Patent Publication Number: US-9892906-B2

Title: Lamp and headlighting arrangement for obtaining a color appearance in an automotive headlight

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a § 371 application of International Application No. PCT/EP2014/063536 filed on Jun. 26, 2014 and titled “Lamp and Headlighting Arrangement for Obtaining a Color Appearance in an Automotive Headlight,” which claims the benefit of EP Application No. 13173915.3, filed Jun. 27, 2013. Both PCT/EP2014/063536 and EP 13173915.3 are incorporated herein. 
     FIELD OF THE INVENTION 
     The invention relates to a lamp for use in an automotive headlight and to a headlighting arrangement for a motor vehicle. 
     BACKGROUND OF THE INVENTION 
     Different types of lamps are known for use in an automotive headlight. The present invention relates to incandescent lamps, i. e. lamps where light is generated from one or more filaments arranged within a transparent lamp vessel. 
     Known lamp types comprise lamps where a shield is arranged adjacent to a filament such that light emitted from the filament is partly blocked, and such that an angular shielded region is obtained into which no direct light from the filament is emitted. The obtained illumination beam of light includes a bright/dark cutoff caused by the shield, which may be used to form in a reflector an illumination beam pattern with a bright/dark cutoff, which may be used e. g. for low beam illumination. An example of a double filament lamp where a shield is provided adjacent to one of the filaments is a H4 lamp. Other lamps, in particular single filament lamps such as e. g. a H7 lamp do not provide a shield. 
     Automotive regulations cover geometrical parameters of an automotive lamp, such as the position and size of filaments as well as functional parameters, such as the color of the light emitted. Such regulations provide that the illumination beam of light emitted from the lamp to serve the purpose of illuminating the road in front of the motor vehicle is required to have a white color, i. e. the color of the emitted light must be within a specified white field of color coordinates. 
     DE 10 2010 002 084 A1 describes a halogen incandescent lamp for a vehicle front reflector comprising, in one embodiment, a lamp vessel with two filaments, of which one serving for low beam lighting is arranged adjacent to a shield. The lamp vessel comprises an optical filter to obtain violet coloring of the light emitted. In different embodiments, a color filter may be applied to a single filament lamp without a shield, and the lamp vessel may be fully or partially covered by the color filter. The light emitted from the lamp is within the white field of the ECE regulations, but has a violet coloring, such that the vehicle may be recognized by the light color. In a specific embodiment, it is disclosed that part of the lamp vessel is not covered by a color filter, resulting in an uncolored central part of the light beam and a colored edge region of the light beam. Part of the light beam is therefore colored. The coloring of this part of the beam should also remain with the boundaries set by the regulations and therefore only a limited color change is possible. 
     SUMMARY OF THE INVENTION 
     It may be considered an object of the invention to provide an improved lamp suited for automotive headlights, in particular a lamp which provides a substantial white illumination beam, which beam is still perceived to have a pleasant light color. 
     This object is achieved by a lamp according to claim  1  and by a headlighting arrangement according to claim  12 . Dependent claims refer to preferred embodiments of the invention. 
     The present inventors have considered that for an optical color appearance of a lamp installed in an automotive headlight, it may not be necessary to obtain a differently colored illumination beam of light (i. e. the main portion of the luminous flux emitted from the lamp, that is emitted into the main illumination directions and is used in a headlighting reflector to form the illumination beam on the road in front of the motor vehicle). Instead, for changing the appearance, i. e. how the light emitted from a head light is perceived, it may be sufficient to change the color of only a peripheral portion of the light, i. e. light emitted from the lamp into directions peripheral to (or even outside of) the main illumination directions. This may lead to a lamp and a headlighting arrangement, which can obtain a strongly colored appearance, while the actual illumination beam is still white, i. e. within the white field defined in the corresponding regulations. 
     According to the invention, a lamp is proposed with at least one filament within a transparent lamp vessel. Preferably, the lamp is a halogen lamp. 
