Patent Abstract:
There is described an ultraviolet light source comprising an ultraviolet bulb, a pulsed microwave energy source for exciting said ultraviolet bulb and an enclosure for enclosing the ultraviolet lamp, the enclosure comprising an optically transparent waveguide. The optically transparent waveguide wholly surrounds the bulb. The ultraviolet light source is particularly suitable for use in the sterilisation of substances; the promotion of photochemical reactions; and the promotion of molecular dissociation in liquids.

Full Description:
TECHNICAL FIELD  
         [0001]    The present invention is in the field of pulsed ultraviolet (UV) light sources.  
         BACKGROUND TO THE INVENTION  
         [0002]    It is known to use ultraviolet (UV) radiation in sterilisation systems for use in the purification of water and the sanitisation of a variety of items. The UV radiation and any ozone produced by the UV radiation with oxygen in the air acts to kill bacteria and germs. It is also known to use ultraviolet (UV) radiation for a variety of other uses including those involving the promotion of photochemical reactions and of molecular dissociation.  
           [0003]    Conventional systems employ microwave energy to excite the source of UV radiation. One problem such systems is that it is difficult to efficiently provide sufficient excitation energy to the UV source and difficult to effectively transfer that energy to the substance or entity to be treated. It is therefore difficult to arrange systems for high energy, high throughput industrial purposes.  
           [0004]    There is now described an ultraviolet light source which enables efficient, high throughput UV treatment to be conducted. The ultraviolet light source comprises an UV lamp which is excited by a microwave energy source. The lamp is enclosed by a waveguide comprising UV transparent material.  
           [0005]    PCT Patent Applications Nos. WO 00/32244 and WO 01/09924 (in the name of the Applicant) describe non-pulsed ultraviolet light sources. The pulsed ultraviolet light sources of the present invention have been found to provide for enhanced efficacy (e.g. enhanced sterilising capability) and reduced power consumption when compared to the earlier described, non-pulsed ultraviolet light sources.  
         SUMMARY OF THE INVENTION  
         [0006]    According to one aspect of the present invention there is provided an ultraviolet light source comprising an ultraviolet bulb; a pulsed microwave energy source for exciting said ultraviolet bulb; and an optically transparent waveguide for guiding pulsed microwave energy originating from said pulsed microwave energy source to the ultraviolet bulb. The waveguide wholly surrounds the ultraviolet bulb.  
           [0007]    Typically, the waveguide forms an enclosure for the ultraviolet bulb.  
           [0008]    The microwave energy source provides pulsed microwave energy to excite the ultraviolet bulb. Pulsed microwave energy sources are known in the art. In general, the ultraviolet light source herein requires pulsing at relatively high power levels at a relatively short pulse width.  
           [0009]    Suitably, the microwave energy source can be pulsed with pulse widths ranging from 100 milliseconds to 0.5 microseconds, preferably from 10 milliseconds to 5 microseconds.  
           [0010]    Suitably, the microwave energy source has a pulse period of from 100 milliseconds to 0.5 microseconds, preferably from 5 milliseconds to 50 microseconds.  
           [0011]    Suitably, the microwave energy source can be pulsed at a frequency of from 2 MegaHertz to 10 Hertz.  
           [0012]    Optimisation of both pulse width and pulse period is preferred.  
           [0013]    Suitably, the peak operating energy of the bulb is from 100 watts to 100,000 watts, preferably from 500 watts to 30,000 watts.  
           [0014]    In aspects herein, the lamp may be excited by both a continuous (i.e. non-pulsed) microwave energy source and a pulsed microwave energy source. In aspects, the ultraviolet light source additionally comprises a continuous microwave energy source, which may be separate from or integral with the pulsed microwave energy source.  
           [0015]    Suitably, the energy consumption of pulsed excitation is significantly lower than that of continuous excitation. Typically, the pulsed energy for excitation is directly dependent on the pulse duty cycle (pulse width/pulse period).  
           [0016]    Suitably, the peak energy value of pulsed excitation is significantly higher than that of the peak energy value of continuous excitation. Typical peak energy ratios are from 1:10 to 1:100 for continuous: pulsed energy levels. In one example, the lamp is excited at steady state by a continuous 100 watt energy source and pulsed at up to 3,000 watts by a pulsed excitation source.  
           [0017]    In aspects, the ultraviolet light source may be arranged for the emission of either monochromatic or polychromatic ultraviolet radiation.  
