Abstract:
A forensic light source which comprises a flexible liquid light guide receiving light from a light source and transmitting it to a selected interference filter which tilts with respect to the light source is disclosed. The filter is mounted for rotation with respect to the output of the light guide. The light exiting the filter is passed through a mixing member made of a randomized fiber optic bundle, that is positioned to receive the output of the filter. The mixing member defines multiple paths for light between the input face and the output face which are configured to disperse light from one mixing member input face region to a plurality of mixing member output face regions.

Description:
TECHNICAL FIELD  
       [0001]     The invention relates to a compact, optionally self-powered, forensic light source with structure for conveniently tilting and rotating a filter wheel holding a plurality of filters to fine tune output wavelength and mix output wavelengths, thus eliminating any spatial dispersion in the output.  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not Applicable.  
       BACKGROUND OF THE INVENTION  
       [0003]     Light sources which output light for a variety of analytic purposes are in wide use today. Such uses primarily involve forensic analysis, although such light sources are of value in a range of other applications. These devices may output white light, colored light or have the ability to output illumination of, to varying degrees, a selectable wavelength.  
         [0004]     Special tools are frequently used by law enforcement personnel when evaluating a crime scene to collect forensic evidence that may be hard to see or invisible to the human eye. Examples of such evidence include bodily fluids, fingerprints on porous and non-porous surfaces, forged documents, explosive residue, and trace evidence e.g., hair, fibers, etc.  
         [0005]     One commonly used tool is a forensic light source that utilizes fluorescent light to detect and record forensic evidence. Subjects illuminated by a forensic light source may be viewed through light filtering goggles, and the output of the source may be filtered to achieve a range of diverse functionalities and corresponding capabilities, with and without the use of chemical developers, powders and dyes.  
         [0006]     At the present time, a wide variety of forensic light sources are employed by law enforcement and other personnel. In one class of devices, a portable light source unit which, for example, may be handheld or supported on a shoulder strap, is adapted to accept an elongated flexible light pipe, which may comprise a liquid light guide, a fiber-optic bundle, or other similar device.  
         [0007]     Recent advances in DNA testing have rendered the gathering of forensic materials of increasing importance. However, even before the advent of DNA testing, the detection of forensic materials such as blood, perspiration, bone, skin, and the like has always been of importance to criminal investigation. For example, bone fragments that can be matched to a body may show that the individual who had suffered the crime may have been at a particular location. Fingerprints may identify individuals because of their unique characteristic. Loose hairs on a victim&#39;s clothes could identify a possible assailant.  
         [0008]     As important as forensic evidence was in the past, it was only one of numerous circumstantial and objective sources of evidence which are weighed by juries and judges in their search for the truth and implementation of criminal justice objectives aimed at punishing and/or preventing criminal activities.  
         [0009]     With the advent of DNA testing, forensic material can yield information which may be interpreted with particular reliability to help in a determination respecting certain types of criminal activity and even more reliable and determinative evidence with respect to other types of criminal activity.  
         [0010]     Accordingly, the detection of forensic materials at a crime scene is of the utmost importance, given the need to make an almost positive connection between a genuinely guilty criminal and a crime scene, and to exonerate innocent people.  
         [0011]     One of the primary tools in detecting forensic materials is the use of light having particular wavelength characteristics. More particularly, various types of forensic light sources include means to direct light onto various parts of a crime scene.  
         [0012]     As noted above, the ability to produce light of different wavelengths is important in a wide variety of applications. Accordingly, wheels containing a plurality of filters having various wavelength bandpass characteristics may be employed. Such wheels are rotated to various angular positions, resulting in the interposition of a selected filter with a selected wavelength bandpass characteristic in front of the light source to filter the light source and produce output light of a desired wavelength. In some devices, these filter wheels are included in a portable light source unit. In other units, a filter wheel is positioned proximate to the output of the fiber-optic bundle.  
         [0013]     One typical device, for example, comprises a light source and a six foot long fiber optic snake-like member which directs light from the light source to a point at which the end of the fiber optic member is pointed. A wheel containing a number of filters is mounted at the end of the fiber optic light pipe. In order to select various wavelengths, the wheel is rotated thus interposing different filters in front of the output of the light pipe. The result is that the filters filter the light as it comes out of the light pipe and allow only the light of a particular wavelength to fall on an object or area to be illuminated.  
         [0014]     Devices in which the filter wheel is positioned proximate to the output of the fiber-optic bundle offer the convenience of quick adjustment of the wavelength of output light by the same hand that is holding the end of the fiber-optic bundle and aiming the output light at the subject to be illuminated.  
         [0015]     Interference filters are of particular value in forensic light sources. In addition to their efficiency, such filters, mounted on wheels enclosed in a light source housing that couples light to a fiber optic bundle, offer the possibility of producing, not just a single wavelength, but a range of wavelengths. This is achieved by tilting the filter. In accordance with Bragg&#39;s law, the wavelength that is output by such a filter is a function of the distance between reflecting planes in the filter. Accordingly, a method for obtaining a range of different wavelengths from a single filter is to tilt the filter wheel. Tilting the filter wheel causes it to pass progressively longer wavelengths, and thus allows users to fine tune the wavelength of output light.  
         [0016]     Generally, prior art forensic light sources comprise small self-contained units which directly output filtered or unfiltered light, that is, usually, colored or white light, respectively. Larger, somewhat more difficult to use units, also use mechanisms for tilting the filter, and further utilize a snake-like fiber-optic bundle or similar member to direct light in a particular direction. Such devices are somewhat difficult to use, as one hand must be used to hold the unit, while the other hand must be used to aim the light.  
       SUMMARY OF THE INVENTION  
       [0017]     In devices in which the tunable light source is embodied by a filter wheel located within the portable light source unit, the length and characteristics of the light pipe, such as a liquid light guide, results in mixing the wavelengths, thus eliminating any spatial dispersion.  
         [0018]     However, if one wishes, instead, to place the filtering mechanism, whether it be on a wheel of filters or whether the filtering mechanism be a single filter, at the output of the liquid light guide, tilting of the filter we cause a non uniform wavelength variation in output light which is a function of the part of the filter through which the light has passed. This cannot be tolerated in many applications. Accordingly, if one is using such a light to inspect an area for evidence, or the like, the picture which is presented, whether it be to the human eye directly, or to a camera of any sort, will exhibit a variation and uniformity which may obscure important features. This may be of particular importance in the case of image resolution using artificial intelligence systems, human inspection, analysis of pictures taken with the forensic light source, and so forth.  