     The lamp vessel comprises a partial color filter, i. e. is provided with a color filter portion. This color filter portion has optical properties such that light passing through it is emitted with a color change. The color filter portion may be provided as a color filter coating on the lamp vessel. 
     Since, the lamp only comprises a partial color filter, the lamp vessel further comprises a color transparent portion, through which light is emitted without a color change. It should be noted that the present invention is mainly concerned with illumination and appearance, such that the above applies to the visible spectrum of light, such that e. g. a portion of the lamp vessel is still regarded as color transparent if it only comprises an ultraviolet or infrared filter. 
     The color transparent portion and the color filter portion are arranged on positions of the lamp vessel specially chosen with regard to the position of the filament and the directions of the light emitted therefrom. Since the illumination beam of light, i. e. the main part of the luminous flux as explained above, should remain at least essentially within the white field defined by regulations, it is emitted, at least mainly, through the color transparent portion of the lamp vessel. Thus, a non-colored illumination is achieved, i. e. an illumination beam that is of white color within the boundaries set by corresponding regulations, in particular ECE regulations relating to halogen lamps. 
     The color filter portion is arranged such that a peripheral and/or scattered portion of light is emitted through it. As will become apparent in connection with preferred embodiments, a peripheral portion of light may be emitted under directions at the periphery of the illumination beam. Further, scattered portions of light may be emitted from the lamp into all directions, not only into the direction of the illumination beam. 
     The skilled person thus recognizes that these scattered and/or peripheral portions of light, which pass through the filter portion of the lamp vessel, will not substantially contribute to the illumination beam of light. Instead, they will be emitted from the lamp into different directions as scattered light and/or into peripheral regions of the illumination beam. 
     Surprisingly, the inventors have found that these scattered and/or peripheral portions of the light that undergo a color change at the color filter portion are sufficient to obtain a color appearance of the lamp operated within a reflector. That is, since the illumination beam of light is reflected from a reflector in a directed way into defined directions close to the optical axis, the headlamp, if viewed under larger angles with the optical axis (i. e. the center of the main illumination direction), may be perceived as emitting a colored beam of light due to the colored peripheral/scattered light portions. 
     Thus, the invention allows to obtain a lamp with non-colored (white in the sense of e. g. ECE regulations) illumination, that is nonetheless perceived as giving a color appearance to the headlamp when in operation. 
     In a preferred embodiment, the lamp comprises an opaque, i.e. non-transparent top cover, which may e.g. be provided as a coating on the top of the lamp, i.e. on the axial end opposite to the electrical connections. According to a preferred embodiment, the top cover has a colored surface. This may be the inner surface, or the outer surface, or both. In a preferred embodiment, it is sufficient to provide a color coating at the outer surface of the top cover. The color of the surface corresponds to the color of the light emitted from the filament through the color filter portion. For example, if the filtered light is perceived green, then the opaque top cover may advantageously be provided in green color, too. This enhances the color appearance and does not substantially influence the illumination beam of light. However, any scattered light portions reflected e.g. within the lamp (in case of an inner colored surface), or at the exterior of the lamp (in case of an outer colored surface) will be perceived as having the same color as the color filtered light. Thus, the coloring effect is enhanced. Additionally, a colored outer surface may be perceived in the headlight even when the lamp is turned off. 
     According to one embodiment, a shield may be arranged adjacent to the filament, such that light emitted from the filament is partially blocked. As will become apparent in the discussion of further preferred embodiments, the filament adjacent to the associated shield may be used for low beam lighting, and there may be a further filament, in particular for high beam illumination, arranged within the lamp vessel. It is then preferred that at least a part of the color filter portion is arranged within the angular shielded region, i. e. in the angular region behind the shield. Such an angular region may be defined of radial directions from the center of the filament located within a central plane perpendicular to a longitudinal axis of the lamp. 
