Specification Title: A Lighting Device, A Vehicle Lamp, and A Motor Vehicle Technical Field The present invention relates to a lighting device, a vehicle lamp comprising such the lighting device, and a motor vehicle including such the vehicle lamp. Background Art The vehicle lamp of a motor vehicle includes a lighting device. In some situations, the lighting device includes a plurality of lighting modules and these lighting modules are expected to provide a steering function. Figure 1A shows a schematic diagram of an exemplary lighting device. As shown in Figure 1A, the lighting device 1 comprises a housing 2 and the light emitting modules 3a, 3b, 3c, 3d set side by side in the housing 2. It is hoped that the light emitting modules 3a, 3b, 3c, 3d can turn synchronously. To achieve the above purpose, one embodiment is to install the light emitting modules 3a, 3b, 3c, 3d on the same steering frame 4. The steering frame 4 comprises a horizontal adjustment arm 41, a vertical adjustment arm 42, an adjustment point 44 located at one end of the horizontal adjustment arm 41, an adjustment point 45 located at one end of the vertical adjustment arm 42, and the same fixed hinge point 43 located at the other end of each of the horizontal adjustment arm 41 and the vertical adjustment arm 42. Nevertheless, the following weaknesses are found with such an embodiment: 1) The total weight of the light emitting modules 3a, 3b, 3c, and 3d independently carried by the steering frame 4 is relatively heavy. The material used for the steering frame 4 needs to be increased to ensure that the stiffness of the steering frame 4 meets the load bearing requirement, which leads to a greater weight of the steering frame 4. 2) The displacement amplitude of the light emitting modules (such as the light emitting modules 3a and 3d shown in Figure 1A) located at the edge of the arranging array of the light emitting modules is large, and may even exceed the expected displacement range (such as the range of the rectangular CF shown in Figure 1A), which also potentially indicates that the vibration characteristics of these light emitting modules located at the edge are poor. 3) To accommodate the steering frame 4 and the light emitting modules 3a, 3b, 3c, 3d, it is necessary to design a large modelling opening in the housing 2, which is usually not expected, and enlarging the modelling opening will increase the risk of light leakage in the lighting device. Summary of the Invention The present invention is proposed to address the aforementioned technical problems and other potential technical problems. A lighting device is provided according to one aspect of the present invention. The lighting device comprises: - A housing; - Two or more light emitting modules, which are arranged in the housing along the first direction; - At least two steering frames, the light emitting modules are installed on the steering frames to turn by means of the steering frames; and - A driving device, which provides a driving force for steering of the steering frames; Wherein the lighting device also comprises a linkage device, which is configured to connect the at least two steering frames and rotate the at least two steering frames synchronously with each other and in the same direction under the driving force provided by the driving device. In addition to being able to rotate the at least two steering frames synchronously with each other and in the same direction, adopting the above-mentioned lighting device according to the present invention can also achieve the following beneficial effects: 1) The steering frame uses less material and has a light weight provided that the load bearing requirement is satisfied; 2) The displacement amplitude of the light emitting module located at the edge of the arranging array of the light emitting modules is small, and the vibration stability is good; and 3) There is no need to design a large modelling opening in the housing to accommodate the steering frames and the light emitting modules. Specifically, the at least two steering frames comprise a first steering frame and a second steering frame. The linkage device comprises a first translational arm and a second translational arm. The first end of the first steering frame in the first direction is hinged to the housing, and the second end of the first steering frame in the first direction is connected to the first translational arm so that the first steering frame can rotate around the first end of the first steering frame. The first end of the second steering frame in the first direction is connected to the second translational arm, and the second end of the second steering frame in the first direction is hinged to the housing so that the second steering frame can rotate around the second end of the second steering frame. Specifically, the first translational arm and second translational arm are configured to be able to move in a translational manner synchronously and inversely