GB2596574A

GB2596574A - Lamp for emitting UV-B radiation & luminaire

Info

Publication number: GB2596574A
Application number: GB2010081.4A
Authority: GB
Inventors: Moutsi Afroditi; Preston Barry; Rogers Sean; Albert Mucklejohn Stuart
Original assignee: Ceravision Ltd
Current assignee: Ceravision Ltd
Priority date: 2020-07-01
Filing date: 2020-07-01
Publication date: 2022-01-05
Also published as: GB202010081D0; WO2022003358A3; WO2022003358A2

Abstract

A gas discharge lamp includes a light source 115 comprising an arrangement of electrodes 104, 109a, 109b and an arc tube 110 containing mercury 111. To generate radiation, the electrodes 104, 109a, 109b are arranged to sustain an electric arc to vaporise the mercury 111 within the arc tube 110 generating radiation in at least the UV-C and UV-B optical ranges. An optical filter 114 is provided that is optically opaque to UV-C radiation and optically transparent to UV-B radiation. The optical filter 114 at least partly houses the light source 115 and is arranged to block UV-C radiation emitted from the light source 115 and allows transmission of UV-B radiation emitted from the light source 115. The lamp may be used in a luminaire (Fig. 4, 450).

Description

LAMP FOR EMITTING UV-B RADIATION & LUMINAIRE The present invention relates to a gas discharge lamp and a luminaire.

In current horticultural practice artificial lighting is used both to supplement natural daylight in glass house settings and provide all the lighting in grow rooms. The main focus of installation designers is often to concentrate on providing Photosynthetically Active Radiation (PAR) with only minimal account taken of wavelengths beyond this range. That is radiation between 400nm and 700nm that photosynthetic organisms are able to use in the process of photosynthesis. Generally this radiation is provided by High-Pressure Sodium (HPS) lamps, Metal Halide (MH) lamps or LEDs or combinations of them.

The inventors have determined that radiation outside of this wavelength range can be important for the quality and yield of crops. In particular Ultraviolet (UV) radiation in the range 280-315nm, defined by the International Commission on Illumination (the CIE) as UV-B radiation, can be sensed by UVR8 photoreceptor which is responsible for initiating a plant stress response. The sensitivity of the UVR8 photoreceptor reaches a maximum in the range 280-290nm.

The stress response produces compounds in the plant which are potentially economically valuable.

The inventors have previously developed a microwave driven metal halide light source which is optimized to provide radiation in the wavelength range 280-550nm. This source has been optimized to supplement HPS light sources in growing environments. This source provides UV-B, UV-A radiation (315-400nm) and some PAR (400-550nm). Trials with strains of industrial hemp with this type of lamp have demonstrated the importance of the UV-B output from the lamp. The plants exposure to UV-B showed a significant increase in the yield of essential oils, i.e. the terpenes and flavonoids that are responsible for flavour and aroma. Enhancing the production of essential oils from plants not only provides a significant economic benefit to growers but also improves the quality of products offered to customers. Other trials have shown that exposure to UV-B radiation is accompanied by a reduction in the incidence of pests and diseases including grey mould, Botrytis cinerea.

However it is more economic to produce radiation in the wavelength range 400-550nm, or indeed 400-700nm, using other light sources, in particular LEDs. The inventors have determined that there is a need for a light source optimized in the range 280-400nm to supplement LED lighting and HPS lamps. Such a lamp should be able to provide UV-B and UV-A levels which are comparable to those produced by natural global solar irradiance.

To this end, the inventors investigated using mercury vapour lamps for horticultural purposes. Figure 1 shows a typical high-pressure mercury lamp intended for general lighting purposes. The high-pressure mercury lamp comprises: a cap 1 (having solder 7 thereon), a stem 2, a resistor 3, a starting electrode 4, a fluorescent coating 5 on the inner surface of the outer jacket 12, a top support 6, a support frame 8, a main electrode 9, an arc tube fabricated from fused silica (quartz) 10 having argon and mercury 11 located therein, and an outer jacket 12 having gas 13 located therein.

Known mercury vapour arc tubes produce high levels of UV-C, which is harmful to organisms. Accordingly, known mercury vapour lamps which consist only of an arc tube, for instance medium-pressure mercury lamps, are not suitable for horticultural purposes. Lamps with an outer jacket which absorb UV-C and UV-B (especially 280-290nm) are also not suitable for horticultural lighting as other light sources are more efficient.

