Abstract:
Illumination systems that include a plurality of illumination devices disposed within a water environment. Such illumination devices having a tube filled with water, at least one light source positioned to project light into the tube, and connected to the illumination devices via light carrying connectors, include one or more voids within each tube wall which extend substantially longitudinally and cause light incident below a critical angle to be reflected hack into the tube. Projected or reflected light above a critical angle that strikes a portion of the wall without a void is transmitted through the tube wall. By adjusting the ratio of voids to non-voids light can be delivered in a controlled manner.

Description:
RELATED APPLICATION DATA 
     This application claims the benefit of U.S. provisional patent applications 61/215,368 filed on May 4, 2009, 61/259,775 filed on Nov. 10, 2009 and 61/265,485 filed on Dec. 1, 2009. 
    
    
     The present invention is directed to illumination devices and systems for providing dense illumination to submerged environments, such as water environments in large tanks designed to grow algae and consume carbon dioxide. 
     BACKGROUND OF THE INVENTION 
     The growth of algae is receiving a significant amount of attention due to its perceived uses as a source of combustible fuel, a source of nourishment, and as a raw material for biodegradable plastics, a consumer of carbon dioxide which is widely viewed as a threat to the environment. Most forms of algae require light to thrive. In light of the anticipated demand for algae, it would be preferable to grow algae in large tanks, for example tanks having a diameter of about 80 meters and a height of about 20 meters. If such tanks are intended to grow algae on a continuous basis, there is a need to supply light throughout the interior of the tank. Light simply directed on the top or outside surfaces of the tank, even if the tank was formed of a transparent material, would be inadequate since the algae close to the surface and sidewalls of the tank would block infiltration of light into the interior of the tank. Improved devices and illumination systems for providing illumination to submerged environments, e.g. bioreactors, are needed. 
     SUMMARY OF THE INVENTION 
     The illumination devices and systems of the present invention are designed to withstand hydraulic pressure at virtually any depth, e.g. in excess of 20 meters, and to provide illumination from substantially the entire length of an illumination device which is positioned in a submerged environment. Some embodiments of the present invention utilize light tubes which are substantially filled with water or other suitable liquid. The illumination emanating from the illumination devices of the present invention may or may not have the same intensity over the length of the illumination device. The amount of illumination emitted at various sections can be controlled. 
     One system of the present invention comprises a plurality of illumination devices disposed within a water environment. At least one and preferably a plurality of sources of illumination are preferably positioned outside of the water environment and are connected to the illumination devices via light carrying connectors, e.g. fiber optic cables or light transport pipes. The illumination devices comprise one or more extractors which collectively extend substantially the entire length of the illuminated devices and to cause the device to emit light over substantially their entire lengths. The extractors reflect light at an angle above a critical angle of incidence so that the reflected light is transmitted through the tube wall(s). 
     Preferred illumination devices of the present invention are generally hollow tubes filled with a clear liquid, such as water, silicone oil or mineral oil. 
     According to another embodiment of the present invention, the tubular portions of illumination devices are formed in segments which are substantially connected end to end. Different segments are provided with different structures. Specifically, according to one embodiment, different segments of a single illumination tube are provided with different amounts of surface areas comprising air-to-other-material interfaces. As described in greater detail below, light striking areas having air-to-other-material interfaces will be reflected back into the interior of the tube if the angle of incidence is below a certain critical angle. 
     According to other embodiments of illumination devices, extractors are positioned within the interior of the tube and/or in or on a surface of the tube in order to reflect light at an angle greater than a critical angle of incidence in order to direct light into the water environment outside of the tube. 
     Light emanating from the tube into the water environment in which the illumination tube is positioned can be used for the growth of organisms, such as algae. The use of liquid filled tubes can provide an illumination system which has a weight and internal pressure similar to the pressure of the intended submerged environment thereby minimizing or eliminating the pressure difference between the exterior (submerged environment) and the tube interior. Other methods, such as the use of pressurized air, may be utilized to minimize the pressure difference between the pressure inside the tube sidewall and the pressures inside or exterior to the tube. 
     At least the exterior surfaces of the tubes are preferably either formed of or coated with a nonstick coating, such as Teflon® FEP material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a single illumination device suspended in a water environment within a tank. 
         FIG. 2  is a longitudinal cross-sectional, segmented view of the main components of the illumination device shown in  FIG. 1 . 
         FIG. 3  is a cross-sectional view of portions of the top of the illumination device shown in  FIG. 2 . 
         FIG. 4  is a close up of the upper portion of the light tube shown in  FIG. 2 . 
         FIG. 5  is the same view as  FIG. 4 , but showing an alternative embodiment of the present invention. 
         FIG. 6  is the same view as  FIG. 4 , but showing a third embodiment of the present invention. 
         FIG. 7  is an enlarged view of the bottom portion of the illumination device shown in  FIG. 2 . 
         FIGS. 8 and 9  illustrate a tube structure which can be used with the illumination device of  FIG. 2 . 
