occurs between two voltage pulses, thereby saving energy used to power the photon emitter for the same transmittance.

[0023] According to an optional feature of the invention, the control unit includes a determining device for determining the peak voltage value of the voltage pulse based on the duration of the phase of AC voltage polarity change and / or based on a second frequency and / or based on the membrane's response time. These determining devices make it possible to compensate for brightness loss due to the extinguishing of the photon emitter during the phase of AC voltage polarity change. Thus, for example, when illumination is performed by a lighting device (which typically requires continuous power to the photon emitter), the peak voltage value is increased compared to the initially required DC power supply mode, so that the same amount of light is transmitted to the photon emitter on average over the period of the power signal as in this DC power supply mode, which is emitted only during the phase when the voltage applied to the membrane is constant. The duration of the polarity change phase depends particularly on the membrane's response time and on the membrane's frequency; therefore, mapping is beneficial when these characteristics may vary.

[0024] The present invention also relates to a left or right front optical unit for a vehicle, the left or right front optical unit including an illumination device according to the invention and capable of performing illumination or signaling functions, the optical unit including a closed outer lens, the film being arranged between a control unit, control device, and photon emitter on one side and the closed outer lens on the other side, so as to mask the control unit, control device, and photon emitter when the illumination or signaling function is not activated.

[0025] The present invention also relates to a light emission method implemented by a lighting device according to the invention or by an optical unit according to the invention, the light emission method comprising the following steps: -The control device applies an AC voltage to the membrane at a second frequency. - The control unit receives the synchronization signal. The control unit applies voltage pulses to the photon emitter at a first frequency, and these voltage pulses are synchronized with the AC voltage by the control unit.

[0026] The present invention also relates to a light emission method implemented by a lighting device according to the invention or by an optical unit according to the invention, the light emission method comprising the following steps: The control unit applies voltage pulses to the photon emitter at a first frequency. - The control device receives a synchronization signal. - The control device applies an AC voltage to the membrane at a second frequency, which is synchronized with the voltage pulse by the control device.

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

[0028] According to an optional feature of the invention, the light emission method according to the invention may include the following steps: determining the peak voltage value of the voltage pulse based on the duration of the phase of AC voltage polarity change and / or based on a second frequency and / or based on the response time of the membrane.

[0029] The optical unit and the emission method according to the invention include advantages similar to those of the lighting device according to the invention.

[0030] Other features and advantages of the invention will become clearer, on the one hand, from the following description, and on the other hand, from the various exemplary embodiments given in an illustrative and non-limiting manner with reference to the accompanying schematic drawings, in which:

[0031] [ Figure 1 (The prior art has already been commented on) shows the AC voltage applied to the PDLC film, the current flowing through the PDLC film, and the associated transmittance of the PDLC film as a function of time.

[0032] [ Figure 2 (Also commented on regarding the prior art) shows the arrival applied over time. Figure 1 The relative values ​​of incident light flux of the PDLC film at AC voltage, and the associated transmittance of the PDLC film.

[0033] [ Figure 3 The illustration schematically shows elements of a lighting device according to the invention in one embodiment.

[0034] [ Figure 4 The invention is shown in the figure. Figure 3 The steps of the light emission method implemented by the lighting equipment,

[0035] [ Figure 5 The arrival data varies over time. Figure 4 The light emission method applied AC voltage to the PDLC film resulted in the relative values ​​of the incident light flux and the associated transmittance of the PDLC film.

[0036] [ Figure 6 The following diagram illustrates the variation in response time with that of the PDLC membrane. Figure 4 The relative values ​​of incident light flux reaching the PDLC film, and the associated light flux ratio, are determined by the light emission method.

[0037] [ Figure 7 The following diagram illustrates the variation of AC voltage applied to the PDLC film with frequency. Figure 4 The relative values ​​of incident light flux reaching the PDLC film, and the associated light flux ratio, are determined by the light emission method.

