Abstract:
A forensic light source and method using an inventive light source comprising a short arc gas vapor discharge lamp is disclosed. A support structure is provided for supporting the source of light. A light guide having first and second ends, is coupled to the source of light at the first end to receive light from the source of light and transmit the light to the second end. The light guide is mounted on the support structure. A filter support member supports a plurality of filters. A portable hand holdable and movable light directing assembly is mounted on the second end of the light guide. The light directing assembly supports the filter support member and provides for movement of the filter support member to a plurality of positions. Each of the positions corresponds to a coupling of a selected one of the filters to the second end, whereby the light emitted from the second end is filtered by the selected filter while the emitted light is directed to various locations through movement of the light directing assembly. A dc power supply has a pulsating dc or constant voltage output.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a non-provisional filing based on provisional application Ser. No. 60/603,751, filed Aug. 23, 2004 and directed to FORENSIC LIGHT SOURCE, the priority of which is hereby claimed. 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention relates to light sources of the type employed in the forensic examination of treated and untreated objects and surfaces and to a method employing such sources.  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0003]     Not applicable.  
       BACKGROUND OF THE INVENTION  
       [0004]     Light sources have been used for many years in connection with the forensic examination of objects and surfaces, for example those found or located at a crime scene. Typical objectives of such examination are detection and photography of blood, fingerprints, hair, bodily fluids, and other traces which may be used, for example, to associate an object or location with a particular individual.  
         [0005]     In order to enhance the detectability and imageability (for example, for the purpose of photography) of trace materials, law enforcement personnel employ a wide range of tools, including fingerprint dusting powder, chemical developers and photography.  
         [0006]     Detection of such traces has spawned sometimes elaborate techniques for enhancing the detectability of evidence. For example, in U.S. Pat. No. 4,258,073 to Payne, the surface under examination is electrostatically charged to encourage the deposit of finely divided carbon to enhance a pattern for visual detection.  
         [0007]     More conventionally, when a fingerprint is fresh, the oil which forms the print generally follows the pattern of the fingerprint ridges in the finger which made the print. If a fine dust is applied to the surface of a fresh print, the dust tends to adhere to the oils in the fingerprint, thus forming a pattern which generally reveals the pattern of the fingerprint.  
         [0008]     Fingerprint dusts were initially selected for their color contrasting qualities as compared to the background. Thus, white dust was used to enhance a fingerprint on a black object and vice versa. Even where the oils of a fingerprint have lost their tackiness due to aging or other phenomena, the amino acids, into which they break down, do cause a minute etching of many surfaces. While this etching is often not visible to the naked eye, and may not become visible with the application of a colored powder, extremely fine fluorescent dusting powders will reveal the fingerprint pattern when illuminated under high intensity light.  
         [0009]     One of the chief tools employed by law enforcement officials remains the light source, which started as a simple incandescent flashlight, but now preferably takes the form of vapor arc lamps. Such lamps generally comprise a glass or ceramic bulb. The bulb surrounds a pair of electrodes and defines a chamber. The chamber is filled with a desired material to be vaporized and electrically stimulated into a light emitting state by an electrical arc or plasma positioned adjacent the two electrodes. An electrical current passing through a gaseous vapor which has been excited into a state of conductivity to form a plasma arc has the potential of emitting light with an efficiency which far exceeds that of an incandescent lamp filament. In addition, the potential exists for emission of wavelengths deep into the ultraviolet. Light emitted by such arc vapor lamps may be the direct output of the excited plasma which forms the arc, or it may be a stimulated radiation in a desired range. Such stimulated radiation would be provided by a phosphorescent coating on the inside of the glass bulb, which might, for example, receive ultraviolet radiation and, in response to it, be stimulated to output light in the visible range.  
         [0010]     Forensic light sources on the market today predominantly use metal halide and xenon lamps. Both of these lamp types are far superior to the older incandescent light sources, despite the fact that they require specialized power supplies to operate. As compared to a simple battery or a steady voltage/steady current AC mains power supply as used with incandescent lamps, xenon and metal halide lamps require complex power supplies with a high-voltage arc ignition load, lower steady state operating voltage, and very high reignition voltage.  
         [0011]     For example, a typical metal halide lamp may require an ignitor voltage of 25,000 volts minimum, in the form of a 1000 pulse per second square wave, for hot reignition. Accordingly, a relatively complex power supply, comprising, for example, an electronic ballast, is needed to power the device. Operation of such lamps is also complicated by the temperature of the lamp, with another typical lamp requiring 20,000 volts to re-ignite when hot and 4500 volts to ignite a cold lamp.  