     Light incident in this shielded region will not be direct light from central portions of the filament, but will be composed of light portions scattered at the lamp vessel or at holding wires arranged within the lamp vessel for fixing the filaments and/or the shield. Additionally to these scattered light portions, a part of the color filter portion may also receive, as will be visible from preferred embodiments, direct light from the filament. However, this will preferably correspond to peripheral light portions, i. e. outside of the angular range of the illumination beam of light. Generally, it is preferred that the largest part of the color filter portion is arranged within the shielded region. 
     According to a further preferred embodiment of the invention, the color filter portion is formed as a partial cylinder surface over an angular region that is as least as wide as the angular shielded region. Further preferred, the angular region of the color filter portion may be slightly broader than the angular shielded region, i. e. such that the color filter portion is arranged over the full angular shielded region and overlaps to a certain, limited degree with the edges of the non-shielded region. In this case, additional to the scattered light portions passing through the color filter portion within the shielded region, there will be peripheral portions of the light emitted from the filament which are directly emitted through the color filter portion. However, these peripheral portions will appear in the headlamp under peripheral angles of the resulting illumination beam. For example, the color filter portion may have an angular width which is 120-160% of the width of the angular shielded region, i. e. such that there may be e. g. 1-30% overlap on one or both sides. 
     Preferably, the color filter portion may be arranged non-symmetrically relative to the shield. In particular, there may be an overlap between the color filter portion and the non-shielded region of different size at both opposing side edges of the shield. 
     In longitudinal extension and position, the color filter portion is arranged preferably adjacent to the filament and/or the shield. For example, the color filter portion may have a longitudinal extension, measured along a longitudinal axis of the lamp, which is 50-300%, further preferred 150-250% of the longitudinal extension of the shield. In an upright position of the lamp, with the electrical connections arranged below, it is preferred that a lower edge of the color filter portion is arranged at substantially the same longitudinal location as the lower end of the filament, the term “substantially” in this respect being understood to enclose deviations of about +/−10% of the filament length. 
     The illumination beam of light may be defined according to the angles under which light forming this illumination beam is emitted, e.g. relative to a measurement plane oriented perpendicular to the longitudinal axis and arranged at the center of one filament. 
     In vertical directions, the illumination beam may be defined to be emitted in directions forming angles of at least +/−30° from this measurement plane. 
     In radial directions, the illumination beam of light may be defined, for a lamp without a shield, to cover the full 360° range of directions within the measurement plane. For lamps including a shield, the illumination beam of light may be defined as light emitted in radial directions over an angular range of e. g. 120°. The light emitted in these directions in the measurement plane will fully pass through the color transparent portion. The color filter portion may then only be arranged outside of the 120° angular range of the illumination beam, such that only peripheral portions emitted outside of the 120° angular range pass through it. 
     Preferably, the color filter portion may be obtained by a corresponding coating provided on the lamp vessel, preferably on the outside of the lamp vessel. 
     The color filter coating may be e. g. a sol-gel coating, in particular a sol-gel nanocoating, or, alternatively, a luster coating. The color effect achieved may be e.g. green, yellow, pink/purple, orange or blue. 
     The level of absorption may be chosen in accordance with the desired color effect. Generally it is preferred to provide the color filter coating to achieve absorption levels of 5% or above, for most colors of 30% or above. In preferred embodiments, a level of absorption which has proven advantageous varies for the different color effects. While for yellow color a preferred absorption level may be relatively low with only e.g. 4-20%, in particular 5-11%, preferred absorption levels for other colors such as green, pink/purple, orange and blue will be e.g. 30-70%, in particular 40-60%. 
     In one embodiment, the color filter portion is provided as a cylinder shape around one part of the lamp vessel, and the color transparent portion is provided also as a cylinder shape around the lamp vessel, surrounding the filament. Preferably, the color filter portion is provided around a lower portion of the lamp, i.e. looking at an upright oriented lamp with the electrical connections oriented below, the color filter portion may extend in axial direction from a pinch portion (where the lamp vessel is sealed, and electrical wires may extend through the seal). 