         FIGS. 10 and 11  illustrate different configurations of the tube shown in  FIG. 8 . 
         FIGS. 12 and 13  are top and side cross-sectional views, respectively, of a tube of an alternative embodiment of the present invention which can be used with the illumination device of  FIG. 2 . 
         FIGS. 14 and 15  are top and side cross-sectional views, respectively, of a third tube which can be used with the illumination device shown in  FIG. 2 . 
         FIG. 16  is a schematic illustration of the interfaces between materials used with one embodiment of the present invention. 
         FIG. 17  is a cross-sectional view of portions of the top of an alternative embodiment of an illumination device of the present invention. 
         FIGS. 18 and 19  are top and side cross-sectional views, respectively, of a light distribution tube of an alternative embodiment of the present invention. 
         FIGS. 20 and 21  are top and side cross-sectional views, respectively, of a light distribution tube of an alternative embodiment of the present invention. 
         FIG. 22  is a longitudinal cross-sectional, segmented view of a liquid filled light distribution tube of one embodiment of the present invention. 
         FIGS. 23 and 24  are partial top and side cross-sectional views, respectively, of the light distribution tube illustrated in  FIG. 24 . 
         FIG. 25  is a longitudinal sectional view of a light distribution tube and a light source. 
         FIGS. 26A through 26D  are a succession of cross-sectional views of the light distribution tube shown in  FIG. 25  showing the changing configuration of the 3-dimensional light distributor within the light distribution tube. 
         FIGS. 27 and 28  are cross-sectional, segmented views of one embodiment of a continuous bioreactor of the present invention. 
         FIG. 29  is a close-up of the cross-sectional view of a portion of the bioreactor shown in  FIG. 28 . 
         FIG. 30  is a close-up of the cross-sectional view of a portion of the bioreactor shown in  FIG. 27 . 
         FIG. 31  illustrates an alternative embodiment of the present invention. 
         FIG. 32  illustrates a still further embodiment of the present invention wherein a single light source is utilized to illuminate a plurality of tubes. 
         FIG. 33  illustrates an illumination system wherein illumination devices are illuminated from the bottom of a tank. 
         FIG. 34  is a longitudinal sectional view of one embodiment of the present invention. 
         FIG. 35  is a cross-sectional view taken along lines  35 - 35  of  FIG. 34 . 
         FIG. 36  is close-up view of a portion of  FIG. 34 . 
         FIG. 37  is close-up view of an alternative embodiment of the present invention. 
         FIG. 38  is a close up view of a portion of further embodiment. 
         FIG. 39  is a cross-sectional view taken along lines  39 - 39  of  FIG. 38 . 
         FIG. 40  is a close up view of a portion of a still further embodiment. 
         FIG. 41  is a cross-sectional view taken along lines  41 - 41  of  FIG. 40 . 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments of the present invention are directed to illumination devices and systems for providing high density illumination in submerged environments. For example, the environments may comprise large bioreactors comprising tanks filled with water in which algae is growing and into which carbon dioxide is provided. While certain embodiments of the present invention and certain figures focus on a single illumination device comprising a single light tube, the illumination systems of the present invention may comprise many illumination devices spaced by distances equal to or less than the diameter of the illumination tube itself. Therefore, large tanks used to grow algae may comprise hundreds or thousands of the disclosed illumination devices. For example, if only one tube is used in each square meter of the cross section of a circular cylindrical tank having a diameter of 80 meters, approximately 5,000 tubes extending the full depth of the tank would be required. Closer positioning, i.e. increasing the density of the illumination tubes and therefore providing more illumination, will increase the number of illumination devices needed. According to other embodiments of the present invention, at least some tubes in an illumination system are positioned at different depths and do not extend substantially the full depth of the tank. For example, it may be desirable to provide more illumination in the top portion of a tank where algae may be present in a higher concentration or density. 
       FIG. 1  illustrates a single light illumination tube of the present invention positioned within a water environment in a large tank. As used herein, the term “water environment” is used to indicate an environment comprising liquid water and may also comprise other components such as algae, other liquids and/or gases, either in solution and/or in a suspension with the water. One embodiment of the present invention utilizes a large number of illumination devices positioned, preferably generally vertically, within a tank containing a water environment comprising algae and carbon dioxide. In other embodiments described below, the light distributing tubes are not positioned vertically, but are generally horizontal. 