         [0012]     While metal halide lamps are more efficient than, for example, incandescent lamps, the intense light output required by modern forensic techniques makes powering metal halide forensic light sources with battery power substantially impractical.  
         [0013]     Notwithstanding the above complications, metal halide lamps, because of their relatively uniform and spectrally complete production of light across the visible spectrum (with some additional output in the infrared and ultraviolet ranges) are generally preferred as lamps in forensic light sources. Metal halide lamps have an output radiation intensity which is greater than other types of lamps used in forensic light sources, particularly in the visible region of the spectrum.  
         [0014]     In some cases, it may be desirable to have a very high output of ultraviolet light. When the provision of a relatively high intensity of ultraviolet output is important, xenon arc lamps are the preferred choice for the lamp in a forensic light source. Like metal halide lamps, compared to incandescent lamps, xenon lamps are relatively efficient. However, while xenon lamps have an emission spectrum more like daylight, including substantial emission in the ultraviolet and infrared ranges, their electrical driving requirements are considerably more demanding. Accordingly, xenon source power supplies are heavy and expensive and are impractical in connection with battery power. Moreover, xenon lamps contain materials which are under very high pressure, even when cold and thus present a potentially hazardous situation in the event of bulb breakage.  
         [0015]     Recently, improved operation has been achieved through the use of DC electrical sources for lamps in forensic light sources. However, problems respecting poor ultraviolet emission of such lamps (for example those sold under the trademark Cermax), fragility and attendant danger due to bulb breakage, poor efficiency and so forth remain.  
       SUMMARY OF THE INVENTION  
       [0016]     While, in principle, it is possible to employ a mercury vapor lamp in a forensic light source, the high-pressure of a mercury vapor lamp and its corresponding fragility often limit the employment of mercury vapor lamps to specialized ultraviolet applications, such as the curing of plastics, for example, the ultraviolet curable plastic materials used in dentistry. In accordance with the invention, however, a lamp which contains, when it is operating in its steady state a substantial mercury vapor component, is employed as the light generating element of the inventive forensic light source. The lamp has a short arc length and includes bulb gas components similar to those in halogen lamps.  
         [0017]     A forensic light source constructed in accordance with the present invention comprises a source of light comprising a short arc gas vapor discharge lamp. A support structure is provided for supporting the source of light. A light guide having first and second ends, is coupled to the source of light at the first end to receive light from the source of light and transmit the light to the second end. The light guide is mounted on the support structure. A filter support member supports a plurality of filters. A portable hand holdable and movable light directing assembly is mounted on the second end of the light guide. The light directing assembly supports the filter support member and provides for movement of the filter support member to a plurality of positions. Each of the positions corresponds to a coupling of a selected one of the filters to the second end, whereby the light emitted from the second end is filtered by the selected filter while the emitted light is directed to various locations through movement of the light directing assembly. A dc power supply has a pulsating dc or constant voltage output.  
         [0018]     The short arc gas vapor discharge lamp may be a Ushio EmArc lamp.  
         [0019]     The filter support member may comprise a wheel with a plurality of filters mounted around a point of rotation and the filter support member may further comprise a mounting structure configured to rotatably mount the wheel about the point of rotation. In accordance with the invention, the wheel is positioned to be rotated by a finger of a user. Preferably, the filter support members comprise a mounting structure configured to rotatably mount the wheel about the point of rotation, and the wheel is positioned to be rotated by the thumb of a user. The filter support member comprises a wheel with a plurality of filters mounted around a point of rotation  
         [0020]     The filter support member defines a plurality of detentes and a spring member is mounted on the light directing assembly and positioned to releasably engage one of the detentes. Each of the detentes is positioned to correspond to alignment between its respective one of the filters and the second end, when a respective detente is engaged by the spring member. Each of the detentes corresponds to a respective one of the filters.  
         [0021]     A heat sink may be coupled to the first end of the light guide. The light guide may be a liquid light guide.  
         [0022]     A dc power supply having a pulsating dc or constant voltage output for powering the source of light may use.  
         [0023]     In accordance with the invention, the inventive method for the forensic examination of evidence using a light source comprises generating light using a short arc gas vapor discharge lamp. A support structure supports the source of light. A filter support member supports a plurality of filters positioned to receive the output of the source of light. The generating of the light is done by exciting a mixture of mercury, xenon and metal halide in a bulb. The short arc gas vapor discharge lamp is excited with pulsating or smooth substantially direct current, whereby substantially only one electrode is caused to emit light.  
