EP2404289B1 - Lighting device having a main body made of transparent material - Google Patents

Description

The invention relates to a lighting device according to the features of the preamble of patent claim 1 and a method for producing such a lighting device.

In such lighting devices, the body has the shape of a letter or other symbol or logo to be displayed in a luminous manner.

Such lighting devices are known for example from the document WO03 / 075249 A1 , The example in the FIGS. 1 to 9 this document provided with the reference numeral 2 basic body consists of an angled sheet metal. It is closed by a light-conducting cover element 3, in particular made of acrylic glass. The light-emitting diodes are glued by means of a two-sided adhesive tape on one of the two parallel sections of the U-shaped sheet metal body near the transverse leg. The distribution of the light over the entire light exit surface of the U-shaped body should be done by reflections on the bands formed by the sheets. In FIG. 8 a measure is shown, which should improve the illumination of the entire area. An angle is adhered to the lower surface of the leg between the two mutually parallel portions of the U-shaped main body; to allow the reflection of the light rays of the light-emitting diodes on the entire area of the light-transmitting light-emitting surface. The embodiments in FIGS. 26 and 27 of the drawings alternatively disclose a U-shaped sheet-metal housing open towards the wall as a basic body, which only allows the light to exit towards the wall. Furthermore, a Embodiment disclosed in which both the visible front surface and the wall-side rear surface is used as a light exit surface.

In all cases, the main body must have a significant height relative to its width to ensure that the reflection of the light rays on the walls of the U-shaped sheet metal housing results in a complete illumination of the entire light exit surface.

The publication US 2002/0153257 A1 describes a lighting device with a housing which comprises a bottom and side walls, as well as with a lid. A strip of electrical conductors, on which light-emitting diodes are arranged, is applied to the outer side wall of the housing. Again, it is problematic to achieve a homogeneous illumination of the visible surface. The publication DE 299 12 986 U1 describes a character-like highlighter with a light-equipped, light-conducting body made of plastic, in particular in the form of a plate. The photoconductive plate has in its lateral edge region a narrow channel in which light-emitting diodes are arranged. Alternatively, a narrow channel is mounted in the middle of the plate, where back-to-back light emitting diodes are arranged in each case in the outer regions of the plate.

The object of the invention is to provide an easily manufacturable lighting device with excellent lighting properties, the body can be made very compact. Furthermore, the object of the invention to provide a method for producing such a lighting device.

This object is achieved by the totality of the features of claim 1.

In the body of translucent material, in particular acrylic glass, a cavity open on one side is milled back, wherein the Width and length of the cavity is slightly smaller than the width and length of the base body, so that at least one along the periphery of the body extending, closed edge web runs in the rear region of the body, wherein the adhesive strip with the light-emitting diodes over the entire length of the edge web the inside of which is applied, that light-emitting diodes are arranged on the mutually facing inner sides of opposing edge land sections and illuminate the massive light-conducting body in front of the cavity, wherein the cavity is closed by a lid.

There are luminous letters known that consist entirely of PMMA, also called acrylic glass. Here holes or slots are cut into the acrylic glass body. In these slots or holes elongated LEDs are inserted. Subsequently, the cavity in the slot or hole is potted with hardening plastic, so that the diode is firmly enclosed in the body of translucent material. The main disadvantage of this embodiment is that in case of failure of a diode, the entire lighting device must be replaced. An expansion and replacement of the potted LEDs of the lighting device are not possible.

In contrast, the present invention proposes, in the case of a base body made of light-transmitting material, such as acrylic glass, to mill a cavity on the back side. The contour of the cavity corresponds to the contour of the lighting device (eg the shape of a letter), the width and length of the cavity being slightly smaller than the width and length of the base body. In this way, creates a circumferential closed edge web, preferably with a width of a few millimeters. When the body surrounds an open section (such as the letter "B ° or the number" 8 "), several circumferential closed edge webs are created when the cavity is attached.

The main body may in particular consist of milky translucent material. The acrylic glass may in practice have a light transmission in the range of 40 to 80%. Optimal results were achieved in the range of 60%. The milky cloudy coloring of the acrylic glass causes a diffuse light distribution over the entire cross section of the lighting device. If a bright but spot-like illumination of the front side of the lighting device is desired, the base body can be made transparent and possibly only have a diffusely transparent cover layer.