[0038] [ Figure 8 [This shows that] in Figure 3 In the case of lighting equipment used for emitting signal beams, the arrival time varies according to... Figure 4 The light emission method applied AC voltage to the PDLC film resulted in the relative values ​​of the incident light flux and the associated transmittance of the PDLC film.

[0039] [ Figure 9 The following illustrates the steps of another light emission method according to the invention in another embodiment of the invention.

[0040] according to Figure 3 As shown in one embodiment of the invention, a vehicle is intended to be equipped with a lighting device 1 according to the invention, which includes one or more photon emitters 3, particularly light-emitting diodes, and a control unit 2 controls the power supply to the one or more photon emitters and thus controls the brightness of the one or more photon emitters.

[0041] The control unit 2 includes a voltage pulse source (the voltage is in the form of a square wave) and a modification device for modifying the frequency of these voltage square waves (referred to as the first frequency in this application). The voltage pulse source supplies voltage square waves to the light-emitting diode 3, that is, supplies a voltage signal that takes a zero value between two voltage square waves and takes a non-zero voltage value V greater than or equal to the bias voltage of the light-emitting diode 3 on each voltage square wave. L Or peak value. Therefore, between two voltage square waves, LED 3 does not emit any light, and when these LEDs are subjected to the voltage V of the voltage square wave... L At that time, they emit light flux In order to modulate the light intensity emitted by LED 3, the duration T1 of the voltage square wave (in Figure 5 The term (indicated by the middle label) can be selected as the zero-voltage duration T0 between two consecutive voltage square waves (in... Figure 5 (The duration is indicated by the symbol) or more or less shorter. The control unit 2 includes modification means for modifying these corresponding durations, and therefore includes modulation means for modulating the luminous intensity emitted by the light-emitting diode 3, in particular according to a control signal used to activate the illumination beam, low beam, signal beam, or daytime running light (DRL). In fact, in this embodiment of the invention, the light-emitting diode 3 is capable of performing different illumination or signaling functions over time. Luminous flux emitted by LED 3 The light is directed toward the closed outer lens, allowing the light flux to pass through the liquid crystal film 4, which comprises liquid crystal dispersed in a polymer (referred to as a PDLC film). The control device 5 applies an AC voltage V to the liquid crystal film. ACThe AC voltage has a frequency known as the second frequency.

[0042] The control device 5 includes an AC voltage source, and as in the prior art, the electrical cycle of the AC voltage source includes a first phase during which the voltage is constant and positive, followed by a second polarity change phase corresponding to a decreasing voltage slope, then a third phase during which the voltage is constant and has a value opposite to that during the first phase, and finally a fourth polarity change phase corresponding to a rising voltage slope.

[0043] According to the present invention, the lighting device 1 includes a synchronization device 10, which is used to synchronize the AC voltage V AC Synchronization with voltage pulses emitted by control unit 2. In this embodiment of the invention, synchronization device 10 includes a transmitting device for sending a synchronization signal h to control unit 2, and this transmitting device is integrated into control device 5. Control unit 2 then uses this synchronization signal h to synchronize the voltage pulses with AC voltage V. AC Synchronization, as mentioned below Figure 4 The explanation given.

[0044] The lighting device 1 is integrated into the vehicle's left or right front optical unit, which is capable of performing lighting or signaling functions. The PDLC film 4 is positioned opposite, for example, glued to, the closed outer lens of the optical unit, and inside the closed outer lens. The PDLC film 4 thus allows the control unit 2, control device 5, and light-emitting diode 3 to be masked when the lighting or signaling function is not activated and the PDLC film is in an opaque or nearly opaque mode.

[0045] Figure 4 The steps of a light emission method 100 implemented by a lighting device 1 are shown.

[0046] The first step 110 is that the control device 5 applies an AC voltage V to the PDLC film 4 at a second frequency (e.g., 100Hz). AC In this step, the detection device, integrated into the control device 5 and forming part of the synchronization device 10, detects the AC voltage V. AC The polarity change phase begins, and a voltage pulse is emitted at the beginning of each polarity change phase, thereby forming a synchronization signal h, which is sent to the control unit 2.