           [0018]    The dominant wavelength of the ultraviolet light source may be selected according to the particular application for which the light source is to be used.  
           [0019]    In one aspect, the dominant wavelength of the ultraviolet light source is from 240 nm to 310 nm, particularly 254 nm. Such wavelengths have been found to be particularly useful for sterilisation, purification or sanitisation applications.  
           [0020]    In another aspect, the dominant wavelength of the ultraviolet light source is from 140 to 260 nm, preferably from 150 to 220 nm, most preferably from 160 to 200 nm, particularly 182 nm or 185 nm. Such wavelengths have been found to be particularly useful for use in promoting molecular dissociation reactions.  
           [0021]    In a further aspect, the dominant wavelength of the ultraviolet light source is from 310 to 400 nm, preferably from 320 to 380 nm, most preferably from 330 to 370 nm, particularly 346 nm. Such wavelengths have been found to be particularly useful for use in promoting certain photochemical reactions.  
           [0022]    The ultraviolet light produced by the ultraviolet light source herein may additionally be channelled as a light source of high intensity. Suitable uses would include lighting within buildings and lighting for vehicles such as cars, lorries and buses.  
           [0023]    By optically transparent waveguide it is meant a waveguide that is substantially transparent to the ultraviolet radiation employed herein, typically having a transparency of greater than 50%, preferably greater than 90% to UV radiation.  
           [0024]    The waveguide controls the flow of ultraviolet radiation therefrom. The control function typically includes the prevention of the release of harmful or unnecessary ultraviolet radiation frequencies.  
           [0025]    In aspects, the waveguide is provided with a sleeve (e.g. a quartz sleeve) and the material of that sleeve is selected to preferentially allow different wavelengths of UV radiation to escape. The exact nature of the waveguide and its control function can be tailored to fit the purpose of use.  
           [0026]    Suitably, the ultraviolet bulb has no electrode. That is to say it is an electrode-less bulb such as one comprising a partially evacuated tube comprising an element or mixtures of elements in vapour form. Mercury is a preferred element for this purpose, but alternatives include mixtures of inert gases with mercury compounds, sodium and sulphur. Halides, such as mercury halide are also suitable herein. Amalgams are also suitable herein including indium/mercury amalgam.  
           [0027]    Inevitably, such electrode-less bulbs emit a spectrum of wavelengths, dependent on the chemical nature of the core element or elements. Embodiments employing multiple lamps of different spectrum characteristics are envisaged herein.  
           [0028]    In one aspect, the waveguide controls the flow of microwave energy therefrom. Control of the microwave energy which passes through the waveguide is useful in embodiments of the invention which make use of both UV and microwave radiation.  
           [0029]    In another aspect, the waveguide blocks at least the majority of the flow of microwave energy therefrom.  
           [0030]    Suitably, the waveguide comprises a sleeve therefor, and said sleeve is comprised of quartz or a UV-transparent plastic material. In general, a sleeved waveguide will be cylindrical in form.  
           [0031]    Different configurations of waveguide and sleeve can be envisaged. In one aspect the waveguide is rectangular in form and has a quartz sleeve provided therearound. In another aspect, the waveguide is cylindrical in form (e.g. comprised of a metallic screen or mesh). Rectangular quartz-sleeved waveguides are in general more expensive than cylindrical mesh waveguides.  
           [0032]    Suitably, the waveguide or any sleeve therefor is coated with a coating which assists in controlling the flow of ultraviolet and/or microwave energy therefrom. The coating may be applied to either or both of the inner or outer surfaces of the waveguide. Partial coatings are also envisaged.  
           [0033]    Suitably, a system for cleaning the waveguide or any sleeve therefor (e.g. the quartz tube) is incorporated herein. Suitable cleaning systems include those based upon fluid flow, such as flow of water, air or gas. Cleaning agents such as detergents may be employed as necessary.  
           [0034]    Suitably, the waveguide or any sleeve therefor comprises a conducting material. The conducting material may be integral, or applied as an internal or external coating or liner. The liner may directly contact the inner surface of the waveguide or be spaced therefrom.  
           [0035]    In aspects, any sleeve for the waveguide and/or the ultraviolet bulb is coated with a coating that assists in modifying the wavelength of emitted light.  
           [0036]    In other aspects, the waveguide is constructed to ensure control of the escape of microwave energy. For example, the waveguide can be adapted to include different hole spacings, wire thicknesses and overall configurations.  