The edge bar provides an optimal surface for attaching the adhesive strip with the LEDs. There are ready self-adhesive strips with regularly mounted light-emitting diodes known in which the electrical conductors are integrated directly. The light emitting diodes are formed by surface mountable components, so-called SMD components. The distance between two consecutive light-emitting diodes, that is, the distance from the center of the LED to the center of the next LED, is usually in the range between 5 mm and 40 mm. By varying the distance, the desired luminance of the lighting device can be set exactly. The tapes supplied as rolls with several meters in length can be cut and contacted at predetermined locations between two light-emitting diodes. For this purpose, a connection cable can be soldered to the conductor tracks in the adhesive strip. The mounting of such light-emitting diodes on the inside of the opposite edges of the cavity of an acrylic glass body is very simple and fast. Furthermore, the adhesive tapes or at least portions of the adhesive tapes can be exchanged if individual light-emitting diodes are damaged.

The tapes can be provided with monochrome light emitting diodes that emit light in a specific wavelength. Furthermore, the adhesive tapes can be provided with white light LEDs. White light LEDs usually consist of three individual diodes, the light in deliver different colors. Consequently, it is also possible to use adhesive tapes with RGB light-emitting diodes, in which the individual diodes with the colors red, green or blue can be controlled individually and thus the color of the light emitted by the light-emitting diode can be varied.

A cover whose contour substantially corresponds to the surface of the lighting device or of the base body covers the cavity. At the same time, the cover provides privacy, so that the user can not look at the inside of the lighting device. The lid also protects the electronic components of the lighting device against contamination or mechanical stress. Finally, it can be achieved depending on the property of the lid that the illuminated letter glows backwards or that no light emerges on its rear side.

Since the light emitting diodes of edge bars on both sides of an elongated portion of the lighting device radiate into the cavity and are arranged relatively close to each other, the high luminance light is distributed uniformly over the entire surface of the lighting device. This is promoted in particular by the fact that the LEDs are arranged on the mutually facing inner sides of opposite sections of the edge web or the edge webs.

The front of the body, that is, the side facing away from the cavity on the back side, may be provided in practice with a translucent cover layer. Especially with colored illuminated letters, but also with white illuminated letters, a cover layer can be used which reflects the desired color very bright. The cover layer may additionally be polished in order to improve the visual impression of the illuminated letter. The cover layer can be easily glued to the remaining portion of the body. The top layer can be made of high quality acrylic glass, so that the production of the remaining body made of simple acrylic glass offers cost advantages.

The peripheral edge web may have a rear translucent portion. This causes light from the LEDs can escape through the edge bar on its back. In conjunction with an opaque lid, z. B. of metal, so creates a thin luminous strip in the region of the edge of the back of the lighting device. In combination with a transparent or diffusely translucent cover can be achieved that the entire back of the illuminated letter is translucent.

If the lid is made of opaque material, its cavity-facing side may have a light color. This leads to a reflection of the light rays impinging on the lid to the opposite side of the cavity, where they enter the base of acrylic glass and illuminate it.

As mentioned, the lid may be made of translucent material to promote the leakage of light to the back. The lighting device in the form of a letter can for example be mounted at a small distance from a wall. Back light causes a corona effect, that is, a ring of light surrounding the letter.

As mentioned, the luminance of the entire visible front side is very high in a massive light-conducting base body illuminated from the side edge web. With the lighting device according to the invention can be at a low height of the body in the order of 35 mm without unduly high heat generation homogeneous luminance in the order of 1,000 to 2,000 cd / m ² achieve. The luminance to be achieved can be perfectly controlled by the LED distance. Should lower luminance be required, the distance of the LED be increased without affecting the uniformity of the illumination. It also does not bother that additional elements, such as a thread for a fastening screw in the plastic material of the body are mounted in the region of the cavity. The cover may be fastened to the base body with a fastening screw which is screwed into a threaded bore in the base body. It can also be provided a plurality of fastening screws to secure the lid to the body.

