WO2018060047A1

WO2018060047A1 - Uv solid state output unit

Info

Publication number: WO2018060047A1
Application number: PCT/EP2017/073899
Authority: WO
Inventors: Vincent Stefan David Gielen
Original assignee: Philips Lighting Holding B.V.
Priority date: 2016-09-27
Filing date: 2017-09-21
Publication date: 2018-04-05

Abstract

A solid state UV output unit comprises a closed chamber, having a gas pocket within the chamber, and an outer wall, wherein at least a portion of the outer wall is flexible such that a volume of the gas pocket and hence the volume of the closed chamber may be varied by flexing of the outer wall portion. A solid state UV output device is mounted in the chamber. One of more of these units may be provided in a vessel containing a liquid. By controlling the flexing of the portion of the outer wall, the buoyancy may be controlled so that the unit or units are able to move within the liquid. The flexing is for example controlled by heating.

Description

UV solid state output unit

FIELD OF THE INVENTION

This invention relates to solid state UV output units.

BACKGROUND OF THE INVENTION

The use of UV light - in particular UV-C light - for the purification of water, or more precisely the disinfection and sterilization of water, (hereafter referred to, for the sake of simplicity, as water purification or purification of water) is a well-known and well established technical practice. UV-C light at sufficiently short wavelengths is mutagenic to bacteria, viruses and other micro-organisms. At a wavelength of around 265 nm, UV breaks molecular bonds of DNA in the cells of micro-organisms, producing thymine dimers in the DNA, thereby destroying the DNA structure necessary to reproduce the cell, rendering them harmless or prohibiting growth and reproduction.

More recently, demand has grown for UV-C water purification devices which can utilize technologies from the fast developing field of UV-C LED light sources. It is well known, for example, that semiconductor materials from the group of IIIA-nitrides:

have direct band gaps that can be used to generate electromagnetic radiation in the wavelength of ultraviolet (UV). For instance, (ALGa_1-xN (0 < x < 1)) is often utilized as the component for a light emitting diode (LED), generating UV radiation below 365 nm.

In terms of the above mentioned water purification technology, UV-C LED solutions confer numerous advantages over more traditional fluorescent or incandescent UV- C lamps, including for example fast switching capability, small form factor, long lifetime, and a significantly 'cleaner' material composition - comprising few hazardous or harmful component materials.

Typical UV-C LED packages or modules use a glass (quartz glass, sapphire or fused silica) window transparent or translucent to UV-C, which is attached to a ceramic cavity. The UV-C LED packages are delivered as a chip or packaged solid state die, and make use of packaging and assembly technologies known from the electronics industry (and more specifically from power electronics). In this way, standardized and mass exploited assembly and interconnection technologies and platforms are available. The integration of various electrical functions (e.g. drivers) can easily be done at low cost, within the form factor volume of an LED module.

By enabling miniaturized modules, the module can be brought in very close vicinity to the application. For the example of water purification, the module can make close contact with the water and can even be used inside the water, thereby creating an optimal interaction between light and water.

One option is to integrate the module into a side or base wall of a vessel which contains the water to be purified. However, water reservoirs (for example in air humidifiers or water tanks) are usually not optimally shaped to allow irradiation of the full volume with a UV source or sources mounted at the vessel wall. In particular, the UV light may not penetrate into the full volume, and the water may be static so there is no flow of water.

There is therefore a need for a design which provides irradiation of the full volume of a vessel.

SUMMARY OF THE INVENTION

The invention is defined by the claims.

According to an aspect of the invention, there is provided a solid state UV output unit, comprising:

a closed chamber, having a gas pocket within the chamber;

an outer wall, wherein at least a portion of the outer wall is flexible such that a volume of the gas pocket and hence the volume of the closed chamber may be varied by flexing of the outer wall portion; and

a solid state UV output device mounted in the chamber.

This UV output unit has a volume which may be varied by flexing an outer wall. This in turn influences the density since the mass of the closed chamber is fixed, and hence the buoyancy. This means that depending on the flexing of the outer wall, the unit can be controlled to sink or float in a liquid to be irradiated. This provides a moving dynamic UV source, allowing it to reach areas within a vessel which are unable to be reached by a static unit, so that a complete volume can be irradiated.

The unit may further comprise a wireless power receiving system for receiving power to drive the solid state UV output device. When the output device is turned on, the unit generates heat (as well as light) and this causes expansion of the gas pocket, so that the buoyancy changes and the unit moves within the vessel. For example it may start to float, whereas when the UV output device is turned off, it may start to sink.

