Tubular electrodeless lamp

Abstract

An electrodeless discharge lamp (100) having one or more fixed light emitting bulbs (21, 211, 212, 213) within a common electrically conductive envelope to confine an electromagnetic excitation field provided by a plurality of sources. Each bulb can be excited by a plurality of electromagnetic radiation sources or a single electromagnetic radiation source. A tubular implementation of the lamp with two magnetron or transistor electromagnetic sources facing each other at the ends of the tubular bulb is particularly suitable for mounting at the focal line of a parabolic trough reflector. Some variants incorporate bulbs of different constituent elements and can individually set the excitation level to control the spectrum of the emitted light.

Description

TECHNICAL FIELD

[0001] The present invention relates to a discharge lamp, in particular an electrodeless discharge lamp, wherein a luminous plasma is generated by electromagnetic (EM) energy waves or waves in the range between high frequency (HF) and microwaves. BACKGROUND

[0002] High Intensity Discharge (HID) lamps are known for their high efficiency in converting energy into visible light. Compared to traditional incandescent or halogen lamps, HID lamps have a good light-to-heat ratio, making them suitable for various applications requiring as much visible light per watt as possible. Such applications include lighting for streets, sports facilities, stadiums, shopping centers, exhibitions, as well as artificial lighting systems for plant growth and for testing photovoltaic equipment.

[0003] A discharge lamp generally consists of a transparent bulb containing a chemical composition that can be excited into a luminous state by a suitable energy source. HID lamps are traditionally powered by electrical energy, wherein a discharge is sent through a chemical composition, usually made of tungsten, which is heated and ionized into a luminous plasma between two electrodes, also usually made of tungsten. The composition is an inert carrier gas, preferably a noble gas such as neon, xenon, argon or krypton, which contains active components, also known as fill materials, typically metal salts such as metal halides.

[0004] By removing the electrodes and providing electromagnetic energy instead of electrical energy to excite the chemical composition, the metal parts can be completely omitted from the bulb. This brings several advantages. First, the glass-metal interface in the bulb is avoided, reducing costs and increasing the service life of the bulb. Furthermore, more kinds of active components that are chemically incompatible with metal electrodes, such as sulfur, selenium, tellurium, etc., can be used for light generation.

[0005] The source of electromagnetic radiation to power the electrodeless plasma discharge lamp can be an electromagnetic generator, which is typically a microwave source such as a magnetron or a solid state device such as a transistor that emits electromagnetic radiation in a suitable electromagnetic spectrum band, such as one of the ISM radio bands including 6.78 Mhz, 13.56 Mhz, 27.12 Mhz, 40.68 Mhz, 433 Mhz, 915 MHz, 2.45 GHz or 5.8 Ghz bands. Magnetrons or transistor amplifiers are readily available at attractive prices, so they are often the preferred choice as power source for plasma lamps.

[0006] To avoid the formation of hot spots, which is a common problem in electrodeless discharge lamps, and overheating of the bulb material, the bulb is usually kept rotating, which causes various operational and stability problems.

[0007] EP2721631 provides a solution to overcome the rotational requirement. The fixed bulb described in this document is equipped with dielectric rods that couple the electromagnetic source to the electric bulb to ensure a better temperature distribution in the plasma bulb. The invention uses the method disclosed in this prior art document.

[0008] Although a better temperature management is achieved in EP2721631, the distribution of the electromagnetic energy, such as microwaves, is not completely uniform throughout the electric bulb and the different regions of the heated and ionized plasma continue to limit the performance of the discharge lamp, especially the luminance. Also, a better absorption of the electromagnetic energy in specific regions can help to attenuate the energy in electric bulbs with an elongated shape or a greater geometrical complexity. The luminance of the discharge lamp is limited by the power of the electromagnetic source and the thermal limitations of the bulb envelope.

[0009] It is an object of the invention to provide an electrodeless electromagnetic powered discharge lamp with increased luminance. The invention further aims at extending the range of suitable bulb shapes for the discharge lamp. SUMMARY

[0010] According to the invention, these objects are achieved by the object of the claims of the invention, in particular by the independent claim.

[0011] In particular, the object of the invention is achieved by an electrodeless discharge lamp for providing visible light and / or infrared light and / or UV radiation, comprising an electrically conductive envelope that is at least partially transparent for visible light or / and infrared light or / and UV radiation, one or more fixed light emitting bulbs within the electrically conductive envelope, a plurality of electromagnetic sources, the one or more bulbs being filled with a composition of constituents that emit light when in a plasma state, each electromagnetic source having an output terminal that radiates an electromagnetic field for ionizing and heating the composition of constituents in the one or more bulbs to bring the bulb filling into a plasma state.

