METHOD AND SYSTEM FOR PREVENTING FOULING OF SURFACES

Abstract

A method of anti-fouling of a surface while said surface is at least partially submersed in an liquid environment, comprising: providing an anti-fouling light; distributing at least part of the light through an optical mediumcomprising a silicone material and/or UV grade fused silica; emitting the anti-fouling light from the optical medium and from the surface.

Claims

1. A module for anti-fouling of a surface comprising: an emission surface configured to distribute light in a direction away from the surface, and: an optical medium comprising: at least one light source contained therein, said at least one light source configured to generate a light; wherein the optical medium is configured to distribute at least part of the generated light through the optical medium by internal reflection, wherein the optical medium and the emission surface are configured to be distributed over the surface.

2. The module of claim 1, wherein the emission surface comprises one of: a transparent surface of the optical medium and a coating applied to a surface of the optical medium.

3. The module of claim 1, wherein the optical medium comprises: a first layer; and a second layer, wherein the first layer and the second layer are separated from each other.

4. The module of claim 3, wherein the first layer and the second layer are separated by a plurality of spacers forming at least one of: spaces and pockets between the first layer and the second layer.

5. The module of claim 4, wherein the at least one of spaces and pockets are filled with one of: a gas and a liquid.

6. The module of claim 5, wherein the at least one of: spaces and pockets are arranged in a pattern to form at least one of: a regular pattern and an irregular pattern.

7. The module of claim 6, wherein the regular pattern is one of: a linear (channel), a rectangular, and a honeycomb.

8. The module of claim 1, wherein the at least one light source is arranged in a two dimensional grid.

9. The module of claim 1, wherein a distance between two adjacent ones of said at least one light source is one of: uniform and variable.

10. The module of claim 1, wherein said emission surface is liquid tight.

11. The module of claim 1, wherein the optical medium comprises a material selected from a group comprising at least one of: silicones and UV grade silica.

12. The module of claim 1, wherein the optical medium further comprising: a light spreader.

13. The module of claim 1, wherein the optical medium further comprising: a plurality of spatially distributed UV grade translucent particles embedded therein.

14. The module of claim 13, wherein a density of the spatially distributed UV grade translucent particles increases from within the optical medium towards the emission surface.

15. The module of claim 1,wherein the at least one light source is at least one of a Light Emitting Diode (LED) and an Organic Light Emitting Diode (OLED).

16. The module of claim 1, wherein the lighting module is shaped as one of a: a tile and an elongated strip.

17. The module of claim 1, wherein the light is one of: a UV light and a visible light.

18. The module of claim 1, the optical medium further comprising: a wavelength conversion material configured to: convert the light, generated at a first wavelength to a second wavelength, wherein the second wavelength is in a UV range.

19. The module of claim 16, wherein the UV light is in a wavelength range of about 240 nm to about 280 nm.

20. The module of claim 17, wherein the UV range is about 240 nm to about 280 nm.

21. A module for anti-fouling of a surface, comprising: a medium, arranged substantially planar to the surface, comprising: a first layer; a second layer, and a plurality of walls separating the first layer and the second layer, said plurality of walls forming a plurality of channels between the first layer and the second layer; and a plurality of light sources arranged with respect to the plurality of channels, wherein the channels are configured to distribute by total internal reflection, light generated by the plurality of light modules.

22. The system of claim 21, wherein the channels are filled with one of: a gas and a liquid.

23. The module of claims 21, wherein the channels comprise a material selected from a group comprising at least one of: silicones and UV grade silica.

24. The module of claim 21, wherein the medium is arranged in one of: a tile and an elongated strip.

25. The module of claim 21, wherein a distance between neighboring light sources is one of: uniform and variable.

26. The module of claim 25, wherein the distance between neighboring light sources is based on a desired light output power.

27. The module of claim 21, wherein the plurality of light sources are arranged in one of: a foil and an electronic textile.

28. The module of claim 21, wherein the two dimensional grid is arrange in one of: a chicken-wire structure, a close-packed structure, a rows/columns structure, a regular structure and an irregular structure.

29. The module of claim 21, comprising: a plurality of spatially distributed UV grade translucent particles embedded within the channels.

30. The module of claim 29, wherein a density of the spatially distributed UV grade translucent particles increases from within the first layer to the second layer.

31. The module of claim 21, wherein the plurality of light sources are selected from a group consisting of: a Light Emitting Diode (LED) and an Organic Light Emitting Diode (OLED).