Accordingly the invention seeks to provide a gas discharge lamp and a luminaire that mitigates at least one of the above-mentioned problems, or that at least provides an alternative gas discharge lamp and luminaire.

According to a first aspect, there is provided a gas discharge lamp.

The gas discharge lamp can include a light source. The light source can include an arrangement of electrodes. The light source can include an arc tube. The arc tube can contain mercury. In order to generate light, the electrodes can be arranged to sustain an electric arc to vaporise the mercury within the arc tube. The arc tube can be arranged to generate UV-C radiation. The light source can be arranged to generate UV-B radiation.

The gas discharge lamp can include an optical filter. The optical filter can be optically opaque to UV-C radiation. The optical filter can be optically transparent to UV-B radiation. The optical filter can be integral to the light source. The optical filter can be arranged to block UV-C radiation emitted from the light source. The optical filter can be arranged to allow transmission of UV-B radiation emitted from the light source.

UV-B radiation is radiation having a wavelength in the range 280-315nm. UV-C radiation is radiation having a wavelength in the range 100-280nm.

The invention provides a highly efficient lamp for generating UV-B radiation, while substantially eliminating emissions of UV-C radiation. This makes the lamp particularly suitable for use in the horticultural sector in growing rooms. In particular, the invention provides an economic apparatus to trigger the UVR8 plant photoreceptor, and potentially other UV plant receptors for use in commercial horticultural applications.

High-pressure mercury discharge is a light source which generates significant radiation in the UV-C range (100-280nm), the UV-B, UV-A and the visible ranges. The inventors have determined that it is significantly more efficient than metal halide lamps in producing UV-B radiation. Previously the drawback of large amounts of UV-C radiation, which is extremely harmful to living organisms, prevented mercury vapour lamps for being used for horticultural purposes. However by applying an optical filter that blocks the UV-C radiation, that type of lamp then becomes suitable for use in a horticultural context.

Compared with an electroded discharge in mercury, a microwave discharge is somewhat less efficient. This is attributed to the power coupling between the microwaves and the mercury plasma. The depth into the plasma to which the microwaves can penetrate is controlled by the skin depth which results in maximum power being dissipated off axis. This leads to an increase in thermal conduction losses and a lowering of the maximum discharge temperature. In an electroded lamp the maximum power is dissipated on the axis of plasma producing a higher maximum discharge temperature making the plasma noticeably more efficient. For this reason, an electroded mercury discharge is preferred to a microwave discharge.

The table below shows the UV-B and UV-A outputs from 250W and 400W mercury arc tubes in fused silica (quartz) outer jackets. It can be seen from these data, even accounting for luminaire and filter losses, such lamps are capable of economically delivering UV-B and UV-A radiation at levels very comparable to global levels of solar radiation in the UV range, especially UV-B.

UV-B UV-A

250W Lamp 11 Watts 19 Watts 400W Lamp 21 Watts 36 Watts The light source can be arranged to generate radiation in the UV-A range. The optical filter can be optically transparent to UV-A radiation. The optical filter can be arranged to allow the transmission of UV-A radiation from the light source. UV-A radiation is defined as light having a wavelength in the range 315-400nm.

The light source can be arranged to generate visible light. The optical filter can be optically transparent to visible light. The optical filter can be arranged to allow transmission of visible light from the light source. Visible light is considered by the CIE as light having a wavelength in the range 360-830nm.

The optical filter can include glass arranged to block UV-C radiation transmission.

The glass can have a thickness of greater than or equal to 2mm, and preferably that is greater than or equal to 3mm. The glass can have a thickness of less than or equal to 6mm, is preferably less than or equal to 5mm, and more preferably is less than or equal to 4mm. The optical filter can include boron. The optical filter can comprise a borosilicate glass.

The optical filter can comprise the lighting emitting surface of the luminaire. The optical filter can comprise a first jacket that houses at least part of the light source. The first jacket can be an outer jacket, for example an outer jacket that houses the arc tube. The first jacket can be an outermost jacket. The first jacket can be hermetically sealed.

The optical filter can be tubular. The optical filter can have a first end that is distal from a lamp cap. The first end is typically closed. The filter can have a second end that is proximal the lamp cap. The second end can be open to the atmosphere. The second end can be hermetically sealed.