[0012] The dependent claims relate to optional and possibly advantageous but not necessary features, such as an electrically conductive envelope having at least a region composed of an electrically conductive mesh; a bulb made of fused silica, electromagnetic sources in the microwave range; one or more dielectric rods that are aligned with one of the output terminals of the electromagnetic sources and are positioned between the respective output terminal and the bulb, acting as a dielectric waveguide for the electromagnetic field, coupling the electromagnetic source to the bulb; at least one fixed light emitting bulb is electromagnetically coupled to more than one electromagnetic source; a plurality of fixed light emitting bulbs filled with constituents having different emission spectra and coupled to different electromagnetic sources, and the electromagnetic sources can be operated at variable, independently set power levels; a cross-shaped light emitting bulb or a star-shaped light emitting bulb; a tubular electric bulb with one or two electromagnetic sources at the end; and a concave or parabolic light concentrator.

[0013] Some of the brightening ingredients can be used in the framework of the present invention. Among these, inert gases, the first active ingredient consisting of a mixture of antimony halides or bismuth halides, the second active ingredient consisting of halides or mixtures of halides including one or more of In, Sn, Ag, Cu, Pb, Fe, Hg and Co provide valuable results.

[0014] The present invention achieves an increase in brightness over the prior art electrodeless discharge lamps by coupling a plurality of electromagnetic energy sources to one or more of the lamp bulbs in a discharge lamp formed with one electromagnetic cavity. The electromagnetic energy sources are adapted to ionize and heat the chemical ingredients in the lamp bulbs to their bright plasma state.

[0015] The electromagnetic energy sources include radio frequency (RF) and / or microwave (MW) sources from the HF to the ultra-high frequency (UHF) band, such as magnetrons or one or several transistors generating electromagnetic waves at the desired frequency and intensity. In the following, the energy sources are described as magnetrons. However, the present invention is not limited to the use of magnetrons as electromagnetic energy sources.

[0016] The use of a plurality of magnetrons or other electromagnetic sources further allows more freedom in the design, particularly in relation to the shape of the plasma lamp bulb. Conventional bulbs are limited to substantially spherical, ellipsoidal or short tube shapes due to the electromagnetic energy distribution throughout the lamp bulb.

[0017] Due to the present invention, elongated lamp bulbs can be used for tubular lamps or more complex designs, such as cross-shaped or star-shaped lamps, etc. Preferably, the magnetrons emitting the incident waves are positioned at the distal end of each end of the shape.

[0018] The distributed positioning of the electromagnetic sources allows a more uniform ionization and heating of the ingredients in the elongated lamp bulb. Since the electromagnetic waves emitted by the plurality of electromagnetic sources originate from different locations in relation to the lamp bulb, a better uniformity can be achieved throughout the particular shape of the bulb. The risk of generating local temperature hot spots is thus further reduced, while a more uniform and higher heating and ionization of the plasma as a whole is possible. This prevents the temperature limit of the lamp material, preferably fused silica, from being exceeded in the hot spot areas.

[0019] The use of a plurality of electromagnetic sources in the discharge lamp also provides the possibility of using a plurality of different lamp bulbs, which can be enclosed in the same electrically conductive housing. Each lamp bulb is coupled to an independent electromagnetic source.

[0020] The electrodeless discharge lamp is characterized in that the plurality of independent bulbs, each powered by a separate magnetron or transistor assigned to the respective bulb, provides a plurality of operational freedoms. For example, different ionizable constituent elements can be chosen for the individual electric bulbs. Such different constituent elements can have different spectral properties. Thus, the individual electric bulb can emit light of a different spectrum, depending on which bulb is ignited.

[0021] Furthermore, since the constituent elements in each bulb are ignited by a separately assigned electromagnetic radiation source, the setting of the power level of the electromagnetic source thus provides a further mechanism to adjust or enhance the brightness of the electrodeless plasma lamp. BRIEF DESCRIPTION OF DRAWINGS

[0022] Exemplary embodiments of the present invention are disclosed in the specification and illustrated by the accompanying drawings, wherein:

[0023] Figures 1 and 2 schematically show known discharge lamps.

[0024] Figure 3 is a schematic representation of an embodiment of the present invention employing three magnetrons to ignite a spherical discharge lamp.

[0025] Figure 4 is a schematic representation of a further embodiment of the present invention featuring an elongated bulb of a discharge lamp ignited by two magnetrons positioned at its ends.

