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A PLASMA LIGHT SOURCE WITH LOW METAL HALIDE DOSE The present invention relates to a plasma light In this specification the following terminology is means an actual emitter of together with closely associated components for controlling spread of means a complete light including a light US patent No Matsushita has the following The apparatus has a light transmitting bulb for confining a discharge a fill sealed within the light transmitting bulb and including a rare gas and a metal halide emitting a continuous spectrum by molecular and a discharge excitation source for applying electrical energy to the fill and for starting and sustaining an arc and the metal halide includes one kind of halide selected from the group consisting of an indium a gallium and a thallium or a mixture and in that the light transmitting bulb has no electrodes exposed in discharge space and this construction utilizes the continuous spectrum of molecular radiation of the metal halide and thereby achieves high color rendering properties and high luminous efficacy simultaneously without using mercury as the The desirability of the quantity of halides being equal to or greater than x of internal dimension is In particular this internal dimension is defined as the inner distance in the direction of the electric field of the electrical energy applied to excite the Also the presence of a quantity of zinc equal to or greater than 5 x of internal dimension is It is said to contribute to internal pressure in the This bulb produces a broad spectrum light as shown in the Matsushita reproduced in figure 1 of this The Matsushita Patent speaks of quantities of halides in of wall to wall distance in the direction of the electric In the context of the Matsushita this is straightforward in that the bulb is In our the cavities that we establish discharges in are circular For the avoidance of we measure the distance in the length of the circular cylindrical In tests we have attempted to improve on the Matsushita Patent for horticultural use for where a strong blue and UV region of the spectrum is This is surprising in view of the teaching that metal halide molecular radiation is broad spectrum across the visible This teaching is not only in the above patent but also for instance at which lamps have high luminous efficacy of around lumens per which is about twice that of mercury vapor lights and 3 to 5 times that of incandescent lights and produce an intense white It appears to us that the teaching of the above patent and the Wikipedia abstract does not apply to metal halides in the low concentrations that we have been In these we get different results from those Before setting out our which has been made in research into improved horticultural although it is not restricted to such lights and we expect that our improved lights will be used in other applications for UV we reproduce a plot of solar as seen in figure 2 of this This visible light and radiation both as it reaches the outer atmosphere and as it reaches sea The difference is significant in that plants which have evolved in mountains receive more of certain radiation than they do when grown at sea The biggest difference is in the UV Minimal UV at sea level below the atmosphere absorbing all of At the transition to visible light approximately of incident UV is absorbed at sea At a little over there is still a marked absorption of incident blue The object of the present invention is to provide a light source providing an enhanced of radiation at the blue end of the including into ultraviolet with a view to a supplementing ambient light with atmospherically absorbed light and supplementing artificial light having little or no emission in the UV and blue According to a first aspect of the invention there is provided a plasma light source a lucent envelope or a lucent crucible or fabrication a sealed void containing material excitable as a including at least two metal halides and an inert the two metal halides together being provided in a concentration in use of less than x of an inner distance within the void with electrical energy being applied to excite the discharge with its electric field being in the direction of the For the avoidance of we have measured the distance along the length of the for instance along the length of the sealed plasma as described in our International Patent Application WO of which the abstract is as For operation in the TMOIO mode at a lucent crucible of quartz is in diameter and in A sealed plasma void is placed centrally on the central with an antenna at one but offset from the central axis of the crucible and close to the central It should be specifically noted that the concentration of halides is such that the vapour within the void is unsaturated in In other words there is no liquid This results we believe in strong molecular radiation as well as atomic Preferably the lucent envelope will be a lucent tube sealed at its ends to provide the sealed the length of the tube being in the direction of the wall the lucent envelope will be provided within a central longitudinal bore in a separate lucent It can be fixedly provided within the bore in the separate lucent the lucent crucible can be a body of lucent material having a central longitudinal bore which provides the sealed the length of the bore being in the direction of the The crucible can be as described in our above Application WO Normally in the crucible or the lucent body will be enclosed an HF Faraday surrounding the crucible on an outside and an end thereof and being at least partially light transmitting for light exit from the plasma the arrangement being such that light from a plasma in the void can pass through the plasma crucible and radiate from it via the The Faraday cage can be as described in our above Application WO We have found that the following noble gases are suitable for use as the inert neon argon krypton xenon We have also included Hg in the fill as a We have tested a variety metal halides and results suggest that they can be chosen from bromides and For practical fluorides can only be used in plasma crucibles made of ceramic We believe that the following metals are suitable as halides for our light We recognise that current environmental regulations would preclude use of Cd and Pb in products placed on the The limits for the total metal halide content of the plasma which we believe to be are between x and x 10 6 of the inner distance in the direction of the electric field of the electrical energy applied to excite the Our preferred range is between x 10 8 and x 106 Our preferred range for the inert gas content of the plasma crucible are between x 10 8 and x of the distance in the direction of the electric field of the electrical energy applied to excite the Our preferred range for the content of the plasma crucible are between x 10 6 and x 106 of the distance in the direction of the electric field of the electrical energy applied to excite the We expect the range to be between x 10 5 and x 10 5 