     While it is generally possible to provide a color filter portion which is non-continuous, i.e. provides separate spaced-apart parts of the lamp vessel with the color filter property, it is preferred to provide the color filter portion continuous, i.e. as only one surface bordering on the color transparent portion. In a particulary preferred embodiment, the color filter portion is provided only at the lower portion of the lamp vessel, the color transparent portion is provided directly adjacent to the color filter portion in an upper portion surrounding the filament, and an opaque top cover is provided directly adjacent to the color transparent portion on the top of the lamp. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will become apparent from the following description of preferred embodiments, in which: 
         FIG. 1  shows a side view of a first embodiment of a lamp; 
         FIG. 2  shows a sectional view of the lamp of  FIG. 1  with the section along line A . . . A; 
         FIG. 3  shows a schematic side view of the lamp of  FIG. 1 ,  FIG. 2  arranged in a reflector; 
         FIG. 4  shows in a top view a partly schematic representation of a motor vehicle with a headlight of  FIG. 3 ; 
         FIG. 5  shows a side view of a second embodiment of a lamp; 
         FIG. 6  shows a side view of a third embodiment of a lamp. 
     
    
    
       FIGS. 1 and 2  show a first embodiment of a halogen lamp  10  suited for use in a reflector  14  of a motor vehicle headlight  12  as schematically shown in  FIG. 3 . 
     DETAILED DESCRIPTION OF EMBODIMENTS 
     The lamp  10  shown in the example of  FIG. 1 ,  FIG. 2  is a double filament halogen lamp. A glass vessel  16  which is transparent but has an opaque top  38  encloses a low-beam filament  20  and a high-beam filament  18 , electrically connected and mechanically mounted to mounting wires. The lamp vessel  16  is sealed at a pinch portion  17 , and the mounting wires extend through the pinch seal. An optical shield  22  is also arranged within the vessel  16  at one of the mounting wires and is positioned adjacent to the low-beam filament  20 , i. e. covering the low-beam filament  20  over its full longitudinal extension in the direction of the longitudinal axis L. The shield  22  is provided as a curved metal sheet. It serves to block a portion of light which is emitted from filament  20  in operation into the direction of the shield  22 . 
     As shown in the sectional view of  FIG. 2 , a shielded region  24  is formed in a measurement plane A, oriented perpendicularly to the longitudinal axis L and positioned at the center of the low-beam filament  20 . This shielded region in the example shown covers an angular range of about 150°. 
     An illumination beam portion  40  of the light emitted from the low-beam filament  20  is used, as schematically shown in  FIG. 3 , to achieve a main beam of illumination  40  on the road in front of the motor vehicle. The portion which is here regarded as the illumination beam of light  40 , i. e. the main portion of the luminous flux, is emitted into radial angular regions of a width of 120° as shown in  FIG. 2 , centered in directions opposite to the position of the shield  22 . In the side view of  FIG. 1 , the angular region of the illumination beam of light  40  covers a range of +/−30° from the central plane A. In the context of the present embodiment, the portion of light emitted from the low-beam filament  20  into the thus defined angular regions is referred to as the illumination beam of light  40 , whereas portions of light emitted into angular regions outside of this range are referred to as peripheral portions of light. 
     The above described lamp is of a lamp type known as H4. In the reflector  14  shown in  FIG. 3 , the light of the illumination beam  40  emitted from the lamp  10  is reflected to the front of the motor vehicle to form a low-beam light intensity distribution, i. e. an intensity distribution with a roughly horizontal bright/dark cutoff. This low-beam distribution with a horizontal bright/dark cutoff is obtained in the reflector  14 , because the main illumination beam  40  emitted from the low-beam filament  20  has, due to the partial shielding by the shield  22 , already a bright/dark cutoff in the intensity distribution. In contrast, if the high-beam filament  18  is operated, which has no associated shield, the resulting light intensity distribution formed by the reflector  14  has no bright/dark cutoff. 
