HK1176161A - Light source - Google Patents

Description

Light source

Technical Field

The present invention relates to a light source for a lamp powered by microwaves.

Background

It is known to excite a discharge in a closed chamber to produce light. Typical examples are sodium discharge lamps and fluorescent tube lamps. The latter uses mercury vapor that produces ultraviolet radiation, which in turn excites the phosphor to produce light. Such lamps produce significantly more luminous flux per watt of electrical energy consumed than tungsten filament lamps. However, it has the disadvantage that electrodes are required in the closed chamber. Since these electrodes can carry the current required for discharge, they age and eventually fail.

The applicant has developed lamps for electrodeless bulbs, such as the lamp in patent application PCT/GB2006/002018 (applicant's "' 2018 lamp"), the bulb for a lamp in patent application PCT/GB2005/005080, and the matching circuit for a microwave-powered lamp in patent application PCT/GB 2007/001935. These applications all relate to electrodeless operated lamps in which a light emitting plasma is excited in a bulb with microwave energy. Early proposals for coupling microwave energy into a bulb using airwaves were proposed by, for example, the fushon Lighting Corporation in its U.S. patent No. 5,334,913. If an air waveguide is used, the bulb volume is large because the physical dimensions of the waveguide are only a small fraction of the wavelength of the microwaves in air. Although this may not be a problem, for example, when used for street lighting, this may result in lamps of this type not being widely used. To this end, applicants' 2018 lamp employs a dielectric waveguide that significantly reduces the wavelength at the operating frequency of 2.4 Ghz. Such lamps are suitable for use in domestic appliances such as rear projection televisions.

As disclosed in the applicant's international patent application PCT/GB2008/003829, WO 2009/063205, there is provided a light source powered by microwave energy, the light source having:

a solid plasma crucible of transparent material for the exit of light therefrom, the plasma crucible having a sealed void (void) therein,

a Faraday cage surrounding the plasma crucible, the cage being at least partially transparent for light to exit from the plasma crucible, while the Faraday cage is microwave-enclosed,

a filling of material excitable by microwave energy in said hollow for forming a luminous plasma therein, and

an antenna arranged in the plasma crucible for transmitting plasma-inducing microwave energy to the filling, the antenna having:

a connection extending to the exterior of the plasma crucible for coupling to a microwave energy source;

the arrangement is such that light from the plasma in the void can propagate through the plasma crucible and radiate out of the plasma crucible via the shield.

As used in this application and this specification:

"transparent" means that the material described by the term as transparent is transparent or translucent;

by "plasma crucible" is meant a closed body enclosing a plasma, which is located in the mid-air when the filling in the mid-air is excited by microwave energy from the antenna.

Disclosure of Invention

It is an object of the present invention to provide an improved light source powered by microwave energy.

According to the present invention there is provided a light source powered by microwave energy, the light source having:

a dielectric body, the material of which is transparent, for the exit of light therefrom,

a hollow located within the dielectric body;

a microwave-sealed faraday cage surrounding the dielectric body,

the dielectric body within the faraday cage provides a microwave resonant cavity,

a sealed plasma enclosure of transparent material in the mid-air within the dielectric body,

means for disposing the plasma enclosure within the hollow relative to the dielectric body,

a filler sealed in the plasma enclosure, the material of the filler being excited by microwave energy to form a light-emitting plasma, and

an antenna extending within the faraday cage for transmitting plasma-inducing microwave energy to the filler, the antenna having:

a connection extending to the exterior of the body for coupling to a microwave energy source.

Typically the body and the enclosure are of the same material, preferably quartz.

Preferably, the sealed plasma enclosure is formed from a drawn tube, the drawn tube providing a smooth inner bore. The tube may be received in the bore of the dielectric body with a gap. This configuration provides a smooth inner bore of the enclosure and avoids any stress due to intense heat of the plasma that could cause cracks in the hollow of the dielectric body. Preferably, the gap is minimal within the faraday cage, for example in terms of microwave resonance within the body.

It will be appreciated that the tubular closure may be sealed by welding to the quartz cover and inserting the entire structure into the bore of the body. The entire structure may be positioned by welding the cover to the body, particularly if the body is quartz. However, this configuration is not easy to manufacture.

Typically, the closure is formed by necking the tube of the closure. After filling and sealing, the necked-down portion may be supported by a disc welded to the end of the hollow.

In another embodiment, at least one tubular portion of the closure tube outward of the necked-down portion is non-necked and is welded to the body. The or each tubular portion outwardly of the necked-down portion may be swaged to match the void to which it is fused. Alternatively, one or both tubular portions of the closure tube outward of the necked-down portion are fused into one or both corresponding tubes attached to the surface of the body at the closure-bearing void of the body.