[0026] Figure 5a and 5b is a schematic representation of an embodiment of the present invention showing the position of the plasma electric bulb in its electromagnetic housing in a light concentrator, wherein

[0027] 5a shows an embodiment wherein the plasma electric bulb is completely enclosed by the electromagnetic housing, and

[0028] 5b shows an embodiment wherein the housing assumes a semi-dome shape connected to the convex curvature of the light concentrator, wherein the enclosure formed by the housing and the light concentrator contains the plasma electric bulb.

[0029] Figure 6 is a schematic representation of a further possible embodiment of the present invention showing a cross-shaped bulb of a discharge lamp having a magnetron positioned at each of its ends.

[0030] Figure 7 is a schematic representation of a further possible embodiment of the present invention showing a discharge lamp featuring two different elongated, linearly arranged bulbs, the individual magnetrons of which are enclosed in an electromagnetic housing.

[0031] Figure 8is a schematic representation of a further possible embodiment of the present invention showing a discharge lamp characterized by three independent elongated bulbs, whose individual magnetrons are arranged in a Y-shape and enclosed in an electromagnetic housing. DETAILED DESCRIPTION

[0032] With reference to Figure 1, the known discharge lamp 20 uses a dielectric rod 22 to improve the energy transfer to the electric bulb 21. In its preferred embodiment, the present invention shares the features described in said prior art document. Preferably, but not necessarily, the present invention also uses the dielectric rod 22 to benefit from its advantages in temperature management in the electric bulb.

[0033] Figure 2 shows a variant of the known discharge lamp, in which the magnetron 41 has its output terminal 47 supported by a ceramic isolator 48 and coupled to a 3 / 4 wavelength waveguide 82. The bulb 21 is equipped with a dielectric quartz rod 22, manufactured integrally with the bulb 21, which is inserted into the waveguide 82 and held in place by a collet 85 or any suitable fixing component.

[0034] The discharge lamp 20 of the present invention comprises a fixed, sealed bulb 21 filled with chemical composition ingredients suitable to generate radiation when it is in its ionized and heated plasma state 35. The chemical composition ingredients include inert gases, such as noble gases, and active ingredients, which define the spectral properties of the emitted light. The radiation emitted by the plasma 35 is in the visible and / or infrared and / or ultraviolet (UV) spectral range. The electric bulb 21 of said discharge lamp 20 is at least partially transparent to visible or infrared or UV radiation.

[0035] Suitable chemical composition ingredients for the discharge lamp include photoactive ingredients known in the art. Due to the absence of electrodes or metallic parts in the electric bulb of the RF or MW powered discharge lamp, active ingredients that are chemically incompatible with metallic materials can also be used as active ingredients in an inert atmosphere. Such alternative active ingredients include sulfur, selenium, tellurium, etc.

[0036] In its preferred embodiment, the active ingredients of the present invention include a first active ingredient consisting of a mixture of antimony halide or bismuth halide, and a second active ingredient comprising a halide or a mixture of halides of one or more of In, Sn, Ag, Cu, Fe, Pb, Hg and Co in an inert gas.

[0037] The electric bulb 21 can be made of any suitable material that meets the temperature and pressure requirements of its application in an electrodeless discharge lamp. The preferred material for the electric bulb 21 is fused silica. Alternatively, fused quartz, fused silica, SiO2, or any other appropriate material can be used. In order to be suitable for its application, the bulb material must be able to withstand typical operating temperatures of 600°C to 900°C and internal pressures ranging from 0.1 MPa to 2 MPa.

[0038] The bulb 21 is placed in a light concentrator 51 and a metallic mesh electromagnetic enclosure 53. The concentrator 51 is preferably reflective walled to concentrate the light generated in the bulb 22 into a light beam of a desired aperture and is electrically conductive to avoid the transmission of microwaves out of the lamp assembly. The metallic mesh enclosure is an electrically conductive housing 53 that confines the electromagnetic field inside the lamp 20 and is mechanically and electrically connected to the lamp 20 by any suitable means. The enclosure 53 can also be implemented in variants with a sheet of a suitable transparent, translucent or light-transmissive substrate having a thin electrically conductive layer deposited thereon.

[0039] The discharge lamp further comprises a plurality of electromagnetic sources 411, 412, 413, 414 each having an output terminal 43 radiating an electromagnetic field to ionize and heat the chemical composition contained in the electric bulb.

[0040] In a preferred embodiment, the incident electromagnetic frequency / ies is / are in the microwave range and is / are generated by a magnetron or a transistor 41. The output terminal 43 of the magnetron is adapted to be coupled to a standard wavelength waveguide 82. The output terminal is typically shown as a coaxial transmission line having a central conductor 46 closed by a cap with an aperture 44 or closed in a hollow ¼ wavelength waveguide. The cooling fins 42 are preferably cooled by a forced air flow from a fan (not shown).