[0047] For example, these detection devices more specifically detect AC voltage V AC Changes, or AC voltage V AC A non-zero slope, this change or slope must have an absolute value greater than or equal to a predetermined minimum threshold to trigger detection.

[0048] These detection devices can also detect AC voltage V. AC The voltage pulse is emitted when the polarity change phase ends. In this case, the synchronization signal h consists of two pulses for each polarity change phase, one pulse marking the start of the phase and the other pulse marking the end of the phase.

[0049] The next step 120 is for control unit 2 to receive the synchronization signal h.

[0050] The next step 130 is for control unit 2 to adjust the AC voltage V. AC The duration of the polarity change phase determines the square wave voltage value V to be applied to LED 3. L This stage may depend on the second frequency of the PDLC film and / or the response time of the PDLC film. For example, this duration, along with the AC voltage V, AC The second frequency is determined by control unit 2 using a synchronization signal h, which indicates the start and end of each polarity change cycle. Alternatively, this duration and this second frequency are predetermined.

[0051] In this step 130, the control unit 2 also determines the initial zero voltage duration T between the two voltage square waves based on the desired brightness for performing the lighting or signaling functions provided by the lighting device 1. i The first frequency is a multiple of the second frequency, such as twice the second frequency. The initial zero-voltage duration T is determined based on the initial DC supply voltage of LED 3. i This allows the initial DC supply voltage to be divided into two voltage square waves with an initial zero voltage duration T. i The voltage square wave is provided by the light flux emitted by the light-emitting diode 3 through the PDLC film 4 to provide the desired brightness.

[0052] When the initial zero voltage duration T i If the duration is less than the polarity change phase, control unit 2 determines that the zero voltage duration T0 is equal to the duration of the polarity change phase; otherwise, control unit 2 determines that the zero voltage duration T0 is equal to the initial zero voltage duration T. i .

[0053] When the initial zero voltage duration T i When the zero voltage duration T0 is less than the defined value, the control unit 2 can adjust the square wave voltage value V in this step 130. L In order to compensate for the difference between the zero voltage duration T0 and the initial zero voltage duration T iThe brightness loss caused by the increase in voltage will be sufficient to allow the PDLC film 4 to perform the desired illumination or signaling functions without optimizing the average transmittance of the PDLC film 4. For example, when the initial zero voltage duration T... i When it is zero, this square wave voltage value V compensates for the brightness loss caused by the prolonged extinguishing of LED 3. L The determination can be made by giving the square wave voltage value V to be applied. L A mapping that varies with the duration of the polarity-changing phase.

[0054] As a variant embodiment of step 130, when the synchronization signal h only contains a phase start indication, the control unit 2 derives a second frequency from it, and then uses, for example, a mapping to determine the duration of the polarity change cycle based on the second frequency, and / or determines, based on the second frequency, a square wave voltage value V to be applied to compensate for the brightness loss caused by the extinction of the light-emitting diodes during the polarity change cycle. L For example, control unit 2 uses different mappings depending on the type of PDLC membrane used, so as to adapt this peak V according to the response time of the PDLC membrane. L .

[0055] In the next step 140, control unit 2 uses synchronization signal h to construct a square wave voltage V with a previously determined value. L The voltage square wave signal with a first frequency and a previously determined zero voltage duration T0, wherein the first frequency is an integer multiple of the second frequency determined in the previous step.

[0056] For example, each time a voltage pulse of the synchronization signal h, marking the start of the polarity change phase, is received, the control unit 2 generates a falling edge of the voltage, followed by a rising edge after a time interval equal to the zero voltage duration T0 determined in step 130. The control unit 2 then sends the voltage square wave thus generated to the light-emitting diode 3.