to each other in the second direction transverse to the first direction under driving of the driving device, so as to drive the first steering frame and the second steering frame to rotate synchronously with each other and in the same direction. Adopting the above-mentioned lighting device according to the present invention makes it possible to use fewer driving devices and adopt a compact transmission mechanism to enable the first steering frame and the second steering frame to rotate synchronously with each other and in the same direction. Specifically, one end of the first translational arm in the second direction is connected to the driving device, and the other end of the first translational arm in the second direction is connected to the first steering frame. One end of the second translational arm in the second direction is connected to the second steering frame, and the other end of the second translational arm in the second direction is a free end. Optionally, the linkage device comprises a "gear-rack" structure. The "gear-rack" structure comprises: - A first rack, which is used as the first translational arm; - A second rack, which is used as the second translational arm; and - A gear, wherein the central axis of the gear can be rotatably fixed on the housing, the gear is set between the first rack and the second rack, and the teeth of the gear mesh with the teeth of the first rack and the teeth of the second rack respectively, thus enabling the first rack and the second rack to move in a translational manner synchronously and inversely to each other. In addition to achieving accurate linkage between the first steering frame and the second steering frame, adopting the above-mentioned lighting device according to the present invention can also reduce the number of spherical hinge adjustment nodes/connection points in the linkage device, thereby improving the vibration stability of the linkage device. Preferably, at least one guide member is respectively set on the first rack and the second rack, and at least one guide groove corresponding to the at least one guide member is set in the housing. Specifically, a first set of guide elements and a second set of guide elements are respectively set on both sides of the first rack, the first set of guide elements comprises two or more guide elements, and the second set of guide elements comprises two or more guide elements. A third set of guide elements and a fourth set of guide elements are respectively set on both sides of the second rack, the third set of guide elements comprises two or more guide elements, and the fourth set of guide elements comprises two or more guide elements. A first guide groove, a second guide groove, a third guide groove, and a fourth guide groove are set in the housing. The first set of guide elements is embedded in the first guide groove and can slide along the first guide groove, the second set of guide elements is embedded in the second guide groove and can slide along the second guide groove, the third set of guide elements is embedded in the third guide groove and can slide along the third guide groove, and the fourth set of guide elements is embedded in the fourth guide groove and can slide along the fourth guide groove. Adopting the aforementioned lighting device according to the present invention makes it possible to achieve smooth movement of the first rack and second rack. Optionally, the linkage device comprises a hydraulic transmission structure. The hydraulic transmission structure comprises: - A first actuator cylinder, which is used as the first translational arm; - A second actuator cylinder, which is used as the second translational arm; and - A bidirectional hydraulic circuit, which is constructed to enable the first actuator cylinder and the second actuator cylinder to move in a translational manner synchronously and inversely to each other. Adopting the aforementioned lighting device according to the present invention can achieve accurate linkage between the first steering frame and the second steering frame. Specifically, the hydraulic transmission structure comprises: - A first sleeve, wherein the first actuator cylinder is set in the first sleeve and a first partition is set on the outer peripheral surface of the first actuator cylinder, and the first partition separates the space between the outer peripheral surface of the first actuator cylinder and the inner peripheral surface of the first sleeve into a first cavity and a second cavity that are not connected to each other; - A second sleeve, wherein the second actuator cylinder is set in the second sleeve and a second partition is set on the outer peripheral surface of the second actuator cylinder, and the second partition separates the space between the outer peripheral surface of the second actuator cylinder and the inner peripheral surface of the second sleeve into a third cavity and a fourth cavity that are not connected to each other; - A