Patent Publication Number: US-2023160833-A1

Title: Luminaire element for an inspection tunnel, luminaire strip, and inspection tunnel

Description:
RELATED APPLICATION 
     This application is a national phase of International Application No. PCT/DE2020/100727, filed on Aug. 20, 2020, which claims the benefit of German Application No. 10 2020 110 722.6, filed on Apr. 20, 2020. The foregoing International Application and German Application are incorporated herein by reference in their entirety and for all purposes. 
    
    
     PRIOR ART 
     The invention relates to a luminaire element for an inspection tunnel, to a luminaire strip having an arrangement of luminaire elements, and to an inspection tunnel having an arrangement of a plurality of luminaire strips. 
     Such inspection tunnels are used in vehicle production to inspect, in particular, painted surfaces of motor vehicles. In order to illuminate the workstations, in particular checking stations, on the one hand conventional luminaire elements on a frame substructure are used, which are equipped with fluorescent tubes and are arranged in a different arrangement at angles around the substrate, here the vehicle body or the body parts. These luminaire elements emit diffusely and generate a reflection image on the substrate by a corresponding reflector geometry of the luminaire elements. The orientation of these reflection images, and therefore also of the luminaire elements, is tailored to the special task of looking for faults and is in this case, inter alia, subordinate to ergonomic considerations. With this arrangement of luminaire elements, only a part of the energy used is exploited because of the creation of diffuse light. An increased dazzling effect may also occur for the inspectors. 
     On the other hand, there is another more recent configuration which is based on indirect illumination by single or multiple reflection by means of aluminum slats, onto which light-emitting diodes shine. In this case, horizontally extending slats, which produce a more or less pronounced reflection image on the substrate, are installed along the entire length of the checking station. 
     With this arrangement of luminaire elements, horizontally extending reflection stripes require active searching for reflection lines in the side region of the bodies by the inspector. Large differences in the luminance reflections may lead to a locally differently pronounced reflection line image and to unstable overall perception. Such luminaire arrangements may also be very expensive. 
     DISCLOSURE OF THE INVENTION 
     It is an object of the invention to present a luminaire element for an inspection tunnel, in particular for inspecting painted vehicle bodies, having an improved luminance distribution. 
     It is a further object to provide a luminaire strip having an arrangement of luminaire elements, which has an improved luminance distribution. 
     It is a further object to provide an inspection tunnel having an arrangement of a plurality of luminaire strips, which have an improved luminance distribution. 
     The objects are achieved by the features of the independent claims. Favorable configurations and advantages of the invention may be found in the further claims, the description and the drawing. 
     According to one aspect of the invention, a luminaire element for an inspection tunnel, in particular for checking glossy surfaces, in particular painted surfaces, is proposed, comprising at least two preferably stripe-like arrangements of light sources in a luminaire housing having at least two edge regions lying opposite one another along a longitudinal extent of the luminaire housing. The stripe-like arrangements of the light sources are in this case formed along the longitudinal extent at the edge regions, and a light exit surface of the luminaire housing has a higher radiant intensity along the edge regions than in a central region. 
     Advantageously, the described luminaire structure may lead to an improved luminance distribution with the aid of a new arrangement of the light sources in the luminaire housing. 
     Instead of positioning the light sources centrally with respect to the light exit surfaces as previously, and therefore obtaining a luminance decreasing slowly with a shallow gradient from the center to the edge regions, the light sources are fitted on the two edge regions of the luminaire housing, where the transition from the luminaire housing directly to maximum luminance allows a steep gradient of the luminance. This can increase the likelihood of detecting faults on or in the substrate to be examined, for example a painted surface. In addition, with this arrangement of the light sources large-area zones with a low and relatively homogeneous luminance are also formed. These regions can favor unperturbed inspection, that is to say free of high contrasts, of the surface on extensive fault images such as clouds, haze, holograms, etc. with significantly improved potential for attention of the inspector. Errors during the inspection may therefore be reduced. 