The lamp can include a non-reactive gas, such as nitrogen, located in a space between the optical filter and the arc tube. Typically, the pressure in the space between the optical filter and arc tube is lower than atmospheric pressure. Typically, the pressure in the space between the optical filter and the arc tube is less than or equal to 0.5 atm (50663 Pa). Typically, the pressure in the space between the optical filter and the arc tube is greater than or equal to 0.1 atm (10133 Pa). Preferably, the pressure in the space between the optical filter and the arc tube is around 0.3 atm (30398 Pa).

The lamp can include a second jacket. The second jacket can be intermediate between the first jacket and the arc tube. The second jacket can be arranged to house at least part of the light source, for example the second jacket can be arranged to house the arc tube and is therefore an outer jacket to the arc tube. Thus the first jacket can be arranged to house the second jacket, with the arc tube located within the second jacket.

The second jacket can comprise fused silica (quartz).

The second jacket can be hermetically sealed. The lamp can include a non-reactive gas, such as nitrogen, located in a space between the second jacket and the arc tube. Typically, the pressure in the space between the second jacket and arc tube is lower than atmospheric pressure. Typically, the pressure in the space between the second jacket and the arc tube is less than or equal to 0.5 atm (50663 Pa). Typically, the pressure in the space between the second jacket and the arc tube is greater than or equal to 0.1 atm (10133 Pa). Preferably the pressure in the space between the second jacket and the arc tube is around 0.3 atm (30398 Pa).

The light source can include a first main electrode. The light source can include a second main electrode. Each of the first and second main electrodes can protrude into the arc tube and can be arranged to sustain an electrical arc within the arc tube during normal operation of the lamp.

The light source can include a starter electrode. The light source can include a resistor arranged in series with the starter electrode. The starter electrode can protrude into the arc tube and can be arranged to initiate an electrical arc within the arc tube when the lamp is energised.

The lamp can include an end cap for connecting to an electrical connection, for example in a luminaire.

According to a second aspect there is provided a luminaire.

The luminaire can include a gas discharge lamp. The gas discharge lamp can include a light source. The light source can include an arrangement of electrodes. The light source can include an arc tube. The arc tube can contain mercury. In order to generate radiation, the electrodes can be arranged to sustain an electric arc to vaporise the mercury within the arc tube. The light source can be arranged to generate radiation in the UV-B range. The light source can be arranged to generate radiation in the UV-C range.

The luminaire can include a lamp housing. The lamp housing can house the gas discharge lamp.

The luminaire can include an optical filter. The optical filter can be optically opaque to UV-C radiation. The optical filter can be optically transparent to UV-B radiation. The optical filter can be arranged to block UV-C radiation emitted from the light source. The optical filter can be arranged to allow transmission of UV-B radiation emitted from the light source.

The gas discharge lamp can include the optical filter. The gas discharge lamp can be arranged according to the first aspect.

The lamp housing can include an opening. The optical filter can extend across the opening. The gas discharge lamp can be positioned within the lamp housing such that radiation emitted by the light source exits the lamp housing through Is the optical filter. The optical filter can be in the form of a plate. The opening can be at a front side of the housing. The lamp housing can include at least one optically opaque wall, and preferably a plurality of optically opaque walls. Typically, all housing walls are optically opaque. The wall or each wall can be opaque to at least one of, and preferably each of: UV-A radiation, UV-B radiation, UV-C radiation and visible light. The lamp housing can include at least one of: metal, ceramic and a plastics material. The metal can include at least one of aluminium and steel. The housing can include at least one side wall. The housing can include a rear wall.

The light source can be arranged to generate radiation in the UV-A range. The optical filter can be optically transparent to UV-A radiation. The optical filter can be arranged to allow the transmission of UV-A radiation from the light source.

The light source can be arranged to generate visible light. The optical filter can be optically transparent to visible light. The optical filter can be arranged to allow transmission of visible light from the light source.

The optical filter can comprise glass arranged to block UV-C radiation transmission. The glass can have a thickness of greater than or equal to 2mm, and preferably that is greater than or equal to 3mm. The glass can have a thickness of less than or equal to 6mm, is preferably less than or equal to Smm, and more preferably is less than or equal to 4mm. The optical filter glass can include boron. The optical filter can comprise a borosilicate glass.

The lamp can include a jacket arranged to house at least part of the light source.

The jacket can comprise an outer jacket. The outer jacket can be arranged to house the entire light source. The outer jacket can be arranged to house the arc tube. The outer jacket can comprise fused silica (quartz).

