HK1176162A - Lamp - Google Patents

Description

Lamp with a light source

Technical Field

The invention relates to an electrode discharge lamp.

Background

It is known to excite a discharge in a vessel in order to generate light. A typical example is a fluorescent tube lamp using mercury vapor. Which can be excited to produce ultraviolet radiation. The phosphor is then excited to produce light. Many discharge lamps, such as sodium discharge lamps, are capable of directly producing visible light at the particular discharge frequency of the excitation material used. In terms of power consumption, such lamps are more efficient than tungsten lamps for the light generated per watt. However, it has the disadvantage that electrodes are required within the vessel to initiate the discharge. These electrodes carry the current required for the discharge and therefore degrade and eventually fail.

In one approach to an improved electrodeless bulb Lamp, we have improved the lamps shown in our patent application No. pct/GB2006/002018 entitled "Lamp" (our "' 2018 Lamp"), patent application No. pct/GB2005/005080 on the bulb of the Lamp, and patent application No. pct/GB2007/001935 on the matching circuit for a microwave powered Lamp. Both involve electrodeless-operated lamps in which a light-emitting plasma is excited in a bulb using microwave energy. Our' 2018 lamp uses a dielectric waveguide that can sufficiently reduce the wavelength at an operating frequency of 2.4 Ghz. Such lamps are suitable for use in domestic applications such as rear projection televisions.

Us patent No 6,737,809 describes a light source powered by microwave energy, the light source having:

a body having a sealed hollow therein,

a microwave-sealed faraday cage surrounding the body,

a body and a cavity defining a resonant waveguide,

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

an antenna arranged in the body for inducing a plasma

Microwave energy is delivered to the filler, the antenna having:

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

Following our approach, we combined the bulb and waveguide into a single component, as described in our international patent application No PCT/GB2008/003829, which was filed 11/14 th of 2008 and has been disclosed in publication number WO 2009/063205. In the latter, we describe and claim (with modifications during international prosecution) a light source powered by microwave energy, the light source having:

a body having a sealed hollow therein,

a microwave-sealed faraday cage surrounding the body,

the main body inside the faraday cage is a resonant waveguide,

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

an antenna disposed in the body 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;

wherein:

the body is a solid plasma crucible of a material which is transparent for the light to exit from, and

the faraday cage is at least partially transparent for light to exit from the plasma crucible, the arrangement being such that light from the plasma in the void can propagate through the plasma crucible and radiate out of the plasma crucible via the cage.

We call this Light source a Light Emitting Resonator (LER). As used in LER specification (WO 2009/063205):

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

"plasma crucible" refers to an enclosure enclosing a plasma, which is located in the void when the fill in the void is excited by microwave energy from an antenna.

In our LER lamp, the plasma is driven at a higher power. Thin-walled electrode lamps with the same internal dimensions are likely to fail at such high powers because the internal wall temperatures are high. When the general LER plasma chamber works, the load of the wall is more than 50W.cm^-2. Conventional fused silica arc tubes for conventional lighting applications operate at less than 25w.cm^-2. Wall loading is defined as the total power dissipated in the LER lamp divided by the internal surface area of the plasma chamber. We believe that higher wall loads are possible due to the heat dissipation capability of the LER lamp. Heat is conducted away from the vicinity of the plasma chamber by radiation and convection, and is dissipated from a relatively large surface area. Convection may be forced or naturally occurring.

We now believe that thick-walled electrodeless lamps can operate at powers of the same order as LER, and that the excitation material filling the void is also of the same order as in LER.

Disclosure of Invention

It is an object of the present invention to provide an improved light source.

According to the present invention, there is provided an electrode lamp comprising:

a transparent crucible having a sealed hollow therein,

a pair of electrodes carried by the crucible at opposite ends of the hollow and extending into the hollow, an

A filling of material in said void excitable by the current flowing between said electrodes, for forming a light-emitting plasma therein;

wherein:

the thickness of the wall of the lucent crucible is at least equal to the cross-sectional dimension of the hollow in the thickness direction.

The apparatus is such that, in use:

light from the plasma in the void is able to propagate through and radiate out of the plasma crucible, and

the heat from the plasma can be conducted from the hollow to the surface of the crucible to be dissipated there, thus maintaining the crucible at a stable operating temperature.

It is anticipated that a large amount of heat will be dissipated from the crucible surface by convection, and a large amount of heat will also be dissipated by radiation.

In addition, it is desirable to radiate heat from the interior material of the crucible, particularly from the portion near the hollow. To date, there is no means by which the precise location of origin of the radiated heat can be measured. That is, there is no means capable of measuring the amount of heat radiated from each round tube or shell in view of the crucible consisting of the gradually enlarged cylinder or shell. We believe that our thick-walled lamps do dissipate a significant proportion of heat by radiation from the crucible material near the hollow.