     With reference to  FIG. 1 , this embodiment comprises a light source  10  connected to a light injector housing  30  by a fiber optic cable  20 . The light injector housing can optionally be provided with a lens for collimating the light and/or filtering the light as desired. This embodiment also comprises a tube  40  substantially filled with a liquid  50 , e.g. distilled water. A transparent, conical end cap  60  is positioned at the bottom of tube  40  in this illustrated embodiment. While the illustrated end cap is preferably transparent and conical, the end cap need not be transparent and can have other shapes. In this embodiment where the bottom of the tube  40  is spaced somewhat from the bottom of the tank  101 , a transparent end cap advantageously allows illumination of the water environment in the area generally below the illumination device. The tube  40  of  FIG. 1  is suspended from the top of the tank  100  by support  90 . In this illustrated embodiment, the entire illumination portion is submerged in the water environment  110 . A mirror or partial mirror  70  is provided proximate the end cap  60  in order to reflect light back up into tube  50 . This embodiment also advantageously comprises a fluid feed tube  80  and a fluid egress tube  81  which connect with an ingress port and an egress port, respectively, and which are used to fill and maintain the level of water in tube  40 . The structural details of various embodiments of tube  40  are described below in connection with other figures. 
       FIG. 2  shows some additional detail of the illumination device and tank of  FIG. 1 . With reference to  FIG. 2 , the illustrated light source  10  comprises a housing  11 , a bulb  12  and a reflector  13 , e.g. an elliptical reflector, which directs light onto the proximal end  21  of fiber optic cable  20  as indicated by the dashed arrowed lines. Since a major portion of the tube  40  will be filled with water according to this embodiment, and since tube  40  may have a diameter of, for example, about 6 to 10 inches and a length of, for example, 18 meters, the water filled tube would be very heavy and would require special handling. Therefore, it is desirable to fill tube  40  while the bioreactor tank is, being filled. From the present description and drawings, it will be appreciated that the tube structure will not be required to support all of the weight of the interior water if the water pressure is simultaneously applied to the exterior of the tube. This can be accomplished by filling the tube and the tank simultaneously. Water ingress tube  80  provides for the supply of water or other suitable liquid while egress tube  81  allows air and/or other fluids to flow out of the tube. Ingress tube  80  and egress tube  81  thus allow the tube to be filled while tank  100  is being filled. Tubes  80 ,  81  also allow the fluid level in the tube to be monitored and for the tube  40  to be pressurized or depressurized as desired, if the structure of the tube otherwise permits pressurization and or depressurization. The tubes are preferably filled until water flows smoothly out of egress tube  81 . Additionally, after some period of use, the level of water in the tube should be checked since the tube may move during use and unintended air pockets which were not totally filled during initial filling may have been dislodged. As noted below, according to this embodiment of the present invention, care is taken to minimize the likelihood of unintended air pockets within the tubular structure. 
       FIGS. 2 and 3  shows a pair of hangers  93 , shock absorbing springs  91  and a collar flange  92  which connect an upper support housing, e.g. a steel tubular sleeve, to the top of the tank  100 . Upper support  95  extends downwardly to approximately the distal end  22  of fiber optic cable  20  and is secured to light injector housing  30 . 
     As best illustrated in  FIG. 4 , light exiting the distal end  22  of the fiber optic cable  20  is directed through an optical lens  32  and thereafter into the tube  40  in this illustrated embodiment of the present invention. Light injector housing  30  of this embodiment comprises an outer housing  34  and an inner housing  36 . A space is provided between outer shell  34  and inner shell  36  to allow the ingress and egress of water, air and other fluids as indicated by the arrows in  FIG. 4 . The interior surface  37  of inner housing  36  may be provided with a reflective coating to better direct light downwardly into the tube  40 . The external surface  35  of outer housing  34  is preferably provided with a Teflon® other nonstick coating in order to minimize adherence of the algae or other organic or inorganic material in the water environment. According to this embodiment of the present invention, the space between the distal end  22  of fiber optic cable  20  and the top of optical lens  32  is preferably air but could also be water, e.g. distilled water. In order to seal this space, a gasket  31  is positioned below optical lens  32  to secure optical lens  32  to inner shell  36 . Illustrated lens  32  is a planar convex lens which substantially collimates the light which strikes the top of lens  32  at an angle of incidence no greater than about 30° to provide a substantially collimated beam of light to tube  40 . As used herein, the term “substantially collimated” is used to indicate that at least 90% of the light is entering the tube is at an angle of less than 10° to the longitudinal axis. 
     A ring  33 , preferably formed of a rigid material allows screws (not shown) or other fasteners to be used to secure gasket  31  to inner housing  36 . Sealant may also be used. In the embodiment of the present invention shown in  FIG. 4 , the lower portion of inner housing  36  is generally vertical and spaced from the similarly shaped inner walls of outer housing  34 . Spacers  39  are placed intermittently around the circumference of the illumination device and also receive fasteners for securing the outer housing  34  and the upper portion of tube  40  to the lower portion of inner housing  36 . 
     A flat glass disc  38  or optionally a lens is preferably positioned below optical lens  32  in order to provide an additional seal. If an air pocket is provided in the light injector housing  30 , added buoyancy is provided to the illuminator, particularly to the upper portion of the illuminator. 