The outer jacket can be hermetically sealed. The lamp can include a non-reactive gas, such as nitrogen, located in a space between the outer jacket and the arc tube. Typically, the pressure in the space between the outer jacket and arc tube is lower than atmospheric pressure. Typically, the pressure in the space between the outer jacket and the arc tube is less than or equal to 0.5 atm (50663 Pa). Typically, the pressure in the space between the outer jacket and the arc tube is greater than or equal to 0.1 atm (10133 Pa). Preferably the pressure in the space between the outer jacket and the arc tube is around 0.3 atm (30398 Pa).

The light source can include a first main electrode. The light source can include a second main electrode. The first and second main electrodes can protrude into the arc tube and can be arranged to sustain an electrical arc within the arc tube during normal operation of the lamp.

The light source can include a starter electrode. The light source can include a resistor. The resistor can be arranged in series with the starter electrode. The starter electrode can protrude into the arc tube and can be arranged to initiate an electrical arc within in the arc tube when the lamp is energised.

The luminaire can include a reflector arranged to direct at least some of the light generated by the lamp out of the housing. The reflector can be arranged to direct radiation through the housing opening. The reflector can be arranged to direct radiation through the optical filter extending across the opening.

The luminaire can include a ballast arranged to restrict the amount of current passing through the arc tube.

The ballast can be provided by electronic control gear or a choke control gear. The control gear can be mounted in the housing. The control gear can be mounted externally of the housing. An electronic control gear providing a square wave output is preferred as this increases the total radiation from the light source.

According to a third aspect there is provided a method of irradiating plants with UV-B radiation. The method can include providing at least one gas discharge lamp according to the first aspect. The method can include connecting the gas discharge lamp to an electrical power supply. The method can include positioning the gas discharge lamp relative to the plants such that UV-B radiation emitted by the lamp irradiates the plants.

According to a third aspect there is provided a method of irradiating plants with UV-B radiation. The method can includes providing at least one luminaire according to the second aspect. The method can include connecting the luminaire to an electrical power supply. The method can include positioning the luminaire relative to the plants such that UV-B radiation emitted by the luminaire irradiates the plants.

According to another aspect there is provided a luminaire, including: a housing; and a gas discharge lamp according to any configuration described herein.

According to another aspect there is provided a gas discharge lamp according to any configuration described herein.

Embodiments of the invention will now be described by way of example only with reference to the drawings, wherein: Figure 1 is a side view of a prior art high-pressure mercury vapour lamp; Figure 2 is a diagrammatic side view of a gas discharge lamp according to a first embodiment of the invention; Figure 3 is a diagrammatic side view of a gas discharge lamp according to a second embodiment of the invention; Figure 4 is a diagrammatic cross-sectional view of a luminaire and lamp according to a third embodiment of the invention; Figure 5 is a diagrammatic side view of a gas discharge lamp for use in the luminaire of Figure 7; Figure 6 is a diagrammatic side view of another gas discharge lamp for use in the luminaire of Figure 7; and Figure 7 is a diagrammatic cross-sectional view of a luminaire according to a fourth embodiment of the invention.

Figure 2 shows a gas discharge lamp 100 according to a first embodiment of the invention. The lamp 100 comprises a high-pressure mercury vapour discharge lamp.

The lamp 100 includes a cap 101 arranged for engagement with an electrical connection 453 of a luminaire 450 (see Figure 4). The electrical connection 453 connects the lamp 100 to a power supply and typically a mains power supply. The cap 101 has a PGZ18 configuration. An advantage of the PGZ18 configuration for the cap 101 is that it ensures precise placement of the lamp 100 within the luminaire 450 to ensure maximum optical efficiency, and reproducibility of the precise placement. That is, the orientation of the lamp 100 with respect a luminaire reflector 452 and housing 451 will always be consistent.

The lamp 100 includes a gas discharge light source 115. The light source 115 includes a starting electrode 104, a first main electrode 109a, a second main electrode 109b, and an arc tube 110 having mercury 111 located therein. The arc tube 110 is sealed. The arc tube 110 is optically transparent to UV-C radiation, UV-B radiation, UV-A radiation and visible light. The first main electrode 109a is located at a first end 110a of the arc tube. The second main electrode 109b is located at a second end 110b of the arc tube. The first end 110a of the arc tube is proximal to the cap 101. The second end 110b of the arc tube is distal from the cap 101. The starter electrode 104 is located at the first end 110a of the arc tube. The arc tube 110 includes at least one noble gas, preferably argon at a low pressure, typically less than or equal to 0.15 atm (15000 Pa) to facilitate lamp starting. A resistor 103 is connected in series with the starting electrode 104.