           [0037]    Suitably, the waveguide comprises a conducting mesh. Preferably, the conducting mesh comprises a high frequency conducting material selected from the group consisting of copper, aluminium and stainless steel.  
           [0038]    The ultraviolet bulb has any suitable shape and size, including elongate forms such as a cigar-shape. The bulb size can be tailored. Typical bulb diameters are from 5 to 200 mm, for example 38 mm.  
           [0039]    Embodiments are envisaged in which plural bulbs are employed. The bulb may be similar in type e.g. of similar size and operating temperature or combinations of different bulb types may be employed. The number of bulbs employed is tailored to the purpose of use. Typically from 2 to 25 bulbs are employed, such as from 3 to 18 bulbs. Various forms of arrangement of the plural bulbs are envisaged including random or informal arrangements, side-by-side arrangements, sequential arrangements, array arrangements and clusters. The bulbs may be arranged in serial, parallel or mixed serial and parallel electrical circuit arrangements.  
           [0040]    The optically transparent waveguide has any suitable shape, such as cylindrical or rectangular forms. The length and size of the waveguide is tailored to fit the particular purpose of use and to provide an enclosure for the necessary bulb(s).  
           [0041]    Suitably, the ultraviolet bulb has an operating temperature which maximises the chosen bulb characteristics. Typical operating temperatures are from 10° C. to 900° C., for example 40° C. to 200° C. and the operating temperature will be selected and optimised according to the purpose of use.  
           [0042]    Suitably, the pulsed microwave energy source comprises a magnetron or other suitable microwave-producing device with suitable pulsing circuitry.  
           [0043]    Suitably, the ultraviolet light source additionally comprises a system for cleaning the waveguide or any sleeve thereof (e.g. a quartz sleeve).  
           [0044]    Suitably, the ultraviolet light source additionally comprises a pathguide to guide the pulsed microwave energy from the pulsed microwave energy source to the ultraviolet bulb.  
           [0045]    In one aspect the pathguide defines an essentially linear path for the microwave energy.  
           [0046]    In another aspect, the pathguide defines a non-linear path such as a path defining an angle, such as a right angle.  
           [0047]    Suitably, the pathguide comprises a coaxial cable.  
           [0048]    Suitably, the ultraviolet light source additionally comprises a housing for said waveguide. Preferably, the housing has an inlet and an outlet and the housing is shaped to guide fluid flow from the inlet past the waveguide (e.g. along a protective sleeve for the waveguide) to the outlet. Preferably, the fluid comprises air or a liquid such as water. Suitably, the ultraviolet light source additionally comprises a pump for pumping fluid from the inlet, past the waveguide to the outlet. Alternatively, gravity may be utilised to encourage fluid flow.  
           [0049]    The choice of materials for use in the housing and any fluid flow piping arrangements can be important. Typically, the materials will be selected which are resistant to corrosion and which do not leach contaminants to the system. Seal materials are also carefully selected with typical seal materials including Chemraz (trade name), Teflon (trade name), encapsulated Viton (trade name) and GORE-TEX (trade name).  
           [0050]    According to another aspect of the present invention there is provided a lamp comprising an ultraviolet bulb, said bulb being excitable by pulsed microwave energy; and an optically transparent waveguide for guiding pulsed microwave energy originating from a pulsed microwave energy source to the ultraviolet bulb, wherein said waveguide wholly surrounds the ultraviolet bulb.  
           [0051]    Preferably, the ultraviolet bulb has no electrode.  
           [0052]    According to a further aspect of the present invention there is provided a method of sterilising a substance comprising applying pulsed microwave energy to an ultraviolet lamp to produce ultraviolet radiation of dominant wavelength of from 240 nm to 310 nm; and exposing the substance to said ultraviolet radiation, wherein an optically transparent waveguide guides said pulsed microwave energy to said ultraviolet lamp and said waveguide wholly surrounds the ultraviolet lamp.  
           [0053]    The sterilising method aspect herein is suitable for use in sterilising a variety of substances including water for human consumption; waste water and sewage; metallic and non-metallic objects including medical instruments; air in buildings such as hospitals, offices and homes; and in prolonging the shelf-life of foodstuffs (e.g. fruit and vegetables) by killing bacteria on the surface thereof.  
           [0054]    The sterilising method aspect herein is suitable in one aspect for use in air-conditioning systems for use in vehicles such as cars, lorries and buses. The system will be sized and shaped to fit within the air-conditioning system of the vehicle and will typically therefore have a size less than the size it would possess when used in large scale air and water treatment applications.  