     Advantageously, an advantageous luminance distribution may be achieved by on the one hand high contrasts at the transition of the luminaire housing to the light exit surface and unperturbed, optically uniform regions. 
     A high system efficiency may be achieved with the low-loss radiation principle. 
     According to one advantageous configuration of the luminaire element, the light exit surface of the luminaire housing may comprise at least a diffuser and a cover lens. According to another advantageous configuration of the luminaire element, a multiprism lens may furthermore be arranged between the diffuser and the cover lens. 
     The luminaire structure is based on the principle of backlighting, the light rays passing before leaving the luminaire element through a lens stack, which preferably consists of a diffuse lens, a multiprism lens and a protective cover lens. 
     The multiprism lens may in this case, in particular, be used for additional reduction of a possible dazzling effect for the inspector. 
     According to one advantageous configuration of the luminaire element, the light sources may comprise one or more light-emitting diodes and/or one or more fluorescent tubes and/or one or more light guides. 
     Light-emitting diodes (LEDs), for example mid-power LEDs having a luminous flux of from 20 to 200 lumens and a luminous efficiency of about 180 lumens/watt, may preferably be used as lighting means. Alternatively, however, other designs may also be used according to the fluorescent tube concept. Light-emitting diodes and fluorescent tubes are very energy-efficient and long-lasting lighting means, and can therefore keep the operating costs low. When using light guides, the lighting means may be arranged at a central location and for example supplied favorably with energy, and also cooled. 
     According to one advantageous configuration of the luminaire element, the light sources may be configured with variable color, in particular as light-emitting diodes (LEDs) having an adjustable color temperature. 
     Light sources having LEDs with a variable color temperature may optionally be used. In this way, for example, the light color may be matched to the hue of the substrate or to the preference of the inspector. The LEDs may be mounted on a luminaire insert consisting of, for example to increase the reflection, white-painted sheet steel or sheet aluminum or a plastic sheet, and cabled. The associated drivers of the LEDs may, for example, be mounted on the rear side of the luminaire insert. In the event of a defect of the drivers or the LEDs, the luminaire housing may be opened from the rear side in order to replace the luminaire insert together with the LEDs and drivers. Rear-side opening of the housing may, for example, be carried out by removing a cover, which is fastened for example by means of screws on the housing body. The fastening of the cover may also alternatively be carried out by means of locking levers or the like. The luminaire inserts may for example be screwed, clamped or otherwise fastened in the luminaire housing. 
     The color temperature of the light sources in a luminaire element may either be fixed or, for example, vary between 2700 K (warm-white) and 6500 K (cold-white). For example, a “zebra arrangement” is also possible, in which alternately cold-white and warm-white luminaire elements or other sequences are used. 
     The luminaire elements may be configured to be dimmable. The degree of dimming may, for example, be tailored to the hue of the substrate. The hue of the luminaire element may be matched to the hue of the substrate. 
     According to one advantageous configuration of the luminaire element, the luminaire housing may comprise end-side terminal regions transversely to the edge regions, which are configured to connect neighboring luminaire elements. This way, a plurality of luminaire elements may favorably be assembled to form a longer luminaire strip, in order to examine larger substrates. 
     According to one advantageous configuration of the luminaire element, the end-side terminal regions may be configured as standardized terminal elements for mechanical and/or electrical connection of neighboring luminaire elements. In this way, a plurality of luminaire elements may be assembled efficiently to form a longer luminaire strip, in order to examine larger substrates. 
     According to one advantageous configuration of the luminaire element, the luminaire housing may be configured curved in the shape of an arc, the light exit surface being oriented toward a concave inner side of the arc-shaped curvature. Curved luminaire elements may favorably be assembled to form a curved luminaire strip in order to inspect large objects, for example in an inspection tunnel. 