[0057] Figure 5 This demonstrates the luminous flux emitted by the light-emitting diodes 3 when they are supplied with a voltage square wave signal constructed according to step 140 of the light emission method 100. The evolution, but in step 130, the square wave voltage value V L It has not yet been adjusted to compensate for the brightness loss caused by the diode's extinction during the polarity change phase. The corresponding voltage curve over time is... Figure 5 Relative luminous flux, indicated in bold. The curve, which corresponds to luminous flux. And the maximum value is one. In this exemplary application of the light emission method 100, the first frequency is selected to be twice the second frequency, thereby making it possible not to supply power to the light-emitting diode 3 at each polarity change stage.

[0058] Figure 5 It also reproduced the effect of being subjected to AC voltage V AC The transmittance T of the PDLC film 4 T Evolution over time.

[0059] It can be seen that each extinguishing duration of LED 3 (corresponding to relative luminous flux) Zero relative luminous flux between two square waves This corresponds to the low luminous flux transmission region 41, that is, to the AC voltage V. AC The polarity change phase. Therefore, when the light-emitting diode 3 emits light, the light passes through the PDLC film 4, which benefits from its better 70% transmittance in this embodiment of the invention. Therefore, the light flux is subjected to... The average transmittance of the PDLC film is 70%, instead of the 68% in the prior art. Of course, other types of PDLC films can be used, with transmittances that may differ from 70%, for example, 80% transmittance during the constant voltage supply phase.

[0060] Another curve shows the luminous flux emitted by the light-emitting diodes 3 when they are supplied with a voltage square wave signal constructed according to step 140 of the light emission method 100. The evolution, but in step 130, the square wave voltage value V has been adjusted. L This is to compensate for the brightness loss caused by diode deactivation during the polarity change phase. The corresponding voltage curve over time is... Figure 5 Relative luminous flux represented by a thin line The curve, which corresponds to luminous flux. value divided by luminous flux The value of .

[0061] Figure 6 The relative luminous flux is shown. The evolution of the value with the second frequency, corresponding to the luminous flux. The square wave voltage V is emitted by LED 3, which is supplied with a square wave voltage signal. L Adjustments are made based on the second frequency to compensate for the brightness loss caused by the polarity change phase. As shown in curve L2, this is partly due to the light flux transmitted through the film. The ratio between the luminous flux emitted by the LED 3, which is supplied with an initial DC supply voltage, and the luminous flux emitted by the LED 3 remains constant at 70%, thus achieving maximum transmittance of the PDLC film 4 regardless of the value of the second frequency. To obtain this result, the higher the second frequency, the higher the relative luminous flux. The value and therefore the square wave voltage V adjusted in step 130 L The higher the value, the better.

[0062] Figure 6 The relative luminous flux is shown. The value will not change according to the second frequency because it is supplied to LED 3 to generate luminous flux. The value of the square wave voltage V L The light flux transmitted through the film was not adjusted to compensate for the brightness loss caused by the polarity change phase. Therefore, as shown in curve L1, the light flux transmitted through the film... The ratio between the light flux emitted by the LED 3, which is supplied with an initial DC supply voltage, and the light flux emitted by the LED 3, on the other hand, decreases sharply according to the second frequency.

[0063] Curve L represents the light flux transmitted through the membrane in the prior art. The ratio between the luminous flux emitted by the LED 3, which is supplied with an initial DC supply voltage, and the luminous flux emitted by the LED 3. This ratio decreases with the second frequency, but still provides a luminous flux ratio. Higher brightness.

[0064] Similarly, Figure 7 The relative luminous flux is shown. The evolution of the value of luminous flux with the response time of the PDLC film used. The square wave voltage V is emitted by LED 3, which is supplied with a square wave voltage signal. L Adjustments are made based on this response time to compensate for the brightness loss caused by the polarity change phase. As shown in curve L20, this is partly due to the light flux transmitted through the film. The ratio between the light flux emitted by the LED 3, which is supplied with an initial DC supply voltage, and the light flux emitted by the LED 3 remains constant at 70%, thus representing the maximum transmittance of the PDLC film 4, regardless of the response time of the PDLC film. To achieve this result, the longer the response time of the PDLC film, the higher the relative light flux. The value and therefore the square wave voltage V adjusted in step 130 L The higher the value, the better.

