JP5563209B2 - Lamp - Google Patents

Description

  The present invention relates to a lamp provided with a light guide, and more particularly to a lamp with improved light emission efficiency from the light guide.

As a structure for enhancing the design effect, a lamp using a light guide is provided for an automobile lamp. For example, in Patent Document 1, a step-like reflection surface portion is formed on the back surface of a block-shaped light guide, light is incident from the lower surface of the light guide, and the light guided inside the light guide is reflected on the reflection surface portion. The lamp | ramp which reflects toward the front of a lamp | ramp is comprised. In this lamp, since the lighting of the reflecting surface portion is brightly lit, by arbitrarily forming the pattern shape of the reflecting surface portion when the lamp is viewed from the front, a lamp having a light emitting pattern with an excellent design can be easily formed. Can be obtained.
JP 2007-227356 A

  In such a lamp, when the area of the light guide is designed to be large, in order to obtain a high luminous intensity over a wide range of the light guide, a large number of light sources are arranged facing each other at a plurality of locations on the light guide. A configuration may be adopted in which light enters the light guide. For example, as shown in FIG. 5B, a planar light guide 21A disposed in the lamp housing is disposed in a state of being inclined in a direction perpendicular to the optical axis Lx of the lamp, and the top and bottom of the light guide The light emitted from the LED elements 26 arranged corresponding to the respective end surfaces of the light is condensed by the condensing lens 27 and is incident on the light guide surface portion 22 formed thick in the light guide 21A. Further, stepped (stepped) reflecting surface portions 28a and 28b are formed on the rear surface of the light guiding surface portion 22 where the light of the light guide 21A is guided, and the light guided through the light guiding surface portion 22 is reflected on the reflecting surface portion 28a. , 28b and emitted toward the front of the lamp along the lamp optical axis Lx. Thereby, it is possible to guide light over a wide area of the light guide 21A and reflect and emit light to obtain a lamp having a high luminous intensity as a whole.

  By the way, when the light guide 21A is disposed so as to be inclined in the vertical direction with respect to the lamp optical axis Lx as described above, that is, the light guide surface portion 22 for guiding the light of the light guide is required in the vertical direction. In the case where light is incident from the upper end surface and the lower end surface of the light guide surface portion 22, the surfaces of the reflection surface portions 28a and 28b for reflecting each incident light are arranged at an angle. The angle is designed to reflect light in a direction along the lamp optical axis Lx. Therefore, in the case of this light guide 21A, in the reflection surface portion 28a that reflects the light from the upper end surface, the surface angle of the reflection surface portion 28a, that is, the light guide direction that is the light guide direction of the light guided through the light guide surface portion 22. Since the inclination angle of the reflection surface with respect to the optical axis is a small angle θa, the critical condition of light at the reflection surface portion 28a can be easily satisfied. However, since the surface angle of the reflection surface portion 28b that reflects light from the lower end surface is a large angle θb with respect to the light guide axis, the critical condition of light at the reflection surface portion 28b cannot be satisfied, and the light is guided. Most of the light passes through the reflecting surface portion 28b and leaks outside. For this reason, the reflection efficiency at the reflection surface portion 28b is reduced, and the emission efficiency of light emitted toward the front of the lamp is reduced. In particular, the light emission intensity in the lower region of the light guide 21A is lower than the light emission intensity in the upper region, the use efficiency of light contributing to illumination is reduced, and the light emission in a uniform light emission state in the entire region of the light guide. It becomes difficult to perform illumination.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a lamp that enhances light emission efficiency in a light guide and enables light emission with uniform brightness over the entire region of the light guide.

The present invention includes a light guide that is formed in a plate shape, guides light incident from a light incident surface to the inside, reflects the light guided toward the front of a lamp on a reflection surface portion, and guides the light. A lamp including a light guide unit including a light source that causes light to be incident on different light incident surfaces of the light body, wherein the light guide directs the light incident from each incident surface toward the front of the lamp, and the lamp optical axis. The vertical cross-sectional shape is formed in a substantially "<" shape so that a plurality of light guide surface portions that guide light at different angles inclined with respect to the front of the lamp are formed, and the light guide is The thin portion of the region and the thick portion of the region surrounded by the thin portion constitute the light guide surface portion, and the end surface of the step portion between the thick portion and the thin portion is light. It is configured as an incident surface, and the light guide is fixed to the lamp at the periphery of the thin portion. While supporting the light source is characterized by being directed in the direction in which light incident on the light guide member is inclined with respect to the "V" shaped in bent lamp optical axis of the light guide.

