LAMP WITH HEAT-SHIELDING ELEMENT

Abstract

A lamp has a light emitting element within a sealed transparent vessel. The vessel comprises a cylindrical section with a longitudinal axis L in parallel to a longitudinal axis F of the light emitting element. In order to provide a lamp suited for compact reflectors, a heat shielding element is arranged to shield at least infrared light. The heat shielding element is arranged in parallel to the longitudinal axis F of the light emitting element and has an axial extension of at least 80% of the light emitting element. The heat shielding element is arranged to shield infrared light emitted into directions perpendicular to the longitudinal axis F covering a circumferential extension of 20°-120° measured in cross section.

Claims

1. A lamp comprising: a light emitting element arranged within a sealed transparent vessel, the vessel comprising at least a cylindrical section with a longitudinal axis (L) arranged in parallel to a longitudinal axis of the light emitting element, the cylindrical section of the vessel enclosing the light emitting element; and a heat shielding element arranged to shield at least infrared light emitted from the light emitting element, the heat shielding element being arranged in parallel to the longitudinal axis (F) of the light emitting element and having an axial extension of at least 80% of an axial length of the light emitting element, the heat shielding element being arranged to shield infrared light emitted from the light emitting element into directions perpendicular to the longitudinal axis (F) of the light emitting element covering a circumferential extension of at least 20° and at most 120° measured in cross-section from the longitudinal axis (L) of the light emitting element, and the heat shielding element, when the lamp is arranged horizontally within a reflector of a vehicle headlight, being arranged above the light emitting element.

2. The lamp of claim 1, wherein the heat shielding element is provided as a coating arranged on the vessel.

3. The lamp of claim 2, wherein the coating is an infrared filter coating allowing transmission of visible light range while reflecting infrared light.

4. The lamp of claim 2, wherein the coating is a mirror coating.

5. The lamp of claim 1, wherein the heat shielding element is arranged to cover at least the axial length of the light emitting element.

6. The lamp of claim 1, wherein the axial extension of the heat shielding element is in a range of about 80% to about 125% of an axial length of the light emitting element.

7. The lamp of claim 1, wherein the light emitting element is a filament wound around a longitudinal filament axis, and wherein at least a first holding wire and a second holding wire extend from a lamp cap to hold the filament, at least a part of the first holding wire extending in parallel to the filament at a distance thereto, and wherein the heat shielding element is arranged symmetrically to an axial symmetry plane defined through the longitudinal filament axis and the first holding wire.

8. The lamp of claim 1, wherein the light emitting element is a filament, chosen such that the lamp has a nominal power of at least 60 W at a voltage of 13.2 V.

9. The lamp of claim 1, wherein the heat shielding element is at least partly reflective of visible light, and the heat shielding element is shaped to create a mirror image of the light emitting element, the mirror image being located between the light emitting element and the heat shielding element.

10. The lamp of claim 1, wherein the heat shielding element is comprised of a plurality of coatings applied on top of each other forming an interference filter.

11. The lamp of claim 1, wherein the heat shielding element is a metal shield arranged at a distance from the cylindrical section, the metal shield being fixed to the lamp.

12. The lamp of claim 11, wherein the metal shield is fixed to a cap of the lamp.

13. The lamp of claim 1, wherein the vehicle headlight is arranged within the reflector, and wherein the reflector is made of a plastic material with a reflective coating.

14. The lamp of claim 13, wherein within a cross sectional plane arranged within a center of the light emitting element, a distance (d) between the light emitting element and a top portion of the reflector is 30 mm or less.

15. The lamp of claim 13, wherein the plastic material is a thermoplastic material.

16. The lamp of claim 15, wherein the thermoplastic material comprises at least one of, PC-HT, or PEI, or PSU, or PES.

17. The lamp of claim 1, wherein the heat shielding element has a partial cylindrical shape.

18. The lamp of claim 17, wherein the cylindrical shape is bordered by straight edges.

19. The lamp of claim 11, further comprising a bulb that is positioned in proximity to the metal shield such that the metal shield at least partially blocks convection of heated air from the bulb.

20. The lamp of claim 11, wherein at least a front portion of the metal shield is at least one of, a circular shape, or a square shape or an angular shape.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG. 1 shows in a symbolical side view an automotive headlight with a lamp arranged within a reflector;

[0032] FIG. 2 shows a longitudinal sectional view of a first embodiment of a lamp;

[0033] FIG. 3 shows a cross-sectional view of the lamp of FIG. 2, with the section taken along A . . . A in FIG. 2;

[0034] FIG. 4 shows a longitudinal sectional view of a second embodiment of a lamp;

[0035] FIG. 5 shows a cross-sectional view of the lamp of FIG. 4 with the section taken along B . . . B;

[0036] FIG. 6 shows a longitudinal sectional view of a third embodiment of a lamp;

[0037] FIG. 7 shows a top view of the lamp of FIG. 6.