first channel, which connects the second cavity and the fourth cavity to each other; and - A second channel, which connects the first cavity and the third cavity; Wherein the first cavity, the second cavity, the third cavity, the fourth cavity, the first channel, and the second channel constitute the bidirectional hydraulic circuit. Adopting the aforementioned lighting device according to the present invention makes it possible to achieve smooth movement of the first actuator cylinder and second actuator cylinder. Optionally, the first end of the first steering frame in the first direction is hinged to the housing through a first elastic spherical hinge. The second end of the second steering frame in the first direction is hinged to the housing through a second elastic spherical hinge. The other end of the first translational arm in the second direction is hinged to the first steering frame through a third elastic spherical hinge, and one end of the second translational arm in the second direction is hinged to the second steering frame through a fourth elastic spherical hinge. In addition to achieving accurate linkage between the first steering frame and the second steering frame, adopting the above-mentioned lighting device according to the present invention can also reduce the number of spherical hinge adjustment nodes/connection points in the linkage device, thereby improving the vibration stability of the linkage device. Specifically, the first direction is the vertical direction of the lighting device, and the at least two steering frames are configured to drive the two or more light emitting modules to rotate around the horizontal axis. Each of the first and second steering frames comprises a vertical adjustment arm extending in the first direction and a horizontal adjustment arm extending in the third direction transverse to the first direction. The first steering frame and the second steering frame are arranged symmetrically to mirror each other relative to the horizontal axis in the first direction. Adopting the aforementioned lighting device according to the present invention enables the at least two steering frames to rotate around a horizontal axis. According to another aspect of the present invention, a vehicle lamp is provided. The vehicle lamp comprises the lighting device according to the previous aspect of the present invention. A motor vehicle is provided according to another aspect of the present invention. The motor vehicle comprises a vehicle lamp according to the previous aspect of the present invention. Description of Accompanying Drawings To make it easy to understand the present invention, the present invention will be described in more detail below based on exemplary embodiments and in conjunction with the accompanying drawings. In the drawings, identical or similar reference labels are used to denote identical or similar members. It should be understood that the drawings are merely schematic, and the dimensions and proportions of the members in the drawings are not necessarily precise. [Fig. 1A] shows a schematic diagram of an exemplary lighting device. [Fig. 1B] shows a schematic diagram of a lighting device according to an exemplary embodiment of the present invention. [Fig. 2A] and [Fig. 2B] respectively show a stereoscopic view and a front view of the lighting device according to an exemplary embodiment of the present invention. [Fig. 2C], [Fig. 2D], and [Fig. 2E] respectively show a partial sectioning left view, partial sectioning right view, and partial cutaway stereoscopic view of the lighting device in Figure 2A. [Fig. 2F] shows an enlarged cross-sectional view taken along the cutting plane F-F in Figure 2B. [Fig. 3A] and [Fig. 2B] respectively show a schematic diagram of the movement status of the lighting device in Figure 2C. [Fig. 4A] and [Fig. 4B] respectively show a partial cutaway stereoscopic view and a partial cutaway left view of the lighting device according to another exemplary embodiment of the present invention. [Fig. 5A] and [Fig. 5B] respectively show a schematic diagram of the movement status of the lighting device in Figure 4B. Embodiments Overview of Principles The principles and drawbacks of an exemplary lighting device have been illustrated in the above "Background Art" section with reference to Figure 1A. The principles of the lighting device according to an exemplary embodiment of the present invention will be described next with reference to Figure 1B. As shown in Figure 1B, the lighting device 1' according to an exemplary embodiment of the present invention comprises: a housing 2; two or more light emitting modules (four light emitting modules in this exemplary embodiment: the first light emitting module 3a, the second light emitting module 3b, the third light emitting module 3c, and the fourth light emitting module 3d), these light emitting modules 3a, 3b, 3c, 3d being arranged in the housing 2 along the first direction (which is the vertical