[0041] In the prior art lamp illustrated in figure 1, the bulb 21 is mounted on top of a dielectric rod 22 which is in turn axially attached to a quartz socket 25 whose internal dimensions correspond to the external dimensions of the microwave terminal 43 so that the latter can be inserted into the socket 25. The socket is slightly longer than the terminal so that an air gap 19 is preserved between the inner wall of the socket 25 and the terminal 43.

[0042] Figure 3 A possible embodiment of a multiple magnetron discharge lamp 100 is shown in which a plurality of magnetrons 411, 412 and 413 can be arranged to increase the electromagnetic energy delivered to the spherical electric bulb and thus the luminosity of the light emitting ionized plasma in the plasma region 35. The electric bulb is enclosed in an electromagnetic housing 53 which is penetrated by the wavelength waveguide 82 and the collet 85.

[0043] The electric bulb of the present invention is a stationary light emitting bulb. In a preferred embodiment, the electromagnetic waves are transmitted to the bulb through dielectric rods 221, 222, 223. The dielectric rods are aligned with the output terminals of the magnetron or transistor antennas and are placed between the respective output terminals and the bulb. The dielectric rods physically connect the magnetrons to the electric bulb. As depicted in figure 2, they can be held in the inner cavity of the wavelength waveguide 82 and the collar 85.

[0044] The dielectric rods 221, 222 and 223 enhance the energy transfer efficacy between the magnetron or transistor amplifier and the electric bulb, the dielectric rods acting as dielectric waveguides for the electromagnetic field, thus allowing the electric bulb to operate in a fixed mode.

[0045] Figure 4 The illustrated embodiment shows the preferred location of two magnetrons or transistor amplifiers 411 and 412 in a tubular electric bulb. To ensure uniform ionization and heating of the plasma throughout the elongated bulb, the two magnetrons are placed at its extremities. The energy source at each extremity allows the size of the electric bulb to be extended to such a tubular shape.

[0046] The long tubular electric bulb with high luminance is particularly suitable for high uniformity luminance applications where high intensity is desired. The elongated bulb can for example be arranged in parallel on a flat surface, thus to provide a substantially rectangular or other shaped illuminated surface.

[0047] As illustrated in Fig. 5, the electric plasma bulb 21 is positioned at the focal point of a light concentrator 51. The shape of the concentrator is adapted to direct the reflected light towards its opening. Its preferred shape is a concave, elliptical or parabolic bowl shape, where the curvature of the bowl can be chosen to define the aperture of the reflected light beam.

[0048] As Figure 5a illustrated, the electrically conductive housing 53 can completely enclose the electric plasma bulb 21. Alternatively, as Figure 5b illustrated, it can be connected with the inner wall of the electrically conductive area of the light concentrator 51, thus providing an enclosed space containing the electric plasma bulb 21.

[0049] Uniform illumination of a discharge electric bulb with multiple tubular extensions is feasible by placing a magnetron or transistor amplifier at the end of each extension. The number of tubular extensions is not limited. A cross-shaped bulb is depicted in Figure 6 , employing a magnetron or transistor amplifier 411, 412, 413, 414 at each of its extremities. Other tubular shapes of a single electric plasma bulb powered by multiple magnetrons, such as a star, a ring, etc. are possible.

[0050] The present invention is not limited to the use of a single bulb within a discharge lamp. In fact, multiple electric plasma bulbs 211, 212, each powered by a magnetron 411, 412, can be included in a discharge lamp 100. Each magnetron or transistor amplifier can be operated independently at a selected power level and frequency. Preferably, the electric bulbs share the same enclosed electrically conductive housing 53. Figure 7 and Figure 8 Fig. 5 illustrates a possible embodiment of such a multiple electric plasma bulb discharge lamp. Such an arrangement is suitable for various different shapes, including Figure 7 other elongated shapes as shown in Fig. 6 or Figure 8Y-shaped as shown in Fig. 1.

[0051] The active components in each individual bulb of a multi-bulb discharge lamp can be varied. This allows the excitation level to be set individually to control the spectrum of the emitted light. The lamp shows different color spectra of the bulbs it ignites. The difference adjustment of the individual electric bulbs allows the introduction or enlargement of a continuous brightness control of the electric bulb, i.e. a "dimming effect". A certain degree of dimming is achieved by adjusting the power of the ignition electromagnetic source. The use of multiple electromagnetic sources widens the range of adjustable brightness. Furthermore, multiple electromagnetic sources enable a higher granularity or fine tuning within the range of luminous intensity.