         [0024]     In accordance with the inventive method, the light output by the system is filtered to match the expected emission wavelength of a forensic marker material. The evidence may be marked with a material selected from the group consisting of dusting powders, chemicals appliable in liquid form and glues. The generating of light is done by exciting a mixture of mercury, xenon and metal halide in a bulb. The light output by the system is filtered to match the expected emission wavelength of a forensic marker material. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]     Several devices implementing the present invention will be understood from the following description taken together with the drawings, in which:  
         [0026]      FIG. 1  is a schematic view of a forensic light source constructed in accordance with the present invention;  
         [0027]      FIG. 2  is a schematic view of an alternative forensic light source constructed in accordance with the present invention and employing a plurality of selectable filters for filtering the output of the source;  
         [0028]      FIG. 3  is a schematic view of another forensic light source constructed in accordance with the present invention and employing a fiber optic bundle;  
         [0029]      FIG. 4  is a top plan view of yet another forensic light source constructed in accordance with the present invention and employing a fiber optic bundle;  
         [0030]      FIG. 5  is a front view of the forensic light source of  FIG. 4 ;  
         [0031]      FIG. 6  is a side view of the forensic light source of  FIG. 4 ; and  
         [0032]      FIG. 7  is a block diagram electrical components of the forensic light source of  FIG. 4 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0033]     Referring to  FIG. 1 , a forensic light source constructed in accordance with the present invention is illustrated. The inventive forensic light source  10  comprises a lamp  12 . Lamp  12  includes a pair of electrodes  14  and  16  (housed within a clear quartz envelope (or bulb) and is powered by a pair of conductors  18  and  20  housed within the bulb. The bulb of lamp  12  also contains a mixture of mercury, xenon and metal halide.  
         [0034]     Power is supplied by a power supply  22 , which may be based on battery power, comprising one or more batteries. Alternatively, an AC power supply may be employed and which may be plugged into the alternating current mains. If desired, rechargeable batteries may be employed, and optionally an AC power supply may supply the desired power, and recharge the battery when the battery needs recharging.  
         [0035]     The system is cooled by a fan  24  which is also powered by power supply  22 . Light output by the system is focused by an elliptical reflector  26  which includes a pair of focal points. One of these focal points coincides with the electrical discharge adjacent electrode  14  which is the electrode which emits light. The other focal point is positioned at point  28 , which functions as the source position for a virtual point source which, in turn, may be focused into a converging beam, a diverging beam or a pencil or parallel bundle of any desired width of light by a lens  30 . Alternatively, light may be focused onto the input face of a fiber optic bundle as in some of the alternative embodiments described below.  
         [0036]     The system is enclosed in a housing  32 . Housing  32  may be made of sheet metal, such as steel or aluminum, or any suitable material.  
         [0037]     During operation, lamp  12  is powered by power supply  22  and is caused to emit light. Similarly, power is sent to blower  24  which draws air through perforations  33  in housing  32  and exhausts air through perforations  35  in housing  32 . This acts to cool the system.  
         [0038]     Optionally, the output of the forensic light source may be filtered as it outputs lens  30  by a filter  34 . Filter  34  may be tilted, as is known in the art, in the directions indicated by arrows  36  in order to shift the wavelength of output light. Such wavelength shifting will work with an interference filter in accordance with Bragg&#39;s law.  
         [0039]     In accordance with the invention, lamp  12  is a short arc vapor lamp of the type incorporating a mixture of mercury, xenon and metal halide. When power is supplied to electrodes  14  and  16 , an arc is formed between the electrodes and a light emitting plasma generates both heat and light. The generated heat causes the mercury to evaporate, thus insuring an adequate output in the ultraviolet range.  
         [0040]     The subject lamp is particularly advantageous in the case of a forensic light source. For example, in the case of a forensic light source, the powering of the device by batteries is of particular importance, as a convenient source of AC current may not be available.  
         [0041]     In addition, because of the efficiency provided by the lamp employed in the inventive system, battery life is extended while light output is improved substantially. While such factors may be irrelevant in other circumstances, the use of the inventive system with a battery provides substantial advantages in the context of evidence gathering.  
         [0042]     At the same time, because the contents of lamp  12  are not under high-pressure, the likelihood of a dangerous accident is greatly reduced. Again this feature is of particular relevance in the context of a forensic light source, where the area where it is being used may be in disarray and an individual using the same may trip, or the device may be put in a relatively unsecured location from which it may fall, tip over or the like. Such an accident may also result in loss of evidence.  