direction in this exemplary embodiment, as shown in Figure 2C and Figure 2D); and at least two steering frames 4a and 4b (specifically the first steering frame 4a and the second steering frame 4b), wherein the light emitting modules 3a, 3b, 3c, 3d are respectively installed on the steering frames 4a, 4b to steer by means of the steering frames 4a and 4b. In this exemplary embodiment, the first light emitting module 3a and the second light emitting module 3b are installed on the first steering frame 4a, and the third light emitting module 3c and the fourth light emitting module 3d are installed on the second steering frame 4b. The steering frame 4 in Figure 1A can be compared with the steering frames 4a, 4b in Figure 1B to indicate that the basic structure of the steering frame 4 in Figure 1A is similar to that of each of steering frames 4a, 4b in Figure 1B, except that the steering frames 4a and 4b are symmetrically arranged to mirror each other. Similar to the steering frame 4 in Figure 1A, the steering frame 4a and steering frame 4b comprise a vertical adjustment arm extending in the first direction, a horizontal adjustment arm extending in the third direction (the direction vertical to the paper in Figure 2C) transverse to the first direction, an adjustment point located at one end of the horizontal adjustment arm, an adjustment point located at one end of the vertical adjustment arm, and the same fixed hinge point located at the other end of each of the horizontal adjustment arm and the vertical adjustment arm. The steering frame 4a and steering frame 4b are symmetrically arranged to mirror each other relative to the horizontal axis (as shown in Figure 2B). As shown in Figure 1B, the lighting device 1' also comprises a linkage device, which is configured to connect at least the steering frames 4a, 4b and to rotate at least the steering frames 4a, 4b synchronously with each other and in the same direction under the driving force provided by the driving device (not shown in the figure). Overall Structure Next, a more detailed structure of the lighting device according to an exemplary embodiment of the present invention will be described next in conjunction with Figures 2A to 2F. Figures 2A and 2B respectively show a stereoscopic view and a front view of the lighting device according to an exemplary embodiment of the present invention. Some components in the lighting device are omitted in Figures 2A and 2B to better illustrate the internal structure of the lighting device. Figures 2C, 2D, and 2E respectively show a partial sectioning left view, partial sectioning right view, and partial cutaway stereoscopic view of the lighting device in Figure 2A. One portion of the housing for the lighting device is cut off in Figures 2C to 2E, and some components are omitted in the lighting device with a view to better illustrating the internal structure of the lighting device. Figure 2F shows an enlarged cross-sectional view taken along the cutting plane F-F in Figure 2B. As shown in Figures 2A to 2E, in the lighting device 1' according to the present exemplary embodiment, the linkage device 5 comprises a first translational arm 5a and a second translational arm 5b. The first end (i.e., the upper end) of the vertical adjustment arm of the first steering frame 4a in the first direction is hinged to the housing 2, and the second end (i.e., the lower end) of the vertical adjustment arm of the first steering frame 4a in the first direction is connected to the first translational arm 5a so that the first steering frame 4a can rotate around the first end (i.e., the upper end) of the vertical adjustment arm of the first steering frame 4a, specifically around the horizontal axis H ₁ H ₁ ' shown in Figure 2B. The first end (i.e., the upper end) of the vertical adjustment arm of the second steering frame 4b in the first direction is connected to the second translational arm 5b, and the second end (i.e., the lower end) of the vertical adjustment arm of the second steering frame 4b in the first direction is hinged to the housing 2 so that the second steering frame 4b can rotate around the second end (i.e., the lower end) of the vertical adjustment arm of the second steering frame 4b, specifically around the horizontal axis H ₂ H ₂ ' shown in Figure 2B. As shown in Figure 2C, preferably, the first end (i.e., the upper end) of the vertical adjustment arm of the first steering frame 4a in the first direction is hinged to the housing 2 through the first elastic spherical hinge 41a. The second end (i.e., the lower end) of the vertical adjustment arm of the second steering frame 4b in the first direction is hinged to the housing through the second elastic spherical hinge 42b. As shown in Figures 2C to 2E, the lighting device 1' also comprises a driving device 6. The driving device 6 provides a driving force for the steering of the steering frames 4a, 4b, and comprises a telescopic rod 61 and a manual drive port 7. The driving