According to the present invention, the light guided through the plurality of light guide surface portions constituting the light guide is guided in a direction inclined toward the front of the lamp, so that the guided light is forwarded to the front of the lamp. The angle of the reflecting surface part to be reflected can be formed at a small angle with respect to the light guiding direction to satisfy the critical angle condition, and the reflection efficiency at the reflecting surface part is improved and the entire light guide body is covered. A lamp that emits light with uniform brightness can be realized. In particular, the light source uses a light guide with a low refractive index, that is, a light guide with a small critical angle, because the light incident on the light guide is directed in the direction of the light guide being bent into a “<” shape. Even in this case, the critical angle condition can be easily satisfied.

Oite the present invention, the light guide is cross-sectional shape as each of the light guide face of the different light incident surface disposed pairs direction protrudes toward the front of the lamp is formed substantially "V" shaped. For example, the light guide is composed of a light guide surface portion that is inclined upward and a light guide surface portion that is inclined downward so that a horizontal ridge line is formed on the front side, and the upper end surface and the lower end surface of each light guide surface portion are formed. Each of the light incident surfaces is provided with at least one LED element as a light source in the horizontal direction. At this time, it is preferable that the upper and lower light incident surfaces are parallel to the ridge line, and a plurality of light sources are arranged in a line on a virtual line along the light incident surface. The reflective surface is configured as a linear step reflecting surface is cross-sectional shape inclined with respect to the light guiding direction of the light, in particular linearly arranged extending along the edge. The light from the LED elements disposed on the upper and lower sides is guided through the upper and lower light guide surface portions, reflected at each reflective surface portion with high efficiency, and emitted toward the front of the lamp. A lamp that illuminates the upper region and the lower region with high brightness and uniform brightness can be configured.

Further, in the present invention, the light guide is composed of a thin portion in the peripheral region and a thick portion in a region surrounded by the thin portion, and the thick portion is configured as a light guide surface portion, and the thick portion The end surface of the step portion of the thin portion is configured as a light incident surface, and the light guide is fixedly supported to the lamp at the peripheral portion of the thin portion. The thick and thin portions of the light guide are integrally formed of a transparent material to simplify the configuration, and the light guide is fixedly supported on the lamp around the periphery to increase the support strength. Further, since light is not guided to the thin portion, only the thick portion or the reflection surface portion emits light, and the light emitting region has an appearance of floating in the air, thereby improving visibility and a design effect.

  Next, Example 1 of the present invention will be described. 1 is a front view of a first embodiment in which the present invention is applied to a right tail combination lamp TCL of an automobile, FIG. 2 is a vertical sectional view taken along line II-II in FIG. 1, and FIG. 3 is a horizontal sectional view taken along line III-III in FIG. It is. In these drawings, a lamp body 11 having a container shape that can be mounted on the rear right side of the body of an automobile and opened on the front surface (rear side of the automobile), and a transparent front cover 12 attached to the front opening of the lamp body 11 are shown. And the lamp housing 1 is constituted. The front cover 12 is inclined in the vertical direction in the vertical direction in accordance with the bulge of the vehicle body, and horizontally in the horizontal direction along the side surface of the vehicle body so as to constitute a part of the vehicle body shape of the automobile. It has a curved shape. Further, the tail combination lamp TCL of the first embodiment includes a tail lamp unit 2, a stop lamp unit 3, and a turn signal lamp unit 4. Although the illustration and description of the left tail combination lamp are omitted here, the left tail combination lamp has a symmetrical configuration with respect to the right and left tails.

  FIG. 4 is a schematic exploded perspective view of a main part of the right tail combination lamp TCL. In the lamp housing 1, a stop lamp unit 3 is disposed in a rear region, and a tail lamp unit 2 is disposed in front thereof. The turn signal lamp unit 4 is disposed in the frontmost lower region in the lamp housing 1. Further, an extension 5 as a pseudo reflector for covering the peripheral area in the lamp housing 1 is disposed and supported in the front area of the stop lamp unit 2 in the lamp housing 1. An opening 51 having a required size is provided in the region, and the stop lamp unit 3 and the tail lamp unit 2 are exposed to the front of the tail combination lamp TCL through the opening 51. The turn signal lamp unit 4 is disposed on the lower region on the front side of the extension 5.