           [0055]    According to a further aspect of the present invention there is provided a method of promoting the dissociation of a molecular entity comprising applying pulsed microwave energy to an ultraviolet lamp to produce ultraviolet radiation of dominant wavelength of from 140 to 260 nm; and exposing the molecular entity to said ultraviolet radiation, wherein an optically transparent waveguide guides said pulsed microwave energy to said ultraviolet lamp and said waveguide wholly surrounds the ultraviolet lamp.  
           [0056]    In one aspect, the molecular entity is borne in a fluid such as air or a liquid and the fluid flows past the enclosure. A specific example of this is in the clean up of ballast seawater from the holds of ships wherein contaminants in the ballast water are dissociated by application of ultraviolet radiation.  
           [0057]    A further specific example of molecular dissociation applications based on fluid flow is in the dissociation of organic material, such as Total Oxidisable Carbon (TOC) in rinse water for use in the electronics, semiconductors pharmaceuticals, beverage, cosmetics and power industries. The process involves the production of OH• radicals which oxidise any hydrocarbon molecules in the rinse water. Optionally, other oxidants may be employed such as ozone and hydrogen peroxide. Typically, polishing deionisation beds, featuring nuclear-grade resin materials are placed downstream of the TOC reduction units to remove any ionised species and restore the resitivity of the water.  
           [0058]    In another aspect, the molecular entity is borne on a surface and the ultraviolet radiation is applied to the surface to eliminate any bacterial contaminants by disinfection. The molecular entity may, for example be a contaminant on the surface which is rendered harmless by its molecular dissociation.  
           [0059]    In one example, the surface is of a food product such as a meat, dairy, fish, fruit or vegetable product and the ultraviolet radiation is applied to the surface to dissociate any contaminants such as chemical residues including pesticides.  
           [0060]    In another example, the surface is an industrially-produced product such as a packaging product for example, a medical packaging product, a foil bag, cup or lid, or a glass or plastic bottle, and the ultraviolet radiation is applied to the surface to dissociate any contaminants arising from the industrial process.  
           [0061]    In a further example, the surface is the surface of any equipment used in the manufacture of food products or industrially produced products such as the surface of any reactors or conveyors.  
           [0062]    According to a still further aspect of the present invention there is provided a method of promoting a photochemical reaction in a substance comprising applying pulsed microwave energy to an ultraviolet lamp to produce ultraviolet radiation of dominant wavelength of from 310 to 400 nm; and exposing the entity to said ultraviolet radiation, wherein an optically transparent waveguide guides said pulsed microwave energy to said ultraviolet lamp and said waveguide wholly surrounds the lamp.  
           [0063]    In one aspect, the substance is borne in a fluid such as air or a liquid and the substance-bearing fluid flows past the enclosure.  
           [0064]    In another aspect, the substance is borne on a surface and the ultraviolet radiation is applied to the surface.  
           [0065]    Preferably, the substance is selected from the group consisting of surface treatment materials including paints, toners, varnishes (e.g. polyurethane varnishes), stains and laminating materials.  
           [0066]    Laminating is for example, used in the production of various electronic components, data storage devices including compact discs and packaging materials including blister packages.  
           [0067]    In another method aspect herein, the exposure of a biological substance to wavelengths of less than 200 nm or from 300-400 nm has been found to help to prevent DNA recovery. This may for example, be of use in the elimination of biological contaminants and pests e.g. insects.  
           [0068]    In the method aspects herein, the microwave energy suitably has a pulse width of from 100 milliseconds to 0.5 microseconds, preferably from 10 milliseconds to 5 microseconds. Suitably, the microwave energy has a pulse cycle of from 100 milliseconds to 0.5 microseconds, preferably from 5 milliseconds to 50 microseconds. Optimisation of both pulse width and pulse cycle is preferred.  
           [0069]    Suitably, the peak operating energy of the bulb is from 100 watts to 100,000 watts, preferably from 500 watts to 30,000 watts.  
           [0070]    According to a further aspect of the present invention there is provided an ultraviolet light source comprising a plurality of ultraviolet bulbs; a pulsed microwave energy source for exciting said plurality of ultraviolet bulbs; and an optically transparent waveguide for guiding pulsed microwave energy originating from said pulsed microwave energy source to the plurality of ultraviolet bulbs, wherein said waveguide wholly surrounds the plurality of ultraviolet bulbs.  