The closure may be supported at one end only by the tube, the other end of the hollow being open. Alternatively, the closure is still supported by the tube only at one end, but the other end of the hollow is closed.

Preferably, the holes in the body have a diameter greater than the outer diameter of the plasma enclosure, thereby forming a thermal barrier between the enclosure and the body.

In one embodiment, the closure is sealed with a slight constriction, leaving it contiguous with its original tubular member. This can be used to accommodate an antenna extending into the body, thereby eliminating the need for a separate antenna bore in the body. In this embodiment, the tube extends out of the body and is attached to another tube that extends back into the body, thereby creating a longer thermal path between the closure and the body.

Any gap between the closure and the body is preferably sealed independently of the closure. The gap may be evacuated for further thermal isolation or may be filled with a gas, typically an inert gas such as nitrogen. Although it is contemplated that there will be some convection of the nitrogen, this structure still significantly isolates the plasma enclosure from the dielectric body.

Drawings

To facilitate an understanding of the invention, specific embodiments thereof will now be described by way of example and with reference to the following drawings, in which:

FIG. 1 is a schematic perspective view of a light source according to the present invention;

FIG. 2 is a side cross-sectional view of a microwave resonant body including a bulb included in the light source of FIG. 1;

FIG. 3 is a similar view of a second resonant body;

FIG. 4 is a similar view of a third resonant body;

FIG. 5 is a similar view of a fourth resonant body;

figure 6 is a similar view of a variant of the fourth resonant body.

Detailed Description

Referring to the drawing, a lamp 1 of the invention is powered by a magnetron 2 via a coupling circuit 3. Specific details regarding coupling circuit 3 are given in co-pending patent application No.0907947.6, 5, 8, 2009. Since it does not form part of the present invention per se, it will not be described in detail herein.

The lamp has a microwave resonator body 11 of transparent quartz material supported by the end face 4 of the aluminum end piece 5 of the coupling circuit 3. The resonant body and the end piece are circular and of the same diameter, whereby a perforated faraday cage 12 is clamped to the coupling end piece by means of a tension band 6 via the end face 14 of the resonant body and its peripheral side 15, thereby fixing the resonant body to the end piece. This detail is similar to that described by the applicant in patent application No.0907947.6, which is incorporated by reference.

The resonant body has a central hole 16 in which a closed bulb 17 enclosing the plasma is inserted. The bulb 17 is also quartz and has an outer diameter that fits closely to the hole. The bulb itself is a drawn quartz tube 18 and therefore has a smooth inner bore 19. An end cap 20 is welded to the quartz tube and encloses a quantity of material which can be excited to produce a light-emitting plasma in the bulb when microwaves are fed into the body via the antenna 7 in the bore 21 of the resonant body. The body is dimensioned to provide resonance within the faraday cage within the body 11, the bulb 17 and the fill-containing void 22 in the bulb. There are very small gaps between the bulb and the resonant body, which can be considered for resonance purposes. The bulb is fixed in the body by means of a seal 23.

This configuration avoids the possibility of cracking due to micro-cracks that may exist after the hole 16 is drilled, which in use are subjected to the very high temperatures of the material-induced plasma within the hollow. Preferably, the plasma and the gas body supporting it are contained in smooth and micro-crack-free holes of the bulb.

Turning to fig. 3, an alternative construction of the bulb is shown, in which the bulb 31 is formed from a drawn quartz tube, with a necked-down seal 32. Likewise, the quartz tube fits tightly into the bore 33 in the body 34. At the end of the bore, the neck is swaged (upset) 35 and sealed 36 into the bore. A structure with a small void 37 in the seal 36 is finally formed, but this structure is effective for resonance purposes, being a solid body with only a plasma void 38 in the bulb 31.

A variant is shown in fig. 4, in which the bulb 51 formed from drawn quartz tube with the necked-down seal 52 has a diameter smaller than the diameter of the bore 53 in the body 54. The bulb is supported within the body by supporting the neck 55 of the bulb within a perforated disc 56. This forms a seal with both the neck and the body. As a result, the bulb is thermally insulated from the dielectric body and can operate hotter due to less heat being conducted to the body via the neck. This structure prevents thermally induced stress due to the difference in expansion of the bulb and the body because the coefficient of thermal expansion of quartz is low. However, the bulb may also be located in a hole 53 having a perforated disc 56 on one end and no holes on the other end. The sealed void 57 around the bulb may be evacuated prior to sealing or filling with a body of inert gas, such as nitrogen. Whether the void is evacuated or filled with a gas, it has a small but theoretically determinable effect on the microwave frequency at which resonance is established within the body.