  The stop lamp unit 3 is disposed in a container-shaped S-body 31 having an S (stop) -reflector 32 integrally formed therein and having a substantially rectangular front view, and a front opening of the S-body 31. An S-clear lens 33 having a required lens step formed on the rear surface, and a plurality of S-LEDs arranged and supported on the upper and lower surfaces of the S-body 31 side by side and emitting red light. It is comprised with the element 34. FIG. The rear surface of the S-body 31 is formed stepwise in the horizontal direction, and the S-LED elements 34 are arranged stepwise in the horizontal direction. The S-reflector 32 has a vertical cross-sectional shape in which two parabolic reflectors are arranged in a mountain shape with the front facing forward, and the S-LED element 34 mounted on the support substrate 35 is connected to each parabolic reflector. Fixed support at the focal position. The S-LED element 34 is supplied with power via a wiring that does not appear in the figure provided on the support substrate 35, and emits light when the vehicle is braked. The red light emitted when the S-LED element 34 emits light is reflected by the S-reflector 32 and is condensed as a light beam substantially parallel to the lamp optical axis Lx, and the lens when passing through the S-clear lens 33. By the step, a required light distribution pattern is obtained and transmitted through the front cover 12 and emitted to the rear of the automobile.

  The tail lamp unit 2 is configured as a light guide unit having a light guide 21. The light guide 21 is formed in a plate shape bent with a transparent resin having light transmittance, and is disposed on the rear side of the extension 5, and the central region of the light guide 21 extends from the opening 51 of the extension 5. It has come to be exposed. The central region exposed from the opening 51 of the extension 5 is formed as a thick portion 22 having a large thickness, but the region extending outward from the entire periphery of the thick portion 22 is larger than the thick portion 22. Is also formed as a thin portion 23 having a small thickness. The light guide 21 is firmly and stably supported in the lamp body 11 by screws or the like that do not appear in the drawing at the support pieces 24 provided at a plurality of positions on the peripheral edge of the thin-walled portion 23, here, at the four corner positions. . The light guide 21 has a horizontal cross-sectional shape that is gently curved along the curved shape of the front cover 12, but the vertical cross-sectional shape protrudes forward of the lamp. It is made into the shape bent in the shape of "<" in the center of each. That is, the light guide 21 is shaped such that a ridge line extending in the horizontal direction protruding forward is formed substantially at the center of the front surface in the vertical direction of the thick portion 22.

  The thin-walled portion 23 has a total of six edges, ie, two edge portions facing each other in the vertical direction and four edge portions facing each other in the left and right directions, in this case. In the edge portion, LED support portions 25 having a shape in which the edge portion of the thin portion 23 is bent and raised in the plate thickness direction are formed, and a plurality of red T-LED elements are respectively formed on the inner surfaces of these LED support portions 25. 26 is supported. Each T-LED element 26 is arranged in a line along an imaginary line having a substantially equal interval along the end surface 22i of the thick portion 22, and the light emitting surface is substantially perpendicular to the end surface 22i. The light guide 21 is directed in a direction bent in a “<” shape, and is supported so as to emit light along this direction. A band-shaped condensing lens body 27 having a lens-shaped cross section is integrally fixed to a position of the thin portion 23 facing the light emitting surface of each T-LED element 26. The T-LED element 26 and the condenser lens body 27 are not exposed to the front of the lamp by the extension 5.

  The configuration of the light guide 21 will be described in detail with reference to FIG. This figure is an enlarged sectional view of the light guide unit in the vertical direction. A step portion due to a difference in thickness from the thin portion 23 is formed at the periphery of the thick portion 22 of the light guide 21, and an end surface 22 i of the thick portion 22 in the step portion is configured as a light incident surface. Yes. Among the light incident surfaces 22i, the light incident surfaces 22i arranged above and below are directed substantially parallel to the ridge line extending in the horizontal direction of the light guide surface portion 22 formed in a "<" shape. The T-LED element 26 supported on the inner surface of the LED support portion 25 is configured to be supplied with power via a wiring that does not appear in the drawing, and the light emitting surface of each T-LED element 26 has the light collecting surface. The light incident surface 22 i is disposed opposite to the light lens body 27. The condensing lens 27 is formed in an elongated plate shape along the light incident surface 22 i of the thick portion 22 and is integrated with the inner surface of the thin portion 23 by adhesion or the like, and faces the light emitting surface of the T-LED element 26. The portion to be formed is formed into a spherical shape, and the red light emitted from each T-LED element 26 is condensed into a substantially parallel light beam by the condenser lens body 27 and is incident on the thick portion 22 from the light incident surface 22i. Light is guided through the thick portion 22.