[0052] As Figure 3 , 4 and 6, the multiple electromagnetic sources of the discharge lamp claimed in the present invention can be electromagnetically coupled to one fixed electric bulb. As Figure 7 and 8 illustrate, in an alternative embodiment, the multiple electromagnetic sources are coupled to one electric bulb each, wherein multiple electric bulbs are comprised in one discharge lamp.

[0053] Reference numerals used in the drawings

[0054] 19 air gap

[0055] 20 discharge lamp

[0056] 21 bulb

[0057] 22 dielectric rod

[0058] 23 light diffuser

[0059] 25 insertion hole

[0060] 35 plasma region

[0061] 41 magnetron

[0062] 42 cooling fin

[0063] 43 terminal / electromagnetic wave emitter (partially sectioned)

[0064] 44 aperture

[0065] 46 coaxial line

[0066] 47 RF terminal

[0067] 48 insulator

[0068] 51 light concentrator

[0069] 52 support collar

[0070] 53 electromagnetic housing

[0071] 82 3 / 4 wavelength waveguide

[0072] 85 collet

[0073] 100 multiple magnetron discharge lamp

[0074] 211 first light bulb

[0075] 212 second light bulb

[0076] 213 third light bulb

[0077] 221 first dielectric rod

[0078] 222 second dielectric rod

[0079] 223 third dielectric rod

[0080] 411 first magnetron

[0081] 412 second magnetron

[0082] 413 third magnetron

Claims

1. An electrodeless discharge lamp (100) for providing visible light and / or infrared light and / or UV radiation, the electrodeless discharge lamp comprising: An electrically conductive housing (53) at least partially transparent to visible light and / or infrared light and / or UV radiation, at least one fixed light-emitting bulb (21, 211, 212, 213) within the electrically conductive housing (53), a plurality of electromagnetic sources (411, 412, 413, 414), one or more of which bulbs are filled with a composition which emits light when in a plasma state, each electromagnetic source having an output terminal which radiates an electromagnetic field for ionizing and heating the composition in the one or more bulbs to bring it into a plasma state, wherein the fixed light-emitting bulb has a plurality of tubular extensions, the electromagnetic sources being located at the ends of the extensions, the electrodeless discharge lamp comprising one or more dielectric rods (221, 222, 223, 224) which are aligned with one of the output terminals of the electromagnetic sources and are positioned between the respective output terminal and the bulb (21, 211, 212, 213), the dielectric rods acting as dielectric waveguides for the electromagnetic field, coupling the electromagnetic sources to the bulb (21, 211, 212, 213).

2. The electrodeless discharge lamp (100) as claimed in claim 1, wherein the electrically conductive housing has at least a region consisting of an electrically conductive mesh (53).

3. The electrodeless discharge lamp (100) as claimed in claim 1, wherein the bulb is made of fused quartz, fused silica or SiO2.

4. The electrodeless discharge lamp (100) as claimed in claim 1, wherein the electromagnetic sources are in the high-frequency and microwave range.

5. The electrodeless discharge lamp (100) as defined in claim 1, wherein the composition of at least one bulb comprises: - an inert gas, a first active component consisting of a mixture of antimony halide or bismuth halide, a second active component consisting of a halide or a mixture of halides of one or more of In, Sn, Ag, Cu, Fe, Pb, Co and Hg.

6. The electrodeless discharge lamp (100) as claimed in claim 1, wherein at least one fixed light-emitting bulb (21) is electromagnetically coupled to more than one electromagnetic source (411, 412, 413, 414).

7. The electrodeless discharge lamp (100) as claimed in claim 1, comprising a plurality of fixed light-emitting bulbs (211, 212, 213), wherein the bulbs are filled with a composition having a different emission spectrum and are coupled to different electromagnetic sources (411, 412, 413), and the electromagnetic sources can be operated at variable power levels, wherein the power levels of the electromagnetic sources can be set independently of one another.

8. The electrodeless discharge lamp (100) as claimed in claim 1, comprising a cross-shaped light-emitting bulb (21) or a star-shaped light-emitting bulb.

9. The electrodeless discharge lamp (100) as claimed in claim 1, wherein the fixed light-emitting bulb (21, 211, 212, 213) has a substantially tubular shape and is electromagnetically coupled to one electromagnetic source (411, 412, 413) at one end or to one electromagnetic source (411, 412) at each of two ends.

10. The electrodeless discharge lamp (100) as defined in claim 9, comprising a concave or parabolic light concentrator (51).

11. The electrodeless discharge lamp (100) as defined in claim 10, wherein the light concentrator (51) has at least an electrically conductive area and the electrically conductive area of the light concentrator (51) is part of the electrically conductive housing (53).

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