         [0043]     In accordance with the present invention, yet further advantages are provided as compared to prior art systems in as much as lamp  12  is operated with DC current, preferably a battery or relatively smooth DC similar (supplied by a low voltage battery or the AC mains) to the direct current provided by a battery. The result is that the luminous spot is maintained adjacent one electrode  14 , which is made coincident with one of the focal points of the elliptical reflector  26 . Consequently, light tends to focus at focal point  28  and such focus is relatively distortion free, resulting in the production of good pencils, points and cones at the output of lens  30 .  
         [0044]     This compares with the situation where both electrodes may emit light and high quality focusing is relatively difficult to achieve.  
         [0045]     In accordance with the present invention, the most effective lamp found for use as lamp  14  is a lamp selected from the EmArc series manufactured by Ushio which has offices in California.  
         [0046]     These EmArc mercury and metal halide mixture lamps have excellent efficiency and spectral range and are operated with direct current.  
         [0047]     Moreover, the advantages of greater output of light, longer battery life, better shaped output and greatly reduced risks of danger due to bulbs exploding is provided without compromising the quality or power output of the lamp.  
         [0048]     In the discussion of alternative embodiments below, analogous parts are, where practical, given numbers which are multiples of 100 different from the reference numerals of the elements indicated in connection with the description of the  FIG. 1  embodiment.  
         [0049]     An alternative embodiment of the light source of the present invention is illustrated in  FIG. 2 . Alternative light source  110  comprises a power supply  122 , which may be based on battery power or on AC power. Alternative light source  110  comprises a lamp  112 . Lamp  112  includes a pair of electrodes  114  and  116  and is powered by a pair of conductors  118  and  120 .  
         [0050]     The system is cooled by a fan  124  which is also powered by power supply  122 . Light output by the system is focused by an elliptical reflector  126  which includes a pair of focal points. One of these focal points coincides with the discharge adjacent electrode  114 . The other focal point is positioned at point  128 , which functions as the source position for a virtual point source which, in turn, may be focused by a lens  130  into a converging beam, a diverging beam, a point on the input face of a fiber optic bundle, or a pencil of light. The system is enclosed in a housing  132 . Housing  132  may be made of sheet metal or any suitable material.  
         [0051]     During operation, lamp  112  is powered by power supply  122  and is caused to emit light. Similarly, power is sent to blower  124  which draws air through perforations  133  in housing  132  and exhausts air through perforations  135  in housing  132 .  
         [0052]     Optionally, the output of the inventive forensic light source may be filtered as it outputs lens  130  by any one of several filters  134  mounted for selection on the circumferential edge of a rotatably mounted wheel. Filters  134  may be tilted, as is known in the art, in the directions indicated by arrows  136  in order to shift the wavelength of output light.  
         [0053]     Focusing of the system illustrated in  FIG. 1  and the system illustrated in  FIG. 2  may be achieved by a variety of lens configurations and mechanisms. For example, with reference to the  FIG. 2  embodiment, lens  132  may be moved as indicated by arrows  140  and  142 . Alternatively, a lens may be omitted from the design.  
         [0054]     In contrast to the system illustrated in  FIG. 1 , light source  110  includes a plurality of filters  134  (for example, six filters) which may be arranged on a wheel  144 , which rotates on a hub  146 . If desired, wheel  144  may be mounted for tilting to achieve wavelength shifting in the passed wavelength. Wheel  144  may also include an empty hole without a filter for the passage of light without filtering. In addition, if desired, the output of the source may be passed into a fiber optic member  148 , mounted in a conventional manner to housing  132 .  
         [0055]     In using the inventive source, many materials, such as dyes, in addition to fluorescent dusting powders may be used. Inspection of treated and untreated evidence may be done using the specialized light output of the high intensity inventive source and optionally a filter which passes light having a limited range of wavelengths. Depending upon the material used, which material may be either a fluorescent dusting powder, dye, or other marker material, light having a wavelength which substantially coincides with a known excitation wavelength of the marker is employed. The characteristic of the marker is that, upon illumination with light at one of its excitation wavelengths, it will fluoresce, or emit light. Such fluorescence is typically at a longer wavelength as compared to the excitation wavelength.  
         [0056]     Examination of evidence may also optionally be enhanced through the use of color filtering glasses or filters, whose color filtering characteristics are tuned to maximize the image to be detected. As noted above, the excitation wavelength is varied through the use of filters at the source. While such devices are very efficient in filtering light, every filter has its own fixed characteristics. These include its center wavelength, bandwidth and transmission coefficient. Thus, if one wishes to have flexibility, the embodiment of  FIG. 2 , including filter tilting and a wheel of filters and an open hole is of particular value. Moreover, as new dyes and powders are introduced, appropriate filters may be selected and tilted as necessary. The possibility also exists to change a filter wheel or the filters in a wheel.  