     According to one advantageous configuration of the luminaire element, the central region of the light exit surface may have a lower transparency than the edge region; in particular, the central region may be configured opaquely. 
     In this way, zones with a high contrast may be achieved at the edge region of the luminaire element, in particular for the perception of point faults. Differently bright zones of the light exit surface may improve the recognition of extensive faults, for example clouds, haze, etc., in a painted surface. 
     In order to be able to generate a plurality of light stripes in the reflection image with a luminaire element, an opaque stripe or a plurality of stripes may for example be applied internally, for example centrally, on the light exit surface. This stripe may then advantageously be configured to be highly reflective toward the light source space. Under certain circumstances, it may also be advantageous to separate the space between the LEDs and the lens stack, with the aim of providing regions having different light colors. For this purpose, for example, a separating wall may divide this space, for example centrally. This separating wall may then also be configured to be highly reflective. In this case, the two LED strips on the right and left of the separating wall may then be configured with different color temperatures. Without a separating wall, different hues may also be produced by means of color filters, which may be placed in the region of the lens stack. 
     According to one advantageous configuration of the luminaire element, the luminaire housing may be configured to be openable on the rear side, and the luminaire housing may in particular be configured with a maintenance opening on the rear side. In this way, defective light sources and/or driver stages may be replaced easily, without having to fully dismount the luminaire element. 
     According to one advantageous configuration of the luminaire element, the light sources may be arranged on a carrier element. The carrier element is in particular configured to be reflective toward the light exit surface. In this way, the contrast of the emerging light beam can advantageously be increased in order to increase the reflection on the substrate to be examined. Different color temperatures of the light sources may thus also favorably be produced in the luminaire element 
     According to one advantageous configuration of the luminaire element, the luminaire housing may be configured closed. Advantageously, the light sources may are arranged adhesively bonded on a carrier element. A further variant is that the luminaire housing is configured closed and designed as a “disposable lamp”. The luminaire insert with light sources and drivers may then, for example, be adhesively bonded in the luminaire housing. 
     According to a further aspect of the invention, a luminaire strip having an arrangement of luminaire elements is proposed, wherein the luminaire elements are connected to one another at their end-side terminal regions. In particular, the luminaire elements may in this case be arranged at least regionally on a line curved in the shape of an arc, the light exit surfaces of the luminaire elements being oriented toward a concave inner side of the arc-shaped curvature. 
     According to one advantageous configuration of the luminaire strip, end pieces may be formed by planar luminaire elements, between which curved luminaire elements are arranged. 
     The individual luminaire elements joined to form a luminaire strip, which may for example have an arc-like structure, may thus be screwed to one another on their end sides. For this purpose, for example, 6 bent luminaire elements, each with a length of 1420 mm, and 2 planar luminaire elements, each of 750 mm, may be used. Because the light exit surface approximately has the length of the luminaire housing, only minimal sections on which the light exit surface is interrupted are formed in the circumferential direction. With this virtually continuous light exit surface, a reflection image which is advantageous since it is almost uninterrupted may be formed on the substrate. 
     In order to combine individual luminaire elements having an individual length of for example 1400 mm to form a continuous luminaire strip, to avoid light-free regions these may be screwed together or plugged together on the head sides. 
     Here, for example, the energy supply and the control signals could, for example, be forwarded from one luminaire element to the next via the plug connection, in particular a standardized plug connection. 
     According to a further aspect of the invention, an inspection tunnel having a tunnel longitudinal axis is proposed, in particular for checking glossy, in particular painted vehicle bodies, having an arrangement of a plurality of luminaire strips. In this case, the luminaire strips are arranged next to one another transversely to the tunnel longitudinal axis, the light exit surfaces of the luminaire elements being oriented on a concave inner side of the arc-shaped curvature of a tunnel wall toward a central region of the tunnel longitudinal axis. 
     By the concentric arrangement of the luminaire elements, the light rays are directed substantially onto the substrate, that is to say for example a painted vehicle body. This on the one hand increases the luminous efficiency, and on the other hand reduces the direct dazzling of the inspectors. 