       FIG. 5  shows an alternative embodiment of light injector housing and is similar to the view of  FIG. 4  with the exception of the type of lens utilized. In the embodiment shown in  FIG. 5 , a fresnel lens  132  replace the planar convex optical lens  32  shown in  FIGS. 2 and 4 . Alternatively, a bi-convex optical lens may be utilized. In this embodiment, a liquid is not utilized in the space between the distal end  22  fiber optic cable  20  and Fresnel lens  132 . A liquid, such as water, would interfere with the functioning of the Fresnel lens. 
       FIG. 6  shows a third embodiment of the light injector housing. According to the embodiment of  FIG. 6 , a lens is not utilized. Some commercially available fiber optic cables emit light at an angle of about 30 degrees from the axis of the fiber optic cable. As described below, certain applications of the present invention will not require and/or will not benefit from light which is collimated by a lens such as those shown in  FIGS. 4 and 5 . Therefore, some embodiments will not utilize a lens in the light injector housing. 
       FIG. 7  shows an enlarged view of the bottom portion of the illumination device shown in  FIG. 2  wherein the bottom of tube  40  is provided with an end cap  60  comprising a diffusing, preferably translucent and most preferably transparent, conical lower portion  61  which allows light to pass into the water environment. A mirror  65  is supported by a gasket  66  which is held in place by fasteners (not shown) which pass through support ring  67 , gasket  66 , spacers  68 , tube  40  and the upper, substantially vertical portion  69  of end cap  60 . Spacers  68  positioned between mirror support  66  and the upper, interior surface of end cap  60  are not continuous around the circumference of the tube and therefore provide gaps for fluid to flow between end cap  60  and mirror support  66 . Thus water, other suitable liquids, air or other gases are permitted to flow relatively freely into and out of the space below mirror  65  inside end cap  61 . In this illustrated embodiment, mirror  65  is partially reflective thereby reflecting only a percentage, e.g. 20%, of the light back up into the tube and allowing substantially the remainder of the light to be transmitted downwardly through the conical portion  61  of end cap  60 . As an alternative to a partially reflective mirror, mirror  65  could simply be provided with a noncontinuous structure which covers only a portion of the area defined by the bottom of tube  40 . 
     If desired, some or all of the structure used at the bottom of the tube, such as for the mirror support  66 , support ring  67 , and/or spacer  68  can be formed of relatively heavy materials in order to assist in weighing the bottom of the illumination device down. The water environment may not be stable and may be somewhat turbulent in order to facilitate mixture of gases, algae and other constituent components, and or to accommodate a large flow of CO 2 . Therefore, extra weight near the bottom of the illumination device will tend to keep the device more vertical in the tank. Additionally, end cap  60  is preferably coated with or made from a nonstick material, such as Teflon® FEP, in order to minimize adhesion by dirt, algae, or other matter which would block the desired transmission of light. 
     The following is a description of various embodiments of tubular structures which are useful with the illumination devices and illumination systems of the present invention. While each of these embodiments is illustrated in the form of substantially circular cylinders, other shapes and configurations may be utilized. Circular cylinders are believed to be preferred because they have a minimal surface area and are more readily made such that they are structurally sound. 
     Each of the illustrated illumination devices comprises a body portion, preferably in the form of a circular cylinder, which emits light over substantially its entire length. In certain applications, for example when utilized in a tank having a depth of about 20 meters, it may be preferable to form tubes in segments for ease of manufacture and shipping. It may also be desirable in certain applications to utilize segmented tubes wherein different segments have different characteristics in order to provide different amounts of illumination at different positions outside the tube. The tubes  40  are not necessarily uniform along their entire length. For example, it may be desirable to permit more light to emanate from an upper portion of the tube  40  where the concentration of algae in the water may be greater than at a lower region of the tank where the algae concentration may be lower. Each of the illustrated tubular light tubes is filled with a column of water, e.g. distilled water, or another fluid which readily transmits light. For most applications it is currently believed that a clear liquid is preferred, however, it may be desirable in certain applications to use fluids which provide advantageous effects to the wavelength of the light emitted from the illumination device. 
       FIGS. 8 and 9  are cross-sectional top and side views, respectively, of a first embodiment of a tube of the present invention. According to this illustrated embodiment, tube  40  is in the form of a twin walled tube comprising an outer wall  41 , an inner wall  42  and a plurality of ribs  44 . In the illustrated embodiment, tube  40  is formed as an integrally extruded tube. Hollow portions  43  of the tube  40  between spacers  44  can be left hollow or can receive inserts  45 . The inserts can be formed of the same material as the inner wall  42  and outer wall  41 . One preferred material is Teflon® FEP, made by DuPont which is a fluorinated ethylene propylene. Other inserts can be liquid, e.g. water, which has an index of refraction close to FEP. 
     Depending upon the material used to form the tube, light striking interfaces, e.g. the interface between the inner wall  42  and the hollow cavity  43 , at an angle of incidence below a predetermined critical angle will be internally reflected back into the tube interior at locations where there is no insert  45  in a hollow cavity  43 . However, where an insert  45  is positioned within the hollow spaces, light will pass through the sidewall of tube  40  to the exterior water environment. 