     The light emitted from the filament  20  is of white color. In the present context, a white color will be referred to for light fulfilling the ECE requirements in this respect, i. e. for light with color coordinates within the white field. 
     As the light emitted from the filament  20  passes through the glass wall of the lamp vessel  16 , it remains white, i. e. does not undergo a color change. According to the present embodiment, the lamp  10  comprises a color filter portion provided as a color filter coating  30  on the outside of the lamp vessel  16 . 
     There are different possible embodiments of a color filter coating  30  which serves to absorb certain wavelengths of incident light, such that a white beam of light passing through the color filter coating  30  undergoes a color change. Also, different color effects may be achieved, such that the filtered light assumes e.g. green, yellow, pink/purple, orange, or blue color. 
     In preferred examples, coatings with different absorption properties may be provided for different colors, e.g. with about 40% absorption for green, about 10% absorption for yellow, about 60% absorption for orange and about 50% absorption for blue, and about 60% absorption for a pink/purple color filter coating  30 . 
     Further, the opaque top coating  38  is provided with the same color as achieved by the color filter coating  30 . 
     Of the light emitted from the low-beam filament  20 , the illumination beam of light  40 , as defined by the above angular regions, passes through a portion of the lamp vessel  16  with no color filter, which in the present context will be referred to as a color transparent portion  32  of the lamp vessel  16 . 
     As visible from  FIG. 1 ,  FIG. 2 , the color filter coating  30  of the first embodiment is applied to the lamp vessel  16  as a partial ring around the circumference of the lamp vessel  16 , thus forming a partial cylinder surface. In longitudinal extension, along the longitudinal axis L, the color filter coating  30  overlaps the longitudinal extension of the low-beam filament  20 ; the lower ends thereof coincide, whereas the longitudinal extension of the color filter coating  30  is about twice the longitudinal extension of the low beam filament  20 . 
     In the measurement plane A, the color filter coating  30  is provided over the entire angular range of the shielded region  24 . However, as shown, the color filter coating  30  extends beyond the shielded region  24  on both sides and overlaps with the non-shielded region by about 30° on one side of the shield  22 , and by about 5° on the other side. The color filter coating  30  is thus arranged non-symmetrically to the shield  22 , with a wider first peripheral portion  26   a  on one side and a more narrow second peripheral portion  26   b  on the other. 
     The optical effect achieved by the partial color filter coating  30  is as follows: Since the color filter coating  30  is arranged such that the above defined illumination beam of light  40  passes only through the color transparent portions  32  of the lamp vessel  16 , light emitted from the lamp  10  into the directions of the illumination beam of light  40  is not affected by the color filter coating  30 . Thus, the illumination beam of light  40 , as reflected by the reflector  14  of the headlight  12 , achieves a non-colored illumination on the road in front of a vehicle  34  ( FIG. 4 ). 
     However, light emitted from the filament into the peripheral regions  26   a ,  26   b  (in the central plane A, shown in  FIG. 2 ) pass through the color filter coating  30  and undergo a color change. Thus, these portions of light emitted from the lamp  10  will be correspondingly colored light. However, since this applies only to peripheral portions  26   a , 26   b  which in the reflector  14  are reflected under larger angles with the optical axis O, these will not substantially contribute to the color of the illumination in front of the motor vehicle, but will be reflected into peripheral directions, arranged at greater angles with the optical axis O. 
     A further portion of light which will appear colored is scattered light passing through the color filter coating  30  in the shielded region  24 . While the shielded region  24  is shielded from direct light from the low-beam filament  20 , there will be a certain amount of light emitted from the low-beam filament  20  which is scattered, e. g. partially reflected at the wall of the lamp vessel  16 , or at the holding wires therein, etc. This scattered portion of light will have a comparatively small amount of luminous flux as composed to the illumination beam  40 . However, the scattered portion of light will be emitted as colored light into directions outside of the illumination beam  40 , i. e. into directions where it will be noticeable if the headlight  12  is observed not directly from the front, but under larger angles with the optical axis O. 