32. The module of claim 21, wherein the generated light is one of: a UV light in a wavelength range of about 240 nm to about 280 nm.

33. A system for protecting a surface of a marine object subjected to bio-fouling, the system comprising: at least one module, configured to be positioned adjacent to the surface, each of the at least one module comprising: an emission surface configured to distribute light in a direction away from the surface, and: an optical medium comprising: at least one light source contained therein, said at least one light source configured to generate a light; wherein the optical medium is configured to distribute at least part of the generated light through the optical medium by total internal reflection.

34. The system of claim 33, wherein the marine object is selected from a group of: stationary objects and movable objects.

35. The system of claim 34, wherein the stationary objects comprising at least one of: pipes, marine stations, water inlets, swimming pools, and water treatment plants.

36. The system of claim 34, wherein the movable objects comprising at least one of: ships and submarines.

37. The system of claim 33, wherein the at least one module arranged in one of: a tile and an elongated strip.

38. The system of claim 33, wherein the at least one module is attached to the surface of the marine object.

39. The system of claim 33, wherein the at least module is adjacent to the surface of the marine object.

40. The system of claim 33, wherein the emission surface comprises one of: a transparent surface of the optical medium and a coating applied to a surface of the optical medium.

41. The system of claim 33, wherein the optical medium comprises a material selected from a group comprising at least one of: -silicones and UV grade silica.

42. A system configured to anti-foul a surface subjected to bio-fouling, the system comprising: at least one module, configured to be positioned proximate the surface, each of the at least one module comprising: at least one light emitting diode contained within a liquid tight encapsulation, said at least one light emitting diode configured to generate a light; and: a medium comprising: an emission surface, positioned on a first surface of the medium, the emission surface configured to support the medium in distributing at least part of the generated light substantially homogeneously through the medium wherein said medium being configured to distribute said light through the emission surface.

43. The system of claim 42, wherein the at least one module is arranged in one of: a tile and an elongated strip.

44. The system of claim 42 wherein said at least one light emitting diode is configured to generate said light in a UV wavelength range.

45. The system of claim 42, wherein said at least one light emitting diode is configured to generate said light in a visible wavelength range.

46. The system of claim 45, the medium further comprising: a wavelength conversion material configured to: convert the visible wavelength light into a UV wavelength light.

47. The system of claim 42, wherein the medium is optically transparent.

48. The system of claim 42, wherein the medium comprises: a plurality of optically transparent channels.

49. The system of claim 42, wherein the medium comprises: a plurality of layers having one of: different composition and particle density.

50. The system of claim 49, wherein the plurality of layers may be one of: formed and sprayed on a prior layer.

51. The system of claim 42, wherein the emission surface comprises one of: a surface of the optical medium and a coating applied to a surface of the optical medium.

52. The system of claim 42, further comprising: a light spreader positioned opposite a corresponding one of the plurality of I light emitting diode.

53. The system of claim 42, wherein the plurality of light emitting diodes are contained within the medium.

54. The system of claim 42, wherein the plurality of light emitting diodes are positioned on the medium.

55. The system of claim 42, the medium further comprising: a plurality of scatterers comprising one of: air bubbles, imperfections, silica, glass and mica.

56. The system of claim 55, wherein said plurality of scatterers distribute said light at least one of: away from and toward, the surface.

57. The system of claim 55, wherein said scatterers comprise: spatially varying density particles.

58. The system of claim 42, wherein the surface subjected to bio-fouling is configured to be submersible.

59. A foil, configured to anti-foul a surface, said foil comprising: a plurality of light sources configured to generate a light in at wavelength band comprising at least one of: a visible light band and a UV light band; and an optical medium configured to: receive the generated light; and distribute, within the optical medium, said light in a direction substantially parallel to the surface; and a plurality of imperfections, within the optical medium, directing portions of the light away from the optical medium .

60. The foil of claim 60, wherein the optical medium further comprising: a emission layer.

61. The foil of claim 60, wherein the emission layer is one of: a layer of the optical medium and a coating on the optical medium.

62. The foil of claim 59, wherein the foil is arranged as one of: sized limited in two orthogonal directions perpendicular to a thickness of the foil and size limited in only one direction perpendicular to a thickness of the foil.

63. The foil of claim 59, wherein the foil is configured to be placed on or proximate to the surface.

64. The foil of claim 60, wherein the emission layer is substantially planar.

65. The foil of claim 59, wherein the plurality of light sources are configured in one of: a chicken-wire pattern, a close-packed pattern, a rows/columns pattern, a regular pattern and an irregular pattern.