     The hollow central tubes shown in  FIGS. 8 and 9  are filled with water, preferably distilled water, and are positioned in a water environment. Water has an index refraction of about 1.33 while Teflon® FEP made by DuPont has a very close index of refraction of about 1.35. The index of refraction of the Teflon® FEP is close to that of water when compared with that of air which has an index of refraction of about 1.0 and common, transparent polycarbonate which has an index of refraction of about 1.58. Common glass has an index of refraction of about 1.5, while borosilicate has an index of refraction of about 1.47 and that of Crown glass (pure) can be 1.54. In light of the similar indices of refraction of water and FEP, light traveling through a portion of the illustrated tube which contacts the FEP insert, i.e. not a hollow cavity, will be less likely to be internally reflected. 
       FIG. 9  generally illustrates a beam of light being internally reflected on the left interior side of tube  40  which does not have an insert in a hollow portion  43 , while a beam of light impinging at the same angle on the right side of the tube passes through the sidewall of the tube in an area corresponding to an insert  45 . 
       FIGS. 10 and 11  illustrate either an alternative embodiment of the present invention or a different segment of tubing used as part of a segmented tube, but wherein more of the hollow portions  43  have been filled with inserts  45 . Compared to the section of tube illustrated in  FIG. 8 , from the present description, it will be understood that light is permitted to pass through more areas of tube sidewalls of tube  40  in the tube segments illustrated in  FIGS. 10 and 11  which are filled with more inserts  45 . 
     Since most light which travels up and down the tube will preferably be traveling at an angle of less than 30° to the longitudinal axis of the tube, the use of inserts in this embodiment will generally prescribe where light is transmitted from the tube and where light is internally reflected. 
       FIGS. 12 and 13  illustrate another embodiment of the present invention. In this embodiment, tube  140  comprises an outer wall  141  preferably formed of a nonstick material such as Teflon® FEP. Outer wall  141  can also be formed of material such as polycarbonate, PVC, acrylic or glass. A plurality of spacers  142 , preferably formed of a plastic material in an arcuate shape, separate an inner wall  143  from outer wall  141 . Spacers can be formed of other materials such as metals, e.g. aluminum, wood or ceramics. Inner wall  143  can be formed of materials such as those described above for outer wall  141  and is, most preferably, formed of the same material as outer wall  141 . Spacers  142  therefore define a space  144  between outer wall  141  and inner wall  143 . Additionally, an extractor  145  which is preferably an opaque, textured material is positioned inside inner tube  143 . For example, one preferred extractor is made by the 3M Company of St. Paul, Minn. and is a matte white Scotchcal® which is preferably adhered to a textured substrate. According to this embodiment of the present invention, light traveling down tube  140  which strikes an extractor  145  will be scattered and will thereby strike another portion of interior tube  143  at an angle of incidence greater than the critical angle of refraction and will therefore pass through the tube to the exterior environment. Extractors  145  can be tapered as desired. 
       FIGS. 14 and 15  illustrate a further embodiment of the present invention wherein tube  240  comprises an outer tube  241  and a spaced inner tube  244  which can both be formed of the same material as outer tube  141  of  FIG. 12 . Positioned interiorly of outer tube  241  is a diffusing film  242  which can be formed of, for example, one or more of polycarbonate velvet, matte or suede textured films. Diffusing film  242  is preferably continuous and scatters light. Positioned interiorly of the diffusing film  242  and outside of inner tube  244  is at least one and preferably a plurality of intermediary film spacers  243 . Spacers  243  can be formed of a film, e.g. a transparent polished/polished polycarbonate film, or a rigid, clear, arcuate segment, e.g. a polycarbonate. Air gaps  245  exist between spacers  243 . According to this embodiment of the present invention, when light traveling down tube  240  strikes a portion of the interior tube  244  corresponding to both an intermediary film spacer  243  and the diffusing film  242 , some of the light will be directed out of the tube. Specifically, most of the light which is not internally reflected by the interior surface of the inner tube will be directed out of the tube in these portions of the tube. 
       FIG. 16  is a diagrammatic illustration of how light passes through components of the present invention. According to this illustration,  401  illustrates a column of liquid, for example distilled water. Column  402  is an FEP tube. Column  403  represents a space, i.e. an air gap. Column  404  represents a diffusing film and column  405  represents an exterior tube formed of FEP. Column  406  represents a water environment outside of exterior tube  405 . Material  407  represents a spacer. The space(s) between spacers  407  define the air gaps  403 . As indicated by the downwardly directed arrow on the right in  FIG. 16 , light traveling down the interior column of water  401  will pass through the interior tube  402  of FEP since water and FEP have a very close index of refraction. However, when the light hits the interface between interior tube  402  and air space  403 , since the light would be passing from a medium having a higher index of refraction to a medium having a lower index of refraction (air), light which is incident at an angle below the critical angle is internally reflected. The downward arrow on the left of this Figure represents light which passes through the interior tube  402  to the spacer  407  which has a higher index of retraction than interior tube  402 . This light continues outwardly to diffusing layer  404  where it is then scattered in different directions including directions which cause it to travel through exterior tube  405  and into the water environment  406 . 