           [0071]    According to a further aspect of the present invention there is provided a lamp comprising a plurality of ultraviolet bulbs, said plurality of bulbs being excitable by pulsed microwave energy; and an optically transparent waveguide for guiding pulsed microwave energy originating from a pulsed microwave energy source to the plurality of ultraviolet bulbs, wherein said waveguide wholly surrounds the plurality of ultraviolet bulbs. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0072]    Preferred embodiments of the ultraviolet light source in accord with the present invention will now be described with reference to the accompanying drawings in which:  
         [0073]    [0073]FIG. 1 is a schematic representation of a first ultraviolet light source herein;  
         [0074]    [0074]FIGS. 2 a  and  2   b  are schematic representations of second and third ultraviolet light sources herein;  
         [0075]    [0075]FIGS. 3 a  and  3   b  are schematic representations of fourth and fifth ultraviolet light sources herein;  
         [0076]    [0076]FIG. 4 is a schematic representation of a sixth ultraviolet light source herein suitable for use in combined UV and microwave methods;  
         [0077]    [0077]FIG. 5 is a schematic representation of a seventh ultraviolet light source herein;  
         [0078]    [0078]FIG. 6 is a schematic representation of an eighth ultraviolet light source herein;  
         [0079]    [0079]FIG. 7 is a schematic representation of a ninth ultraviolet light source herein;  
         [0080]    [0080]FIG. 8 is a schematic representation of a tenth ultraviolet light source herein;  
         [0081]    [0081]FIG. 9 is a cross-sectional view of an ultraviolet lamp herein comprising twelve UV bulbs; and  
         [0082]    [0082]FIG. 10 is a schematic representation of a suitable pulsed microwave energy wave herein.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0083]    The present invention is here described by means of examples, which constitute possible embodiments of the invention.  
         [0084]    [0084]FIG. 1 shows an ultraviolet light source comprising an ultraviolet lamp  10  enclosed by cylindrical enclosure  20 . The cylindrical walls of the enclosure  20  are comprised of quartz material which is transparent to UV radiation. A conducting copper mesh  30  is provided to act as a waveguide. First end of the cylindrical enclosure has blocking end flange  22  provided thereto. The second end is provided with coupling flange  24  which couples with right angled pathguide  40  which in turn connects with rectangular pathguide  50 . Magnetron  60  acts as a pulsed microwave energy source to feed pulsed microwave energy into the rectangular waveguide  50 , thence into the right angled pathguide  40  and finally to the ultraviolet lamp  10  which is excited thereby.  
         [0085]    The enclosure  20  is within tubular housing  70 . The housing  70  has a fluid inlet  72  and a fluid outlet  74  provided thereto. In use, fluid flows from the inlet  72  past the enclosure  20  and towards the outlet  74 . As the fluid flows past the enclosure  20  it is irradiated with UV radiation produced by the ultraviolet lamp  10 . The radiation itself passes through the UV transparent walls of the enclosure  20   a ,  20   b  to contact the fluid. In one aspect, the fluid is water and the dominant wavelength of emitted UV radiation is 254 nm.  
         [0086]    [0086]FIGS. 2 a  and  2   b  show related ultraviolet light sources herein. Both comprise ultraviolet mercury discharge lamp  110   a ,  110   b  enclosed by cylindrical enclosure  120   a ,  120   b . The cylindrical walls of the enclosure  120   a ,  120   b  form a sleeve comprised of quartz material which is transparent to UV radiation. A conducting copper mesh waveguide  130   a ,  130   b  is provided to the inner surface of the sleeve. The enclosure  120   a ,  120   b  has air or nitrogen circulating therein. First end of the cylindrical enclosure has blocking end flange  122   a ,  122   b  provided thereto. The second end is provided with coupling flange  124   a ,  124   b  which couples with water-tight chamber  150   a ,  150   b  which contains brass waveguide  140   a ,  140   b  and magnetron  160   a ,  160   b . The magnetron  160   a ,  160   b  acts as a pulsed microwave energy source to feed pulsed microwave energy into the brass waveguide  140   a ,  140   b  and thence to the ultraviolet lamp  110   a ,  110   b  which is excited thereby.  