     The width of the individual luminaire strips may for example be 200 mm, and the free space between the light arcs may for example be 500 mm. in this way, both a sufficiently large number of contrast transitions is available, and sufficient visually “unperturbed” space, which is likewise needed for inspection of the overall substrate. 
     Advantageously, by the use of the described luminaire strips with the luminaire elements according to the invention in such an inspection tunnel, a vehicle body may be optically modulated out by the nature of the illumination. 
     The checking station may be able to be positively experienced by the inspector by virtue of the new type of illumination, which leads to better efficiency in the inspection of the substrate. 
     In this way, highly purposeful work tailored to the body is possible with a low fatigue effect. By a ratio devised in detail of the luminances of the inspection space to the environment, it is possible to achieve a low dazzling effect and therefore psychologically stable observation by the inspector. 
     Improved ergonomics due to a significantly reduced dazzling effect and reflection orientation may thus be implemented in such a way that no inconvenient (head) movements need to be performed when looking for faults. 
     More reliable inspection is made possible by virtue of an almost continuous reflection image on the body. 
     With the inspection tunnel according to the invention, application possibilities are offered in the field of fault checking, for example of large substrates such as bodies or even completed vehicles. Furthermore, these checking stations may also be used for other substrates, such as fenders, mirror casings, etc. in addition, favorable possibilities of use are also offered other than use for checking paint, by uniform lighting of further workstations. 
     According to one advantageous configuration of the inspection tunnel, the luminaire strips may be arranged spaced apart in a predetermined grid spacing. In this way, favorable reflection patterns may be established for purposeful inspections of particular fault patterns of substrates. Fault checking may thus also be achieved favorably over a wide range from locally limited fault patterns to large-area fault patterns. 
     According to one advantageous configuration of the inspection tunnel, luminaire elements of different luminaire strips may comprise light sources with a different color temperature, particularly in the range of between 2700 K and 6500 K. 
     The color temperature may be constant within a luminaire strip and a neighboring luminaire strip may have a different color temperature. In particular, in this case neighboring luminaire strips may have alternating sequences of high and low color temperatures. 
     The light color of the light sources in a luminaire strip may either be fixed or, for example, vary between 2700 K (warm-white) and 6500 K (cold-white). For example, a “zebra arrangement” is also possible, in which alternately cold-white and warm-white luminaire strips or other sequences are used. 
     The luminaire elements may be configured to be dimmable. The degree of dimming may, for example, also be tailored to the hue of the substrate and may also match the hue of the luminaire element to the hue of the substrate. 
     According to one advantageous configuration of the inspection tunnel, regions between the luminaire strips may comprise surfaces with predetermined, in particular different reflectances. In particular, the material of the surface may in this case have reflectances of between 20% and 70%, preferably between 27% and 55%, in relation to a wavelength range of visible light and with normal light incidence. 
     Each light stripe generates above-described bright/dark contrast regions on the substrate due to entry into and exit from the light stripes, at the transition of which the faults, for example paint inclusions, which appear as a pointwise deviation of a planar surface, can be recognized as a line deformation. 
     In order to be able to perceive a sufficient contrast on bright, for example white, surfaces as well, a minimum contrast ratio of 1:1.7 has been determined for an exemplary environmental luminance. The layout of a luminaire element may be carried out on this basis. In order to provide a psychologically stable environment (“stable observation”) under these conditions in the interfacial area of very bright and very dark substrates, the necessary reflectances of the materials which may be applied between the luminaire strips may be determined. 
     These reflectances may, for example, be between 27% and 55%, respectively in relation to a wavelength range of visible light and with normal light incidence. 
     It may also be advantageous to configure the space between the luminaire strips with matt panels, for example in the architectural colors according to Le Corbusier or other natural earth hues which impart a pleasant room ambience. The panels may for example be formed from textile, plastic, wood or sheet metal. A foil may be used as a coating with a hue. 