         [0019]     In accordance with the present invention, objectives of compactness, continuously variable wavelength adjustment and single-handed operation are achieved in the context of a system which comprises a light source contained within a housing. Light is focused by the optics and passed through a filter positioned on the housing of the forensic light source at the output of the forensic light source. In accordance with a preferred embodiment, the hand of the user that is holding the unit may be used to rotate a wheel holding one or more filter wheels to select a desired filtering characteristic or no filtering. Grasping is done with the four fingers of the hand, with the thumb being used to rotate the filter wheels.  
         [0020]     The housing includes a handle attached to the housing which allows the housing to be grasped by a user. Light is output from the housing through a filter wheel mounted on the housing. A plurality of filters, for example six filters may be mounted in the filter wheel. Alternatively, five filters may be mounted within the filter wheel, and the sixth position left open to output unfiltered white light.  
         [0021]     The filter wheel is positioned to allow for filter selection using the thumb of the hand which is grasping the handle of the housing, while the other four fingers engage the handle to hold the housing in position. The same is achieved by having the filter wheels mounted in front of the output of the light source within the housing which is grasped by the hand.  
         [0022]     In connection with this, it is noted that if one simply provides for filter tilting in forensic light sources where the filter is positioned at the output of the unit, the difference in path length between the unfiltered output of the light guide and the filter causes a corresponding wavelength variation across the beam output from the filter. This difference is a result of the different path length through the filter between the unfiltered light output of the light guide and the various parts of the filter. More particularly, in the case where the path length is relatively large, the filter tends to pass light of relatively longer wavelength. The particular wavelength selected is a function of Bragg&#39;s law.  
         [0023]     As a consequence of these variations in the output wavelength, light exiting a filter in a system where the filter wheel is carried inside the housing of the light source suffers from the condition of producing various wavelengths at the filter output which vary from the primary wavelength of the filter through a range of longer wavelengths, which range of length is greater for increasingly greater angles of filter tilt. This range of longer wavelengths does not present a problem in fiber optic light guide bundle systems, because, as long as the light guide is of a typical length, it has the characteristic of mixing these wavelengths together, because of the various path lengths which are associated with the different rays of light passing through the light guide, the result is to mix them substantially uniformly with a distribution across the diameter of the light guide output face. The result is a substantially uniform illumination with substantially the same wavelength content across the output face of the forensic light source.  
         [0024]     However, if one wishes, instead, to directly use the output of the filtering mechanism, whether it be on a wheel of filters or whether the filtering mechanism be a single filter, wavelength variation in output light which passes through various parts of the filter will be visible. Accordingly, if one is using such a light to inspect an area for evidence, or the like, the picture which is presented, whether it be to the human eye directly, or to a camera of any sort, will exhibit a variation and non-uniformity which may obscure important features. This would be expected to be of particular importance in the case of image resolution using artificial intelligence systems, human inspections, demographic analysis of pictures taken with the forensic light source, and so forth.  
         [0025]     In accordance with the invention, this problem is solved through the provision of a forensic light source comprising a source of light, and a flexible light guide for receiving light from the source. The output of the light guide is passed through a filter on a filter wheel mounted for rotation and tilting with respect to the output of the light guide. Light exiting the filter is passed through a mixing member. The output of the mixing member may then be used as the output of the system for forensic lighting purposes. In accordance with the preferred embodiment of the invention, the mixing member may be a relatively short rod of transparent material, made, for example, of quartz, or other material if ultraviolet light output is not needed.  
         [0026]     Alternatively, the mixer may be made of randomized fiber-optics. However, a liquid light guide is preferred because randomized fiber-optics tend to show multiple small spots in the focused output beam.  
         [0027]     Still yet another approach is the use of an integrating sphere which performs the function of integrating or mixing the light output. The sphere is coated on the inside with a strongly reflecting material, and features an entrance port and exit port. After high numbers of reflection, the rays exit and have lost any spatial non uniformity information. However, the use of such integrating sphere systems suffer from the disability of relatively greater reductions in the amplitude of light output by the system, and a space requirement concern not well adapted for hand-held use.  
         [0028]     Similarly, an optical system may be designed for integrating the filter output, but ray tracing would seem to have relatively large losses in such a system, because ray tracing would seem to imply not collecting all the light exiting the system. This would have the additional disadvantage of causing losses so great that the handle would be warmed to the point of even causing burns.  
         [0029]     Still yet another alternative embodiment of the present invention contemplates the manufacture of special liquid light guides that feature an F number which is compatible with 1 inch diameter filters, as this is the size of filters which are currently in use in forensic systems around the world. Such a liquid light guide allows the use of lenses between the light guide and the tiltable filters. This limits the spatial dispersion in the system, and such a solution would increase the cost of the system, as such light guides would have to be produced especially for such a system. Accordingly, such light guides would involve customizations for forensic allocations and accordingly low production volumes from the current light guide standard of numerical average or 0.588 corresponding to a half convergence angle of 36 degrees.  
         [0030]     Similarly, an optical system may be designed for integrating the filter output, but ray tracing would seem to predict relatively large losses in such a system, because ray tracing would seem to imply not collecting the entire light exiting the liquid light guide. This would have the additional disadvantage of causing losses so great that the handle would be warmed to the point of even causing burns.  
         [0031]     Still yet another alternative embodiment of the present invention contemplates the manufacture of special liquid light guides that feature an F number which is compatible with one inch diameter filters, as this is the size of filters which are currently in use in forensic systems around the world. Such a liquid light guide allows the use of lenses between the light guide and the tiltable filters that limit spatial dispersion in the system, although such a solution increases the cost of the system, as such light guides have to be produced especially for such as system. Accordingly, such light guides involve customizations for forensic allocations and accordingly low production volumes from the current light guide standard of numerical average of 0.588 corresponding to a half convergence angle of 36 degrees.  
         [0032]     In accordance with the preferred embodiment of the invention, a mixing rod having a 12 mm diameter and a length between 60 and 80 millimeters is used in connection with a high collection input lens (for example F/1) and an outlet lens, with a 90 mm focal light.  