The lamp 100 includes a pinch seal 102 and support frames 108. The electrodes 104, 109a, 109b are connected to the cap 101 via molybdenum foils embedded in the pinch seal 102 and the support frames 108. The support frames 108 support the arc tube 110, electrodes 104, 109a, 109b and resistor 103 and maintains them in fixed positions relative to the cap 101.

The lamp 100 includes an optical filter 114. The optical filter 114 is arranged to block transmission of UV-C radiation emitted by the light source 115, while being transmissive of UV-A radiation, UV-B radiation and visible light emitted by the light source 115. The optical filter 114 is in the form of a first jacket, and preferably is an outermost jacket.

The lamp 100 includes a second jacket 112. The second jacket 112 houses the light source 115, and is therefore an outer jacket to the arc tube. The second jacket 112 is optically transparent. It is transmissive to UV-C radiation, UV-B radiation, UV-A radiation and visible light. The second jacket 112 is preferably made from fused silica (quartz), which is highly transmissive for UV radiation and has a very low thermal expansion.

However, the second jacket 112 can be made from any other material that is highly transmissive of UV radiation and visible light. The second jacket 112 is hermetically sealed. The second jacket 112 contains a non-reactive gas 113, which surrounds the light source 115. The non-reactive gas 113 can be any suitable gas, and is preferably nitrogen. Preferably the non-reactive gas 113 is at a relatively low pressure, for example in the range 0.1 atm (10133 Pa) and 0.5 atm (50663 Pa), and is preferably around 0.3 atm (30398 Pa).

Thus the second jacket 112 is positioned intermediately between the arc tube 110 and the optical filter 114. Thus the first jacket 114 surrounds the second jacket 112, and hence the arc tube 110. The optical filter 114 can be made from any suitable material. For example, the optical filter can be made from a borosilicate glass, such as the borosilicate glass produced by Schott UK Limited under the trade name Schott DURAN®. Typically, the optical filter 114 has a thickness of greater than or equal to 2mm. Typically, the optical filter 114 has a thickness of less than or equal to 6mm. Typically, the optical filter 114 has a thickness in the range 2.5 to 4.5 mm. The thickness of the filter can be varied to adjust UV-B transmission. As well as having the appropriate optical properties, borosilicate glass also has a low coefficient of thermal expansion and has good resistance to thermal shock.

As shown in Figure 2, the optical filter 114 can be in the form of a tube, which is closed at one end. The closed end of the tube is distal from the cap 101. The space 116 between the optical filter 114 and the second jacket 112 is open to atmosphere.

In use, the light source 115 uses an electric arc through vaporised mercury to produce radiation. The starter electrode 104 is used to initiate a discharge which vaporises the mercury and the main electrodes 109a, 109b sustain the arc of electricity in normal use. UV-C radiation, UV-B radiation, UV-A radiation and visible light generated by the light source 115 radiates out of the arc tube 110 and passes through the second jacket 112. When the radiation reaches the optical filter 114, the optical filter 114 blocks transmission of the UV-C radiation but allows transmission of the UV-B radiation, UV-A radiation and visible light.

This ensures that the lamp 100 is particularly suited to horticultural applications since harmful UV-C radiation is not emitted from the lamp 100, whereas the desirable UV-B, UV-A radiation and visible light ranges are emitted from the lamp. Furthermore, high-pressure mercury vapour lamps have a long lifetime, typically of the order of 25000 hours. Thus the lamp 100 provides a highly efficient means for irradiating plants with desirable UV radiation, without providing any (or minimal amounts) harmful UV-C radiation.

Figure 3 shows a gas discharge lamp 200 according to a second embodiment of the invention. The lamp 200 comprises a high-pressure mercury discharge lamp, and functions in a similar fashion to the first embodiment.

The second embodiment is similar to the first embodiment in that it includes a cap 201, a stem 202, a resistor 203, a starting electrode 204, support frames 208, a first main electrode 209a, a second main electrode 209b, an arc tube 210 having mercury 211 located therein, and an optical filter 214 as an outer jacket. However there are some structural differences between the second embodiment and the first embodiment. In the second embodiment there is no second jacket 112 that is intermediate between the arc tube 110 and the outer optical filter 114. That is, the arc tube 210 is housed immediately within the optical filter 214. The optical filter 214 is hermetically sealed. The space between the arc tube and the optical filter 214 is filled with a non-reactive gas 213, which surrounds the light source 215. The non-reactive gas 213 can be any suitable gas, and is preferably nitrogen. Preferably the non-reactive gas 213 is at a relatively low pressure, for example in the range 0.1 atm (10133 Pa) and 0.5 atm (50663 Pa), and is preferably around 0.3 atm (30398 Pa).