66. The foil of claim 59, wherein the plurality of light sources are arranged within the optical medium.

67. The foil of claim 59, wherein the plurality of light sources are arranged on a surface of the optical medium.

68. The foil of claim 59, wherein the optical medium is transparent to said light.

69. The foil of claim 59, wherein the optical medium comprises a plurality of channels therein.

70. The foil of claim 69, wherein the channels are transparent to said light.

71. The foil of claim 69, wherein the channels are filled with at least one of: a gas and a liquid.

72. The foil of claim 59, wherein the plurality of light emitting diodes are contained in a liquid tight encapsulation.

73. The foil of claim 59, wherein the plurality of imprefections are selected from a group consisting of at least one of: air bubbles, scratches, indentations, silica, glass and mica.

74. The foil of claim 59, wherein the surface is configured to be submersed in a liquid.

75. The foil of claim 59, wherein the surface is subject to bio-fouling.

76. The foil of claim 69, wherein the optical medium is one of: a material comprising silicon and a silica.

77. The foil of claim 75, wherein the optical medium wherein a reflective index of said imperfections is different than a reflective index of said optical medium.

78. The foil of claim 69, wherein the channels are comprised of one of: a material comprising silicon and a silica.

79. The foil of claim 78, wherein the channels further comprising: a plurality of imperfections wherein a reflective index of said imperfections is different than a reflective index of said channel.

80. A foil, configured to anti-foul a surface, said foil comprising: a plurality of light sources configured to generate a light in at wavelength band comprising at least one of: a visible light band and a UV light band; and an optical medium configured to: receive the generated light; and distribute, within the optical medium, said light in a direction substantially parallel to the optical medium; and selectively output portions of said light substantially perpendicular to the distributed direction of light .

81. The foil of claim 80, wherein the optical medium is one of: a material comprising silicon and a silica.

82. The foil of claim 81, wherein the optical medium further comprising: a plurality of regions wherein a reflective index of said regions is different than a reflective index of said optical medium, wherein said light is output at the plurality of regions.

83. The foil of claim 80, wherein the optical medium comprises: a plurality of channels, wherein said channels comprised of one of: air, a liquid, a material comprising silicon, and a silica, the channels further comprising: a plurality of regions wherein a reflective index of said regions is different than a reflective index of said channel, wherein said light is output at the plurality of regions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0054] FIG. 1 shows a ships hull suffering from fouling;

[0055] FIG. 2 is a graph showing UV Light Threshold Limited Values (TLV) according to the American Congress of Governmental and Industrial Hygienist's (ACGIH);

[0056] FIG. 3 is a graph showing a germicidal action spectrum for different biological materials as a function of light wavelength;

[0057] FIG. 4 is a graph showing a transmission spectrum for different types of glass;

[0058] FIG. 5 is a bar graph showing the relative spectral power distribution of typical Philips low pressure tubular fluorescent ultraviolet (TUV) lamps;

[0059] FIG. 6 is a bar graph showing the relative spectral power distribution of Philips medium pressure discharge lamps (HOK and HTK types);

[0060] FIG. 7 is a schematic cross section view of a light module with a light guide;

[0061] FIG. 8 shows a general concept of light guiding used in embodiments;

[0062] FIGS. 9(a)-9(b) show a realised planar light guide embodiment;

[0063] FIGS. 10(a)-10(b) show wedge shaped light guide embodiments;

[0064] FIGS. 11(a)-11(b) show direct-lit light guide embodiments;

[0065] FIG. 12 shows an embodiment comprising a redistribution reflector and a wavelength conversion material;

[0066] FIG. 13 shows a light guide comprising gas-filled channels;

[0067] FIG. 14 shows an embodiment comprising distributed embedded flakes.

[0068] FIG. 15 shows an embodiment of a chicken-wire grid.

DETAILED DESCRIPTION OF EMBODIMENTS

[0069] While the disclosure has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the disclosure is not limited to the disclosed embodiments. It is further noted that the drawings are schematic, not necessarily to scale and that details that are not required for understanding the present invention may have been omitted. The terms upward, downward, below, above, and the like relate to the embodiments as oriented in the drawings, unless otherwise specified. Further, elements that are at least substantially identical or that perform an at least substantially identical function are denoted by the same numeral.

