WO2009066243A2

WO2009066243A2 - Discharge lamp

Info

Publication number: WO2009066243A2
Application number: PCT/IB2008/054846
Authority: WO
Inventors: Sven Schellinger
Original assignee: Philips Intellectual Property and Standards GmbH; Koninklijke Philips Electronics NV
Current assignee: Philips Intellectual Property and Standards GmbH; Koninklijke Philips NV
Priority date: 2007-11-22
Filing date: 2008-11-19
Publication date: 2009-05-28
Anticipated expiration: 2010-05-22
Also published as: WO2009066243A3

Abstract

It is provided a discharge lamp (10) comprising a burner (14) for emitting light connectable to a socket (12) for mechanical connection to a lighting device, where¬ in the burner (14) comprises a discharge vessel (20) for providing a discharge arc (30), and a reflector (22) arranged adjacent to the coolest area and/or lowest area of the dis- charge vessel (20) during operation. It was found that in the discharge vessel (20) salts (24) may condense to the glass body of the discharge vessel (20), wherein the condensa¬ tion occurs mainly at the coolest area of the discharge vessel (20) during operation. Due to the reflector (22) the transmitted light (40) can be reflected back to the salts (24) leading to an absorption of the discolored transmitted light (40) or to an interfering with the discolored light (38) reflected by the salts (24). This in turn leads to a reduced amount of discolored light.

Description

DISCHARGE LAMP

FIELD OF THE INVENTION

The invention relates to the field of discharge lamps, particularly high intensity discharge (HID) lamps or ceramic discharge material (CDM) lamps or high pressure discharge (HPD) lamps, which may be used as motor vehicle lamps for illumi- nating a street or the like.

BACKGROUND OF THE INVENTION

From US 7,279,826 B2 an HID lamp is known, which is arranged inside a motor vehicle lamp housing. The HID lamp comprises a reflector pointing towards an opening of the lamp housing, so that light emitted by the HID lamp is reflected to a street instead of being absorbed by the lamp housing.

Due to the specific technology of discharge lamps the emitted light may comprise a certain percentage of discolored light differing in color from the mainly white color provided by a discharge arc inside a burner of the discharge lamp. Thus, there is a permanent demand to reduce the amount of discolored light. SUMMARY OF THE INVENTION

It is an object of the invention to provide a discharge lamp comprising a reduced amount of discolored light. This object is achieved by a discharge lamp, particularly HID- or CDM- or HPD-lamp, comprising a burner for emitting light connectable to a socket for mechanical connection to a lighting device, wherein the burner comprises a discharge vessel for providing a discharge arc, and a reflector arranged adjacent to the coolest area and/or lowest area of the discharge vessel during operation. The discharge lamp may comprise the socket, which may be adapted for mechanically connecting the discharge lamp to a lighting device, like a motor vehicle lamp.

It was found that in the discharge vessel salts may condense to the glass body of the discharge vessel, wherein the condensation occurs mainly at the coolest area of the discharge vessel during operation. In the case that the salts are liquid the liquid salts flow to the lowest area of the discharge vessel with respect to gravity. When the discharge lamp is used for a motor vehicle lamp, the discharge lamp is normally arranged in horizontal direction, so that the coolest area of the discharge vessel is the lowest area at the same time. Regarding, for instance, a Xe-HID-lamp the light emitted by the dis- charge arc inside the discharge vessel is partially discolored to yellow by reflection by and/or transmission through the condensed and/or liquid salts. The reflector of the discharge lamp according to the invention is used for reflecting the discolored light due to a transmission, this means a passing through, of light emitted by the discharge arc through the condensed and/or liquid salts inside the discharge vessel. Further light emitted by the salts may be reflected. Due to the reflector, which may be arranged only in the area of the discharge vessel, the transmitted light, this means the light passed through the salts, can be reflected back to the salts leading to an absorption of the discolored light or to an interfering with the discolored light reflected by the salts. This in turn leads to a reduced amount of discolored light. Further a color temperature of ca. 5000K or higher can be expected for the discharge lamp according to the invention. Particularly the built in space is reduced, since a reflector of a lamp housing can be saved.

In a preferred embodiment the chromaticity coordinate of the light emitted by the discharge lamp comprises a X-coordinate in the range of 0.360 - 0.395, preferably 0.365 - 0.385, most preferred 0.375 - 0.380 and a Y-coordinate in the range of 0.360 - 0.395, preferably 0.370 - 0.390, most preferred 0.380 - 0.390 in the CIE 1931 diagram. By these chromaticity coordinates it is achieved that the color point of the emitted light is close to the black body locus due to the CIE diagram.