DESCRIPTION OF EMBODIMENTS

[0038] FIG. 1 shows a symbolic representation of a vehicle headlight 10 of the reflector type, including a lamp 20 mounted within a reflector 12. The lamp 20 is a halogen incandescent lamp with a filament 22 as light emitting element within a transparent glass bulb 24. The lamp 20 comprises a lamp cap 26 shown only symbolically, mounted within a mounting position 14 of the reflector 12.

[0039] The reflector 12 comprises a reflector body with an inner reflector surface 16. The reflector body 12 is made out of a thermoplastic material, such as PSU, PC-HT, PEI or PES. Light emitted from the light emitting element 22 of the lamp 20 is reflected at the reflector surface 16 to form an illumination beam B to illuminate in front of a vehicle.

[0040] In operation of the lamp 20, heat is generated by the light emitting element 22. For example, the preferred embodiment of a lamp 20 is disposed to have an electrical power of 69 W if operated at a voltage of 13.2 V. A relatively large proportion of the electrical power is not converted into light, but generates heat that is dissipated within the reflector by convection, conduction (through the lamp cap 26) and radiation, i.e. emission of infrared light.

[0041] The invention is aimed in particular towards compact headlights with a relatively small distance between the light emitting element 22 and the reflector surface 16. The critical distance is shown in FIG. 1 as d, measured directly above the light center of the emitting element 22 in a plane perpendicular to a longitudinal axis L of the lamp 20. In compact reflectors, the distance d may be as small as 30 mm or less, for very compact reflectors even 25 mm or less.

[0042] In particular, the heat load on a top portion 18 of the reflector 12 may be critical due to convection, which is directed upward from the light emitting element 22, in addition to the infrared radiation.

[0043] While the reflector 12 may be made out of a material which is able to tolerate high temperature even over a long time, such as metal, glass or thermoset, in particular BMC, thermoplastic materials are preferred as being more light weight and offering both processing advantages and superior surface quality. However, their long-term temperature tolerance is limited, thus creating potential problems in particular in very compact reflectors.

[0044] A heat shielding element 30 is provided to reflect infrared light emitted from the light emitting element 22 into the direction of the top portion 18 of the reflector, so as to reduce the heat load onto this most critical part of the reflector.

[0045] In the following, embodiments of a lamp to be used in such a reflector will be described in detail. Generally, lamps may be used with dimensions e.g. according to newly proposed halogen types H18 (single filament lamp) or H19 (two-filament lamp).

[0046] FIG. 2 shows a first embodiment of a lamp 20 with a symbolically shown lamp cap 26 and a burner 28. A filament is held within the bulb 24 by holding wires 32, 34 extending from the lamp cap 26, including a first, longer holding wire 32 and a second, shorter holding wire 34. The end portion of the first holding wire 32 extends in parallel to the filament 22. In the horizontal position as shown in FIG. 2, which is the usual position during operation within a vehicle headlight, the first holding wire 32 is arranged directly above the filament 22, as also visible from the cross-sectional view in FIG. 3.

[0047] The bulb 24 comprises a pinch portion 36 mounted to the lamp cap 26, a central cylindrical portion 38 surrounding the filament 32 and an opaque covering 42 at the top portion. The central longitudinal axis L is defined as the center of the cylindrical portion 38.

[0048] The filament 22 is oriented in longitudinal direction within the bulb 24, i.e. with its longitudinal axis F arranged in parallel to the longitudinal axis L of the lamp 20, in the embodiment shown with a small offset.

[0049] The lamp 20 comprises as a heat shielding element a shielding portion 30 of the cylindrical portion 38 of the bulb 24, where an infrared filter coating 40 is applied. The infrared filter coating may preferably be comprised of a plurality of layers forming an interference filter, e.g. consecutive layers of Nb.sub.2O.sub.5 and SiO.sub.2 of carefully selected layer thickness to achieve the desired spectral filter response. The infrared filter layer 40 is strongly reflecting for infrared light, in particular for infrared light of wavelengths starting at 1000 nm. Light in the visible range will be transmitted through the infrared filter coating 40, although inevitably a small portion thereof will still be reflected, because in practice the spectral response of an interference filter will not be that of an ideal band-stop filter only for light in the infrared range.

[0050] The size and positioning of the filter portion 30 is selected according to both thermal and optical considerations. To achieve the desired thermal effect of reducing heat load on the top portion 18 of the reflector 12, the infrared filter portion is arranged above the filament 22 to reflect infrared light from the filament 22 into the direction of the critical top part 18. On the other hand, the size and position of the shielding portion 30 is chosen to minimize optical effects on the resulting beam B.