The cap 201 comprises an Edison type screw cap, instead of a PGZ18 configuration, and includes a stem 202 that is suited to the Edison type screw cap 201.

Figure 4 shows a luminaire 450 according to a third embodiment of the invention. The luminaire 450 includes a housing 451, a reflector 452, a gas discharge lamp 100 according to Figure 2, and an electrical connector 453.

The housing 451 includes at least one side wall 451a, and typically a plurality of side walls 451a, a rear end wall 451b, and an opening 451c at a front side thereof Thus the luminaire 450 shown in Figure 4 is of a type commonly referred as an "open luminaire", that is, a luminaire where there is no optical filter located in or on the housing between the lamp and the irradiated surface. Instead, the optical filter is part of the lamp 100 and therefore the luminaire 450 as a whole does not emit UV-C radiation.

The housing 451 can be made from any suitable material. For example, the housing 451 can be made from at least one of: metal, ceramic and a plastics material. For example, the metal can comprise at least one of: aluminium; and steel. The housing can be arranged to have both specified IP and IK ratings. The IP rating relates to protection against ingress and is defined in IEC60509 while 1K rating refers to resistance to external mechanical impacts and is defined in IEC62262.

The lamp 100 is located within the housing 451 at a location between at least part of the reflector 452 and the opening 451c. The lamp 100 is typically located adjacent the reflector 452. The reflector 452 can be shaped to at least partially surround the lamp 100. The reflector 452 is arranged and positioned to direct at least some of the radiation emitted by the lamp 100 through the opening 451c towards the surfaces to be irradiated. A suitable material for the reflector 452 is ALANCO GmbH & Co's Alanod MIRO® UP. This material has excellent UV reflectivity to below 250nm. The reflector 452 is able to reflect at least UV-B radiation, and preferably UV-A radiation and visible light.

The lamp 100 is mounted to the electrical connector 453. The electrical connector 453 is configured to receive the PGZ18 cap 101. The electrical connector 453 is connected to an electrical power source, typically a mains electrical power source through a ballast.

The luminaire 450 preferably includes a ballast, such as electronic control gear (not shown) or a choke control gear (not shown), that is arranged to limit the current passing through the lamp 100. The ballast can be located within the housing 451 or can be located externally of the housing 451. The electronic control gear can be especially adapted for use with any of the gas discharge lamps 100, 200, 500, 600 disclosed herein. The electronic control gear can be arranged to enable switching and dimming.

For example, the electronic control gear can be provided with external communication means to facilitate switching and dimming.

It will be appreciated that instead of using a gas discharge lamp 100 according to first embodiment of the invention, the luminaire 450 can include a gas discharge lamp 200 according to the second embodiment of the invention. In this case, the electrical connector 453 is configured to receive the Edison screw cap 201.

The luminaire 450 of Figure 4 provides a simple and efficient arrangement for emitting UV-B, UV-A radiation and visible light without emitting UV-C radiation. Accordingly the luminaire 450 of Figure 4 is suitable for horticultural applications for similar reasons to the first and second embodiments.

Figure 5 shows a gas discharge lamp 500 for use in a luminaire 750, which is described below in relation to Figure 7. The gas discharge lamp 500 is similar to the gas discharge lamp 100 of Figure 2 in that it includes a cap 501, a pinch seal 502, a resistor 503, a starting electrode 504, support frames 508, a first main electrode 509a, a second main electrode 509b, an arc tube 510 having mercury 511 located therein, and an outer jacket 512 having a non-reactive gas 513 such as nitrogen located therein. The main difference between the gas discharge lamp 500 of Figure 5 and the gas discharge lamp 100 of Figure 1 is that the gas discharge lamp of Figure 5 does not include an optical filter for blocking UV-C radiation emitted by the light source 515. The optical filter is included in the luminaire 750 of Figure 7 (see below).