The use of a translucent material such as acrylic glass as the main body of the lighting device has the disadvantageous property that the heat of the light emitting diodes is relatively poorly transported away. In order to avoid overheating in densely arranged light-emitting diodes or very powerful light-emitting diodes, a heat-conducting layer, preferably a metal layer, may be arranged on the inside of the edge web. On this metal layer of the adhesive strip is glued. The thermally conductive layer causes a distribution of the heat of the LEDs over at least the entire surface of the edge web. From here, the heat can either enter the material of the body or be discharged by convection or radiation into the cavity. The metal layer can be glued down to the support surface of the aluminum cover, so that a heat-dissipating connection between the aluminum lid of the lighting device and the LEDs is formed. The heat is conducted via the adhesive strips carrying the LEDs into the metal layer and through the metal layer into the cover, via the outside of which it is discharged into the ambient air.

The extending from the front to the back side wall of the lighting device may be provided with an opaque coating. As a rule, customers wish to emit light either only through the visible front side of a luminous letter or possibly through the back to generate a corona effect. The opaque Coating the side wall prevents unwanted light leakage through this side wall.

It is also possible to provide the visible from the front outside of the lighting device with an opaque coating. This gives a luminous letter that emits light only to the rear. This illuminated letter can be made very flat. Characterized in that the base body and the edge webs are made of translucent material, the production of an exclusively backlit lighting device which radiates over its entire back or even over the visible area of the edge web to the rear, with little effort and high luminance possible.

With a lit luminous letter, the distance between the back and the front of the illuminated lettering can be between 25 and 40 mm to ensure sufficiently high illumination. In the back-emissive embodiment, where the front is opaque coated, the height of the illuminated letter can be reduced to 20 mm. Nevertheless, a satisfactory light distribution is achieved.

The opaque coating may consist of a light-tight lacquer which is applied in several layers. Preferably, white is first painted in order to achieve the highest possible reflection in the main body of the illuminated letter. Thereafter, a black layer is painted, which has an absolute opacity to prevent light from shining through. Finally, the desired exterior color is applied.

In particular, in broad lighting devices, so in letters, numbers or symbols with a large distance between the opposing edge webs can be arranged in the middle of the cavity, a central web of translucent material, in particular acrylic glass, the protrudes from the main body and extends substantially parallel to the edge web. In practice, this center bar can have a diffusely reflecting surface. This central web can be generated when milling the cavity. By milling, it receives a milky-rough surface, which reflects light partially diffuse and partially lets through. The penetrating light component ensures that no darkening of the front side of the lighting device occurs in the region of the central web itself. The diffusely reflected light component increases the illumination of the lighting device in the central region of the cavity and thus counteracts a darkening of the front side from the edge toward the middle. In other words, the surface of the central web lights up brightly due to its diffuse-reflecting properties and forms a second light source whose light rays penetrate into the main body and penetrate to the front side thereof. In this way, it is ensured even with wide lighting devices that forms no dark area in the middle between the edge webs. In practice, the center bar can reach as far as the lid, which covers the cavity.

Finally, the invention relates to a method for producing a lighting device with a base body, in which a flexible adhesive strip with mutually spaced light-emitting diodes and integrated conductor tracks are arranged.

This method is inventively created by the entirety of the features of claim 15.

• Fig. 1 zeigt eine Draufsicht auf vier erfindungsgemäße Leuchtvorrichtungen.
• Fig. 2 zeigt die Rückansicht der Grundkörper der Leuchtvorrichtungen aus Fig. 1.
• Fig. 3 zeigt die Deckel der vier Leuchtvorrichtungen aus den Fig. 1 und 2.
• Fig. 4 zeigt eine Draufsicht auf einen Klebestreifen mit Leuchtdioden für die Leuchtvorrichtungen aus den Fig. 1 bis 3.
• Fig. 5 zeigt eine Seitenansicht des Klebestreifens aus Fig. 4.
• Fig. 6 zeigt eine Querschnittsansicht einer ersten Ausführungsform einer Leuchtvorrichtung.
• Fig. 7 zeigt eine Querschnittsansicht einer zweiten Ausführungsform einer erfindungsgemäßen Leuchtvorrichtung.
• Fig. 8 zeigt eine Querschnittsansicht einer weiteren Ausführungsform mit Mittelsteg.

Embodiments of the invention will be described below with reference to the accompanying drawings.