     A still further portion of light which will appear colored is scattered light reflected at the surface of the opaque, colored top cover  38 . This scattered light will also be emitted into different directions, also outside of the illumination beam  40 . 
     In consequence, the optical effect obtained by the described lamp is such that the illumination beam of light  40  emitted from the lamp and reflected within the headlight  12  by the reflector  14  to illuminate the road in front of the motor vehicle  34  will be white (in the sense of the ECE regulations). However, if the headlight  12  is observed from the side, the scattered portion of light passing through the color filter coating  30  in the shielded region  24 , the peripheral portions  26  of light passing from the low-beam filament directly through the color filter portion  30 , and any scattered light portions reflected at the colored top  38  will achieve a strongly colored appearance in the headlight. 
       FIG. 4  shows in a top view how the illumination beam pattern  40  of the headlight  12  is reflected onto the road in front of a motor vehicle  34  under relatively small angles with the optical axis O. Under these directions, a illumination beam  40  from the lamp  10  is effective, such that this illumination beam pattern is white. 
     However, to an observer  36  looking from the side, i. e. under greater angles with the optical axis O, the scattered and reflected light portions and peripheral light portions  26  are strongly visible, such that the headlight  12  appears colored. 
     The lamp  10  can thus be used as a standard automotive halogen lamp, e. g. a H4 lamp, which fully conforms to all regulation and standard requirements, while at the same time a surprising coloration effect may be observed in the headlight  12 . 
       FIG. 5  shows an example of a further embodiment of a lamp  110  with a differently shaped color filter coating  130 . Since the second embodiment largely corresponds to the first embodiment, like parts are designated by like reference numerals. 
     In the example of  FIG. 5 , the color filter coating  130  is not provided as a partial cylinder shape, but has, in the side view shown, a lower edge that is oriented under an angle to the measurement plane. As visible, the color filter coating  130  is arranged such that the main illumination beam  40  only passes through the color transparent portion  32  and remains uncolored. 
       FIG. 6  shows a still further embodiment of a lamp  210 . Again, parts corresponding to the first and second embodiments are designated by like reference numerals. 
     The lamp  210  of the third embodiment is a single filament lamp, where consequently no shield is provided adjacent to the filament  20 . For this type of lamp, which may e.g. be a H7 lamp, a color filter coating  230  as shown may be provided in a lower portion of the lamp vessel  16 . The color filter coating  230  has a cylinder shape surrounding the lamp vessel  16 . In the example shown, the color filter coating  32  extends between a pinch seal portion  17  and an upper edge. The upper edge of the color filter portion  230  is arranged below the filament  20 . The color transparent portion  32  of the lamp vessel  16  is arranged directly adjacent, above the color filter portion  230  and surrounds the filament  20 , such that, as visible from  FIG. 6 , the main illumination beam  40  only passes through the color transparent portion  32 . Provided above and directly adjacent to the color transparent portion  32  is an opaque top covering  38 , which is colored in the same color as the color filter portion  230 . 
     In the case of the lamp  210  which does not have a shield, both the color transparent portion  32  and the color filter portion  230  are cylinder-shaped and cover all 360° of radial directions. The lamp  210  achieves, as described above for the first and second embodiments, a white main illumination beam  40 . However, due to reflection at the color top cover  38  and due to peripheral light portions as well as scattered light colored by the color filter portion  230 , the light emitted from the lamp  210  and from a headlightl  1  equipped with the lamp  210  is perceived as having a color appearance. 
     The invention has been illustrated and described in detail in the drawings and foregoing description. Such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. 
     A skilled person will recognize that a number of modifications may be made to the above described lamp. For example, the size and position of the color filter coating  30  may vary as long as a main illumination beam  40  remains uncolored. 
     In the claims the word “comprising” does not exclude other elements, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims or are described above in mutually different embodiments does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.