     The light supplied to the light distributing tubes of the embodiments shown in  FIGS. 8-18  is not necessarily substantially collimated, however for light distributing tubes having large aspect ratios, e.g. a 60 foot long tube having a diameter of 6 inches, it may be desirable to supply a substantially collimated beam of light. 
       FIG. 17  illustrates one embodiment of the present invention which is useful with a liquid filled light distribution tube of the type disclosed in Applicants&#39; co-pending U.S. provisional patent application Ser. No. 61/215,368 filed on May 4, 2009. According to this embodiment of the present invention, light from a first laser light source  510  and a second laser light source  511  are transmitted, via a fiber optic light carrier, to a light distribution tube. Laser light sources  510  and  511  can be used simultaneously, sequentially and/or alternatively to provide light of different wavelengths to the light distribution tubes. 
       FIGS. 18 and 19  illustrate an alternative embodiment of the present invention wherein a liquid filled light distribution tube comprises a tube within a tube. According to this embodiment of the present invention, the light distribution tube whose interior is substantially filled with a liquid  605  as describe above comprises exterior wall  610 , an optical light film  620 , a plurality of extractors  630  and an inner wall  640 . This embodiment of the present invention does not depend upon a collimated source of light in order to efficiently transmit light along substantially its entire length but preferably has an angle of divergence not greater than about 28°. Light directed into the tube will be internally reflected by the optical light film if it strikes the optical light film at an angle of incidence of less than about 28°. The extractors  630  have an effect similar to the extractors described above wherein light striking extractor  630  will be reflected toward sides of tube  600  at angles greater than the maximum angle of internal reflection as shown by arrows P and will pass through the optical light film  620  and outer walls  610 . Light striking optical light film  220  at lesser angles of incidence will be internally reflected as shown by arrows R until reaching a mirror end cap (not shown) or subsequently striking extractor  230 . 
       FIGS. 20 and 21  illustrate another liquid filled light distribution tube comprising an outer wall  750  formed of Teflon FEP (hereinafter “FEP”), an inner wall  760  formed of FEP and a plurality of spacer rings  770  also formed of FEP. Rings  770  preferably extend around the entire circumference of inner wall  760 . The spaces  780  between the spacer rings  770  are preferably filled with air. The interior of the tube, i.e. interior of inner wall  760 , is filled with a liquid, e.g. water. Since FEP has an angle of refraction close to that of water, light striking areas of the tube which have a spacer ring  770 , i.e. which are formed of three layers of FEP, will generally continue on its path out of the tube. However, light striking the interface between inner tube  760  formed of FEP and the air between the spacer rings  770  will be internally reflected since the index of refraction of air is substantially less than that of FEP. Arrows R and P in  FIGS. 20  and  21  indicate light being internally reflected and passing through the tube walls, respectively. 
     According to an alternative to the embodiment shown in  FIGS. 22 and 23 , the spacer rings are formed of a reflective material and the spaces between the spacer rings are filled with water. In this embodiment, the light will pass through the tube in the areas between the spacer rings and be reflected in the areas of the spacer rings. 
       FIGS. 22-24  illustrate a liquid filled light distribution tube of one embodiment of the present invention wherein tube  800  is substantially filled with a liquid  805 , preferably a clear liquid such as water, and is provided with a light extractor  810 , such as matte white Scotchcal® made by the 3M company of St. Paul, Minn., positioned on the inside of tube  800 . As best shown in  FIG. 22 , a fiber optic light carrier  820  is connected to a lens housing  840  by a ferrule  830 . Light exiting fiber optic light carrier  820  is directed through a lens  850 , such as the illustrated Fresnel lens, which substantially collimates the light for transmission down the length of tube  800 . Light striking extractor  810  will be reflected toward sides of tube  800  at angles greater than the maximum angle of internal reflection as shown by arrows P and will pass through the walls of tube  800 . Most of the light which does not contact the extractor  810  will either go directly to mirror end cap  860  for reflection back up the tube or will strike interior walls of tube  800  at angles less than the maximum angle of internal reflection as shown by arrows R and will be internally reflected by the walls of tube  800 . Exterior tube  800  can be formed of acrylic, glass, polycarbonate, PVC and/or FEP. The indices of refraction of the liquid inside the tube and the tube wall are preferably as close as possible. Additionally, the exterior of outer wall  40  is preferably either formed of or provided with a coating which has low-friction and low-reactivity properties, as well as high light transmission. While the interior liquid is preferably water, other liquids such as mineral oil or silicone oil, or the like could also be utilized. It is also within the scope of the present invention to use light sources which are not carried by fiber optics. 