  The thick wall portion 22 is configured as a light guide surface portion in the present invention, and is configured by combining a plurality of light guide surface portions inclined at a required angle in a direction perpendicular to the lamp optical axis Lx. That is, in the first embodiment, as described above, the substantially upper half of the thick portion 22 is inclined forward and downward from the upper edge portion toward the central portion, and light incident from the upper T-LED element 26 is inclined. It is comprised as a light guide surface part which guides light along a direction. Further, the substantially lower half of the thick portion 22 is inclined forward and upward from the lower edge portion toward the central portion, and is guided to guide the light incident from the lower T-LED element 26 along the inclined direction. It is configured as an optical surface portion, and these are integrated to form a “<” shape. That is, it has a configuration in which two light guide surface portions that guide light at different inclination angles toward the front of the lamp are combined. Further, the rear surface of the thick portion 22 of the light guide 21, in other words, the rear surfaces of the plurality of light guide surface portions 22, have a required pattern shape as viewed from the front of the lamp, here a shape close to a horizontally long ellipse. A reflective surface portion 28 having a triple loop pattern shape in which three loop patterns are concentrically arranged is formed. The reflection surface portion 28 is formed so that the rear surface of the light guide surface portion 22 has a step shape (stepped shape) with a substantially linear cross section. Angle of the reflective surface portion 28 so that the light is reflected toward the front of the lamp when projected onto the reflective surface portion 28, that is, an angle with respect to the light guide axis that is the traveling direction of light guided through the light guide surface portion 22 Is designed at an angle θa. Here, since the inclination angles of the upper and lower light guide surface portions 22 are symmetric with respect to the lamp optical axis Lx, the surface angles θa of the respective reflection surface portions 28 are designed to be equal to each other. In the first embodiment, the reflecting surface portion 28 has a large number of microspherical steps that do not appear in the figure but protrude slightly spherically toward the rear, and the light reflected by the reflecting surface portion 28 has a slight amount of light. Light is collected at an angle, and then diffused and directed to the front of the lamp to obtain a required irradiation angle.

  The turn signal lamp unit 4 has an elongated curved TS-body 41 integrally including a TS (turn signal) -reflector 42 that has a parabolic shape in cross section in the vertical direction and extends in the horizontal direction. A plurality of amber-colored TS-LED elements 44 are mounted on the TS-body 41 located immediately below the reflecting surface of the TS-reflector 42. The TS-body 41 is inserted and arranged in a window portion 52 provided in a lower region of the extension 5. Further, on the front side of the TS-body 41, there is a transparent TS-clear lens 43 that is disposed horizontally horizontally along the front edge of the extension 5 and has a required lens step formed on the rear surface. It is arranged. The TS-LED element 44 is supplied with power through the TS-body 41, and emits light in a blinking state when a direction instruction operation of the automobile is performed. When each TS-LED element 44 emits light, the amber color light emitted is reflected by the TS-reflector 42 and condensed in a state close to a parallel light flux, and when it passes through the TS-clear lens 43, a required distribution is obtained by a lens step. The light pattern is transmitted through the front cover 12 and emitted to the rear of the automobile.