         [0087]    The enclosure  120   a ,  120   b  is within tubular housing  170   a ,  170   b . The housing  170   a ,  170   b  has a fluid inlet  172   a ,  172   b  and a fluid outlet  174   a ,  174   b  provided thereto. In use, fluid flows from the inlet  172   a ,  172   b  past the enclosure  120   a ,  120   b  and towards the outlet  174   a ,  174   b . As the fluid flows past the enclosure  120   a ,  120   b  it is irradiated with UV radiation produced by the ultraviolet lamp  110   a ,  110   b . The radiation itself passes through the UV transparent walls of the enclosure  120   a ,  120   b  to contact the fluid. In one aspect, the dominant wavelength is 254 nm.  
         [0088]    [0088]FIGS. 3 a  and  3   b  show ultraviolet light sources similar in structure to the ultraviolet light sources of FIGS. 2 a  and  2   b  but for use in treatment of airborne substances. Both comprise ultraviolet mercury discharge lamp  210   a ,  210   b  enclosed by cylindrical enclosure  220   a ,  220   b . The cylindrical walls of the enclosure  220   a ,  220   b  are comprised of quartz material which is transparent to UV radiation. A conducting copper mesh waveguide  230   a ,  230   b  is provided to the inner surface of the waveguide. The enclosure  220   a ,  220   b  has air or nitrogen circulating therein. First end of the cylindrical enclosure has blocking end flange  222   a ,  222   b  provided thereto. The second end is provided with coupling flange  224   a ,  224   b  which couples with airtight chamber  250   a ,  250   b  containing brass waveguide  240   a ,  240   b  and magnetron  260   a ,  260   b . The magnetron  260   a ,  260   b  acts as a pulsed microwave energy source to feed pulsed microwaves into brass waveguide  240   a ,  240   b  and thence to the ultraviolet lamp  210   a ,  210   b  which is excited thereby.  
         [0089]    The enclosure  220   a ,  220   b  is within tubular housing  270   a ,  270   b . The housing  270   a ,  270   b  has an air inlet  272   a ,  272   b  and an air outlet  274   a ,  274   b  provided thereto. In use, air flows from the inlet  272   a ,  272   b  past the enclosure  220   a ,  220   b  and towards the outlet  274   a ,  274   b . As the air flows past the enclosure  220   a ,  220   b  it is irradiated with UV radiation produced by the ultraviolet lamp  210   a ,  210   b . The radiation itself passes through the UV transparent walls of the enclosure  220   a ,  220   b  to contact the air, thereby treating molecular entities carried in the air.  
         [0090]    In variations, the systems of FIGS. 1;  2   a  and  2   b ;  3   a  and  3   b  may be provided with cooling systems to enable the cooling of the magnetron and/or lamp.  
         [0091]    [0091]FIG. 4 shows a cabinet ultraviolet light source herein suitable for use in treating objects herein. Ultraviolet mercury discharge lamp  310  is enclosed by cylindrical enclosure  320 . The cylindrical walls of the enclosure  320  are comprised of quartz material which is transparent to UV radiation but only partially transparent to microwave radiation. A conducting copper mesh waveguide  330  is provided to the inner surface of the enclosure  320 . The enclosure  320  optionally has air or nitrogen circulating therein. First end of the cylindrical enclosure has blocking end flange  322  provided thereto. The second end is provided with coupling flange  324  which couples with linear pathguide  340  which in turn connects with magnetron  360 . The magnetron  360  acts as a pulsed microwave energy source to feed pulsed microwaves into pathguide  340  and thence to the ultraviolet lamp  310  which is excited thereby.  
         [0092]    The enclosure  320  is within housing  370  which has an entry door  380  provided thereto. In use, items to be treated are placed in the housing  370 . The items are irradiated with pulsed UV radiation produced by the ultraviolet lamp  310  and by pulsed microwave radiation deriving from the magnetron  360 . The radiation itself passes through the UV transparent and microwave partially transparent walls of the enclosure  320  to contact the items. Optionally, the housing  370  may be provided with UV transparent shelves for the items. An inner reflective lining, for example an aluminium foil lining, may also be provided to the housing  370 .  
         [0093]    [0093]FIG. 5 shows an ultraviolet light source comprising an ultraviolet bulb  410  enclosed by cylindrical enclosure  420 . The cylindrical walls of the enclosure  420  are comprised of quartz material which is transparent to UV radiation. The quartz tube enclosure  420  is provided with a cleaning system comprising wiper  480  which is mounted for movement on track  482 . The track  482  is arranged parallel to the enclosure  420  and the movement of the wiper  480  is powered by motor  484 .  