         [0033]     A quartz rod may be obtained from Technical Glass Products of 881 Callendar Blvd.,Painesville Twp., Ohio 44077. The rod is polished very finely on the ends and the cylindrical sidewall in order to avoid light leaks. The rod is held in a metal tube with just two areas of contact that its ends where it is supported by narrow lips to minimize the light losses, and where epoxy for index of refraction matching is used to further eliminate light losses.  
         [0034]     This rod may be made of BK7, quartz or similar material, or in the case where ultraviolet light is not required it may be made of glass. This rod is finely polished on both ends and on its cylindrical sidewall. General Electric epoxy is used to cement the system together, as the index of refraction of the cement must be carefully matched to avoid local losses. Generally the use of General Electric epoxy in optical systems for the purpose of index of refraction matching is well-known in the art. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0035]     The present invention may be understood from the following drawings, which illustrate only several embodiments of the invention, and in which:  
         [0036]      FIG. 1  is a diagrammatic view of a forensic light source according to the present invention illustrating the output of the light guide being passed through a filter mounted for rotation, then through a mixing member with the output to be used as a forensic output light;  
         [0037]      FIG. 2  illustrates an alternative mixing member comprising a plurality of transparent integrating spheres contained within a cylindrical member;  
         [0038]      FIG. 3  illustrates a randomizing fiber optic member;  
         [0039]      FIG. 4  illustrates an alternative housing configuration for the inventive forensic light source;  
         [0040]      FIG. 5  illustrates yet another alternative housing configuration;  
         [0041]      FIG. 6  is a diagrammatic detailed illustration showing how movement of a disk-like support member results in the rotation of the fiber optic member for the purpose of wavelength shifting;  
         [0042]      FIG. 7  is a diagrammatic illustration showing illustrative optics at the input and output of the mixing member;  
         [0043]      FIG. 8  illustrates an embodiment of the invention with two filters on rotation mechanisms allowing them to be rotated equal amounts in opposite angular directions simultaneously;  
         [0044]      FIG. 9  is a diagrammatic view in cross-section of another example of a forensic light source constructed according to the present invention;  
         [0045]      FIG. 10  is a cross-sectional view along lines  10 - 10  of  FIG. 9 ;  
         [0046]      FIG. 11  is a cross-sectional view along lines  11 - 11  of  FIG. 10 ;  
         [0047]      FIG. 12  is a bottom plan view along lines  12 - 12  of  FIG. 9 ;  
         [0048]      FIG. 13  is a perspective view of the embodiment of  FIG. 9 ;  
         [0049]      FIG. 14  is a view similar to that of  FIG. 13  illustrating an elongated light directing member;  
         [0050]      FIG. 15  is a diagrammatic view of a forensic light source similar to that of the  FIG. 9  embodiment, showing an alternative rotating mechanism;  
         [0051]      FIG. 16  is a view along lines  16 - 16  of  FIG. 15  illustrating only the filter support rotation mechanism;  
         [0052]      FIG. 17  is a view along lines  17 - 17  of  FIG. 15  illustrating only the filter support rotation mechanism;  
         [0053]      FIG. 18  is a diagrammatic illustration of a forensic light source according to the present invention having a pair of independently adjustable filters;  
         [0054]      FIG. 19  illustrates wavelength shifting of the mounting structure of the light source of  FIG. 18 ;  
         [0055]      FIG. 20  illustrates a rectangular randomizing optical member;  
         [0056]      FIG. 21  illustrates yet another randomizing optical member;  
         [0057]      FIG. 22  illustrates another forensic source member with an alternative filter tilting mechanism;  
         [0058]      FIG. 23  illustrates the source of  FIG. 22  coupled to a power supply and light source unit;  
         [0059]      FIG. 24  illustrates mechanical details of the tilting arrangement of the source of  FIG. 23 ;  
         [0060]      FIG. 25  illustrates the details of structure of a heat sink useful in the embodiment of  FIG. 24 ; and  
         [0061]      FIG. 26  illustrates the heat sink of  FIG. 25  viewed along the lines  26 - 26  of  FIG. 25 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0062]     Referring to  FIG. 1 , a forensic light source  10  constructed in accordance with the preferred embodiment is illustrated. Light source  10  comprises a lamp  12  for producing light, such as white light. Lamp  12  may be one of the many alternatives employed in the art, such as a xenon lamp. Lamp  12  is coupled by a plurality of wires  14 ,  16 ,  18 , and a switch  20 , to a battery  22 , which may be of any desired type, such as lithium ion.  
         [0063]     A handle  23  allows the device to be conveniently held and aimed during use.  
         [0064]     The output of lamp  12  is sent to a lens  24 , which focuses it onto the input face  26  of a liquid light guide  28 . Liquid light guide  28  is configured with a mounting  30  which couples to a mating mounting  32  on housing  34 . Mountings  30  and  32  are positioned at a first end of the light guide  28 . Mountings  30  and  32  may provide for any desired mounting type, such as a screw mounting, a bayonet mounting, or other mounting structure. In a similar fashion, handheld housing  36  is provided with a mounting  38  which mates with a mounting  40  on the other end of light guide  28 .  
         [0065]     Light exiting the face  42  of liquid light guide  28  passes through a pair of 18.5 mm focal length lenses  44  and  46 . Light is next passed to a wheel  48  having a plurality of filters  50  mounted for rotation about an axle  52 . Lenses  44  and  46  and output face  42  are positioned in alignment with each other and are further positioned to output substantially all of the light exiting face  42  through one of the filters  50 , depending upon which filter  50  is rotated into the output position.  
         [0066]     The output of the selected filter  50 , is, in turn, coupled to a lens  54 , which is positioned to receive substantially all of the light output by the selected filter  50 . This light is then coupled into the input face  56  of mixing rod  58 , which may be made of quartz, for example, and has a diameter of ten centimeters and a length of between 16 and 80 cm, although the diameter and length may be varied as a function of the optical system and the desired degree of mixing. It is also noted that a relatively long mixing optic  58  can be tolerated in the system. Longer optics may be employed for better mixing. The output of mixing optic  58  is, in turn, coupled to an output lens  60  which has a focal length of, for example, 90 mm. Output lens  60  may be a 90 mm lens of the type typically used in a 35 mm camera, and then used to focus the beam at various working distances ranging from, for example, 2 cm to 5 m. Moreover, by adjustment of lens  60 , the size of the beam presented by the system over the area to be inspected for forensic evidence may be varied, as desired. As will be understood from the within description, light focused into a relatively small area will be relatively intense, while light focused into a wider area will exhibit less intense illumination.  