[0065] Figure 7 The relative luminous flux is shown. The value will not change based on the response time of the PDLC film because it is supplied to the light-emitting diode 3 to generate luminous flux. The value of the square wave voltage V L It was not adjusted to compensate for the brightness loss caused by the polarity change phase. Therefore, as shown in curve L10, the light flux transmitted by the film... The ratio between the light flux emitted by the light-emitting diode 3, which is supplied with an initial DC supply voltage, and the light flux emitted by the light-emitting diode 3, which is supplied with an initial DC supply voltage, decreases sharply depending on the response time of the PDLC film.

[0066] Curve L0 represents the light flux transmitted through the membrane in the prior art. The ratio between the luminous flux emitted by the LED 3, which is supplied with an initial DC supply voltage, and the luminous flux emitted by the LED 3. This ratio decreases with the response time of the PDLC film, but still provides a higher luminous flux. Higher brightness.

[0067] Figure 8 This demonstrates the luminous flux emitted by the light-emitting diodes 3 when they are supplied with a voltage square wave signal constructed according to step 140 of the light emission method 100. The evolution, in which in step 130, the square wave voltage value V L The settings have not yet been adjusted to compensate for the brightness loss caused by the diode's extinction during the polarity-changing phase, and the first frequency is set to eight times the second frequency. Considering that the zero-voltage duration T0 is greater than the duration of the polarity-changing phase, this adjustment is not necessary to achieve the desired brightness. Therefore, the corresponding relative luminous flux... The curves form very small square waves that widely surround each low luminous flux transmission region 41. In this exemplary application of the light emission method 100, the lighting device 1 produces daytime running lights that require very low brightness.

[0068] at last, Figure 9 The steps of another light emission method 200 implemented by a lighting device 1 according to the present invention are shown.

[0069] The first step 210 is for the control unit 2 to determine the first frequency of the voltage square wave signal to be applied to the light-emitting diode 3 and the zero voltage duration T0 between the square waves according to the lighting or signaling function to be performed by the lighting device 1, so as to generate the desired brightness through the PDLC film 4.

[0070] The second step 220 involves the control unit 2 applying a square wave voltage signal to the light-emitting diode 3 at a first frequency determined in the previous step, the signal having a previously determined voltage duration T0 between square waves. In this step 220, the control unit 2 replicates the square wave voltage signal and sends it to the control device 5; the square wave voltage signal constitutes a synchronization signal h.

[0071] The third step, 230, involves the control device 5 receiving the synchronization signal h.

[0072] Finally, in the fourth step 240, the control device 5 determines a second frequency based on the first frequency, and applies an AC voltage to the PDLC film at the second frequency, synchronized with the voltage pulse sent to the light-emitting diode 3. The second frequency is selected as a divisor of the first frequency, for example, half of the first frequency. Synchronization is performed by the control device 5 so that the sign of the AC voltage changes each time between the falling and rising edges of two consecutive pulses of the square wave voltage signal applied to the light-emitting diode 3.

[0073] In this other transmission method 200 according to the invention, the AC voltage V AC The duration of the polarity change phase can be less than, equal to, or greater than the zero-voltage duration T0 between the two voltage square waves supplied to the light-emitting diode 3. However, this alternative emission method 200 allows for an increase in the average transmittance of the PDLC film compared to the prior art.

[0074] Of course, the present invention is not limited to the examples already described, and many modifications can be made to these examples without departing from the scope of the invention. In particular, features of various variant embodiments of the invention contemplated in this application can be combined to implement the invention, provided that these variants are mutually compatible.