In a preferred embodiment the reflector comprises a color filter, particularly a blue filter, for filtering discolored light due to a transmission of light emitted by the discharge arc through condensed and/or liquid salts inside the discharge vessel. It is due to rough theoretical calculations expected an increased light efficiency, particularly increased integral lumen output, of ca. 30%. Due to the filter the discolored light reflected by the reflector may be added to the discolored light reflected by the salts to provide additional white light instead of providing discolored or annihilated light. Particularly the reflector comprises a weighted absorption chosen such, that during operation the amount of light reflected by the condensed and/or liquid salts and the amount of light transmitted through the condensed and/or liquid salts and reflected by the reflector add each other to mainly white light. Thus, it is possible to adjust the amount of the color- filtered discolored light reflected by the reflector with respect to the discolored light reflected by the salts. The weighted absorption A may be defined as A = 1-R, wherein R is the weighted reflectivity. The weighted reflectivity R and the weighted absorption A are particularly calculated as R = J R(λ)*V(λ) dλ / J V(λ) dλ and A = J A(λ)*V(λ) dλ / J V(λ) dλ, wherein V is the sensitivity of the human eye in dependency of the wave length λ.

Preferably the reflector comprises retro reflection elements, particularly cat-eyes. Due to the retro reflection elements a defined reflection direction can be safeguarded. Particularly it is possible, for instance by using cat-eyes, to reflect the discolored light into the same direction from which the light was coming.

Particularly the reflector is arranged spaced to the discharge vessel and connected to the socket and/or the burner. A specific reflective coating of the burner in the area of the discharge vessel is rendered unnecessary so that it is possible to use the same kind of burner already existing for other applications. Thus, the used burner is adapted to be made by mass production leading to reduced production costs.

In a preferred embodiment the reflector comprises a backlead wire. The backlead wire may be connected to a distal electrode of the burner, this means connected to the electrode arranged opposite to the socket of the discharge lamp. Particularly the reflector itself and/or a reflective coating and/or a line through the body of the reflector may provide the backlead wire. Due to the combination of two different functions to the reflector an additional single backlead wire is not necessary.

Preferably the reflector comprises an insulating layer, particularly an insu- lating coating. This prevents a discharge between the electrodes of the discharge lamp to the reflector, particularly when the reflector comprises the backlead wire. Further the electrical insulation of the reflector reduces the risk of electrical malfunctions.

Generally the design of the reflector may be of any kind. Preferably the reflector is designed mainly as part of a ring cylinder, which may extend in circumferen- tial direction over an angle α of 20° < α < 180°, particularly 30° < α < 120°, preferably 45° < α < 90°. Particularly the reflector is arranged mainly coaxial to the expected discharge arc inside the discharge vessel. A low amount of material is sufficient for the reflector to provide a reflection of mainly all of the discolored light transmitting the salts.

The invention further relates to a motor vehicle lamp comprising a hous- ing and a discharge lamp, which may be designed as previously described, wherein the discharge lamp comprises a socket to which the burner is connected and the discharge lamp is connected to the housing via the socket. The socket of the lamp may be made of an insulating material, preferably a plastic material, for instance PPS (polyphenylene sulfide, (SCeFLt)_n). As previously described the motor vehicle lamp comprises a reduced amount of discolored light due to the specific reflector of the discharge lamp.

Particularly the motor vehicle lamp comprises a lens for guiding light emitted by the discharge lamp, wherein the design of the lens is shortened due to the emitted light shadowed by the reflector. Since a part of the emitted light is reflected by the reflector only a part of the lens may be active during operation. Thus, it is possible to cut the unused part of a normally designed lens away, so that the built in space is reduced. Further a clearly defined bright-dark cut-off may be provided by the reflector and/or the shortened lens. The risk of blinding an oncoming driver is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be apparent from and eluci- dated with reference to the embodiments described hereinafter.

In the drawings:

Fig. 1 is a schematic side view of a discharge lamp according to the in- vention, Fig. 2 is a schematic top view of the discharge lamp of Fig. 1 and Fig. 3 is a schematic detailed view of the discharge lamp of Fig. 1.