         [0067]     As will be understood with reference to  FIG. 1 , filters  50  may be slanted as shown that reference numeral  50   a  in response to tilting of wheel  48  to the position indicated by reference numeral  48   a.    
         [0068]     In accordance with the present invention, it is contemplated that alternative optical elements may be used to perform the mixing function performed by mixing rod  58  in the embodiment of  FIG. 1 . For example, as illustrated in  FIG. 2 , mixing rod  58  may be replaced by a plurality of integrating transparent spheres  158 . Integrating spheres  158  are contained within a cylindrical member  157  including transparent end closures  159  and  161 . In accordance with preferred embodiment the efficiency of the device is improved through the use of a reflective coating  163 , inside of cylindrical member  157 .  
         [0069]     In a manner similar to the functioning of collection and focusing lenses  54  and  60  in the  FIG. 1  embodiment, collection lens  154  focuses light onto transparent input face  159 . Similarly, light output from transparent integrating spheres  158  is focused by lens  160 .  
         [0070]     Still yet another possibility is achieved through the use of a randomizing fiber-optic member as illustrated in  FIG. 3 . In this embodiment, mixing of wavelengths is achieved by a randomizing fiber-optic member  58  comprising a plurality of fiber optic elements  258   a - g  contained within a cylindrical member  257 . In this embodiment, the input faces of fiber optic elements  258   a - g  bear a substantially random spatial relationship to the output faces of fiber-optic elements  258   a - g , thus effectively mixing the output.  
         [0071]     Referring to  FIG. 4 , an embodiment of the invention showing an alternative housing configuration is illustrated. In this embodiment, forensic light source  310  comprises a handle  323  which contains fiber-optic member  328 . A housing  336  contains filter  348 , which is mounted for rotation in the direction indicated by arrow  349  to the position indicated at  348   a . A transparent rectangular mixing assembly  358  may be secured on mounting  365 . In accordance with the invention, mixing assembly  358  includes both a collection lens  354  and a focusing lens  360 .  
         [0072]     Still yet another housing configuration is illustrated in  FIG. 5 . As illustrated in  FIG. 5 , forensic light source  410  comprises a handle  423  which is positioned above fiber-optic member  428 . A housing  436  contains filter wheel  448 , which is mounted for rotation in the direction indicated by arrow  449 , and which may be rotated by engagement of the finger of the user with the periphery  451  of the wheel. An optionally removable (for example by bayonet or screw mount) transparent rectangular mixing assembly  458  may be secured on a mounting  465 . In accordance with the invention, mixing assembly  458  includes both a collection lens  454  and a focusing lens  460 .  
         [0073]     As may be seen from the detail of  FIG. 6 , fiber-optic member  428  is mounted in a cylindrical seat  429  in housing  436 . Seat  429  mates with circular disk-like support member  431 . Disk-like support member  431  is slidably mounted in seat  429  and thus allows the end  433  of fiber-optic member  428  to be rotated as indicated by arrow  435 . Movement of disk-like support member  431  results, for example, in placing the fiber-optic member in the position indicated at  428   a  in  FIG. 6 . The angular orientation of the fiber optic member may be maintained in any desired position through the use of a wing bolt  437  which is tightened against disk  431 .  
         [0074]     An optical arrangement suitable for use in the embodiment of  FIG. 4  is illustrated in  FIG. 7 . In this embodiment, a relatively uniform color effect is achieved through the use of a quartz rod  558 . Input lens  44  is made of quartz. Lens  544  is coupled to the output face  542  of the fiber-optic light guide. Lens  544  is also made of quartz. Light from lens  544  is further focused by lens  545 , passed through filter  550 , which is mounted for rotation, and then focused further by lens  554 . Lens  554  is also made of quartz. Mixing rod  558  has a length of 70 mm and a round cross-section with a diameter of 10 mm. Mixing rod  558  is separated by 13 mm from the output face  554   a  of lens  554 .  
         [0075]     Light from the output face  542  of the fiber-optic light guide is first caused to fall upon lens  544  and then passed on through lens  545  after which it is filtered by filter  550 . The filtered light is then passed through lens  554  through the light mixing guide  558  to result in the creation of an output spot  559  on a workpiece. As noted above, an output focusing length is not absolutely required, although use of one will result in control of the size of the area of illumination  559  at various distances from the system.  
         [0076]     The configuration illustrated in  FIG. 7  may be used in conjunction with a square rod having a 10 mm by 10 mm cross-section and length of 50 mm if an output lens  560  is used. Lens  560 , illustrated in dashed lines, comprises a first plano convex lens  560   a  and a second lens, lens  560   b.    
         [0077]     In the embodiment of  FIG. 7 , all of the optical elements may be made of quartz. Filter  550  may be positioned at any distance from lens  545  which is between lens  545  and lens  554 . After the output light has been mixed and exits face  559  of mixing rod  558 , a wide variety of focusing lens as may be used with configurations well-known to those of skill in the art, depending upon the width of the beam of light desired at a particular distance.  
         [0078]     Still yet another mechanism for achieving color uniformity in the bandpass shifted output of a forensic light source  610  is illustrated in  FIG. 8 . In a manner similar to that of the  FIG. 1  embodiment, a liquid light guide  628  with an output face  642  outputs light to a pair of lenses  644  and  646  which focus light through a wavelength shifting filter  648 . Color equalization is provided by a second filter  658  whose output is focused by an output lens  660  to form an output spot of light  659 . It is contemplated that output spot of light  659  may also be formed as a square, rectangular or other shape.  
         [0079]     In accordance with the embodiment illustrated in  FIG. 8 , filters  648  and  658  are mounted on rotation mechanisms which cause them to be rotated equal amounts in opposite angular directions simultaneously. Thus, for example, filters  648  and  658  may be oriented parallel to each other. Alternatively, they may be oriented in opposite directions with equal angular deviations from the parallel, as illustrated in  FIG. 8 . In addition, it is contemplated in accordance with the invention that filters  648  and  658  are each only one of a plurality of filters, having different wavelength bandpass characteristics, and which are mounted on respective wheels which may be rotated to select the desired filter.  