Figure 6 shows a gas discharge lamp 600 for use in a luminaire 750, which is described below in relation to Figure 7. The lamp 600 comprises a high-pressure mercury gas discharge arc tube 610. The gas discharge lamp 600 includes a first cap 601a, a second cap 601b, support frames 608, a first main electrode 609a, a second main electrode 609b, an arc tube 610 having mercury 611 located therein, and an outer jacket 612. The main differences between the gas discharge lamp 600 of Figure 6 and the gas discharge lamp 500 of Figure 5 is that the gas discharge lamp of Figure 6 has RX7(s) caps at each end of the outer jacket 612, instead of a single Edison type screw cap, and there is no starting electrode nor resistor. Similar to the gas discharge lamp 500 of Figure 5, the gas discharge lamp 600 of Figure 6 does not include an optical filter for blocking UV-C radiation. This optical filter is included in the luminaire 750 of Figure 7 (see below).

Figure 7 shows a luminaire 750 according to a fourth embodiment of the invention. The luminaire 750 includes a housing 751, a reflector 752, a gas discharge lamp 500 according to Figure 5, and an electrical connector 753.

The housing 751 includes at least one side wall 751a, and typically a plurality of side walls 751a, a rear end wall 751b, and an opening 751c at a front side thereof.

The luminaire 750 according to the fourth embodiment of the invention is similar to the luminaire 450 according to the third embodiment of the invention, except that the luminaire 750 includes an optical filter 714 arranged across opening 751c. The optical filter 714 is in the form of a plate that extends fully across the opening 751c. The optical filter 714 is arranged to block transmission of UV-C radiation emitted by the lamp 500, while being transmissive of UV-B radiation, UV-A radiation and visible light emitted by the lamp 500. The optical filter 714 can be made from any suitable material. For example, the optical filter can be made from a borosilicate glass, such as the borosilicate glass produced by Schott UK Limited under the trade name Schott Borofloat®33. Typically, the optical filter plate 714 has a thickness of greater than or equal to 3mm. Typically, optical filter plate 714 has a thickness of less than or equal to 6mm. Typically, the optical filter plate 714 has a thickness in the range 3 to 4 mm. The thickness of the plate can be varied to adjust UV-B transmission. Borosilicate glass with a thickness of less than 3mm can be used as the optical filter plate 714 if it is supported on a UV-C/UV-B transmissive substrate. UV-B transmission can also be adjusted by using alternative borosilicate low iron glasses which generally have a lower transmission than Schott borofloat 33 in the UV-B region. As well as having the appropriate optical properties, borosilicate glass also has a low coefficient of thermal expansion, good resistance to thermal shock, high chemical durability and excellent mechanical strength.

It will be appreciated that instead of using a gas discharge lamp 500 according to Figure 5, the luminaire 750 can include any one of: a gas discharge lamp 200 according to Figure 2, a gas discharge lamp 300 according to Figure 3 and a gas discharge lamp 600 according to Figure 6. The electrical connector 753 can be configured accordingly to receive the appropriate type of cap. When using a discharge lamp 600 according to Figure 6, first and second electrical connectors 753 are provided, one for each end cap 601a, 601b.

It will be appreciated by the skilled person that modifications can be made to the above-mentioned embodiment that fall within the scope of the invention, for example, a luminaire according to the invention can include a plurality of lamps as described herein. For example, a plurality of lamps of the same type or a plurality of lamps of different types.

The lamps can be arranged to have a power rating in the range 40W to 1000W.

Lamp operating voltages can be set to allow for the use of commercially available electronic control gear, for example for electronic control gear that is normally used for metal halide or high-pressure sodium lamps. To achieve this, the light source electrode assemblies can be designed to withstand the higher currents involved.

The apparatus can be arranged to be compliant with safety and electromagnetic compatibility (EMC) standards and regulations.

The lamps can be arranged such that the lamp loading meets the following criteria.

Pin 14.3In P -28.

where Pin = Power input to the arc tube per unit length of arc gap (W.cm-1) and P = Power input to the lamp (W).

Small quantities of mercury halides, excluding fluorides, can be added to the discharge in the arc tube to improve output and or maintenance of the light source.