device 6 can be, but is not limited to, an electric motor or a lead screw, or other suitable driving devices. In addition, as shown in Figures 2C and 2D, one end of the first translational arm 5a in the second direction is connected to the telescopic rod 61 of the driving device 6, and the other end (equipped with a ball head 52a, as shown in Figure 2E) of the first translational arm 5a in the second direction is connected to the first steering frame 4a through, for example, an elastic spherical hinge 42a. One end (equipped with a ball head 52b, as shown in Figure 2E) of the second translational arm 5b in the second direction is connected to the second steering frame 4b through, for example, an elastic spherical hinge 41b, and the other end of the second translational arm 5b in the second direction is a free end. The first translational arm 5a and the second translational arm 5b are configured to be able to move in a translational manner synchronously and inversely to each other in a second direction (as shown in Figures 2C and 2D) transverse to the first direction under the driving force of the driving device 6, so as to drive the first steering frame 4a and the second steering frame 4b to rotate synchronously with each other and in the same direction. Specifically, the linkage device 5 comprises a "gear-rack" structure, which comprises a first rack 50a, the first rack 50a being used as the first translational arm 5a; a second rack 50b, the second rack 50b being used as the second translational arm 5b; and a gear 5c, the central shaft 51c of the gear 5c being rotatably fixed to the housing 2 by the stops 53, 53'. The gear 5c is set between the first rack 50a and the second rack 50b, and the teeth of the gear 5c engage the teeth of the first rack 50a and the teeth of the second rack 50b, respectively, so that the first rack 50a and the second rack 50b can move in a translational manner synchronously and inversely to each other under the driving force of the driving device 6. Preferably, the first rack 50a and the second rack 50b are respectively provided with at least one guide member 51a, 51a', 51b, 51b', and the housing 2 is provided with at least one guide groove 21a, 21a', 21b, 21b' corresponding to the at least one guide member in it. Specifically, first rack 50a is provided with, respectively on both sides, a first set of guide elements and a second set of guide elements. The first set of guide elements comprises two or more (three in this exemplary embodiment) guide elements 51a. The second set of guide elements comprises two or more (three in this exemplary embodiment) guide elements 51a'. The second rack 50b is provided with, respectively on both sides, a third set of guide elements and a fourth set of guide elements. The third set of guide elements comprises two or more (three in this exemplary embodiment) guide elements 51b. The fourth set of guide elements comprises two or more (three in this exemplary embodiment) guide elements 51b'. Correspondingly, the housing 2 is provided with a first guide groove 21a, a second guide groove 21a', a third guide groove 21b, and a fourth guide groove 21b' in it. In this way, the first set of guide members can be embedded in the first guide groove 21a and can slide along the first guide groove 21a. The second set of guide elements can be embedded in the second guide groove 21a 'and can slide along the second guide groove 21a'. The third set of guide elements can be embedded in the third guide groove 21b and can slide along the third guide groove 21b. The fourth set of guide elements can be embedded in the fourth guide groove 21b' and can slide along the fourth guide groove 21b'. In addition, as shown in Figure 2D, the adjustment point of the horizontal adjustment arm of the first steering frame 4a is hinged to the first screw stem 91a of the first horizontal adjustment tool 9a through the fifth elastic spherical hinge 43a. The adjustment point of the horizontal adjustment arm of the second steering frame 4b is hinged to the second screw stem 91b of the second horizontal adjustment tool 9b through the sixth elastic spherical hinge 43b. Operation Method The operation mode of the lighting device according to an exemplary embodiment of the present invention will be described next in conjunction with Figures 3A and 3B. Taking the state of the lighting device in Figure 2C as the initial state, Figure 3A and Figure 3B show schematic diagrams of two moving states of the lighting device shown in Figure 2C. As shown in Figure 3A, the telescopic rod 61 of the driving device 6 extends in the direction shown by arrow A1, enabling the first rack 50a to translate in the direction indicated by arrow A1, thereby driving the first steering frame 4a to rotate upwards around the horizontal axis H ₁ H ₁ ' by an angle of +θ. Meanwhile, the first rack 50a drives the gear 5c to rotate clockwise as indicated by arrow A2, enabling the second rack 50b to translate in the direction