         [0080]     As it may be understood with reference to  FIG. 8 , rotation of filter  648 , in addition to causing a first-order wavelength shift of a given value in the output of filter  648 , will also cause a second-order wavelength variation characteristic across the output of filter  648 . Because filter  658  is rotated by the same magnitude of angle as the angle at which filter  648  is displaced angularly, it will also have a first-order wavelength shift of the same given value. However, because the sign of the angle is opposite, the second-order wavelength variation characteristic across the face of filter  658  is the opposite of the second-order wavelength variation characteristic across the output of filter  648 , the spatial dispersions of filter  648  and  658  combine to cancel each other.  
         [0081]     In the case of all embodiments of the invention, it is necessary for the wheel to be mounted for tilting and rotation simultaneously. The same may be most advantageously achieved in accordance with the present invention by the mechanism illustrated in  FIG. 9 .  
         [0082]     Referring to  FIG. 9 , an alternative inventive forensic light source  710  is illustrated. Forensic light source  710  includes a housing  712  which may be grasped by the user using a handle  714 . More particularly, as illustrated in  FIG. 9 , the user uses the unit by grasping handle  714  with his hand  716 . The unit  710  is controlled by a bandpass filter wavelength selector dial  718 , which takes the form of the rim of a wheel carrying a plurality of filters as will be described in detail below. The user positions his hand  716  in such a manner that thumb  722  of hand  716  may be placed over dial  718  and the thumb may be selectively used to rotate dial  718  to a desired position.  
         [0083]     Handle  714  on housing  712  includes an on/off switch  724 . Switch  724  is used to turn a light source, such as lamp  726 , on and off. Lamp  726 , which may be mounted in housing  712  on shock absorbing supports, may be any of numerous lamps employed in such instruments, such as for example, a xenon lamp or other suitable source. Suitability for employment in forensic light source  710  is determined by the spectral emission of the lamp. In particular, lamps having sufficiently high light output within the desired output range of the instrument are suitable. The exact nature of the xenon lamp or any other suitable lamp is not a feature of this invention.  
         [0084]     The system also includes a fan  728 , which may be powered by being connected electrically in parallel with lamp  726 , whereby actuation of switch  724  results in turning both lamp  726  on and turning fan  728  on, thus providing for the cooling of the unit during use. Fan  728  is mounted adjacent to a port  730  for the input and circulation of air. Port  730  is located on the rear of the unit as illustrated in  FIG. 9 . Port  730  may be a simple circular hole or a plurality of holes and may be covered by a screen (and optionally an air filter) made of wire to prevent the introduction of foreign objects. Because it is desired that there be a flow of air through the instrument, a set of vents  734  are provided near the opposite end of housing  712 .  
         [0085]     In connection with venting it is noted that switch  724  may be made to individually control fan  728  and light source  726 . More particularly, if desired, it is also possible for switch  724  to be a three way switch in which the first position has both the fan and the light source off, in a second position sends power only to fan  728  and in a third position sends power to fan  728  and light source  726 . This allows the light source to be turned off while still continuing cooling, thus preserving the life of the unit.  
         [0086]     As illustrated in  FIG. 9 , the optical system in forensic light source  710  further comprises a reflector  736  positioned to couple light output from lamp  726  to focusing optics  738 . Focusing optics  738  may comprise a plurality of focusing members, such as refractive members  739  and  741  which function to concentrate light directly received from lamp  726  and indirectly received from lamp  276  by reflector  736  to the output of the system.  
         [0087]     A filter wheel  740  is positioned within housing  712 . Referring to  FIG. 10  taken in conjunction with  FIG. 9 , it is seen that filter wheel  740  has a mounting hole  744  which supports filter wheel  740  for rotation on a post  746  ( FIG. 10 ). More particularly, wheel  740  is mounted on post  746  and may be freely rotated to put one of the filters, as described below, on wheel  740  over the output of focusing optics  738  and thus filter such output.  
         [0088]     More particularly, light output from focusing optics  738  passes through a hole  748  ( FIG. 9 ), through one of the filters  752 - 760  or hole  761 , (in the illustrated case through selected filter  752 ), through hole  749 , and then through hole  751  in front wall  750 .  
         [0089]     There is an alphanumeric designation  772  associated with each of the filters. Each alphanumeric designation  772 , such as designation  772 , designates the wavelength of its corresponding filter which is adjacent the location of the alphanumeric designation. For example, alphanumeric designation  772  is adjacent filter  752 , whereas alphanumeric designation  774  is located adjacent to filter  754 . Likewise, another alphanumeric designation  776  is located adjacent filter  758  and corresponds to the characteristics of filter  758 . In similar fashion, alphanumeric designation  778  corresponds to the characteristics of filter  756 . Other alphanumeric designations on the system are not described but are positioned in similar analogous fashion.  
         [0090]     In accordance with the preferred embodiment, the system, or more particularly, filter wheels  740  has a hole, such as hole  761  in wheel  740  which does not include any filter and merely passes all light in order to output an uncolored or “white” light output. Hole  761  is a simple hole, in contrast with holes  780  which support the filters. Holes  780  have a suitable shoulder which supports the filter and are closed by a retainer spring ring  781  of conventional design, a plurality of which are employed in the system, each associated with one of the holes  780  in filter wheel  740 , as illustrated in  FIG. 10 .  
         [0091]     Filter wheel  740  may include a plurality of notches  786  along its periphery. Notches may be used in connection with a ball and spring follower which bears against the wheel and snaps into notches  786  to provide positive stops so that the filter wheel clicks into place in one of six specified positions. Filter wheel  740  may be rotated to any desired position through the use of knurled serrations  787  along its periphery to make rotation easier. In accordance with the preferred embodiment of the invention, the output of light source  726  is output at a fixed point on housing  712 . When hole  761 , which has no filter mounted in it, is lined up with the output point, then the unfiltered output spectrum of lamp  726  will be output by the system.  