• Fig. 1 shows a plan view of four lighting devices according to the invention.
• Fig. 2 shows the rear view of the main body of the lighting devices Fig. 1 ,
• Fig. 3 shows the lid of the four light devices from the Fig. 1 and 2 ,
• Fig. 4 shows a plan view of an adhesive strip with light emitting diodes for the lighting devices of the Fig. 1 to 3 ,
• Fig. 5 shows a side view of the adhesive strip Fig. 4 ,
• Fig. 6 shows a cross-sectional view of a first embodiment of a lighting device.
• Fig. 7 shows a cross-sectional view of a second embodiment of a lighting device according to the invention.
• Fig. 8 shows a cross-sectional view of another embodiment with a central web.

The Fig. 1 to 3 show four light emitting devices whose basic body 1, 2, 3 and 4, respectively, have the shape of the letters "B", "A", "L" and "L".

Each basic body 1-4 consists of a translucent plastic, in particular acrylic glass. In the Fig. 2 the rear views of the body 1 - 4 are shown. It can be seen that the rear sides of the base bodies 1-4 are milled over the largest area of their surface in such a way that a thin edge web remains in each case at the edges. In the case of a simple letter such as the letter "L", the milled cavity on the rear side of the base body 3 or 4 leads to an edge web 10 or 11 which runs closed at its outer periphery. The thickness of the edge web depends on the size of the letters. A typical letter may have a height of the order of 200 mm and a width of between 100 mm and 200 mm. The thickness of the base body can be, for example, between 20 mm and 35 mm. The The width of the body naturally depends on the contour of the letter and is typically between 20 mm and 60 mm.

More complex letters, such as the letter "A", lead to several edge bars. The main body 2 of the letter "A" has a peripheral outer edge web 8 and a circumferential inner edge web 9. In the letter "B", the main body 1 has a peripheral outer edge web 5 and two peripheral inner edge webs 6 and 7.

In the Fig. 2 It can also be seen that on each peripheral edge web 5 - 11 adhesive strips 13 ( 4 and 5 ), which light-emitting diodes 12 carry. The LEDs 12 are in the 4 and 5 better to recognize. These are surface-mounted components, also known as "surface mounted devices" (SMD) in English. The SMD components are mounted on flexible strips, in which the interconnects are integrated, which conduct electricity to the LEDs 12.

The 4 and 5 show the adhesive strip 13, with which the light emitting diodes 12 on the inside of the edge webs 5 - 11 of the base body 1 - 4 are attached. The adhesive strips have a width of, for example, 10 mm. The distance between two light-emitting diodes 12 to each other is typically between 20 mm and 40 mm. Between two light emitting diodes 12, the adhesive strips 13 can be cut at appropriate locations. In the 4 and 5 are more electronic components between the light emitting diodes 12 can be seen. These can serve the color control of the LED. Further, at one end of the adhesive strip 13, a connection cable 14 for the power supply can be seen.

The LED 12 can be monochromatic LED in any color. It is also possible to use existing SMD light-emitting diodes each consisting of three individually controllable individual diodes with different color components (eg red, green and blue), which can be set to any desired color by suitable control electronics.

The Fig. 3 shows the cover 15 to 18 of the lighting devices 1-4. The covers 15-18 have a plurality of screw holes 28 for receiving the heads of fastening screws 25 (FIG. 6 and 7 ) on. The fastening screws 25 are used to attach the cover 15-18 to the base bodies 1-4 and to secure the cover 15-18 to a support frame or support profile which carries the light-emitting devices into a single word and fixes them in a specific spatial position ,

The 6 and 7 show cross-sectional views through two embodiments of a lighting device according to the invention. In each case, a section through the main body 3. The main body 3 consists essentially, that is, more than half its height between the front and back of a solid translucent acrylic glass section 19. On the front of the translucent acrylic glass section 19, another translucent acrylic glass section glued, which has the color of the letter imaged by the light emitting device and a colored, translucent cover layer 20 of the base body 3 forms. The substantially translucent, massive acrylic glass section 19 of the main body before the back cutout serves to conduct and distribute the light of the light emitting diodes 12. The front, about 3 mm thick cover layer 20 of colored acrylic glass forms the visible surface from the outside, which is as bright and uniform in the desired color lights.

The side walls of the base body 3 are each provided with an opaque coating 21, e.g. a paint layer or paint layer provided. This can be, for example, white or aluminum colors and reliably prevents unwanted leakage of light from the side walls.