     The extractor  810  of the embodiment shown in  FIGS. 22-24  can be replaced by a distributor of the type disclosed in U.S. Pat. No. 6,014,489 entitled LIGHT DISTRIBUTING TUBES AND METHODS OF FORMING SAME. A light distributor  1200  which is illustrated in  FIG. 25  is preferably spaced a certain distance from the light input end of the tube  1210  (depending on the beam spread angle of the light beam). The illustrated distributor  1200  can include a light scattering lamination carried on a substrate formed of polycarbonate with a rough or textured surface. One suitable substrate material is sold under the trademark Lexan® Suede by the GE Company. Such a lamination is preferably tightly mated to the rough or textured surface of the substrate and is a thick, white matte film such as Scotchcal sold by the 3M Company. The light distributor  1200  is preferably gradually tapered over its full length, most preferably symmetrically on both edges from a narrow width toward the end of the tube into which light is injected to a width at the distal end which is close to but not greater than one half of the internal circumference of the tube. 
     A relatively inexpensive embodiment of a liquid-filled light distribution tube of the present invention comprises a clear PVC tube with a distributor of the type disclosed in U.S. Pat. No. 6,014,489 disposed in the tube and the tube substantially filled with a clear liquid such as water. The tube is connected to a source of substantially collimated light which is beamed into the tube parallel to the longitudinal axis of the tube. Light striking the distributor will be reflected at the inner tube wall at an angle which will cause most of that reflected light to pass through the tube wall. 
     The embodiments of the present invention shown in  FIGS. 1-26  are liquid filled light distribution tubes designed to operate in a submerged environment such as a bioreactor used to grow organisms such as algae. These embodiments can advantageously distribute light over substantially their entire lengths while having an internal pressure and buoyancy closely compatible with their external environment. 
       FIGS. 27-30  illustrate a bioreactor of another embodiment of the present invention.  FIGS. 27 and 28  are cross-sectional views of a continuous bioreactor wherein a plurality of liquid filled light distributing tubes  910  are positioned generally horizontally in a bioreactor tank  900 . Carbon dioxide is supplied to the bottom of the reactor via supply tubes  920 . Desired additional compounds or organisms, such as algae, can also be supplied to bioreactor  900  via supply tubes  920 . As algae grows and accumulates at the top of the tank  900 , it is moved by a movable skimmer  930  mounted on wheels/rollers  935  and having at least one skim tab  937 , into collection troughs  940  positioned on either side of the tank  900  as best illustrated in  FIG. 27 . Skimmer  930  is supported by a support, e.g. a monorail proximate the top of the tank. Skimmer  930  can be positioned at, above or below the surface of the liquid mixture in the tank. 
       FIGS. 29 and 30  are partial views of the tanks shown in  FIGS. 28 and 27  respectively. With reference to  FIG. 29 , according to this embodiment of the present invention, the light distributor tubes can conveniently be supplied with light from light sources  950  mounted on one or both sides of the light distributor tubes, as desired. The arrows P in  FIG. 30  illustrate light passing from the tubes into the algaeCO 2  mixture in the tank. 
       FIG. 31  illustrates an alternative embodiment of the present invention wherein an illuminator  1000  is positioned outside the top of a tank  1001  and a rigid tube  1005 , for example formed of steel or other durable material, extends partially into the water environment in order to support light distribution tube  40  in water environment  50 . 
       FIG. 32  is similar to  FIG. 31 , however, according to this embodiment of the present invention a single illuminator  1000  is connected to a plurality of rigid tubes  1015  and light is directed into tubes  40  utilizing a partially reflective mirror  1020  which directs 50% of the incident light from illuminator  1000  down into right side tube  40  while fully reflective mirror  100  directs 100% of the remaining light down into the tube  40  on the left side of the drawing. 
       FIG. 33  illustrates an alternative embodiment of the present invention wherein tubes  1300  are supported at the bottom of a tank. These tubes are also illuminated from the bottom with illuminators  1310 . 
     According to an alternative embodiment shown in  FIGS. 34-36 , a tubular bioreactor  1110  is supported in a support trough  1120 . The interior side of the trough  1120  is provided with a reflective surface  1130 , such as a reflective film. The exterior wall  1140  of the bioreactor is at least partially translucent to allow natural sunlight and/or artificial light to pass through the exterior wall(s) and into the interior  1150  for use in the bioreactor, such as for photosynthesis by algae. The interior of outer wall  1140  preferably has low-friction and low-reactivity properties, as well as high light transmission. 
     According to one preferred embodiment of the present invention, the outer wall comprises PTFE and/or Teflon-FEP which is a fluorinated ethylene propylene (herein after “FEP”). FEP has low-friction properties to reduce the amount of algae growing on the interior walls. Additionally, the interior light distribution source  1160 , supports  1180 , and wires  1171  (described below) are also preferably coated with a low-friction material and/or a protective, low-friction tube in order to minimize the adherence of algae or other biological organisms which could impede the transmission of light from the interior light source to the desired working area of the bioreactor and/or the flow of algae through the bioreactor. While Teflon-FEP is currently believed to be preferred, other materials can be utilized for the outer (walls) or for covering the inner source of illumination, such as acrylics, polycarbonates, PVC and/or glass. 