         [0092]     In accordance with the preferred embodiment of the invention, as discussed above, positive engagement of the wheel and maintenance of the position of the wheel at the desired preset points is achieved through the use of a spring follower mechanism which mates with detense or notches  786 . The particular spring follower mechanism used in accordance with the present invention is a spring loaded ball bearing. More particularly, as the filter wheel is rotated, the ball  789  is forced into one of the detents or notches by spring  791  resulting in holding the filter in the desired position, as diagrammatically illustrated in  FIG. 10 .  
         [0093]     In accordance with the present invention, ease of use and light weight may be optionally achieved by separating the light unit from the power supply, whether it be a battery pack or an electrical power supply operated by house current. However, in the embodiment illustrated in  FIG. 9 , a battery pack  798  incorporated within the unit  710  itself powers inventive system  710 .  
         [0094]     In accordance with an alternative embodiment of the invention, the inventive forensic light source  710  may be powered by house current. In this case, a conventional power supply is used and connected by a length of line cord to a house current source.  
         [0095]     Light output through hole  751  in housing  712  is then coupled onto the input face  792  of mixing rod  794 , which may be made of quartz, for example, and has a diameter of ten centimeters and a length of between 16 and 80 cm, although the diameter and length are a function of the diameter of the optical system, and the desired degree of mixing. Mixing route  794  also has rounded edges  795  at both it ends. Rounded edges  795  smooth out the transition from dark to light at the edges of the spot of light output by forensic light source  710 . While such rounded edges are only necessary at the output end of mixing rod  794 , they are included at both ends, so that the rod may be used with either orientation, thus simplifying assembly, use, and so forth. It is also noted that a relatively long mixing optic  794  can be tolerated in the system, and longer optics may thus be employed for better mixing.  
         [0096]     The output of mixing optic  794  is, in turn, coupled to an output lens  796  which has a focal length of 90 mm. Lens  796  is mounted within turret  798 , which in turn is held by annular support  800  on housing  712 . Output lens  796  may be a 90 mm lens of the type typically used in a 35 mm camera, and may be used to focus the beam at various working distances ranging from, for example, 2 cm to 5 m. Moreover, by adjustment of lens  796 , the size of the beam presented by the system over the area to be inspected for forensic evidence may be varied, as desired. As will be understood from the within description, light focused into a relatively small area will be relatively intense, while less intense illumination over a wider area may be employed.  
         [0097]     Ideally, mixing optic  794  has no sharp edges and is chamfered or provided with a round radius at its outpost end  795 . As noted above, the use of a rounded or chamfered edge at the output end gives the output spot of light a uniform smooth look.  
         [0098]     As will be understood with reference to  FIG. 9 , filter wheel  740  may be slanted as shown in phantom lines in  FIG. 9  and  FIG. 11 . This may be done by grasping the knob  802  of lever  804  mounted on U-shaped support  806 . Support  806  is generally U-shaped having an output face  808  and an input face  810 . Hole  748  is defined in input face  810 . Hole  749  is defined in output face  808 . Support  806  is mounted for rotation on a hinge  812  which allows it to be moved in the direction of arrow  814  to the position illustrated in phantom lines in  FIGS. 9 and 11  in chassis  714 , with lever  802  riding in slot  816 .  
         [0099]     When it is desired to use the inventive system, switch  724  is actuated and fan  728  and lamp  726  are activated. Light produced by lamp  726  reflects off reflector  736  and is focused by lens  738 , passing through filter  752 , which has been rotated into position by rotation of wheel  740 . Filter  752  is an interference filter, like the other filters in the system, and outputs colored light which passes through mixing rod  794  and is output in a focused form by lens  796 . When it is desired to shift the wavelength of light filtered by filter  752 , the user grasps knob  802  and moves it to the position shown in phantom lines in  FIG. 12 , from the position illustrated in  FIG. 13 .  
         [0100]     Because filter  752  is tilted at an angle when it is placed in the position shown in phantom lines in  FIG. 9 , it presents a relatively longer path length between layers of the interference filter to light passing through the filter, resulting in the output of light of relatively long wavelength by the system into the input face  792  of mixing rod  794 . Light traveling through mixing rod  794  is reflected, in turn, internally along many different paths. This results in mixing the light input at face  752 . Thus, while there is a chromatic gradient across the face of mixing rod  794 , the output of rod  794  is chromatically uniform.  
         [0101]     In accordance with the invention, it is contemplated that mixing rod  794  is removably mounted on housing  712 . Accordingly, it may be removed and replaced by a fiber-optic flexible light conducting members such as member  818 , as illustrated in  FIG. 14 .  
         [0102]     In accordance with an alternative embodiment of the invention, a forensic light source  910 , illustrated in  FIGS. 15-18 , is constructed substantially the same as the embodiment illustrated in  FIGS. 9-14 , with the exception of the mounting mechanism. In accordance with this embodiment, support  1006  is mounted between a pair of yolks  1022 . Yolks  1022  are mounted for rotation in chassis  914 , as can be seen most clearly in  FIG. 17 . Because of the position of yolks  1022 , tilting of filter  952 , as illustrated in phantom lines in  FIG. 15 , is about an axis  1023  ( FIG. 17 ) which intersects optical axis  1024  of the system, thus allowing the use of larger filters and a greater area of the filter.  
         [0103]     Tilting of wheel  940  may be achieved through the use of handle  1002  by pulling handle  1002  toward the rear of the device, as illustrated in phantom lines in  FIG. 15 . Alternatively, the system may include, instead of handle  1002 , a knob which is rotated, such as knob  1028  which is coupled to the shank  1029  of one of the yolks. Alternatively, the knob may be made much larger, as illustrated by knob  1031  in  FIG. 12 .  
         [0104]     Referring to  FIGS. 18 and 19 , an alternative inventive forensic light source  1110  is illustrated. Forensic light source  1110  is substantially identical to the forensic light source illustrated in  FIGS. 15-17  except that the system includes a pair of separately adjustable filter wheels  1140  and  1142 . Wheels  1140  and  1142  are rotated separately by a pair of knobs  1228  and  1230 . Thus, wheel  1142  may be rotated separately and wheel  1140  left in place, as illustrated in  FIG. 19 .  
         [0105]     Because filters may be combined, bandpass and band reject and other characteristics may be superimposed on each other to get a variety of effects. Tilting of the filters, which is allowed by the system increases the range of these effects dramatically.  