DETAILED DESCRIPTION OF EMBODIMENTS

The discharge lamp 10 illustrated in Fig. 1 comprises a socket 12 to which a burner 14 is connected. The socket 12 comprises a ring-pinstripe 16. The pinstripe 16 comprises two linear pinstripes 18. Further the pinstripes 16, 18 provide a defined bright-dark cut-off. In a discharge lamp 10 according to the projection type the pinstripes 16, 18 may be saved.

The burner 14 comprises a discharge vessel 20, where light is generated. Below the burner 14 with respect to gravity a reflector 22 is arranged. The reflector 22 is shaped like a part of a tube (Fig. 2). The tubular reflector 22 extends in circumferential direction over an angle α of ca. 50°. Due to the design of the reflector 22 the part below the pinstripes 18 is shadowed by the reflector 22 providing a well defined bright-dark cut-off. Further discolored light generated inside the discharge vessel 20 and transmitted through condensed and/or liquid salts 24 can be reflected reducing the amount of discolored light. In the embodiment illustrated in Fig. 2 a backlead wire 26 is lead through the reflector 22 from a distal electrode 28 to the socket 12. As illustrated in Fig. 3 a discharge arc 30 is provided during operation between a proximal electrode 32 and the distal electrode 28 due to a high voltage applied to the electrodes 28, 32. Due to the discharge arc 30 mainly white light is generated. A first beam 34 consisting of mainly white light may leave the burner 14 from the discharge arc 30. A second beam 36 emitted from the discharge arc 30 may be reflected by the salts 24 leading to a reflected beam 38, which may be discolored to for instance yellow light. A third beam 40 may transmit through the salts 24 and may be discolored to for instance yellow light. The third beam 40 is reflected by a reflective layer 42, which particularly comprises a color filter. Due to the color filter the third beam 40 is reflected as filtered beam 44 consisting for instance of mainly blue light. The yellow reflected beam 38 and the blue filtered beam 44 may be added to mainly white light increasing the efficiency of the discharge lamp 10.

While 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 dis- closed embodiments. For example, it is possible to operate the invention in an embodiment wherein the salts 24 discolor the emitted light to a different color than yellow so that not a blue filter but an adapted filter is provided onto the reflective layer 42. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclo- sure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, 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 does not indicate that a combination of these measured cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. Discharge lamp, particularly HID- or CDM- or HPD-lamp, comprising a burner (14) for emitting light connectable to a socket (12) for mechanical connection to a lighting device, wherein the burner (14) comprises a discharge vessel (20) for providing a discharge arc (30), and a reflector (22) arranged adjacent to the coolest area and/or lowest area of the discharge vessel (20) during operation.

2. Discharge lamp according to claim 1, wherein the reflector (22) comprises a color filter, particularly a blue filter, for filtering discolored light (40) due to a transmission of light emitted by the discharge arc (30) through condensed and/or liquid salts (24) inside the discharge vessel (20).

3. Discharge lamp according to claim 2, wherein the reflector (22) comprises a weighted absorption chosen such, that during operation the amount of light (38) reflected by the condensed and/or liquid salts (24) and the amount of light (44) transmitted through the condensed and/or liquid salts (24) and reflected by the reflector (22) add each other to mainly white light.

4. Discharge lamp according to claim 1, wherein the reflector (22) compris- es retro reflection elements, particularly cat-eyes.

5. Discharge lamp according to claim 1, wherein the reflector (22) is arranged spaced to the discharge vessel (20) and connected to the socket (12) and/or the burner (14).

6. Discharge lamp according to claim 1, wherein the reflector (22) comprises a backlead wire (26).

7. Discharge lamp according to claim 1, wherein the reflector (22) compris- es an insulating layer (42), particularly an insulating coating.

8. Discharge lamp according to claim 1, wherein the reflector (22) is designed mainly as part of a ring cylinder, which may extend in circumferential direction over an angle α of 20° < α < 180°, particularly 30° < α < 120°, preferably 45° < α < 90°.

9. Motor vehicle lamp comprising a housing and a discharge lamp (10) according to claim 1, wherein the discharge lamp (10) comprises a socket (12) to which the burner (14) is connected and the discharge lamp (10) is connected to the housing via the socket (12).

10. Motor vehicle lamp according to claim 9, wherein a lens and/or a reflector for guiding light emitted by the discharge lamp (10) is provided, wherein the design of the lens and/or the reflector of is shortened due to the emitted light shadowed by the reflector (22).