It can be seen that the cavity 24 substantially in the rear region of the translucent portion 19 of the main body. 3 is milled. The depth of the cut must correspond at least to the width of the adhesive strip 13, which is for example about 10 mm. Consequently, the edge web 10 is preferably 10 to 15 mm high. The remaining in front of the edge web 10 translucent portion 19, that is, the massive part of the base body 3 extends at least over the height of the edge web and thus at least over half the height of the base body 3. In the embodiment of the Fig. 6 the adhesive strip 13 is glued directly to the inner surface of the peripheral edge web 10 of the base body 3. In the embodiment in FIG Fig. 7 is first glued to the edge web 10 of the base body 3, a thin metal sheet, which forms a heat-conductive layer 22. The adhesive strip 13 is glued to this metal sheet 22. The metal sheet 22 distributes the waste heat of the light emitting diodes 12 uniformly over the entire surface of the peripheral edge web 10. In this way, local overheating of the peripheral edge web 10 can be avoided and a good heat dissipation of the waste heat of the light emitting diodes 12 can be ensured.

In the embodiment in Fig. 7 extends the translucent portion 19 of the body 3 to the back of the body 3. This causes light from the light emitting diodes 12 from the rear edge web 10 radiates backwards. This can be a very desirable effect. The light radiating backwards forms a corona around the illuminated letter.

But there are also cases in which a radiation of light to the rear is not desired. In this case, as in the Fig. 6 shown, the rear portion 23 of the edge web 10 formed of an opaque plastic.

This opaque portion 23 in conjunction with the opaque painted side surface prevents the leakage of light from the LEDs 12 to the entire lighting device, with the exception of their front visible from the front. The opaque portion 23 becomes preferably applied to the back of the translucent portion 19 prior to milling the cavity 24.

The rear side of the lighting device is closed by the cover 17. The lid 17 may be made of aluminum, for example. It is preferably provided on the inside with a light, in particular white or metallic color. The light of the LEDs 12 is thus reflected by the cavity 24 side facing and thrown in the direction of the front of the lighting device. However, the lid 17 may also be made of colored or white translucent material (e.g., acrylic glass) if light is desired to exit from the back of the illuminated letter.

The lid 17 is fixed by means of fastening screws 25 to the base body 3. The fastening screws 25 are screwed into threaded bores 27 within the main body 3. The light-conducting property of the base body 3 prevents the fastening screws 25 from casting shadows on the front side of the main body 3. Between the peripheral edge web 10 and the cover 17, a seal 26, for example made of silicone, is arranged. The seal avoids the ingress of contaminants into the cavity 24 and can avoid the escape of light through the gap between the cover 17 and edge web 10 when choosing an opaque sealing material.

It is also possible to provide a lighting device that emits only to the rear. In this case, the front colored translucent cover layer 20 may be omitted. Instead, the front of the illuminated lettering may be provided with an opaque paint. In this case, of course, the rear portion of the edge webs is translucent. The height of such a trained luminous letter can be further reduced. Essentially, the main body only forms a housing for the light-emitting diodes. This lighting device may have a height from the back to the front in the order of 20 mm.

The Fig. 8 shows an embodiment of the lighting device with a central web 29. Otherwise, the embodiment is substantially identical to the embodiment Fig. 6 match. Only the position of the fastening screw 25 is offset to the left so that it does not extend through the central web 29.

The central web 29 is generated during milling of the cavity 24. The diameter of the milling cutter corresponds to the distance between the opposing surfaces of central web 29 and one of the edge webs 10. The cutting of the milling cutter on the central web 29 on both sides of a partially translucent and diffuse-reflecting structure. On the one hand, this surface structure allows the light to penetrate from the laterally arranged light-emitting diodes 12 and, on the other hand, throws this light back diffusely. This ensures that the illumination of the translucent acrylic glass section 19 and thus the brightness visible on the front does not decrease, especially in its middle region. With translucent acrylic glass sections 19 having a large width, that is, when the opposite inner sides of the edge webs 10 have a large distance from each other, there is a risk that the luminosity of the attached to the edge webs 10 diodes 12 is not sufficient to sufficiently illuminate the central region. Since the surface of the central web 29 diffusely reflects the light of the light emitting diodes 12, a further light source, which in particular ensures the illumination of the central region, is formed in the center of the translucent acrylic glass section 19 by the central web 29. The central web 29 protrudes in the illustrated embodiment to the cover 17, which covers the cavity 24.