         [0106]     While a wide range of filters may be used, in accordance with the present invention, filter wheel  1140  has an open hole, which passes all light, and a plurality of filters. The filters in filter wheel  1140  have the following characteristics: a bandpass filter with a center wavelength of 440 nm with a relatively broad bandwidth in the range of 40 to 50 nm; a bandpass filter with a center wavelength of 490 nm with a relatively broad bandwidth in the range of 40 to 50 nm; a bandpass filter with a center wavelength of 540 nm with a relatively broad bandwidth in the range of 40 to 50 nm; a bandpass filter with a center wavelength of 590 nm with a relatively broad bandwidth in the range of 40 to 50 nm; and a short pass filter with a maximum pass wavelength of 540 nm (which functions as a crime scene scanning filter). The 540 nm filter is known as a crime scene scanning filter because it is most useful in searching over wide areas of a crime scene in order to identify areas for later closer inspection under light of various wavelengths.  
         [0107]     In accordance with the present invention, it is also contemplated that a crime scene will be searched under white light and under light of various wavelengths, particularly in those areas of the crime scene likely to contain various types of evidence. In addition, to the extent that it is known that various specific types of evidence are most visible under the light of one wavelength or another, it is anticipated that in accordance with the invention that areas will be examined with light of the applicable wavelength or wavelengths.  
         [0108]     The user uses light of different wavelengths to inspect the crime scene for materials which will only be revealed by light of a particular wavelength, or which will be revealed in a better and easier to identify fashion by light of a selected wavelength.  
         [0109]     Filter wheel  1142  also has an open hole, which passes all light, and filters with the following characteristics: a bandpass filter with a center wavelength of 415 nm with a relatively broad bandwidth in the range of 40 to 50 nm; a bandpass filter with a center wavelength of 465 nm with a relatively broad bandwidth in the range of 40 to 50 nm; a bandpass filter with a center wavelength of 515 nm with a relatively broad bandwidth in the range of 40 to 50 nm; a bandpass filter with a center wavelength of 565 nm with a relatively broad bandwidth in the range of 40 to 50 nm; a bandpass filter with a center wavelength of 615 nm with a relatively broad bandwidth in the range of about 40 to 50 nm; and a bandpass filter with a center wavelength of 665 nm with a relatively broad bandwidth in the range of 40 to 50 nm.  
         [0110]     In accordance with yet another embodiment of the invention, it is contemplated that the system may incorporate a third filter wheel which has a number of very narrow band reject filters. These may be selected to reject wavelengths which comprise certain commonly occurring excitation wavelengths which constitute noise and present the possibility of overpowering wavelengths which one wishes to detect or photograph.  
         [0111]     While lamps of other power may be used, it is anticipated that the inventive system will be used with a 100 watt lamp.  
         [0112]     Moreover, in accordance with the invention, it is contemplated that filters from both filter wheel  1140  and  1142  may be used simultaneously in order to have a more selective filtering of wavelengths of light output by lamp  1126 . For example, if a filter having a center bandwidth of 415 nm is used simultaneously with the filter having a center bandwidth of 440 nm on the other filter wheel, the resultant filtering will have a center wavelength of approximately 427.5 nm and a bandpass characteristic whose largest wavelength is the longest wavelength passed by the 415 nm filter and a shortest wavelength which is the smallest wavelength passed by the 440 nm filter.  
         [0113]     In this way, inventive system  1110 , though it incorporates only a limited number of filters, can provide that number of wide bandwidth bandpass characteristics (using one of the filters in one of the filter wheels, with the other filter wheel set for an open hole which passes light all wavelengths) and eight narrow bandwidth bandpass characteristics (using combinations of relatively proximate wavelengths from each of the two filter wheels).  
         [0114]     The above configuration allows for the individual use of nine broadband filters (for example, 415 nm, 440 nm, 465 nm, 490 nm, 515 nm, 540 nm, 565 nm, 590 nm, 615 nm), a short pass filter (crime scene scanning filter) and, for example, white light for searching the crime scene.  
         [0115]     Additionally, with the configuration mentioned above, nine additional commercially useful wavelength filtering functions with relatively narrow bandwidth (20 to 25 nm) can be achieved. These narrow bandpass filtering capabilities at intermediate wavelengths are especially useful for photography at a crime scene and in many instances will provide improved contrast photographs.  
         [0116]     For example, using the 415 nm filter of filter wheel  1140  and the 440 nm filter of filter wheel  1142 , one obtains a resultant bandpass with a center wavelength of 427.5 nm; using the 440 nm filter of filter wheel  1142  and the 465 nm filter of filter wheel  1140 , one obtains a resultant bandpass with a center wavelength of 452.5 nm; using the 465 nm filter of filter wheel  1140  and the 490 nm filter of filter wheel  1142 , one obtains a resultant bandpass with a center wavelength of 477.5 nm; using the 490 nm filter of filter wheel  1142  and the 515 nm filter of filter wheel  1140 , one obtains a resultant bandpass with a center wavelength of 502.5 nm; using the 515 nm filter of filter wheel  1140  and the 540 nm filter of filter wheel  1142 , one obtains a resultant bandpass with a center wavelength of 527.5 nm; using the 540 nm filter of filter wheel  1142  and the 565 nm filter of filter wheel  1140 , one obtains a resultant bandpass with a center wavelength of 552.5 nm; using the 565 nm filter of filter wheel  1140  and the 590 nm filter of filter wheel  1142 , one obtains a resultant bandpass with a center wavelength of 577.5 nm; and using the 590 nm filter of filter wheel  1142  and the 615 nm filter of filter wheel  1140 , one obtains a resultant bandpass with a center wavelength of 602.5 nm.  
         [0117]     Further, using the 590 nm filter of filter wheel  1140  and the crime scene scanning filter of filter wheel  1142 , one obtains an asymmetrical filtering characteristic that represents the juxtaposition of the two characteristics of the two filters. There is a sharp decline in fluorescence transmission at the high-end while excitation reflection is blocked. This is useful for highly reflective surfaces, such as aluminum.  