[0051] In the example shown, the shielding portion 30 is of a partial cylindrical shape, bordered by straight edges. In axial direction, the length of the shielding portion 30 is equal to the length of the filament 22. The shielding portion 30 is arranged in parallel to the filament 22 to cover the full axial length thereof.

[0052] In circumferential direction, the extension of the shielding portion 30 extends, as in particular visible from FIG. 3, over an angular range which may be defined by the angles α1, α2 with the horizontal direction. Preferably, the arrangement is symmetrical, such that α1 is equal to α2. A significant shielding effect has been achieved with a circumferential extension of 90° in total, i.e. with both α1, α2 being equal to 45°.

[0053] For vehicle headlights 10 of the reflector type as shown in FIG. 1, the portions of light emitted from the filament 22 into the upper regions 18 of the reflector 12 are used to illuminate areas in front of the vehicle, further away from the optically critical cut-off edge. Thus, for headlights of the reflector type, the described symmetrical arrangement of the shielding portion 30 symmetrically above the filament 22 has proven to introduce optical effects only in non-critical portions of the resulting beam B. Due to the limited extension of the shielding portion 30, the optical effects are thus tolerable, because light emitted from the filament 22 into directions outside of the shielding portion 30 can pass without optical effects such as color change or partial reflection, which is inevitably present at the infrared filter coating 40.

[0054] A certain portion of light in the visible range, which is reflected at the filter coating 40, forms a mirror image of the filament 22, shown in dashed lines in FIG. 3. Since the filter coating 40 is applied on the cylindrical portion 38, it forms a concave, partly reflecting surface bent around the central longitudinal axis L. The filament 22 is arranged below the longitudinal axis L, so that the mirror image will be positioned in between the actual filament 22 and the filter coating 40 as shown. If the mirror image is created in this area, there will be no glare in the resulting beam B of the headlight 10.

[0055] FIG. 4 shows a second embodiment of a lamp 50. The lamp 50 according to the second embodiment corresponds to the lamp 20 according to the first embodiment in many parts. Like parts will be designated by like reference numerals. In the following, only differences between the embodiments will be further explained.

[0056] In the lamp 50 according to the second embodiment, a metal shield 52 is provided as heat shielding element. The metal shield 52 is provided as a thin sheet metal strip which, as visible from FIG. 4, FIG. 5, is fixed to the lamp cap 26 and extends in longitudinal direction of the lamp 50. The metal shield 52 is arranged in parallel to the cylindrical portion 38 of the burner 28.

[0057] The metal shield 52 is bent around the central longitudinal axis L of the lamp 50, as shown in FIG. 5. The shield 52 is arranged at a small distance of e.g. 1-2 mm to the bulb 24.

[0058] As the infrared filter coating 40 in the lamp according to the first embodiment, the shield 52 is arranged above the filament 52 to shield the top portion 18 of the reflector 12. The surface of the metal sheet 52 is reflecting, such that both light in the visible range and in the infrared range is reflected. The top portion 18 of the reflector 12 is therefore shielded from infrared radiation. Further, the shield 52, which is arranged at a certain distance from the bulb 24, also partially blocks convection of heated air directly upward from the bulb 24.

[0059] In circumferential direction, the metal shield 52, as shown in FIG. 5, extends over an angular range of α1, α2 in the same way as in the first embodiment, i.e. preferably symmetrically over a total angular range of 90°.

[0060] In axial direction, the shield 52 extends from the lamp cap 26 up to a position adjacent to the far end of the filament 22 as shown in FIG. 4, thus covering the entire axial length of the filament 22.

[0061] Since the shield 52 is of partly cylindrical shape, concavely bent around the central longitudinal axis L of the lamp 50, the mirror image of the filament 22 is formed above the central longitudinal axis L, shown in FIG. 5 in dashed lines. Thus, glare is avoided.

[0062] FIG. 6, FIG. 7 show a third embodiment of a lamp 60, corresponding to the above described second embodiment. In the following, only differences will be further explained.

[0063] In the lamp 60, a metal shield 62 is provided which extends in axial direction beyond the filament 22, and even beyond the far end of the lamp vessel 36. As shown in FIG. 6, FIG. 7, the shield 62 comprises a front portion 64 bent around the tip of the lamp vessel 36. A front portion of the shield 62 thus acts also as a glare shield, shielding light emitted from the filament 22 into directions which would not strike the reflector 12 of a vehicle headlight.

[0064] The extended, larger shield 62 according to this embodiment is even more effective to distribute heat, in particular in axial direction.

[0065] In a side view, looking along the central longitudinal axis L, the front portion 64 of the shield 62 may e.g. be of circular, square or otherwise angular shape.

[0066] It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. For example, instead of an interference filter coating as described, different types of infrared filter coatings could be used. As a further alternative, instead of an infrared filter coating, also a mirror coating could be used.

[0067] In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word “comprising” does not exclude the presence of elements or steps other than those listed in a claim. The word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.