[0070] FIG. 7 shows as a basic embodiment a cross section of a lighting module 1 comprising a plurality of light sources 3 (here: side-emitting LEDs, wherein the light is emitted primarily from the side of the LED, and more or less parallel to the surface) encapsulated in a liquid-tight optical medium 5 to guide at least part of the light 9 emitted from the light sources 5 via total internal reflection through the optical medium, which optical medium is further provided with optical structures 7 to scatter light 9 and guide the light 9 out of the optical medium 5 towards an object 11 to be targeted with the light (a biofouling organism). The optical medium 5 generally extends in two dimensions significantly further than in the third dimension so that a two-dimensional-like object is provided. Optical structures 7 to scatter light 9 may be spread in one or more portions of the optical medium material, possibly throughout all of it, wherein in such portions the distribion may be generally homogeneous or localised. Scattering centres with different structural properties may be combined to provide, besides optical, also structural characteristics, such as resistance to wear and/or impact. Suitable scatterers comprise opaque objects but largely translucent objects may be used as well, e.g. small air bubbles, glass and/or silica; a requirement is merely that a change in refractive index occurs for the wavelength(s) used.

[0071] The principle of light guiding and spreading light over a surface is well-known and widely applied in various fields. Here, the principle is applied to UV light for the purpose of anti-fouling. It is noted that the idea of making a surface, e.g. the hull of a ship self-lit with UV is a clearly different solution than the current and well established anti-fouling solutions which rely on smooth coatings, chemicals, cleaning, software to control the ship speed, etc.

[0072] Total internal reflection is one way of transmitting light through an optical medium, which is then often referred to as a light guide. To maintain the conditions for total internal reflection, the index of refraction of the light guide should be higher than that of the surrounding medium. However, the use of (partly) reflecting coatings on the light guide and/or use of the reflective properties of the protected surface, e.g. the hull of a ship, itself can also be used to establish the conditions for guiding the light through the optical medium.

[0073] In some embodiments the optical medium may be positioned relative to the protected surface, e.g. the hull of a ship, such that a small air gap is introduced between the optical medium and the protected surface; UV light may travel even betterwith less absorptionin air than in an optical medium, even when this optical medium is designed as a light guiding material. In other embodiments gas-filled channels, e.g. air channels, may be formed within silicone material. An array of separate gas-filled pockets may also be provided, e.g. in a regular pattern like a rectangular or honeycomb-pattern or in an irregular pattern. Instead of gas (e.g. air) filling, channels and/or pockets may be at least partly filled with a UV-transmissive liquid, e.g. fresh and/or purified water. In case a protected surface that is covered with such optical medium is subject to impact, e.g. a ship hitting a dockside, small pockets may soften, redistribute the impact energy and hence protect the surface, wherein liquid-filled pockets may be robuster under deformation than air-pockets which may more easily burst open.

[0074] As most materials have a (very) limited transmittance for UV light, care has to be taken in the design of the optical medium. A number of specific features and/or embodiments, which are dedicated for this purpose are listed in the following:

[0075] A relatively fine pitch of low power LEDs can be chosen, to minimize the distance light has to travel through the optical medium.

[0076] A hollow structure can be used, e.g. a silicone rubber mat with spacers that keep it a small distance away from the protected surface. This creates air channels, through which the UV light can propagate with high efficiency (air is very transparent for UV). Use of gas filled channels provided by such structures allows distributing the UV light over significant distances in a optical medium of material that would otherwise absorb the UV light too strongly to be useful for anti-fouling. Similarly, separate pockets may be formed.

[0077] A special material can be chosen with high UV transparency, like certain silicones or UV grade (fused) silica. In embodiments, this special material can be used only for creating channels for the light to propagate the majority of the distance; a cheaper/more sturdy material can be used for the rest of the surface.

[0078] Further embodiments are disclosed in the accompanying drawings, wherein a main issue is to illuminate a large surface with anti-fouling light, preferably UV light, yet using point light sources. A typical concern is spreading of the light from point sources to surface illumination. In more detail:

[0079] The protected surface area of a typical container ship is 10.000 m.sup.2.

[0080] A typical LED source has an area of 1 mm.sup.2. This is 10.sup.10 smaller.

[0081] Taking the required power levels into account, about 10 LEDs per m.sup.2 may be required

[0082] This means light has to be spread from 1 LED over 1000 cm.sup.2

[0083] As another boundary condition is taken that the solution should be thin (order of magnitude: 1 cm), e.g. for reasons such as: [0084] To be able to add the solution as a coating to a ship [0085] To not increase drag due to an increased cross section size of the ship [0086] To keep (bulk) material costs limited.