         [0118]     Still further variation may be achieved by tilting one or both of the filter wheels. For example, if a 415 nm filter is superimposed with a 450 nm filter, the result will be a peak wavelength output at 432.5 nm, if the 450 nm filter is not tilted. If, however, the 450 nm filter is tuned by being tilted, the peak wavelength passed will become longer, with the increase in wavelength proportional to the angle of tilt. This allows one to bring the output wavelength to a point where it matches exactly the blocking range of a camera long pass or bandpass filter and has substantially zero transmission in the camera filter range. The result is to only allow fluorescent light to pass. There is also the potential to combine typical blocking factors ranging between 10-3 to 10-5, resulting in blocking factors reaching purity levels ranging between 10-6 to 10-10.  
         [0119]     If two bandpass filters are tilted, the result will be an average bandpass which is the average of the effective tilted bandpass wavelengths of both of the filters.  
         [0120]     Thus, the potential is to adjust the bandwidth while the peak wavelength is shifting, further enhancing contrast in, for example, evidence photography. This may be done by tuning down the 450 nm wavelength, shifting the peak down (assuming the combination of a 450 nm filter and a 415 nm filter) and increasing bandwidth allowing more intensity to illuminate the evidence.  
         [0121]     It is further contemplated that three or more filter wheels may be used in accordance with the present invention. The same may be used to provide an increased number of broad band filters. The use of three or more filter wheels will also provide greater flexibility in making combinations of different filters. These filters may also be used together to achieve increasingly narrow bandpass filtering. In addition, the use of three or more filter wheels will allow selection of bandpass widths. For example, it may be desired in some cases to combine a 590 nm filter with a 565 nm filter having a first bandwidth while at other times to combine the same 590 nm filter with a 565 nm filter having a second bandwidth, in order to vary the resultant bandwidth. This can be accommodated through the use of additional filter wheels, or filter wheels with greater numbers of filters on them.  
         [0122]     Still yet another possibility in accordance with the present invention is the employment of a mixing member having a rectangular cross-section. The use of a transparent rectangular cross-section rod to mix wavelengths has the advantage of presenting the possibility of matching the shape of the projected light source on a workpiece to the shape of a utilization device, such as a CCD array, photographic film frame, etc.  
         [0123]     In accordance with the invention, as illustrated in  FIG. 20 , a square mixing rod  1294  made of optically transparent material having a diameter of, for example, 12 mm and a length of 60 mm to 80 mm may be employed, for example, in the embodiment of  FIG. 1 . However, it is noted that in the case of a rectangular mixing member, a lens  1296 , in addition to performing a focusing function is also useful in maintaining the square shape (or rectangular shape) of the image projected by the mixing member.  
         [0124]     In accordance with the invention, it is contemplated that the inventive forensic illumination device may include a number of optional features. For example, the system may include an iris in order to serve to spotlight a relatively small area, or to vary the intensity of light falling on an object, for example, for security purposes, to accommodate photography or to prevent deterioration of a sample. If desired, the light source may be provided with an elliptical reflector with the light source, whether it be a filament, arc gap or the like, with the light source placed at one of the foci of the elliptical reflector. In addition, it is contemplated that the reflector may be provided with an ultraviolet reflective coating to enhance the output of the light source in the ultraviolet portion of the spectrum. Similarly, lenses in the system may be accommodated to transmit a maximum of ultraviolet light being made of appropriate materials and provided with appropriate coatings.  
         [0125]     Likewise, it is contemplated that in addition to using one or more filter wheels, some of the wheels may be made tilting or all of the wheels may be made tilting.  
         [0126]     Likewise, the filters may include only a few filters, for example four or a greater number of filters, for example twelve. Likewise, filter wheels tilting may be limited to, for example, a relatively as small amount of tilting such as ten or twenty degrees, or a range to greater degrees of tilting such as forty degrees.  
         [0127]     Light guides may be liquid light guides or fiber-optic bundles. The system may also include a motorized shutter, or a fish tail may be employed. The power supply may be a plug-in household current power supply, a rechargeable battery, or a non rechargeable battery.  
         [0128]     Referring to  FIG. 21 , yet another possibility for an optical mixing member, such as rod  58 , is a hollow mixing sphere  1358  having an input hole  1392  and an output hole  1393 . The inside  1359  of sphere  1358  is reflective. The inside of sphere  1358  also surrounds a baffle  1361 , which may be reflective, but which will block direct transmission of light from input hole  1392  to output hole  1393 . Multiple reflections within mixing member  1358  result in uniform light output from hole  1393 .  
         [0129]     Another embodiment of the invention is illustrated in  FIGS. 22-26 . In accordance with this embodiment of the invention, as illustrated by the exploded perspective of  FIG. 22 , a forensic light source  1410  comprises a handheld light gun  1411  coupled by a flexible fiber optic light guide or liquid light guide  1413  to a power supply and light source  1415 . Light source  1415  is on wheels  1417  which allow it to be wheeled conveniently around a site while still providing a very light handheld light gun portion  1411 . In particular, a user may use source  1410  by grasping handle  1423  and aiming mixing member  1458  in a desired direction.  
         [0130]     In accordance with this embodiment of the invention, a filter wheel  1448  is mounted on a U-shaped support comprising a forward arm  1508  and a rearward arm  1506 , coupled together by a base  1446 . Arm  1506  includes a tine  1507 . The U-shaped support, comprising a forward arm  1508  and a rearward arm  1506 , coupled together by a base  1446 , is rotated in the direction of arrow  1447  in  FIG. 24 . Rotation is achieved by rotation of cam  1449  which is mounted on support rod  1451  and coupled to knob  1453 . Support rod  1451  is mounted on housing  1436  which is, in turn, closed by housing cover  1437 . As cam  1449  is rotated, its forward surface  1455  bears against tine  1507 , causing rotation in the direction of arrow  1447 . This may be most easily understood from  FIG. 24  which shows the filter rotating mechanism in assembled format  
         [0131]     It is noted that substantial radiant energy, during operation of the system, is input through lens assembly  1444 . Accordingly, a heatsink  1445  including a plurality of heat dissipating wings  1447 , in order to prevent overheating. Heatsink  1445  may be secured to the flange  1447  of lens assembly  1444 .  
         [0132]     While an illustrative embodiment of the invention has been described, it is, of course, understood that various modifications of the invention will be obvious to those of ordinary skill in the art. Such modifications are within the spirit and scope of the invention which is limited and defined only by the appended claims.