  In the tail combination lamp TCL having the above-described configuration, the T-LED element 26 of the tail lamp unit 2 emits light when the tail lamp is turned on as a tail lamp during night driving. The red light emitted from each T-LED element 26 is condensed by the condensing lens body 27, and the end surface of the thick portion 22 of the light guide 21, that is, the incident surface 22 i to the thick portion 22, that is, the light guide surface portion 22. And is guided through the light guide surface portion 22. At this time, light from the T-LED elements 26 disposed on the left and right sides of the light guide 21 is guided in the horizontal direction through the light guide surface portion 22, and the T-LED elements 26 disposed above and below the light guide 21. The light from is guided in the light guide surface portion 22 in the vertical direction. In particular, in the vertical direction, the light guide surface portion 22 is bent in a “<” shape, so that the light from the upper T-LED element 26 is guided obliquely downward with the light guide surface portion 22 facing forward. Then, the light from the lower T-LED element 26 is guided in an obliquely upward direction with the light guide surface portion 22 facing forward. A part of the light guided through the light guide surface portion 22 is reflected toward the front of the light guide 21 at the reflection surface portion 28 and directed in the direction along the lamp optical axis Lx. And it is radiate | emitted from the front surface of the light guide surface part 22 toward the front, and also permeate | transmits the front cover 12, and is radiate | emitted from the tail combination lamp TCL.

  Therefore, when the light emission state is viewed from the front of the tail combination lamp TCL when the tail lamp unit 2 is turned on, the light guide 21 emits red light at a high intensity on the reflecting surface portion 28, and the other areas of the light guide 21 hardly emit light. Or it becomes the appearance which emitted light at low luminous intensity which is slightly reddish. In the first embodiment, since the reflecting surface portion 28 is formed in a triple loop pattern, when illuminated, it has an appearance of emitting light in a red loop pattern arranged in a triple as shown in FIG. Therefore, in the case of the tail combination lamp TCL as a whole, a triple loop pattern with a high luminous intensity in the middle of the opening 51 in the central region of the extension 5 covering the peripheral edge of the lamp housing 1 floated in the air. The appearance of emitting light in such a state is obtained, and the design effect when the tail lamp is turned on is enhanced.

  Here, regarding the reflection state of the light guided by the reflection surface portion 28 of the light guide 21, the light emitted from the left and right T-LED elements 26 and guided through the light guide surface portion 22 in the horizontal direction is as follows. Although it is reflected in the horizontal direction at the reflecting surface portion 28, it is reflected in a state of being diffused at a slight angle in the horizontal direction by the microspherical step of the reflecting surface portion 28, so that the irradiation angle in the horizontal direction required for the tail lamp can be satisfied. . Further, the light emitted from the upper and lower T-LED elements 26 and guided in the vertical direction through the light guide surface portion 22 is reflected in the reflective surface portion 28 in the direction along the lamp optical axis Lx. At the same time, in the minute spherical step of the reflecting surface portion 28, the light is diffused and reflected at a slight angle in the vertical direction, so that the vertical irradiation angle required for the tail lamp can be satisfied. Further, regarding the reflection in the vertical direction on the reflecting surface portion 28, each reflecting surface portion 28 uses the light incident from the upper and lower T-LED elements 26 and guided through the light guiding surface portion 22 to the lamp optical axis Lx. The angle is such that the light is reflected in the direction along the direction. However, in the first embodiment, the light guide surface portion 22 is configured to have a “<” shape that protrudes forward. In the half, the light guide direction is directed forward and downward, and the surface angle θa of the reflecting surface portion 28 with respect to the light guide axis is a small angle. Similarly, in the lower half of the light guide surface portion 22, the light guide direction is directed forward and upward, so the surface angle θa of the reflection surface portion 28 with respect to the light guide axis is also the same angle and a small angle. Thus, the light reflection angle when the light is emitted from the upper and lower T-LED elements 26 and guided through the light guide surface portion 22 and reflected in the direction along the lamp optical axis Lx by the reflection surface portion 28 is less than the critical angle. Reflection efficiency is improved. That is, compared with the conventional light guide 21A shown in FIG. 5B, the light reflection efficiency at the reflecting surface portion 28 is increased, and the light utilization efficiency of the entire lamp is increased. In addition, this makes the reflection efficiency at the reflection surface portion in the entire region of the light guide 21 including the upper region and the lower region in the light guide surface portion 22 uniform, and the light emission state with uniform brightness in the entire region. Become.