         [0094]    A conducting copper mesh waveguide  430  is provided to the inner surface of the enclosure  420 . An end of the enclosure  420  couples with coupling flange  424  which couples with stainless steel cylindrical pathguide  440  which in turn connects with stainless steel rectangular pathguide  450 . Magnetron  460  acts as a pulsed microwave energy source to feed pulsed microwaves into the rectangular pathguide  450 , thence into the cylindrical pathguide  440  and finally to the ultraviolet lamp  410  which is excited thereby.  
         [0095]    The enclosure  420  is within stainless steel housing  470 . The housing  470  has a fluid inlet  472  and a fluid outlet  474  provided thereto. In use, fluid flows from the inlet  472  past the enclosure  420  and towards the outlet  474 . As the fluid flows past the enclosure  420  it is irradiated with UV radiation produced by the ultraviolet bulb  410 . The radiation itself passes through the UV transparent walls of the enclosure  420  to contact the fluid.  
         [0096]    In variations, another form of wiper arrangement may be employed which comprises plural (e.g. two) helical blades (similar to cylindrical lawn mower blades) arranged along the length of the quartz enclosure sleeve  420 . As fluid flows along the outside of the enclosure  420  these blades will rotate and if a suitable material is placed on the inner edge of each blade cleaning of the quartz sleeve  420  will be promoted.  
         [0097]    [0097]FIG. 6 shows an ultraviolet light source comprising two ultraviolet bulbs  510 ,  511  fixed in a mutually parallel arrangement by lamp supports  514 ,  515 . The bulbs  510 ,  511  are enclosed by cylindrical enclosure  520 . An air coolant system is provided to the bulbs  510 ,  511  wherein cooling air is fed into the enclosure  520  through air inlet  526  and circulates past the bulbs before exiting at air outlet  528 . The cylindrical walls of the enclosure  520  are comprised of quartz material which is transparent to UV radiation. The quartz tube enclosure  520  is provided with a cleaning system comprising wiper  580  which is mounted for movement on track  582 . The track  582  is arranged parallel to the enclosure  520  and the movement of the wiper  580  is powered by motor  584 .  
         [0098]    A conducting copper mesh waveguide  530  is provided to the inner surface of the waveguide. An end of the enclosure  520  couples with coupling flange  524  which couples with stainless steel rectangular pathguide  550 . Magnetron  560  acts as a pulsed microwave energy source to feed pulsed microwaves into the rectangular pathguide  550  and thence to the ultraviolet lamp  510  which is excited thereby.  
         [0099]    The enclosure  520  is within stainless steel housing  570  having observation port  571 . The housing  570  has a fluid inlet  572  and a fluid outlet  574  provided thereto. In use, fluid flows from the inlet  572  past the enclosure  520  and towards the outlet  574 . As the fluid flows past the enclosure  520  it is irradiated with UV radiation produced by the ultraviolet bulbs  510 ,  511 . The radiation itself passes through the UV transparent walls of the enclosure  520  to contact the fluid.  
         [0100]    [0100]FIG. 7 shows an ultraviolet light source comprising two ultraviolet bulbs  610 ,  611  fixed in a mutually parallel arrangement by lamp supports  614 ,  615 . The bulbs  610 ,  611  are enclosed by cylindrical enclosure  620 . An air coolant system is provided to the bulbs  610 ,  611  wherein cooling air is fed into the enclosure  620  through air inlet  626  and flows past the bulbs  610 ,  611  before exiting at air outlets  628 ,  629 . The cylindrical walls of the enclosure  620  are comprised of quartz material which is transparent to UV radiation. The quartz tube enclosure  620  is provided with a cleaning system comprising wiper  680  which is mounted for movement on track  682 . The track  682  is arranged parallel to the enclosure  620  and the movement of the wiper  680  is powered by motor  684 .  
         [0101]    A conducting copper mesh waveguide  630  is provided to the inner surface of the waveguide. An end of the enclosure  620  couples with coupling flange  624  which couples with stainless steel rectangular pathguide  650 . Magnetron  660  acts as a pulsed microwave energy source to feed pulsed microwaves into the rectangular pathguide  650  and thence to the ultraviolet bulbs  610 ,  611  which are excited thereby.  
         [0102]    The enclosure  620  is within stainless steel housing  670  having observation port  671 . The housing  670  has a fluid inlet  672  and a fluid outlet  674  provided thereto. In use, fluid flows from the inlet  672  past the enclosure  620  and towards the outlet  674 . As the fluid flows past the enclosure  620  it is irradiated with pulsed UV radiation produced by the ultraviolet bulbs  610 ,  611 . The radiation itself passes through the UV transparent walls of the enclosure  620  to contact the fluid.  