     According to one advantageous configuration of the inspection tunnel, at least one luminaire strip may be arranged extending parallel to the tunnel longitudinal axis, the light exit surfaces of the luminaire elements being aligned toward the tunnel longitudinal axis. 
     For the use of an inspection tunnel to be employed with large substrates, for example bodies, in addition to the luminaire strips extending transversely to the tunnel longitudinal axis, it may be advantageous also to use longitudinally extending luminaire strips of the same design. In this way, it is possible to generate further advantageous reflection patterns, or a contrast change on the substrate. 
     Especially for the inspection of, for example, hoods or trunk lids of a body, it may be advantageous to install longitudinally fitted luminaire strips since in that case a movement of the checker transversely to the body often takes place. With this natural movement of the checker transversely to the body, a bright/dark contrast change therefore takes place without additional head movement. 
     According to one advantageous configuration of the inspection tunnel, luminaire strips may be arranged in the floor in the tunnel longitudinal axis and/or transversely to the tunnel longitudinal axis. 
     If luminaire strips are used in the floor of the inspection tunnel, these may favorably be constructed in terms of luminance profile in a similar way to the luminaire strips fitted in the tunnel wall, and therefore join together to form a uniform reflection image on virtually all regions of the substrate, for example a body. 
    
    
     
       DRAWING 
       Further advantages may be found from the following description of the drawing. Exemplary embodiments of the invention are represented in the drawings. The drawings, the description and the claims contain numerous features in combination. The person skilled in the art will also expediently consider the features individually and combine them to form suitable further combinations. 
       By way of example: 
         FIG.  1    shows a plan view of a luminaire element according to one exemplary embodiment of the invention with section lines B-B and D-D indicated; 
         FIG.  2    shows a longitudinal section through the luminaire element in the section plane D-D according to  FIG.  1   ; 
         FIG.  3    shows an isometric representation of the luminaire element according to  FIG.  1   ; 
         FIG.  4    shows a schematic cross section through the luminaire element in the section plane B-B according to  FIG.  1   ; 
         FIG.  5    shows a schematic cross section through a luminaire element according to a further exemplary embodiment of the invention; 
         FIG.  6    shows a plan view of a bent luminaire element according to a further exemplary embodiment of the invention with a section line A-A indicated; 
         FIG.  7    shows a longitudinal section through the luminaire element according to  FIG.  6    in the section plane A-A; 
         FIG.  8    shows a cross section through an inspection tunnel according to one exemplary embodiment of the invention; 
         FIG.  9    shows a longitudinal section through the inspection tunnel according to  FIG.  8   ; 
         FIG.  10    shows a luminance profile transversely over two luminaire elements according to the invention; and 
         FIG.  11    shows color temperature arrangements of luminaire strips of an inspection tunnel according to one exemplary embodiment of the invention. 
     
    
    
     EMBODIMENTS OF THE INVENTION 
     In the figures, components which are the of the same type or have the same effect are numbered with the same references. The figures merely show examples and are not to be interpreted as restrictive. 
     In what follows, direction terminology with terms such as “left”, “right”, “up”, “down”, “before”, “behind”, “after” and the like is used only for better understanding of the figures and is in no case intended to constitute a restriction of generality. The components and elements represented, their layout and their use may vary in the sense of the considerations of a person skilled in the art and be adapted to the respective applications. 
       FIG.  1    shows a plan view of a luminaire element  10  according to one exemplary embodiment of the invention with section lines B-B and D-D indicated, while the luminaire element  10  in  FIG.  2    may be seen in longitudinal section in the section plane D-D and in  FIG.  3    in an isometric representation. In  FIG.  4   , a schematic cross section in the section plane B-B through the luminaire element  10  is in this regard represented. 