The wireless power receiving system for example comprises an induction coil. When the unit is turned off and has sunk to the location of a transmitting coil, it regains energy to turn on and float again. This provides a cyclic operation with the unit sinking and floating.

The unit may comprise a charge storage device for charging by the wireless power receiving system and for storing charge for operating the solid state UV output device. Thus, once wireless power is received, the unit may remain active for a period of time, before turning off and returning to the wireless charging location.

The unit preferably has negative buoyancy in a medium to be illuminated with UV light when at room temperature or other intended operating temperature. The device will return to room temperature when the solid state UV output device is turned off.

The unit preferably has positive buoyancy in a medium to be illuminated with UV light when at an operating temperature of the solid state UV output device. This is when the UV output device is turned on and a stable temperature has been reached. The unit is for example for UV water treatment.

The gas pocket may contain air. This is the simplest option from a manufacturing point of view, but other gases may be used if desired.

The solid state UV output device for example comprises a UV LED

arrangement. It may comprise one or more UV-C LEDs, but UV-A and UV-B may also be used. These devices are becoming of increasing interest, for example for water purification.

The invention also provides a UV treatment arrangement, comprising:

a vessel for containing a medium to be treated;

one or more solid state UV output units each as defined above in the vessel; and

a power transfer device for transferring power to the one or more solid state UV output units.

This defines an arrangement having a vessel for receiving a liquid to be treated, one or more UV output units which float or sink in the liquid depending on their internal temperature. When they sink, they are re-energized by the wireless power transmitter, which is for example is located outside the vessel, beneath the base of the vessel.

The power transfer device for example comprises a wireless power transmitter located at the base of the vessel, for example outside the vessel beneath the base of the vessel. This provides a charging system which is integrated with the vessel. Alternatively, the power transfer device may be remote from the vessel and the units are removed from the vessel for charging by the power transfer device.

The wireless power transmitter for example comprises an induction coil for electromagnetically coupling to the receiver coil in the UV light output unit or units.

The arrangement for example comprises a water purification system.

In one arrangement, the entire base of the vessel is provided with a wireless power transmitter. However, in another arrangement, the wireless power transmitter is located at the base of a treatment passage within the vessel, wherein the one or more UV output units are contained within the treatment passage.

This means a smaller power transmitter is needed. The UV output unit rises and falls within its treatment passage. While this does not enable the UV output unit to travel throughout the volume of the vessel, it means a flow is generated by the movement of the UV output unit or units. This flow enables the full volume to be treated and it creates a pumping or stirring action in the vessel. This option means the vessel does not need to have a transmitter (induction coil) which covers the full bottom area of the vessel.

Examples in accordance with another aspect of the invention provide a UV treatment method, comprising:

providing power to a solid state UV output unit which comprises a closed chamber with a solid state UV output device mounted in the chamber and storing the provided power;

providing the UV output unit in a location sunk to the bottom of a vessel containing a liquid medium to be treated;

powering the UV output device using the stored provided power, thereby heating the unit such that the chamber increases in volume and the unit floats; and

using the remaining stored power to power the UV output device until the power is dissipated, such that the UV output device turns off, and the unit sinks.

The power may be provided to the UV output unit while the unit is already at the bottom of the vessel. Thus the two "providing" steps may be in either order. In one case, the units are charged and then placed in the vessel and in the other case they are placed in the vessel then charged at that location. The power may be provided to the solid state UV output unit wirelessly, for example by a wireless power transfer system at the base of the vessel. BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the invention will now be described in detail with reference to the accompanying drawings, in which:

Figure 1 shows a UV treatment arrangement;

Figure 2 shows an example of one of the UV output units used in the arrangement of Figure 1;

Figure 3 shows a cut-away perspective view of the UV output unit of Figure 2 and additionally with a fin to induce rotational movement;

Figure 4 shows a first example of a possible arrangement of the vessel;

Figure 5 shows a second example of a possible arrangement of the vessel;

Figure 6 shows the unit rising when the buoyancy has increased;

Figure 7 shows the unit falling when the buoyancy has decreased; and

Figure 8 shows a UV treatment method. DETAILED DESCRIPTION OF THE EMBODIMENTS

The invention provides a solid state UV output unit which comprises a closed chamber, having a gas pocket within the chamber, and an outer wall, wherein at least a portion of the outer wall is flexible such that a volume of the gas pocket and hence the volume of the closed chamber may be varied by flexing of the outer wall portion. A solid state UV output device is mounted in the chamber. One of more of these units may be provided in a vessel containing a liquid. By controlling the flexing of the portion of the outer wall, the buoyancy may be controlled so that the unit or units are able to move within the liquid. The flexing is for example controlled by heating.