  In the tail combination lamp TCL of the first embodiment, the S-LED element 34 of the stop lamp unit 3 emits light when the vehicle is braked. The red light emitted from each S-LED element 34 is reflected by the S-reflector 32 in a condensed state forward along the lamp optical axis Lx, passes through the S-clear lens 33, and forms a required light distribution pattern. Next, the light passes through the light guide 21 of the tail lamp unit 2 and is further emitted to the front of the lamp through the front cover 12. As a result, the entire surface of the S-clear lens 33 emits red light, and this light emission is superimposed on the light emission of the triple loop pattern in the light guide 21 of the tail lamp unit 2. The whole light intensity increases and functions as a stop lamp.

  In the tail combination lamp TCL of the first embodiment, the TS-LED element 44 of the turn signal lamp unit 4 emits light when the direction of the automobile is changed. The amber light emitted from each TS-LED element 44 is reflected by the TS-reflector 42 in a condensed state forward along the lamp optical axis Lx, passes through the TS-clear lens 43, and forms a required light distribution pattern. Further, the light is emitted through the front cover 12 to the front of the lamp. As a result, the entire surface of the TS-clear lens 43 emits light in amber color and functions as a turn signal lamp.

  In the first embodiment, the light guide is formed in a “<” shape in the vertical cross section, but the horizontal cross section may be similarly bent in a “<” shape. In particular, in a lamp having a so-called wraparound portion in which a part of the lamp is extended to the side surface portion of the automobile and the horizontal cross-sectional shape is close to an “L” shape, the light guide is configured to extend to the wraparound portion. In this case, by forming the thick portion of the light guide in a “<” shape in the horizontal direction, the reflection efficiency at the reflection surface portions in the left and right regions of the light guide is the same as described in the vertical direction in the first embodiment. Can be increased.

The light guide according to the present invention has a vertical cross-sectional shape formed in a “<” shape, and light emitted from each LED element and guided through the light guide surface portion of the light guide is forward of the lamp. since configured to light guide at the angle inclined toward the can design a small surface angle of the reflecting surface, the light guide is to be able to satisfy the critical angle when reflected by the reflecting surface portion Become. Therefore, it is not limited to the cross-sectional shape in the vertical direction, and the light guide is arranged around the light guide by combining a plurality of face portions inclined in all directions of the lamp optical axis to form a part of the polyhedron. The light incident from the plurality of LED elements can be reflected with high efficiency toward the optical axis direction of the lamp at the reflection surface portion.

  The present invention is not limited to the tail lamp of the first embodiment, and can be similarly applied as long as it uses a light guide. In addition, the present invention is not necessarily configured as a light guide unit in which LED elements are arranged around the entire circumference of the light guide, but at least LED elements or light sources arranged on opposite sides across the light guide are arranged. The present invention can be similarly applied as long as it is configured as a light body unit.

1 is a front view of a tail combination lamp of Example 1. FIG. FIG. 2 is a vertical sectional view taken along line II-II in FIG. 1. FIG. 3 is a horizontal sectional view taken along line III-III in FIG. 1. 1 is a schematic exploded perspective view of Example 1. FIG. It is vertical sectional drawing which compares the light guide body of Example 1 and a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lamp housing 2 Tail lamp unit 3 Stop lamp unit 4 Turn signal lamp unit 11 Lamp body 12 Front cover 21 Light guide 22 Thick part (light guide surface part)
23 Thin portion 25 LED support portion 26 T-LED element 27 Condensing lens 28 Reflective surface portion TCL Tail combination lamp

Claims (1)

A light guide that is formed in a plate shape, guides the light incident from the light incident surface to the inside, and reflects and emits the guided light toward the front of the lamp on the reflection surface portion; and A light guide unit including a light source that causes light to be incident on different light incident surfaces, wherein the light guide body directs the light incident from each of the incident surfaces toward the front of the lamp to the optical axis of the lamp. A plurality of light guide surface portions that guide light at different angles inclined with respect to each other, and a vertical cross-sectional shape so that each light guide surface portion of different light incident surfaces arranged vertically opposite to each other protrudes toward the front of the lamp Is formed in a substantially “<” shape, and the light guide body is composed of a thin portion in a peripheral region and a thick portion in a region surrounded by the thin portion, and the thick portion is used as a light guide surface portion. And the end surface of the stepped part between the thick part and thin part is light. Is configured as a reflecting surface, is fixed supports lightguide the lamp at the periphery of the thin portion, the light source light incident on the light guide is bent to a "V" shape of the light guide body A lamp characterized by being directed in a direction inclined with respect to a lamp optical axis .

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