indicated by arrow A3, thereby driving the second steering frame 4b to rotate upwards around the horizontal axis H ₂ H ₂ ' by an angle of +θ. In this way, the first steering frame 4a and the second steering frame 4b are synchronized with each other and rotate upward in the same direction, ultimately enabling the light emitting modules 3a, 3b, 3c, 3d installed on the first steering frame 4a and the second steering frame 4b to be synchronized with each other and rotate upward in the same direction. As shown in Figure 3B, the telescopic rod 61 of the driving device 6 retracts in the direction shown by arrow A1', enabling the first rack 50a to translate in the direction indicated by arrow A1', thereby driving the first steering frame 4a to rotate downwards around the horizontal axis H ₁ H ₁ ’ by an angle of -θ. Meanwhile, the first rack 50a drives the gear 5c to rotate counter-clockwise as indicated by arrow A2', enabling the second rack 50b to translate in the direction indicated by arrow A3', thereby driving the second steering frame 4b to rotate downwards around the horizontal axis H ₂ H ₂ ' by an angle of -θ. In this way, the first steering frame 4a and the second steering frame 4b are synchronized with each other and rotate downward in the same direction, ultimately enabling the light emitting modules 3a, 3b, 3c, 3d installed on the first steering frame 4a and the second steering frame 4b to be synchronized with each other and rotate downward in the same direction, but the rotation direction is opposite to the rotation direction shown in Figure 3A. Variant Embodiments Figures 4A and 4B respectively show a partial cutaway stereoscopic view and a partial cutaway left view of the lighting device according to another exemplary embodiment (which can be regarded as a variant embodiment) of the present invention. A portion of the housing of the lighting device has been removed, and some components in the lighting device are omitted in Figures 4A and 4B to better illustrate the internal structure of the lighting device. The overall structure of the lighting device 1" shown in Figures 4A and 4B is basically the same as that of the lighting device 1' described earlier, with the only difference between the two being the structure of the linkage device 5. Specifically, as shown in Figures 4A and 4B, the linkage device 5 comprises a hydraulic transmission structure, which comprises: a first actuator cylinder 50a', the first actuator cylinder 50a' being used as the first translational arm 5a'; a second actuator cylinder 50b', the second actuator cylinder 50b' being used as the second translational arm 5b'; and a bidirectional hydraulic circuit 54a, 54b, 55a, 55b, 51c', 52c', the bidirectional hydraulic circuit 54a, 54b, 55a, 55b, 51c', 52c' being constructed to enable the first actuator cylinder 50a' and the second actuator cylinder 50b' to move in a translational manner synchronously and inversely to each other. More specifically, the hydraulic transmission structure comprises: - A first sleeve 56a, wherein the first actuator cylinder 50a' is set in the first sleeve 56a and a first partition 53a is set on the outer peripheral surface of the first actuator cylinder 50a', and the first partition 53a separates the space between the outer peripheral surface of the first actuator cylinder 50a' and the inner peripheral surface of the first sleeve 56a into a first cavity 54a and a second cavity 55a that are not connected to each other; - A second sleeve 56b, wherein the second actuator cylinder 50b' is set in the second sleeve 56b and a second partition 53b is set on the outer peripheral surface of the second actuator cylinder 50b', and the second partition 53b separates the space between the outer peripheral surface of the second actuator cylinder 50b' and the inner peripheral surface of the second sleeve 56b into a third cavity 54b and a fourth cavity 55b that are not connected to each other; - A first channel 51c', the first channel 51c’ connects the second cavity 55a and the fourth cavity 55b to each other; and - A second channel 52c', second channel 52c’ connects the first cavity 54a and the third cavity 54b; Wherein the first cavity 54a, second cavity 55a, third cavity 54b, fourth cavity 55b, and the first channel 51c', and second channel 52c' constitute a bidirectional hydraulic circuit. Taking the state of the lighting device in Figure 4B as the initial state, Figure 5A and Figure 5B show schematic diagrams of two moving states of the lighting device shown in Figure 4B. As shown in Figure 5A, the telescopic rod 61 of the driving device 6 extends in the direction indicated by arrow B1, enabling the first actuator cylinder 50a' to move in a translational manner in the first sleeve 56a in the direction B1 from the first cavity 54a to the second cavity 55a, the volume of the first cavity 54a increases and the volume of the second cavity 55a decreases, thereby generating a negative pressure in the first cavity 54a and