Use of UV light - in particular UV-C light - for the sterilization of water is well known. UV light at sufficiently short wavelengths is mutagenic to bacteria, viruses and other micro-organisms. At a wavelength of 2,537 Angstroms (254 nm), UV breaks molecular bonds within micro -organismal DNA, producing thymine dimers in the DNA, thereby destroying the organisms, rendering them harmless or prohibiting growth and reproduction. Ultraviolet disinfection of water consists of a purely physical, chemical- free process. UV-C radiation attacks the vital DNA of the bacteria directly. The bacteria lose their reproductive capability and are destroyed. Even parasites such as Cryptosporidia or giardia, which are extremely resistant to chemical disinfectants, are efficiently reduced.

Most typically, germicidal ultraviolet light is delivered by a mercury- vapor lamp, which emits UV light at the germicidal wavelength (mercury vapor emits at 254 nm). Known UV units for water treatment generally consist of a specialized low pressure mercury vapor lamp that produces ultraviolet radiation at 254 nm, or medium pressure UV lamps that produce a polychromatic output from 200 nm to visible and infrared frequencies. Medium pressure lamps are approximately 12% efficient, whilst amalgam low-pressure lamps can be up to 40% efficient. The UV lamp never directly contacts the water, but is housed inside a glass quartz sleeve, submerged in the water, or else mounted external to the water.

Due to the large form factor, inflexible operating mode, and hazardous compositional materials, increasingly attention has turned toward the use of solid state UV- emitting devices, such as UV LEDs within water purification devices. It is well known that group IIIA-nitrides:

have direct band gaps which can be used to generate electromagnetic radiation in the ultraviolet wavelength range.

Figure 1 shows a UV treatment arrangement, comprising a vessel 10 containing a liquid medium 12 to be treated.

A set of UV output units 14 is provided in the vessel. As will be explained in more detail below, each output unit has an adjustable buoyancy, so that over time it floats and sinks in the liquid 12. In this way, the units 14 move throughout the liquid 12 in a semi- random manner thereby making sure the full liquid volume is treated by the UV outputs from the units 14.

The buoyancy of a unit 14 is varied by controlling its volume. In principle, this could be achieved by mechanical means, but in the preferred example, the volume is controlled by heating. The change in volume leads to a change in density which in turn leads to a change in buoyancy. Conversely, if the volume remains the same, the density will remain the same and the buoyancy will stay the same.

The mechanical means for changing the volume could, for example, be a bimetallic strip that is anchored at one end whilst the other end can act upon the flexible portion of the outer wall. Alternatively, the mechanical means could be a mechanical displacement means, for example, a piston. It could be envisioned that the piston is anchored at one end whilst the other end acts upon the flexible portion of the outer wall.

The heating may be provided directly by the LED, i.e., when the LED is illuminated it will generate heat and this heat will increase the pressure of a gas inside the output unit. The change in pressure will lead to a change in volume and therefore a change in buoyancy. Alternatively, the heating may be provided by a heating source incorporated within the output unit, for example, a heating coil.

Figure 2 shows an example of one of the UV output units 14. It comprises a closed chamber 20, having a gas pocket 22 within the chamber. The chamber is defined by an outer wall 24, and at least a portion of the outer wall is flexible such that a volume of the gas pocket 22 and hence the overall volume of the closed chamber may be varied by flexing of the outer wall portion.

The outer wall 24 comprises a flexible water-tight material, such as silicone, for example with a spherical outer shape, defining a UV output unit in the form of a small ball which is placed in a lighting to be treated. Silicone may be a good material for the outer wall as it is flexible, UV transparent and UV resistant.

In addition to the gas pocket, the chamber 20 houses a solid state UV output device 26 carried on a circuit board 28.

When the UV output device 26 is turned on, it generates heat as well as a UV output, and this heat causes expansion of the gas pocket 22 (as well as an increase in pressure). The corresponding increase in volume results in a reduced density, and hence a different buoyancy. Buoyancy can be considered as follows: buoyancy = weight of the displaced fluid. The weight of the displaced fluid is directly proportional to the volume of the displaced fluid. Therefore, if two completely submerged output units have the same mass, but one has a greater volume, the output unit with the greater volume will have greater buoyancy.