LIST OF REFERENCE NUMBERS

1

Basic body of the letter "B"

2

Basic body of the letter "A"

3

Basic body of the letter "L"

4

Basic body of the letter "L"

5

edge web

6

edge web

7

edge web

8th

edge web

9

edge web

10

edge web

11

edge web

12

led

13

tape

14

connection cable

15

cover

16

cover

17

cover

18

cover

19

translucent acrylic glass section

20

colored translucent cover layer

21

opaque coating

22

Sheet metal, heat-conducting layer

23

opaque section

24

cavity

25

fixing screw

26

poetry

27

threaded hole

28

screw

29

center web

Claims (15)

1. A lighting device having a base body (1-4) of translucent material in which several light-emitting diodes (12), which are applied to a flexible adhesive strip (13) having integrated conductors, are arranged at intervals from one another, characterized in that

   - a cavity (24) which is open at one side is milled into the rear of the base body (1-4), the width and length of the cavity (24) being slightly smaller than the width and length of the base body (1-4), so that at least one closed edge web (5-11) running along the periphery of the base body (1-4) runs in the rear area of the base body (1-4),

   - the adhesive strip (13) having the light-emitting diodes (12) is applied to the interior side of the edge web (5-11) over the entire length in such a way that light-emitting diodes (12) are arranged on interior sides of opposing edge web sections that face one another,

   - the solid light-conducting section (19) of the base body (1-4) in front of the cavity (14) is illuminated by the light-emitting diodes (12) on the lateral edge web (5-11), resulting in a high luminous density on the visible front side, and

   - the cavity (24) on the rear side of the lighting device is closed by the cover (15-18).
2. The lighting device as recited in Claim 1, characterized in that the distance between the rear side and the front side of the lighting device is up to 40 mm.
3. The lighting device as recited in Claim 1 or 2, characterized in that the base body (10) has a colored translucent cover layer (20) on the front side opposite the cavity (24).
4. The lighting device as recited in one of the preceding claims, characterized in that the edge web (5-11) has an opaque section (23) on the rear.
5. The lighting device as recited in one of the preceding claims, characterized in that the cover (15-18) is made of an opaque material.
6. The lighting device as recited in Claim 5, characterized in that the side of the cover (15-18) facing the cavity (24) has a color which reflects the light of the light-emitting diodes (12) and reflects it in the direction of the front side of the lighting device.
7. The lighting device as recited in Claim 1 or 2, characterized in that the cover (15-18) is made of translucent material.
8. The lighting device as recited in one of the preceding claims, characterized in that the cover (17) is attached to the base body (3) by a fastening screw (25), and the base body (3) has a threaded borehole (27) into which the fastening screw (25) is screwed.
9. The lighting device according to any one of the preceding claims, characterized in that a heat-conducting layer (22) to which the flexible adhesive strip (13) is glued is arranged on the interior side of the edge web (10).
10. The lighting device as recited in one of the preceding claims, characterized in that a side wall extending from the front side to the rear side is provided with an opaque coating (21).
11. The lighting device as recited in one of the preceding claims, characterized in that the distance between two light-emitting diodes (12) is in the range between 5 mm and 40 mm.
12. The lighting device as recited in one of the preceding claims, characterized in that the base body (1-4) is made of cloudy translucent material.
13. The lighting device as recited in one of the preceding claims, characterized in that a central web (29) made of translucent material, in particular acrylic glass, is arranged at the center of the cavity, and protrudes out of the base body (3) and extends essentially parallel to the edge web.
14. The lighting device as recited in Claim 13, characterized in that the central web (29) has a diffusely reflective surface.
15. A method for manufacturing a lighting device having a base body (1-4) made of a translucent material in which a flexible adhesive strip (13) is arranged with light-emitting diodes (12) situated at intervals and with integrated conductors, characterized by the following steps:

    - a cavity (24) which is open at one side having at least one closed edge web (5-11) running along the periphery of the base body (1-4) is milled into the rear area of the base body, the width and length of the cavity (24) being slightly smaller than the width and length of the base body (1-4);

    - the adhesive strip (13) is glued to the interior side of the edge web (5-11) over the entire length in such a way that light-emitting diodes (12) are arranged on the interior sides of opposing edge web sections that face one another and illuminate the solid light-conducting base body (19) in front of the cavity;

    - the cavity (24) is closed on the rear side of the lighting device by a cover (15-18).

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