     In  FIGS. 35 and 36 , it will be understood that the reaction portion  1150  of the tube  1110  is the space between the outer surface of the inner tube  1164  which surrounds the interior light distribution source  1160  and the interior surface of the outer wall  1140 . In this illustrated embodiment tubes  1140  and  1160  are formed of FEP or are internally and externally, respectively, coated with FEP or another coating having low friction properties in the bioreactor environment. 
     The interior light distribution source  1160  is preferably a substantially continuous light distribution tube or non-smooth light emitting rod which emits illumination along substantially the entire length of the light distribution tube or light emitting rod. If a light distribution tube is utilized, it can be a liquid filled light distribution tube such as one of those described above.  FIG. 35  illustrates a light emitting rod  1162  comprising a non-smooth cast acrylic rod e.g. scored, etched or grooved, surrounded by an interior tube  1165 , e.g. an FEP tube. 
       FIG. 36  illustrates one method of connecting an exterior source of illumination to light emitting rods  1162 . According to this illustrated embodiment, a fiber optic cable  1182  is supplied with illumination from a source (not shown). Fiber optic cable  1182  enters the outer tube  1140  and inner tube  1165  through a support  1180  and then passes into a ferrule  1183  which is connected to a lens housing  1184 . Lens housing  1184  supports a Fresnel lens  1185  which collimates light emitted from the distal end  1181  of fiber optic cable  1182 . In the embodiment illustrated in  FIG. 36 , a support  1180  is connected to exterior wall  1140  and interior tube  1165  in order to provide a water tight conduit for fiber optic bundles  1182 , as well as to provide positional support for interior tube  1165 . 
     The arrows pointing to the right in the reaction portion  1150  of the bioreactor indicate the flow of algae and/or other organisms or compounds, such as carbon dioxide, which will flow through the tubular reactor. 
       FIG. 37  illustrates an alternative embodiment of the present invention wherein the interior light distribution source is in the form of a light emitting rod which is illuminated from both ends. The connectors which are positioned at either end of light emitting rod  2162  are similar to those described above in connection with  FIG. 36 , however instead of using Fresnel lenses, planar-convex lenses  2185  are illustrated. While the embodiment of  FIG. 37  illustrates a light emitting rod, it is also within the scope of present invention to use a light distribution tube, e.g. a liquid filled light distribution tube. 
     Additionally, while each of the illustrated embodiments show a single interior source of illumination, it is within the present invention to use a plurality of elongated light sources which emit light along substantially their entire length. 
       FIGS. 38 and 39  illustrate an alternative embodiment of the present invention wherein interior light distribution source  3160  comprises LED  3172  connected to parabolic reflector  3174  which collimates the LED light and directs it into light emitting rod  3162 . This embodiment comprises a single LED  3172  within reflector  3174 . Rod  3162  and LED  3172  are housed in an outer protective tube  3164 , also preferably made of FEP. In this embodiment, electrical wires  3171  provide electrical energy to LED  3172 . 
       FIGS. 40 and 41  illustrate a similar embodiment to that shown in  FIGS. 38 and 39 , however instead of a single LED  3172  within a single reflector  3174 , this embodiment comprises a plurality of LEDs  3272  and a corresponding reflector  3274  for each LED  3272 , all of which are housed within a single outer protective tube  3264 . While this embodiment illustrates three LEDs, it is also within the scope of the present invention to use a greater number of LEDs to provide either more light or to provide different wavelengths of light. Thus, each of the LEDs can emit light of a different wavelength, if desired. 
     While the illustrated tubular bioreactors of the present invention have been illustrated in a generally horizontally orientation, it is also within the scope of the present invention to orient the tubular bioreactor vertically or at some intermediate angle. It will also be understood that while the illustrated tubes are cylindrical and have circular cross sections, other cross-sectional shapes can be utilized for the tubes without departing from the scope of the present invention, though generally circular cross-sections are presently deemed preferred. 
     These tubular bioreactor embodiments of the present inventions provide the advantage of allowing illumination to be provided to the bioreactor from the sun during daylight hours and alternatively or simultaneously to the interior of the reactor either while the sun is not shining such as during the night and/or on cloudy days. Additionally, the ability to illuminate the reaction area of the bioreactor with different light sources such as LEDs, metal halide lamps and plasma lamps provides the ability to separately provide different wave lengths of light and/or different light stimuli such as pulsed light to the bioreactor. 
     According to another embodiment of the present invention, a tube-within-a-tube bioreactor comprises only an internal light source such as an LDT, liquid filled LDT or LER. Providing an outer wall which is not translucent provides greater control of the light reaching the reaction area of the bioreactor.