B = PfV_dispg

Pf is the density of the fluid, V_disp is the volume of the displaced body of liquid, and g is the gravitational acceleration.

Buoyancy depends on volume and so an object's buoyancy reduces if it is compressed and increases if it expands. Depending on the flexing of the outer wall, the unit can be controlled to sink or float in the liquid 12. The density and temperature of the liquid will also have a direct effect on the buoyancy of the output units. This may mean that differing fluids will require a different output unit. The output units may be tailored to a certain range of liquid temperatures or liquid densities.

The unit 14 has a wireless power receiving system in the form of a receiver inductor coil 30 for receiving power to drive the solid state UV output device 26. It also has a charge storage device 32 which may be a capacitor or battery. The gas pocket 22 floats to the top, so that the orientation of the unit when within the liquid adopts a known orientation. In the example shown, the receiver coil 30 then has a vertical axis of symmetry, and the coil extends around that axis.

Referring back to Figure 1, the base of the vessel 10 has a wireless energy transmitter 34, in the form of a transmitter inductor coil. This is arranged around the same axis of symmetry to provide efficient energy transfer between the coils.

When a unit 14 returns to its original volume, either because it is sufficiently cool to sink in the liquid 12, because it has been turned off and is thus no longer generating heat, or because the mechanical displacement means has returned to its original state, its buoyancy changes and it will sink towards the wireless energy transmitter 34, where it is recharged. This recharging process causes the UV output device to turn on and also causes the battery or capacitor 32 to charge. The resulting heating causes the buoyancy to increase and the unit floats. This takes it out of range of the electromagnetic coupling with the wireless energy transmitter 34 so the stored energy in the battery or capacitor is used. The UV output device then remains active for a period of time, before turning off and cooling. As discussed above, the heating may be provided by an extra heating coil which may be acting independent of the LED. The heating coil may draw its energy from the same storage device as the LED or it may have its own storage device. The benefit to providing an extra storage device and heating coil may be that the LED (which may draw less current than the heater) may remain switched on and emitting UV independent of the heater. This, along with the correct dimensioning of the output unit may mean that the UV LED can emit as it travels downwards through the fluid as well as upwards.

The unit 14 has negative buoyancy (sinks) in the liquid when at room temperature, or at the intended operating temperature of the liquid. The unit has positive buoyancy (floats) in the liquid when at an equilibrium operating temperature of the solid state UV output device or at an equilibriam temperature of the heating coil. This is when the UV output device and/or the heater is turned on and a stable temperature has been reached, where the heat generated is balanced by the heat dissipation.

Figure 3 shows a cut-away perspective view of the UV output unit, and shows the same components as in Figure 2.

During operation, there is thus a cyclic operation of the UV output device, and a corresponding cyclic heating and cooling cycle, charging and discharging cycle and floating and sinking cycle. The example of Figure 2 is based on a spherical UV output unit. The unit may instead have an asymmetric shape to allow the unit the rotate and tumble during its ascent and descent, more effectively irradiating the volume. Figure 3 shows a fin 35 for this purpose. The unit may have any desired outer shape to induce a desired movement trajectory as the unit floats and sinks.

Figure 4 shows a first example of an arrangement of the vessel. The transmitter coil 36 is shown extending around the full periphery of the base of the vessel. Any unit 14 that drops to the base will be coupled to the field of the transmitter coil 36 and energy transfer will take place.

The transmitter coil is driven with a high frequency alternating current and comprises an inverter which receives power from the mains. The unit comprises energy harvesting circuitry for ac-dc conversion and for charging the battery or capacitor.

Suitable circuitry for energy delivery and energy harvesting will be well known to those skilled in the art.

The unit also includes a controller for controlling the charging of the battery or capacitor and controlling the operation of the UV LED. The controller may for example delay operating the UV LED until the battery reaches a particular state of charge, or the capacitor reaches a particular voltage. This will reduce the frequency of the cyclic operation, since the UV LED will then remain on and off for longer periods.

Some vessels may have limited space for the transmitter coil 36. Figure 5 shows an example in which the wireless power transmitter 36 is located at the base of a treatment passage 50 within the vessel. The example shows a single output unit 14 contained within the treatment passage 50 and sunk to the bottom of the treatment passage.