     The luminaire element  10  for an inspection tunnel  100  comprises two stripe-like arrangements  12  of light sources  13  in a luminaire housing  14 . The luminaire housing  14  comprises two edge regions  16  lying opposite one another along a longitudinal extent L of the luminaire housing  14 . The stripe-like arrangements  12  of the light sources  13  are formed along the longitudinal extent L at the edge regions  16 , as may be seen particularly in  FIG.  2    and  FIG.  4   . In this way, a light exit surface  20  of the luminaire housing  14  has a higher radiant intensity along the edge regions  16  than in a central region  30 . 
     The light sources  13  may comprise one or more light-emitting diodes and/or fluorescent tubes and/or light guides. The light sources  13  may in this case be configured with variable color, in particular as light-emitting diodes (LEDs) having an adjustable color temperature. 
     Light-emitting diodes (LEDs), for example mid-power LEDs having a luminous flux of from 20 to 100 lumens and a luminous efficiency of about 180 lumens/watt, may preferably be used as lighting means. Alternatively, however, other designs may also be used according to the fluorescent tube concept. 
     The light sources  13  are arranged for mechanical fastening on a carrier element  32 . The carrier element  32  may in particular be configured to be reflective toward the light exit surface  20  in order to increase the reflection contrasts. 
     The light exit surface  20  of the luminaire housing  14  is formed by a lens stack  22 , which comprises at least a diffuser  24  and a cover lens  28 . Preferably, a multiprism lens  26  may also be arranged between the diffuser  24  and the cover lens  28 , as may be seen in the exemplary embodiment in  FIG.  4   . 
     The luminaire structure is based on the principle of backlighting, the light rays passing, before leaving the luminaire element, through a lens stack  22 , which preferably consists of a diffuse lens  24 , a multiprism lens  26  and a protective cover lens  28 . The multiprism lens may in this case, in particular, be used for additional reduction of a possible dazzling effect for the inspector. 
     The central region  30  of the light exit surface  20  may advantageously have a lower transparency than the edge region  16 . In particular, the central region may be configured opaquely, for example by an opaque stripe, which may also be configured to be reflective toward the light source  13 , being applied onto the diffuser. 
     The luminaire housing  14  comprises end-side terminal regions  18  transversely to the edge regions  16 , which are configured to connect neighboring luminaire elements  10 ,  11 . The end-side terminal regions  18  may advantageously be configured as standardized terminal elements for mechanical and/or electrical connection of neighboring luminaire elements  10 ,  11 . 
     The luminaire housing  14  may be configured to be openable on the rear side, in particular provided with a maintenance opening  34 , as is indicated in  FIG.  2   . Replacement of light sources  13  and/or driver stages may therefore advantageously be carried out from the rear side of the luminaire housing  14 . 
     Alternatively, the luminaire housing  14  may also be configured closed. If replacement of the light sources  13  is therefore not provided, these may also be arranged adhesively bonded on the carrier element  32 . 
       FIG.  5    shows a schematic cross section from the light exit side  20  through a luminaire element  10  according to a further exemplary embodiment of the invention. Arrangements  12  of light sources  13  are arranged along the two edge regions  16 . The central region  30  of the light exit surface  20  may advantageously have a lower transparency than the edge region  16 . In particular, the central region may be configured opaquely, for example by an opaque stripe, which may also be configured to be reflective toward the light sources  13 , being applied onto the diffuser  24 , that is to say on the inner side of the layer stack  22 . 
       FIG.  6    represents a plan view of a bent luminaire element  11  according to a further exemplary embodiment of the invention with a section line A-A indicated.  FIG.  7    in this regard shows a longitudinal section in the section plane A-A through the luminaire element  11 . 