Another embodiment shown in fig. 5 has a bulb 71 also formed from drawn quartz tube, which has a necked-down seal 72 at one end, but from the side facing away from the seal 72, the tube 81 continues with the full diameter of the tube. As in the previous examples, the tube was drawn and the inside was smooth and crack-free. The end 82 of the bulb remote from the seal 72 is sealed and the bulb includes a quantity or fill of excitable material for providing a plasma. The bulb is supported in a hole 73 in a transparent, resonant quartz body 74. Like the bulb end 82, one end of the bore is sealed by: a quartz tube 83 having a relatively large diameter is fused to the body and then necked down and sealed.

Another large diameter tube 84 is welded to the other end of the body and surrounds the bulb tube 81 away from the bulb. The distal ends of the two tubes are welded together by necking the outer tube onto the inner tube, welding the two together, and then removing the respective excess portions. Conveniently, this operation is performed before the tube 83 at the opposite end is necked down and sealed, since the necking down and sealing of the tube 83 is able to drive out the air sealed in the interspace 77 between the bulb and the hole of the resonator body.

The structure is as follows:

positioning the bulb in the center of the hole 73;

providing an insulating gap between the bulb and the body;

providing a longer conduction path along the tubes 81, 84 from the bulb to the hole;

a location 85 (located in the center of the bulb tube 81) of the antenna 77 is provided for introducing microwaves into the body.

In the variant shown in fig. 6, the resonant modes within the body depend only on the diameter of the body and not on its axial length, the resonance being proportionally longer, but the outer tube 841 shorter. This structure enables the antenna 771 to extend into the main body 741 to a greater extent.

It will be appreciated that the embodiments of figures 4, 5 and 6 are particularly capable of operating at low wattage, as the bulbs 51 and 71 may be hotter in operation. Therefore, the filler can keep enough heat required for light-emitting power generation at a lower power.

Claims (15)

1. A light source powered by microwave energy, the light source having:

a dielectric body, the material of which is transparent, for the exit of light therefrom,

a hollow located within the dielectric body,

a microwave-sealed faraday cage surrounding the dielectric body,

the dielectric body within the faraday cage provides a microwave resonant cavity,

a sealed plasma enclosure of transparent material in the mid-air within the dielectric body,

means for disposing the plasma enclosure within the hollow relative to the dielectric body,

a filler sealed in the plasma enclosure, the material of the filler being excitable by microwave energy to form a luminescent plasma, and

an antenna extending within the faraday cage for transmitting plasma-inducing microwave energy to the filler, the antenna having:

a connection extending to the exterior of the body for coupling to a microwave energy source.

2. The light source of claim 1, wherein the body and the enclosure are quartz.

3. A light source as claimed in claim 1 or 2, wherein the void is an aperture in the body and the sealed plasma enclosure is housed in the aperture with a gap between the enclosure and the aperture.

4. A light source as claimed in claim 1, 2 or 3, wherein the sealed plasma enclosure is formed from drawn tube.

5. The light source of claim 4, wherein,

the tubular closure is welded to the quartz cover sealing its ends,

positioning the closure and disc structure by welding the lid to the body, wherein the closure is within the hollow.

6. The light source of claim 4, wherein the closure has a necked, sealed portion of its tube.

7. A light source as claimed in claim 6, wherein the necked-down seal portions are supported by discs welded to the ends of the hollow.

8. The light source of claim 6, wherein at least one tubular portion of the enclosure tube outward of the necked-down portion is un-necked and welded to the body.

9. The light source of claim 8, wherein the or each tubular portion outward of the necked portion is swaged to match the void.

10. The light source of claim 6, wherein one or two tubular portions of the closure tube outward of the necked-down portion are fused into one or two corresponding tubes attached to a surface of the body at a void of the body with a closure.

11. A light source as claimed in claim 10, wherein the closure is supported at one end only by a tube, the other end of the void being open.

12. A light source as claimed in claim 10, wherein the enclosure is supported at one end only by a tubular member, the other end of the hollow being closed.

13. A light source as claimed in any one of claims 8 to 12, wherein the or one of the tubular portions is open and arranged to receive an antenna extending into the body.

14. A light source as claimed in any preceding claim, wherein a gap between the closure and the body is sealed and evacuated independently of the closure.

15. The light source of claim 12, wherein the evacuated gap is filled with an inert gas.