The treatment passage has a smaller base area than the overall vessel, and in the example shown it projects below the remainder of the base of the vessel, to form a projection around which the transmitter coil may be mounted.

In this position, it receives wireless power transfer, to enable the UV output device to be turned on and also for the capacitor or battery to charge. It will remain in this position until heating causes the buoyancy to increase or a mechanical actuator displaces the flexible portion of the outer wall.

The treatment passage constrains the movement of the unit 14 to a vertical path, although the path does not need to be straight, and it could follow a curved path up and down, for example a spiral path which will then be in contact with a larger proportion of the volume of the vessel (as it will be longer). The treatment passage allows the liquid to flow in and out.

Figure 6 shows the unit 14 rising when the buoyancy has increased. The light output device continues to function while there is sufficient stored charge. When the charge has been dissipated, the unit 14 stops emitting UV light, then cools and then sinks as shown in Figure 7. Alternatively, the output unit contains an additional storage device which provides power to a mechanical actuator or a heater. The unit may then sink whilst the light output device continues to emit UV light.

This design does not enable the UV output unit to travel throughout the full volume of the vessel. However, a flow 52 is generated by the movement of the UV output unit or units. This flow 52 enables the full volume to be treated by creating a pumping or stirring action in the vessel.

Figure 8 shows a UV treatment method.

In step 60 power is provided wirelessly to the solid state UV output unit 14, the UV output unit having sunk to the bottom of a vessel containing a liquid medium to be treated (as shown in Figure 5).

In step 62, the wirelessly provided power is stored and the UV output device is powered and hence turned on using the wirelessly provided power. This causes heating of the unit 14 such that the chamber increases in volume and the unit floats such that the wireless power transfer ceases.

In step 64, the remaining stored power is used to power the UV output device until the power is dissipated, such that the UV output device then turns off, and the unit sinks. The process then returns to step 60.

The example above shows spherical units. However, any shape is possible. The example also shows a unitary silicone body with embedded components. The unit may instead be partially rigid (for example having a rigid base) and partially flexible (for example having a flexible top over the gas cavity).

Heating is the most simple way to implement the desired expansion and contraction of the overall volume of the unit. However, mechanical actuation is also possible, by which a charged actuator mechanically deforms the unit to a larger volume condition, and the actuator relaxes when it discharges, in the absence of the wireless power transfer. The larger volume condition may be a convex shape and the smaller volume condition may be a concave shape, for example, so that a portion of the unit is bistable between two different shape conditions, each with a different overall volume. A mechanical actuator may for example be based on a shape memory alloy. This also uses thermal energy for its actuation and can be made very simple in design. The mechanical actuator may also be based on a bimetallic strip or a displacement device, for example a piston inside a cylinder arrangement.

Each unit may have one or more LEDs. There may be only one unit (e.g.

Figure 5), or else several or many units may be present in the liquid (e.g. Figure 4).

Each unit for example has a size (e.g. diameter) of between 20mm and 50mm.

Silicone has been given as an example of a suitable flexible material. Another possible example is thermoplastic polyurethane (TPU). In preferred embodiments, the material may be UV-C resistant and transparent.

The invention may be applied to UV LEDs other than UV-C LEDs, for example to UV-A or UV-B LEDs.

The increase in buoyancy of the UV output unit as it heats up may be a gradual change rather than a step-change. As the temperature of the gas within the unit increases due to the operation of the UV output device, the buoyancy increases due to a change in internal pressure (ΔΡ). This may be from a negative buoyancy to a positive buoyancy.

The buoyancy of the unit will for example pass through the neutral buoyancy threshold before the temperature of the gas within the closed chamber reaches the operating temperature of the solid state UV output device. Alternatively, the change in volume may be a step-change. The design of the outer wall may be such that it has a threshold value, which when passed means that the outer wall quickly transitions from its original volume into the increased volume.

Due to the heat transferring properties of the gas from the solid state UV output device to the outer wall of the unit, the gas may never reach the same temperature as the operating temperature of the solid state UV output device. This is, of course, reliant on certain variables.

The most basic implementation uses air as the gas of the unit. However, it is also possible if desired to alter the heat transferring capabilities of the gas by using, or mixing with, a gas with a higher or lower thermal conductivity. It is also possible to change the material that is used to construct the outer wall and to change the surface area of the unit.