Claims

CLAIMS1 A gas discharge lamp, including: a light source comprising an arrangement of electrodes and an arc tube containing mercury, wherein, in order to generate radiation, the electrodes are arranged to sustain an electric arc to vaporise the mercury within the arc tube, said light source being arranged to generate radiation in at least the UV-C and UV-B optical ranges; and an optical filter that is optically opaque to UV-C radiation and optically transparent to UV-B radiation, wherein the optical filter is arranged to block UV-C radiation emitted from the light source and allow transmission of UV-B radiation emitted from the light source.
2. The lamp according to claim 1, wherein the light source is arranged to generate radiation in the UV-A range, the optical filter is optically transparent to UV-A radiation, and the optical filter is arranged to allow the transmission of UV-A radiation from the light source.
3 The lamp according to claim 1 or 2, wherein the light source is arranged to generate visible light, the optical filter is optically transparent to visible light, and the optical filter is arranged to allow transmission of visible light from the light source.
4. The lamp according to any one of the preceding claims, wherein the optical filter comprises glass arranged to block UV-C radiation transmission.
5. The lamp according to claim 4, wherein the optical filter includes boron.
6. The lamp according to claim 4 or 5, wherein the optical filter comprises a borosilicate glass. nfl
7. The lamp according to any one of the preceding claims, wherein the optical filter comprises a first jacket that houses at least part of the light source.
8. The lamp according to claim 7, wherein the first jacket is tubular.
9. The lamp according to claim 7 or 8, wherein the first jacket is open to atmosphere.
10. The lamp according to claim 7 or 8, wherein the first jacket is hermetically sealed.
11. The lamp according to any one of claims 7 to 10, including a second jacket arranged to house at least part of the light source, wherein the second jacket is located intermediately between the light source and the first jacket.
12. The lamp according to claim 11, wherein the second jacket is hermetically sealed.
13. The lamp according to any one of the preceding claims, including first and second main electrodes.
14. The lamp according to any one of the preceding claims, including a starter electrode, and a resistor arranged in series with the starter electrode.
15. The lamp according to any one of the preceding claims, including an end cap for connecting to an electrical connection.
16.A luminaire, including: a gas discharge lamp having a light source comprising an arrangement of electrodes and an arc tube containing mercury, wherein, in order to generate radiation, the electrodes are arranged to sustain an electric arc to vaporise the mercury within the arc tube, said light source being arranged to generate radiation in at least the UV-C and UV-B optical ranges; a lamp housing that houses the gas discharge lamp; and an optical filter that is optically opaque to UV-C radiation and optically transparent to UV-B radiation, wherein the optical filter is arranged to block UV-C radiation emitted from the light source and allow transmission of UV-B radiation emitted from the light source.
17. The luminaire of claim 16, wherein the gas discharge lamp includes the optical filter and the lamp is arranged according to any one of claims 1 to 15.
18. The luminaire of claim 16 or 17, wherein the lamp housing includes an opening, the optical filter extends across the opening, and the gas discharge lamp is positioned within the lamp housing such that radiation emitted by the light source exits the lamp housing through the optical filter.
19. The luminaire according to any one of claims 16 to 18, wherein the source is arranged to generate radiation in the UV-A range, the optical filter is optically transparent to UV-A radiation, and the optical filter is arranged to allow the transmission of UV-A radiation from the light source.
20. The luminaire according to any one of claims 16 to 19, wherein the light source is arranged to generate visible light, the optical filter is optically transparent to visible light, and the optical filter is arranged to allow transmission of visible light from the light source.
21. The luminaire according to any one of claims 16 to 20, wherein the optical filter comprises glass arranged to block UV-C radiation transmission.
22. The luminaire according to claim 21, wherein the optical filter includes boron.
23. The luminaire according to claim 21 or 22, wherein the optical filter comprises a borosilicate glass.
24. The luminaire according to any one of claims 16 to 23, wherein the lamp includes an outer jacket arranged to house at least part of the light source.
25. The luminaire according to claim 24, wherein the outer jacket is hermetically sealed.
26. The luminaire according to any one of claims 16 to 25, wherein the light source includes first and second main electrodes.
27. The luminaire according to any one of claims 16 to 26, wherein the light source includes a starter electrode, and the lamp includes a resistor arranged in series with the starter electrode.
28. The luminaire according to any one of claims 16 to 27, including a reflector arranged to direct at least some of the radiation generated by the lamp out of the housing.
29. The luminaire according to any one of claims 16 to 28, including a ballast arranged to restrict the amount of current passing through the arc tube.
30. The luminaire according to claim 29, wherein the ballast is provided by electronic control gear or choke control gear.
31.A method of irradiating plants with UV-B radiation, including providing at least one gas discharge lamp according to any one of claims 1 to 15, connecting the gas discharge lamp to an electrical power supply, and positioning the gas discharge lamp relative to the plants such that UV-B radiation emitted by the lamp irradiates the plants.
32.A method of irradiating plants with UV-B radiation, including providing at least one luminaire according to any one of claims 16 to 30, connecting the luminaire to an electrical power supply, and positioning the luminaire relative to the plants such that UV-B radiation emitted by the luminaire irradiates the plants.