     The structure of the bent luminaire element  11  is similar to the structure of the planar luminaire elements  10  represented in  FIGS.  1  to  5   . The difference is that, in the bent luminaire element  11 , the luminaire housing  14  is configured curved in the shape of an arc. The light exit surface  20  is in this case oriented toward a concave inner side of the arc-shaped curvature. The light sources  13  are arranged on the likewise curved luminaire insert  32 . The bent luminaire element  11  also comprises terminal regions  18  at its ends, with which the luminaire element  11  may be mechanically and/or electrically connected to subsequent planar and/or bent luminaire elements  10 ,  11 . 
       FIG.  8    shows a cross section through an inspection tunnel  100  according to one exemplary embodiment of the invention, while a corresponding longitudinal section through the inspection tunnel  100  is represented in  FIG.  9   . 
     The inspection tunnel is used in particular for the inspection of painted vehicle bodies  120  which pass through the inspection tunnel  100  along a tunnel longitudinal axis  102 . The inspection tunnel  100  comprises an arrangement of a plurality of luminaire strips  50 , which are arranged next to one another transversely to the tunnel longitudinal axis  102 . The light exit surfaces  20  of the luminaire elements  10 ,  11  are oriented on a concave inner side of the arc-shaped curvature of the tunnel wall  108  toward a central region of the tunnel longitudinal axis  102 . 
     A luminaire strip  50  in this case comprises a plurality of luminaire elements  10 ,  11 , which are connected to one another at their end-side terminal regions  18 . In particular, the luminaire elements  10 ,  11  are arranged at least regionally on a line curved in the shape of an arc, the light exit surfaces  20  of the luminaire elements  10 ,  11  being oriented toward the concave inner side of the arc-shaped curvature. End pieces  52  of a luminaire strip  50  are in this case formed by planar luminaire elements  10 , between which a plurality of curved luminaire elements  11  are arranged. 
     The individual luminaire elements  10 ,  11  joined to form a luminaire strip  50 , which may for example have an arc-like structure, may thus be screwed to one another on their end sides. For this purpose, for example, 6 bent luminaire elements  11 , each with a length of 1420 mm, and 2 planar luminaire elements  10 , each of 750 mm, may be used. Because the light exit surface  20  approximately has the length of the luminaire housing  14 , only minimal sections on which the light exit surface is interrupted are formed in the circumferential direction. With this virtually continuous light exit surface  20 , a reflection image which is advantageous since it is almost uninterrupted may be formed on the substrate. 
     In order to combine individual luminaire elements  10 ,  11  having an individual length of for example 1400 mm to form a continuous luminaire strip, to avoid light-free regions these may be screwed together or plugged together on the head sides. Here, for example, the energy supply and the control signals could, for example, be forwarded from one luminaire element  10 ,  11  to the next via the plug connection. 
     Because of the concentric arrangement of the luminaire elements  10 ,  11 , the light rays are directed substantially onto the substrate, that is to say for example a painted vehicle body  120 . This on the one hand increases the luminous efficiency, and on the other hand reduces the direct dazzling of the inspectors. 
     The width of the individual luminaire strips  50  may for example be 200 mm, and the free space between the light arcs may for example be 500 mm. In this way, both a sufficiently large number of contrast transitions is available, and sufficient visually “unperturbed” space, which is likewise needed for inspection of the overall substrate. 
       FIG.  9    shows a cross section of an inspection tunnel  100  having a multiplicity of luminaire strips  50 , which are arranged in two so-called measures  110 . The two measures  110  are in this case arranged with a certain spacing from one another so that a vehicle body  120  can be inspected simultaneously in both measures  110 . The individual luminous strips  50  are arranged separated from one another by regions 106. A measure 110 may, for example, have a length of 6.3 m. 
     The luminous strips  50  of a measure are arranged spaced apart in a predetermined grid spacing  104 , which may for example be 0.70 m, while the spacing between the two measures may for example be 0.8 m. 
     The regions  106  between the luminaire strips  50  may comprise material or surfaces with predetermined, in particular different reflectances. In particular, reflectances of between 20% and 70%, preferably between 27% and 55%, in relation to a wavelength range of visible light and with normal light incidence, may in this case be provided, in order to obtain a contrast situation which is as good as possible for examination of substrates. 