[0087] The use of an optical medium, in particular a generally planar light guide is therefore provided. Typical dimensions of a light guide are a thickness of about 1 mm to about 10 mm. In the other directions, there is no real limit to the size, from an optical point of view; in particular not if plural light sources are provided so that decay of light intensity throughout the light guide due to partial outcoupling of light and possibly (absorption) losses are countered.

[0088] Here, it is considered that similar optical challenges apply as with the design of LCD TV backlights, although emission light intensity uniformity is less stringent in anti-fouling than with LCD TV backlights. FIG. 8 shows a lighting module 1 with light sources 3 and a light guide 5 with an additional top layer 13. FIGS. 9A-9B show practical examples of the principle illustrated in FIG. 8 and show a lighting module 1 with LED sources 3 which are positioned along the edge 15 of a light guide 5 and which inject light into the light guide 5. A pattern of scatterers e.g. white dots of paint, or small scratches/dents extract the light in appropriate places, here generally uniform (FIG. 9B), so that a desired, e.g. generally homogeneous, illumination distribution of the environment is achieved.

[0089] FIG. 10(a) shows a LCD TV backlight arrangement wherein a wedge-shaped light guide 5(a) is employed wherein the light from a light source 3 is injected into the light guide 5(a) from the side. The light guide 5(a) is arranged with a pattern of scattering objects 7, such as dots of paint or scratches, on a reflective substrate 17. A wedge shape causes more of the light to be extracted towards the tip end. The prism sheets 19 and LCD panel 21 that orient polarisation states of the light and generate visible light colours are feature that can be omitted in an anti-fouling context.

[0090] FIG. 10(b) shows another wedge shaped light guide 5(b) which is provided itself with a structured side so as to scatter and redistribute light within and out of the light guide 5(b).

[0091] Both the plane light guide and wedge-shaped light guide share the principle of guiding light along a substantial distance substantially parallel to the emission surface. The alternatives shown in FIG. 11a-11(b) (see below) are known as a direct-lit optical medium; here one or more LEDs and/or other light source(s) is present behind a screen e.g. a diffuser and emit light directly towards the object to be illuminated, e.g. a biofouling organism.

[0092] In a side-lit optical medium, often referred to as a light guide, such as those shown in FIG. 8-10(b) a side of the optical medium is illuminated from one or more light sources relatively strongly and further away from the light source(s) the light intensity within light guide is generally more homogeneous, possibly governed by scatterers (FIGS. 9(a)-9(b)).

[0093] In short, a difference betweem side-lit or direct-lit concepts is that in direct-lit situations the light travels no substantial distance parallel to the emission surface. As a result, the light intensity is usually much higher directly in front of the light sources. No real distribution of light is achieved. Thus, in a direct-lit solution a larger intensity variation may be expected between areas directly in front of the light source(s) and area aside thereof.

[0094] FIGS. 11(a) and 11(b) show lighting modules 101(a), 101(b) in cross section view (cf FIG. 7) comprising light sources 3 and optical medium 105(a), 105(b) having an emission surface 23. The wavy line I(a) and I(b), respectively, show the light intensity profile emitted from the emission surface and illustrate that a thicker optical medium 105(b) (FIG. 11(b)) will automatically provide a better light uniformity on the emission surface 23 than a thinner optical medium 105(a) (FIG. 11(a)) of otherwise identical construction.

[0095] However, in the present case such relative intensity variations need not be of much concern. Further, direct lit arrangements potentially also have capability of controlling local intensity variations, which may also be utilised for providing both temporal and spatial intensity variations. Thus, the optical structure provided herewith is relatively simple. As a rule of thumb, for a high level of emission light intensity, the thickness of a optical medium in a direct-lit configuration is generally about equal to the LED pitch. If the LED pitch is 10 cm, this rule of thumb might lead to an optical medium that is about 10 cm thickness, which is thicker than desired. However, the light emission uniformity requirements for the presently intended purpose of anti-fouling do not have to meet substantially uniform lighting requirements and hence a thinner layer may be used in combination with such LED pitch.

[0096] Additional ideas and solutions exist to obtain a better uniformity in a thinner optical structure, such as introduction of scatters and/or reflectors or other light spreaders directly in front of one or more light sources.

[0097] FIG. 12 shows (left hand side) inclusion of a light spreader in the form of a reflective cone 25 in the optical medium 5 with an apex towards the light source 3. This directs the light 9 in a direction having a component substantially parallel to the surface 27 to be protected against fouling. If the cone 25 is not fully reflective nor opaque, some light from the light source will pass through it and creation of shadows leading to reduced or ineffective anti-fouling is prevented.