a positive pressure in the second cavity 55a, the hydraulic fluid in the second cavity 55a is forced into the fourth cavity 55b in the direction indicated by arrow B2 through the first channel 51c', and the hydraulic fluid in the third cavity 54b is sucked into the first cavity 54a through the second channel 52c' along arrow B4, thereby generating a positive pressure in the fourth cavity 55b and a negative pressure in the third cavity 54b, which enables the second actuator cylinder 50b' to move in a translational manner in the direction B3 from the fourth cavity 55b to the third cavity 54b in the second sleeve 56b. In this way, the first steering frame 4a and the second steering frame 4b are synchronized with each other and rotate upward in the same direction, ultimately enabling the light emitting modules 3a, 3b, 3c, 3d installed on the first steering frame 4a and the second steering frame 4b to be synchronized with each other and rotate upward in the same direction. As shown in Figure 5B, the telescopic rod 61 of the driving device 6 retracts in the direction indicated by arrow B1', enabling the first actuator cylinder 50a' to move in a translational manner in the first sleeve 56a in the direction B1' from the second cavity 55a to the first cavity 54a, the volume of the first cavity 54a decreases and the volume of the second cavity 55a increases, thus generating a positive pressure in the first cavity 54a and a negative pressure in the second cavity 55a, the hydraulic fluid in the first cavity 54a is forced into the third cavity 54b in the direction indicated by arrow B4' through the second channel 52c', and the hydraulic fluid in the fourth cavity 55b is sucked into the second cavity 55a through the first channel 51c' in the direction indicated by arrow B2', thereby generating a positive pressure in the third cavity 54b and a negative pressure in the fourth cavity 55b, which enables the second actuator cylinder 50b' to move a translational manner in the direction B3' from the third cavity 54b to the fourth cavity 55b in the second sleeve 56b. In this way, the first steering frame 4a and the second steering frame 4b are synchronized with each other and rotate downward in the same direction, ultimately enabling the light emitting modules 3a, 3b, 3c, and 3d installed on the first steering frame 4a and the second steering frame 4b to be synchronized with each other and rotate downward in the same direction, but the rotation direction is opposite to the rotation direction shown in Figure 5A. The advantage of using the above hydraulic transmission structure is that it can achieve accurate linkage between the first steering frame 4a and the second steering frame 4b when the "gear-rack" structure described earlier is not applicable. For example, when the first steering frame 4a and the second steering frame 4b are far from each other, if the "gear-rack" structure is still used, the size of the gear and/or rack is required to be larger, so the "gear-rack" structure is no longer applicable. In this case, it is more appropriate to adopt the hydraulic transmission structure described above in stead. The lighting devices 1' and 1" described above are suitable for use in vehicle lamps, so they are suitable for use in motor vehicles using such lamps. In addition, although the light emitting modules 3a, 3b, 3c, 3d have been described above as examples, it should be understood that the component with direction adjusted is not necessarily a light emitting module, but can be any other components whose directions are to be adjusted. In addition, the number of light emitting modules arranged on the steering frames is not necessarily four, but greater or smaller. In addition, although the embodiments that the steering frame (and the light-emitting module) rotates around the horizontal axes H ₁ H ₁ ', H ₂ H ₂ ' are described above, it should be understood that the steering frame (and the light emitting module) can actually rotate around the vertical axis VV' (as shown in Figure 2B). However, since the solution that the steering frame (and the light emitting module) rotates around the vertical axis VV' is not the key point to be described for the present invention, it is not detailed in this document, but this does not mean that the technical solution of the present invention does not include the scenario that the steering frame (and the light emitting module) can also rotate around the vertical axis VV'. Although the technical objectives, technical solutions, and technical effects of the present invention have been described in detail in conjunction with specific embodiments in the previous text, it should be understood that the above embodiments are only exemplary, but not restrictive. Within the substantive spirit and principles of the present invention, any modifications, equivalent substitutions, or improvements made by those skilled in the art shall be included within the scope of protection of the present invention.