         [0103]    [0103]FIG. 8 shows an ultraviolet light source based on a series arrangement of a pair of ultraviolet light sources of the type illustrated in FIG. 7. The ultraviolet source comprises two pairs of ultraviolet bulbs  710   a ,  711   a  and  710   b ,  711   b  fixed in a mutually parallel arrangement by lamp supports  714   a ,  715   a  and  714   b ,  715   b . The bulbs  710   a ,  711   a  and  710   b ,  710   b  are each enclosed by cylindrical enclosures  720   a ,  720   b . An air coolant system is provided each pair of bulbs  710   a ,  711   a  and  710   b ,  711   b  wherein cooling air is fed into the enclosures  720   a ,  720   b  through air inlets  726   a ,  726   b  and flows past the bulbs  710   a ,  711   a  and  710   b ,  711   b  before exiting at air outlets  728   a ,  729   a  and  728   b ,  729   b . The cylindrical walls of the enclosures  720   a ,  720   b  are comprised of quartz material which is transparent to UV radiation. The quartz tube enclosures  720   a ,  720   b  are each provided with a cleaning system comprising wiper  780   a ,  780   b  which is mounted for movement on respective track  782   a ,  782   b . The tracks  782   a ,  782   b  are arranged parallel to the enclosures  720   a ,  720   b  and the movement of the wipers  780   a ,  780   b  is powered by motors  784   a ,  784   b.    
         [0104]    A conducting copper mesh waveguide  730   a ,  730   b  is provided to the inner surface of the waveguide. An end of each enclosure  720   a ,  720   b  couples with coupling flange  724   a ,  724   b  which couples with stainless steel rectangular pathguide  750   a ,  750   b . Magnetrons  760   a ,  760   b  act as pulsed microwave energy sources to feed pulsed microwaves into the respective rectangular pathguides  750   a ,  750   b  and thence to the ultraviolet bulbs  710   a ,  711   a  and  710   b ,  711   b  which are excited thereby.  
         [0105]    The quartz enclosures  720   a ,  720   b  are within a stainless steel housing comprising two interconnected arms  770   a ,  770   b  each having an observation port  771   a ,  771   b . The first arm of the housing  770   a  has a fluid inlet  772  and the second arm of the housing  770   b  has a fluid outlet  774  provided thereto. In use, fluid flows from the inlet  772  past the first enclosure  720   a , through passages  773   a ,  773   b , then past the second enclosure  720   b  and finally towards the outlet  774 . As the fluid flows past the enclosures  720   a ,  720   b  it is irradiated with UV radiation produced by the ultraviolet bulbs  710   a ,  711   a  and  710   b ,  711   b . The radiation itself passes through the UV transparent walls of the enclosures  720   a ,  720   b  to contact the fluid.  
         [0106]    Whilst in each of FIGS.  1  to  8  the magnetron is arranged locally to the lamp it may be appreciated that in other embodiments the magnetron is distally located and communicates with the lamp via a coaxial cable feed arrangement. Such coaxial cable feed arrangements are known in the art for example, described in Japanese Patent Publication No. 61046290.  
         [0107]    [0107]FIG. 9 shows in cross-sectional view an ultraviolet lamp herein. The lamp comprises two rows  810   a ,  810   b  of six bulbs forming a six by two lamp array arrangement. The array of bulbs  810   a ,  810   b  is surrounded by a copper mesh  830  having a rectangular cross-section. Both the array of bulbs  810   a ,  810   b  and the copper mesh  830  are enclosed by a quartz tube  820  having a circular cross-section.  
         [0108]    It may be appreciated that lamps comprising plural bulbs in any suitable arrangement may be employed in variations of the ultraviolet light sources shown in FIGS.  1  to  8 .  
         [0109]    [0109]FIG. 10 shows a suitable pulsed microwave energy waveform herein, as would be produced by the magnetron of any of FIGS.  1  to  8  using known pulsing circuitry. The defining characteristics of the waveform are the pulse width (X) which is typically short; the pulse period (Y) which is typically much longer; and the peak operating energy (intensity) of the microwave (Z). It will be appreciated that continuous (i.e. non-pulsed) microwave energy may also be used herein in combination with the pulsed microwave energy to excite the bulb of the ultraviolet light source of the invention.

Technology Classification (CPC): 8