[0098] Further, FIG. 12 shows (right hand side) a wavelength conversion material which is comprised in the optical medium 5. The illustrated embodiment is configured to generate at least part of the anti-fouling light by photo-exciting the wavelength conversion material with light from a light source 30 with light 31 having a first wavelength causing the wavelength conversion material to emit anti-fouling light 9 at another wavelength from the optical medium 5 into the environment E. The distribution of wavelength conversion material in optical medium 5 may be spatially varying, e.g. in accordance with (expected) intensity distributions of (different wavelengths of) light in the optical medium 5.

[0099] FIG. 13 shows an optical medium 205 comprising a first layer 233, a second layer 235 with a plurality of walls 237 and pillars 238 in between separating the first and second layers 233, 235 and creating gas-filled channels 239. The optical medium 205 may be used just as any of the other optical mediums shown herein.

[0100] FIG. 14 shows a portion of an object 300 to be protected against biofouling, comprising an object surface 301, e.g. a ship hull, provided with an optical medium 302 comprising embedded flake-shaped particles 303. (In the drawing, the light sources are omitted.) The flakes 303 are distributed generally parallel to each other and with increasing density from the object surface 301 outwards to an emission surface 304.

[0101] FIG. 15 shows a chicken-wire embodiment where UV LEDs 3 are arranged in a grid and connected in a series of parallel connections. The LEDs can be mounted at the nodes as shown in bottom left of FIG. 15 either through soldering, glueing or any other known electrical connection technique for connecting the LEDs to the chicken wires 4. One or more LEDs can be placed at each node. DC or AC driving can be implemented. In case of DC, the LEDs are mounted as shown at the bottom right (a) of FIG. 15. If AC is used, then a couple of LEDs in anti parallel configuration is used as shown at the bottom right (b) of FIG. 15. The person skilled in the art knows that at each node more than one couple of LEDs in anti parallel configuration can be used. The actual size of the chicken-wire grid and the distance between UV LEDs in the grid can be adjusted by stretching the harmonica structure. The chicken-wire grid may be embed in an optical medium wherein optionally a parallel grid of scattering features are provided as illustrated in FIG. 12.

[0102] Besides anti-fouling application of hulls of ships, the following alternative applications and embodiments are envisioned:

[0103] The disclosure can be applied to a wide variety of fields. Almost any object coming into contact with natural water, will over time be subject to biofouling. This can hinder e.g. water inlets of desalination plants, block pipes of pumping stations, or even cover the walls and bottom of an outdoor pool. All of these applications would benefit from the presently provided method, lighting modules and/or system, i.e. an effective thin additional surface layer, which prevents biofouling on the entire surface area.

[0104] Although UV light is the preferred solution, other wavelengths are envisaged as well. Non-UV light (visible light) is also effective against biofouling. Typical micro-organisms are less sensitive to non-UV light than to UV light, but a much higher dose can be generated in the visible spectrum per unit input power to the light sources.

[0105] UV LEDs are an ideal source for thin light emitting surfaces. However, UV sources other than LEDs can also be used, such as low pressure mercury vapour lamps. The form factor of these light sources are quite different; mainly the source is much bigger. This results in different optical designs, to distribute all the light from a single source over a large area. The concept of light guiding as discussed herein does not change though. Further, a significant contribution of light in desired wavelengths and/or wavelength combinations may be produced.

[0106] Instead of using a thin layer that emits UV light outward in a direction away from the protected surface in order to avoid bio-fouling, biofouling could potentially also be removed by applying UV light from the outside in the direction of the protected surface. E.g. shining a UV light onto a hull or surface comprising a suitable optical medium as described. Thus, a single optical medium emitting anti-fouling light in directions to and away from protected surfaces may be even more efficient.

[0107] The concepts are not restricted to the above described embodiments which can be varied in a number of ways within the scope of the claims. For instance, using light, in particular UV light as an anti-biofouling means can provide an interesting opportunity in other fields. It is unique in the sense that continuous 24/7 protection can be provided, over a large area. The application is especially interesting for the hull of ships, but can also be applied in swimming pools, water treatment plants, etc. Instead of water, biofouling may occur and be treated in other liquid environments, e.g. oils, brines and/or liquids in other environments including food industry.

[0108] Elements and aspects discussed for or in relation with a particular embodiment may be suitably combined with elements and aspects of other embodiments, unless explicitly stated otherwise.