To help understanding of the a specific embodiment thereof and variations will now be described by way of example and with reference to the accompanying in Figure 1 is a graph showing a broad spectrum of light produced by a such as used in US Figure 2 is a plot of solar radiation showing visible and radiation both as it reaches the outer atmosphere and as it reaches sea Figure 3 is a perspective view of a lucent plasma crucible of the Figure 4 is a view of a lucent envelope and such as used in WO which can be used in a variant of the the view is Figure 5 of WO Figure 5 is a similar view of another lucent envelope and such as used in WO which can be used in another variant of the the view is Figure 1 of WO Figure 6 is the output spectral power distribution between 300nm to 550nm for example Figure 7 is the output spectral power distribution between 300mn to 1 lOOnm for example Figure 8 is the output spectral power distribution between 300nm to 550nm for example Figure 9 is the output spectral power distribution between 300nm to 1 lOOnm for example Figure 10 is the output spectral power distribution between 300nm to 550nm for example Figure 11 is the output spectral power distribution between 300nm to 1 lOOnm for example Figure 12 is the output spectral power distribution between 300nm to 550nm for example Figure 13 is the output spectral power distribution between 300nm to 11 OOnm for example Figure 14 is the output spectral power distribution between 300nm to 550nm for example Figure 15 is the output spectral power distribution between 300nm to 1 lOOnm for example Figure 16 is the output spectral power distribution between 300nm to 550nm for example Figure 17 is the output spectral power distribution between 3 OOnm to 1 lOOnm for example Figure 18 is the output spectral power distribution between 300nm to 550nm for example Figure 19 is the output spectral power distribution between 300nm to 11 OOnm for example Referring to Figure a light source 1 to be powered by microwave energy is It is similar to that described in our WO whose abstract is quoted The source has a circularly cylindrical body 2 of forming a solid plasma envelope or Quartz is transparent to visible light and the outer surfaces of the quartz are The crucible could be of translucent ceramic such as We to mean either transparent or The crucible has a length and a diameter Aligned centrally is a void It is short and of small diameter with respect to the dimensions of the crucible The void is sealed by working of the material of the crucible or an additional piece of Methods of sealing are described in our International application A Faraday cage 4 surrounds the curved side surface 5 and one end surface 6 of the It can be of metallic mesh or reticular metallic such that the majority of light passing out of the crucible at these surfaces passes through the whilst microwaves A band 7 of the cage extends around an end of a carrier 8 to which the cage is thereby carrying the A fill of microwave excitable material of metal halide with a mercury buffer in a noble is contained to form a light emitting plasma therein An antenna 10 is arranged in a bore 11 extending within the plasma crucible for transmitting inducing microwave energy to the The antenna has a connection 12 extending outside the plasma crucible for coupling to a source of microwave energy 14 the source being shown Details of such a source and means for feeding microwave energy into the connection are described in International patent application WO More as described in our WO and WO we have moved from a quartz crucible having an excitable material envelope secured within it to an envelope fixed or free within the which we have described as a lucent body as opposed to a crucible as The body has remained sized for microwave Figure 4 is a Figure 5 of WO whose abstract is as follows albeit with altered reference A crucible 101 for a LUWPL is formed from a wave guide body 102 having a central bore 103 through Received within the central bore is a drawn quartz tube having its ends one 141 having been worked flat to be coplanar with one face 121 of The other end 142 has a vestigial tip This is secured to the body at the orifice 122 of the bore in the other face 123 of the The securement is by means of ceramic adhesive compound Figure 5 is a Figure 1 of WO whose abstract is as follows albeit with altered reference A light source 201 to be powered by microwave having a dielectric body 203 or fabrication of material lucent for exit of light a receptacle 222 within the dielectric body or and a lucent Faraday cage 209 surrounding the dielectric body or The dielectric body or fabrication within the Faraday cage forms at least part of a microwave resonant A sealed plasma enclosure 221 of lucent material within the receptacle 222 has a means not visible for locating the plasma enclosure within the receptacle with respect to the dielectric body or In the language of the present and of WO are the present envelope and bore in the For the avoidance of the lucent bodies and envelopes of WO or WO can be used with the fills of the present as exemplified Further for the avoidance of the distance in the direction of the applied electric field is the internal distance in the length in Figure 1 and the equivalent directions and distance in the lucent bodies and envelopes of WO or WO In the latter the envelope can be provided with means location means such as in that fused on lugs locating in recesses in the body from the Alternatively the bore can be and the envelope can be plain with other location means In the following examples of lucent crucibles in which we have lit we use which has a dielectric constant of as the material of the lucent crucible and we operate at a frequency of At an input power of approximately 265 we have tested the performance of plasma crucibles containing mixtures Example A Sbl3 GaBr3 1 All3 xlO7 Total metal halides x 1 O7 Hg xlO5 Xe xlO8 Example B Sbl3 GaBr3 1 O7 AlBr3 107 Total metal halides x 1 O7 Hg Xe xlO8 Example C Sbl3 xlO7 O7 Til O7 Total metal halides x 107 Hg O5 Xe O8 Example D O7 GaBr3 x Snl2 O7 Total metal halides x Hg x 1 O5 Xe Example E GaCl3 x ZnCl2 x O7 Total metal halides x 1 O7 Hg x 10 Xe x IQ8 Example G xlO7 InCl x 107 Total metal halides x 107 Hg xlO5 Xe Example H GaBr3 O7 Sbl3 xl07 Total metal halides xlO6 Hg x 105 Xe Summary of output 300 to 550 and 300 to 1100 nm at capsule input power of 265 W Example 300 to 550 nm 300 to 1100 nm Example A Example B Example C Example D Example E Example G Example H Rank by Blue Blue UV o Example Capsule nm nm Ratio run n nm nm w 6970 Example H 6868 Example C 6971 Example E 7180 6524 Example A 6910 Example B 6896 73 m Rank by 400 to 490 m Blue Blue UV a Example Capsule nm nm Ratio nm nm nm nm m m 6868 Example G 6970 73 c Example D 6524 m Example A 6910 Example B 6896 CO Example E 7180 Example C 6971 m o o o The resulting spectra are show in Figures 6 7 Figures 8 9 Figures 10 1 1 Figures 12 13 Figures 14 15 Figures 16 17 Figures 18 19 there is no example insufficientOCRQuality
CLAIMS:

1. A plasma light source comprising:

• a lucent envelope or a lucent crucible or fabrication having:

• a sealed void containing

• material excitable as a plasma, including

• at least two metal halides and

• an inert gas;

the two metal halides together being provided in a concentration in use of less than 5.0 x 10-6 mol/cm of an inner wall-to-wall distance within the void with electrical energy being applied to excite the discharge with its electric field being in the direction of the wall-to-wall distance.

2. A plasma light source as claimed in claim 1, wherein the concentration of halides is such that the vapour within the void is unsaturated in use.

3. A plasma light source as claimed in claim 1 or claim 2, wherein there is no pool of excitable material in use.

4. A plasma light source as claimed in claim 1 , claim 2 or claim 3, wherein the lucent envelope is a lucent tube sealed at its ends to provide the sealed void, the length of the tube being in the direction of the wall-to-wall distance.

5. A plasma light source as claimed in claim 4, wherein the lucent envelope is provided within a central longitudinal bore in a separate lucent body.

6. A plasma light source as claimed in claim 5, wherein the lucent envelope is fixedly provided within the bore in the separate lucent body.

7. A plasma light source as claimed in claim 1, claim 2 or claim 3, wherein the lucent crucible is a body of lucent material having a sealed, central longitudinal bore which provides the sealed void, the length of the bore being in the direction of the wall-to-wall distance.

8. A plasma light source as claimed in claim 5, claim 6 or claim 7, wherein the crucibel or lucent body is enclosed by:

• an HF electromagnetic-wave-enclosing Faraday cage:

• surrounding the crucible on an outside and an end thereof and

• being at least partially light transmitting for light exit from the plasma crucible,

the arrangement being such that light from a plasma in the void can pass through the plasma crucible and radiate from it via the cage.

9. A plasma light source as claimed in any preceding claim, wherein the inert gas is a noble gas or a mixture of noble gases, preferably chosen from: neon (Ne), argon (Ar), krypton (Kr), xenon (Xe).

10. A plasma light source as claimed in any preceding claim, wherein the fill includes mercury as a buffer.

11. A plasma light source as claimed in any preceding claim, wherein the halides are chosen from chlorides, bromides and iodides and the lucent envelope or crucible is of quartz or ceramic.

12. A plasma light source as claimed in any one of claims 1 to 10, wherein the halides are chosen from fluorides and the lucent envelope or crucible is ceramic material.

13. A plasma light source as claimed in any preceding claim, wherein the halides are chosen from the halides of Al, As, Bi, Cd, Ga, Ge, In, Nb, Pb, Sb, Sn, Ti, Tl, V, Zn.

14. A plasma light source as claimed in any preceding claim, wherein the total metal halide content of the plasma crucible is between 1.60 x 10-8 and 4.99 x 10-6 mol/cm of the inner wall-to-wall distance in the direction of the electric field of the electrical energy applied to excite the discharge.

15. A plasma light source as claimed in claim 14, wherein the total metal halide content is between 4.10 x 10-8 and 1.85 x 10-6 mol/cm.

16. A plasma light source as claimed in any preceding claim, wherein the inert gas content of the plasma crucible is between 1.00 x 10-8 and 3.25 x 10-6 mol/cm of the wall-to-wall distance in the direction of the electric field of the electrical energy applied to excite the discharge.

17. A plasma light source as claimed in any preceding claim, wherein the Hg buffer content of the plasma crucible is between 1.25 x 10-6 and 1.25 x 10-6 mol/cm of the wall-to-wall distance in the direction of the electric field of the electrical energy applied to excite the discharge.

18. A plasma light source as claimed in claim 17, wherein the Hg buffer content is between 1.2 x 10-5 and 7.5 x 10-5 mol/cm.