In broad terms, a net heat gain (the sum of the heat dissipated by the circuitry within the unit and the heat transferred from the medium surrounding the unit into the unit) that exceeds the net heat loss (due to heat transfer across the surface of the unit) will result in an an internal temperature increase and therefore an increase in buoyancy. This is because a change in temperature within the chamber will result in a change of pressure leading to a change in volume.

The example above is based on providing operation of the units while they are in the liquid (water) by wireless power transfer. This provides an integrated charging system.

An alternative is to have a non- integrated charging system. This may take the form of a separate charging station where the units are placed when taken out of the fluid reservoir. Once charged, they can be placed in the fluid reservoir. They will then provide UV radiation and heat up in the same way as described above, or the volume may be changed using mechanical means as described above. In this way, they will start in a sunk location at the base of the reservoir, and then float when the stored energy is converted to light and heat, until the stored energy is dissipated. A single charge may be all that is required, so that the units are then removed for recharging and for use with a different fluid reservoir.

The charging may be using wireless power transfer, as in the examples above. However, if the units are charged in a separate charging station, they may also be charged using electrodes or connectors.

The UV output unit may be either on or off. However, it is also possible to control the unit in a more analog manner. For example by controlling the current level, the pulse width modulation duty cycle, or the frequency of the LED operation, the buoyancy can be controlled. This may for example result in output units which are suspended at a certain level, without floating to the surface or sinking to the bottom.

The reservoir may be filled and emptied manually or automatically. There may be a continuous flow in and out of the reservoir (creating an in-line system) or there may be discrete filling and then emptying of the reservoir. Examples of possible use are in water reservoirs in air humidifiers or water tanks.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. A solid state UV output unit (14), comprising:

a closed chamber (20), having a gas pocket (22) within the chamber;

an outer wall (24), wherein at least a portion of the outer wall is flexible such that a volume of the gas pocket (22) and hence the volume of the closed chamber may be varied by flexing of the outer wall portion;

a solid state UV output device (26) mounted in the chamber;

a wireless power receiving system (30) for receiving power to drive the solid state UV output device; and

a charge storage device (32) for charging by the wireless power receiving system and for storing charge for operating the solid state UV output device.

2. A unit as claimed in claim 1, wherein the wireless power receiving system (30) comprises an induction coil.

3. A unit as claimed in any preceding claim, wherein the volume of the closed chamber is varied using a mechanical actuator acting upon the flexible outer wall portion.

4. A unit as claimed in claims 1 and 2, wherein the volume of the closed chamber is varied by heating a gas in the gas pocket.

5. A unit as claimed in any preceding claim, wherein the unit has negative buoyancy in a medium to be illuminated with UV light when at room temperature or other intended operating temperature of the medium.

6. A unit as claimed in any preceding claim, wherein the unit has positive buoyancy in a medium to be illuminated with UV light when a stable temperature is reached during operation of the solid state UV output device.

7. A unit as claimed in any preceding claim, for UV water treatment.

8. A unit as claimed in any preceding claim, wherein the gas pocket (22) contains air.

9. A unit as claimed in any preceding claim, wherein the UV output device (26) comprises a UV LED arrangement, for example one or more UV-C LEDs.

10. A UV treatment arrangement, comprising:

a vessel (10) for containing a medium to be treated;

one or more solid state UV output units (14) each as claimed in any preceding claim in the vessel; and

a power transfer device for transferring power to the one or more solid state UV output units (14).

11. An arrangement as claimed in claim 10, wherein the power transfer device comprises a wireless power transmitter located at the base of the vessel, for example outside the vessel beneath the base of the vessel.

12. An arrangement as claimed in claim 11, wherein the wireless power transmitter comprises an induction coil (36).

13. An arrangement as claimed in claim 10, 11 or 12, comprising a water purification system.

14. An arrangement as claimed in any one of claims 10 to 13, wherein the power transfer device is located at the base of a treatment passage (50) within the vessel, wherein the one or more output units are contained within the treatment passage (50).

15. A UV treatment method, comprising :

providing wireless power to a solid state UV output unit (14) which comprises a closed chamber with a solid state UV output device mounted in the chamber, a wireless power receiving system, and a charge storage device;

storing the provided wireless power in the charge storage device; providing the UV output unit in a location sunk to the bottom of a vessel containing a liquid medium to be treated;

varying the volume of the closed chamber by flexing a flexible portion of an outer wall of the solid state UV output unit.