     In addition, at least one luminaire strip  50  may be arranged extending parallel to the tunnel longitudinal axis  102  in an inspection tunnel  100 , the light exit surfaces  20  of the luminaire elements  10 ,  11  being aligned toward the tunnel longitudinal axis  102 . 
     Furthermore, it is also possible for luminaire strips  50  to be arranged in the floor  124  in the tunnel longitudinal axis  102  and/or transversely to the tunnel longitudinal axis  102 . 
     Especially for the inspection of, for example, hoods or trunk lids of a body  120 , it may be advantageous to install longitudinally fitted luminaire strips  50  since in that case a movement of the checker transversely to the body  120  often takes place. With this natural movement of the checker transversely to the body  120 , a bright/dark contrast change therefore takes place without additional head movement. 
       FIG.  10    shows a luminance profile transversely over two luminaire elements  10  according to the invention, which are arranged spaced apart by a region  106 . In this case luminance regions  60  may be seen at the edge regions  16  of the luminaire elements  10  with a very high luminance. The increase and decrease of the luminance take place very steeply in these regions  60 , so that a high contrast occurs there, which is conducive to the perception of point faults on a substrate. Between the luminance regions  60  with a high luminance, a region  62  of low luminance may be seen in the central region  30  of the luminaire elements  10 . The region  106  between the two luminaire elements  10  comprises a dark region  64 . 
     Light sources  13  having LEDs with a variable color temperature may optionally be used. In this way, for example, the light color may be matched to the hue of the substrate or to the preference of the inspector. 
     Possible color temperature arrangements of luminaire strips  50  of an inspection tunnel  100  according to one exemplary embodiment of the invention are represented in  FIG.  11   . 
     Luminaire elements  10 ,  11  of different luminaire strips  50  of an inspection tunnel may comprise light sources  13  with different color temperatures. In particular, the color temperatures may vary in the range of between 2700 K and 6500 K. Neighboring luminaire strips  50  may in this case have alternating sequences of high and low color temperatures. 
     The light color of the light sources  13  in a luminaire strip  50  may either be fixed or, for example, vary between 2700 K (warm-white) and 6500 K (cold-white). For example, alternately cold-white and warm-white luminaire strips  50  or other sequences may be used. 
     The luminaire elements  10  may be configured to be dimmable. The degree of dimming may, for example, be tailored to the hue of the substrate. The hue of the luminaire element  10  may be matched to the hue of the substrate. 
       FIG.  11    represents various possible color temperature arrangements S 1  to S 9 . This representation is not however intended to be restrictive, and other color temperature combinations are readily conceivable. 
     Luminaire elements  50  with a high color temperature  70  are in this case represented in white, while luminaire elements  50  with a medium color temperature  72  are represented dotted and luminaire elements  50  with a low color temperature  74  are represented densely dotted. Further levels are, however, represented between them. The arrows indicated are intended to illustrate the profile of the color temperatures from high color temperatures  70  to low color temperatures  74 . For the sake of clarity, only certain luminaire elements  50  are provided with references. 
       10  luminaire element 
       11  bent luminaire element 
       12  stripe-like arrangement of light sources 
       13  light source 
       14  luminaire housing 
       16  edge region 
       18  terminal region 
       20  light exit surface 
       22  lens stack 
       24  diffuser 
       26  multiprism lens 
       28  cover lens 
       30  central region 
       32  luminaire insert 
       34  maintenance opening 
       50  luminaire strip 
       52  end piece 
       60  high contrast 
       62  low luminosity 
       64  dark region 
       70  high color temperature 
       72  medium color temperature 
       74  low color temperature 
       100  inspection tunnel 
       102  tunnel longitudinal axis 
       104  grid spacing 
       106  region 
       108  tunnel wall 
       110  measure 
       120  vehicle body 
       124  floor 
     L longitudinal extent