Claims

1. A lighting device (1) for a vehicle, the lighting device comprising: -At least one photon emitter (3), - Control unit (2), the control unit is used to control the photon emitter (3) and is capable of applying a voltage pulse to polarize the photon emitter (3), causing the photon emitter to emit light. - A liquid crystal film (4), particularly a PDLC, which is capable of transmitting or blocking at least a portion of the light emitted by the photon emitter (3), and - Control device (5), which is capable of applying an AC voltage (V) to the membrane (4). AC ), The lighting device (1) is characterized in that it includes a synchronization device (10) for synchronizing the AC voltage (V) applied to the membrane (4). AC () is synchronized with the voltage pulse applied to the photon emitter (3).

2. The lighting device (1) for a vehicle as claimed in claim 1, wherein, The control unit (2) and / or the control device (5) are configured to use the synchronization device (10) such that at the AC voltage (V AC The voltage pulse is not applied during the polarity change of the voltage pulse.

3. The lighting device (1) for a vehicle as described in claim 1 or 2, wherein, The control unit (2) is capable of applying the voltage pulse at a first frequency, and wherein the control device (5) is capable of applying the AC voltage (V) to the membrane (4) at a second frequency. AC ).

4. The lighting device (1) for a vehicle as claimed in any one of claims 1 to 3, wherein, The synchronization device (10) includes a transmitting device for sending a synchronization signal (h) to the control unit (2).

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

6. The lighting device (1) for a vehicle as claimed in any one of claims 1 to 3, wherein, The synchronization device includes a transmitting device for sending a synchronization signal to the control device (5).

7. The lighting device (1) for a vehicle as claimed in claim 6, wherein, The control device (5) is capable of setting the AC voltage (V) between the falling edge and rising edge of two consecutive pulses in the voltage pulse based on the synchronization signal. AC The sign changes each time.

8. The lighting device (1) for a vehicle as described in claim 3 and claim 6 or 7, wherein, The control device (5) is capable of making the AC voltage (V AC The second frequency is equal to the first frequency or an integer divisor of the first frequency.

9. The lighting device (1) for a vehicle as claimed in any one of claims 3 to 8, wherein, The control unit (2) includes a determining device for determining the AC voltage (V). AC The peak voltage value (V) of the voltage pulse is determined by the duration of the polarity change phase of the voltage pulse and / or by the second frequency and / or by the response time of the membrane (4). L ).

10. A left front or right front optical unit for a vehicle, the left front or right front optical unit including an illumination device (1) as claimed in any one of claims 1 to 9 and capable of performing an illumination or signaling function, the optical unit including a closed outer lens, the film (4) being disposed between the control unit (2), the control device (5), the photon emitter (3) on one side and the closed outer lens on the other side, so as to mask the control unit (2), the control device (5) and the photon emitter (3) when the illumination or signaling function is not activated.

11. A light emission method implemented by a lighting device (1) as described in claim 3 and claim 4 or 5, or by an optical unit as described in claim 10 when referring to claim 3 and claim 4 or 5, the light emission method comprising the following steps: The control device (5) applies the AC voltage (V) to the membrane (4) at the second frequency. AC ), The control unit (2) receives the synchronization signal (h). The control unit (2) applies a voltage pulse to the photon emitter (3) at the first frequency, the voltage pulse being transmitted through the control unit (2) and the AC voltage (V). AC )synchronous.

12. A light emission method implemented by a lighting device (1) as described in any one of claims 3 and 6 to 8, or by an optical unit as described in claim 10 when referring to any one of claims 3 and 6 to 8, the light emission method comprising the following steps: The control unit (2) applies a voltage pulse to the photon emitter (3) at the first frequency. The control device (5) receives the synchronization signal. The control device (5) applies the AC voltage (V) to the membrane (4) at the second frequency. AC The AC voltage (V) AC The control device (5) is synchronized with the voltage pulse.

13. The light emission method as described in claim 11 or 12, wherein, The AC voltage (V) AC Each sign change occurs between the falling and rising edges of two consecutive pulses in the voltage pulse.

14. The light emission method as described in claim 13, further comprising the following steps: According to the AC voltage (V) AC The peak voltage value (V) of the voltage pulse is determined by the duration of the polarity change phase of the voltage pulse and / or by the second frequency and / or by the response time of the membrane (4). L ).

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