In our LER lamps, the ratio of the outer diameter to the hollow diameter is typically greater than 5. This allows the size of the crucible to be configured as a resonant cavity, in other words, such a size of the crucible can be used as a function of the microwave drive frequency.

In the present invention we can use such a ratio of hollow to crucible size, but it is not necessary to estimate this large ratio. In fact, it is desirable that the cross-sectional dimensions of the crucible be very small for microwave resonance. However, for a given hollow cross-section, the cross-sectional dimensions greatly exceed those of conventional lamps.

The hollow in the lucent crucible may be sealed around the electrode.

By pressure or squeeze sealing or

Sealing by vacuum shrinkage or

By cup-like sealing or

Sealing by graded glass.

Preferably, molybdenum in ribbon form, or any material with a similarly low coefficient of thermal expansion and high electrical conductivity, extends through the seal in the crucible and electrically connects the electrode to the outside of the crucible.

Preferably, a sealable evacuation tube is provided for introducing a material excitable by an electric current into the hollow in the lucent crucible.

Drawings

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

FIG. 1 shows a perspective view of a first lamp of the present invention; and

fig. 2 is a schematic central cross-sectional view of a second lamp of the invention.

Detailed Description

Referring first to fig. 1, a lamp 1 has a lucent crucible 2 made of a thick-walled quartz tube. The end 3 of the tube is closed and comprises a tungsten electrode 4. A hollow 5 is defined in the crucible. The tube has a bore of 5mm and a wall thickness T of 10 mm. The hollow thus has a transverse cross-section C of 5mm and a length L of 12 mm. The hollow is filled with an excited material, typically a metal halide and a rare earth gas. The actual filling may be selected according to the desired spectrum of emitted light.

For comparison purposes, the outside surface area of the tube corresponding to the hollow length is

2πRL

R is the radius of the tube and L is the length of the void. For the lamp in FIG. 1, the surface area is

2×π×12.5×12=942.48mm²。

Given that the convective and radiative heat losses from a surface are only proportional to that surface area, the length of a conventional 1mm thick thin-walled electrode lamp with an equal surface area is

12×12.5/3.5=42.86mm。

In other words, by increasing the thickness of the wall to form a thick wall lamp, the length can be reduced by more than 3 times. This is very beneficial in terms of its use in lighting to focus the light it emits. It is known that optical systems are more efficient when the light source controlled by the system is close to a point source. As can be seen by this comparison, the exemplary lamp of the present invention produces light over a very short length, thereby significantly increasing the lighting efficiency. It is desirable that this increase in efficiency reduces the number of lighting devices, even by half. This halving is not only operational but also capital cost.

It is known to the skilled reader of this specification that the electrodes may be incorporated into the lamp in any number. Thus, only one embodiment has been described.

Referring to fig. 2, a thick-walled lamp 11 has molybdenum cup seals 10 attached to both ends. The seal has tungsten electrodes 14 extending into the hollow 15 formed by the bore of the thick walled tube. The seal also includes a tungsten cup 16 having a feathered edge 17 disposed in the end of a short, thin-walled quartz tube 18, the quartz tube 18 being fused to the end of the thick-walled quartz tube 12. The electrodes are brazed to the cups at joints 19. The lamp may be filled with its inert gas and metal halide fill, or other excitable material, through an auxiliary exhaust tube 20 in front of the cup seal.

It is anticipated that for high power, the diameter of thick walled pipes can be increased to more than twice the diameter of the hollow bore, and for low power, the wall thickness can be reduced to equal the diameter of the hollow bore.

The lamp may be driven in any conventional manner, including with a primary voltage with a series choke.

Claims (7)

1. An electrode lamp having:

a transparent crucible having a sealed hollow therein,

a pair of electrodes carried by the crucible at opposite ends of the hollow and extending into the hollow; and

a filling of material in said void excitable by the current flowing between said electrodes, for forming a light-emitting plasma therein;

wherein:

the thickness of the wall of the lucent crucible is at least equal to the cross-sectional dimension of the hollow in the thickness direction.

2. The electrode lamp of claim 1, wherein the void in the lucent crucible is sealed near the electrode by pressure sealing or press sealing.

3. The electroded lamp of claim 1, wherein the void in the lucent crucible is sealed adjacent the electrode by vacuum shrink sealing.

4. The electrode lamp of claim 1, wherein the void in the lucent crucible is sealed near the electrode by a cup seal.

5. The electroded lamp of claim 1, wherein the void in the lucent crucible is sealed adjacent the electrode by a graded glass seal.

6. An electrode lamp according to any of the preceding claims, wherein a strip of molybdenum or any material with a similar low coefficient of thermal expansion and high electrical conductivity extends through the seal in the crucible and electrically connects the electrode to the outside of the crucible.

7. An electrode lamp according to any one of the preceding claims, wherein a sealable extraction tube is provided for introducing a material excitable by an electric current into the hollow in the lucent crucible.