         [0057]     As can be seen from the above, numerous advantages are provided by the inventive, efficient, superiorly focused, fuller ranged and versatile system. Naturally, the inventive system is advantageous in having the possibility of very high intensity output light at a selected wavelength. Moreover, the same is achieved without increased power consumption and excessive heat energy, which would otherwise stress the rest of the system.  
         [0058]     Referring to  FIG. 3 , in accordance with the invention, a forensic source  210  may take the form of a housing  232  containing a lamp  212  (of the type sold by Ushio under the EmArc trademark with optics substantially arranged as in the embodiments of  FIGS. 1 and 2 . The output of lamp  212  is coupled to a fiber-optic bundle  250 , with wavelength selection performed by a selected filter on a filter wheel  244  (or a pair of filter wheels) which are positioned at the end of fiber optic bundle  250 . Filter wheel  244  comprises a generally circular member within which a plurality of filters are mounted at the circumferential periphery of the wheel.  
         [0059]     Filter wheel  244  is mounted for rotation in the directions indicated by arrows  251 , and may be rotated by the thumb  253  of a user grasping a handle  252  with his hand. This can be most convenient because handle  252  is at the output end of fiber optic bundle  250 . Alternately, filters located in a filter wheel  244 ′ (illustrated in phantom lines in  FIG. 3 ) may instead be located in housing  232  and controlled by direct mechanical linkage or a remote-control at the output of fiber optic bundle  250 . Light rays  254  emitted by lamp  212  are focused by reflector  226  onto the input face  256  of fiber optic bundle  250 .  
         [0060]     Other alternatives are the placement of a battery power supply externally (for example, a battery pack or linkage to a car battery) or use of a removable AC power supply that has a dedicated position in a compartment located in forensic source  210 . A mechanical shutter  258  may be mounted for sliding, rotary, or other motion to be positioned over input face  256  of fiber optic bundle  250  to block the output of light from the system. Such motion may be achieved using a knob  260 .  
         [0061]     The system may also employ band reject filters on a filter wheel. Similarly, goggles (bandpass and/or band reject) may be employed in connection with the inventive forensic light source.  
         [0062]     Referring to  FIGS. 4-6 , an embodiment of the inventive forensic light source  310  is illustrated. Source  310  comprises a lamp  312  contained within an elliptical reflector  326 . The lamp is of the type described in connection with the embodiments of  FIGS. 1-3 . Likewise, the optics in connection with which lamp  312  is used may be substantially the same as those described in connection with the embodiments of  FIGS. 1-3 . The system may be grasped and carried around by a handle  315 .  
         [0063]     A fuse assembly  321  (which also includes conventional electrical fluctuation filtering circuitry) supplies power to a 200 watt power supply  322 , comprising an electronic ballast which powers lamp  312 , whose light emitting electrode is schematically indicated in phantom lines in the figure. Lamp  312  is housed in reflector  326 . A second power supply  323  powers a plurality of blowers or fans which cool the unit. These fans are mounted over holes in housing  332  to permit the intake or exhaust of air to form a desired cooling airflow. More particularly, the inventive system comprises a fan power supply  323  which supplies power to an intake fan  325 . Intake fan  325  draws air along path  325   a  through an exhaust fan  327 , cooling the lamp and power supply  323 .  
         [0064]     An intake fan  329  draws air along path  329   a  and exhausts it through holes  331 . Fan  335  draws air in the direction of path  335   a , cooling a coupling  362  within which a fiber optic light guide bundle, such as that illustrated in the earlier embodiments, may be mounted. Fan  335  has its airflow guided and concentrated by a cowl  364 , which extends around coupling  362 . Coupling  362  may be made of metal, such as a lightweight aluminum or other similar alloy. The use of lightweight aluminum has the additional advantage of providing for effective transfer of heat generated at the face of the fiber optic bundle to the cooling airflow.  
         [0065]     Light may be blocked by a mechanical shutter  358  operated by a knob  360 . The system may be turned on and off by a switch  370 . In similar fashion, a secondary switch  372  may be used to turn the lamp on and off.  
         [0066]     Referring to  FIG. 7 , the system is powered by the AC mains  373 . Power to ballast power supply  322  is coupled by switch  372  to drive lamp  312 . More particularly, switch  370  couples power via fuse  321 , which provides power to switch  372 . Switch  370  also couples power to a suitable fuse arrangement  374 , which in turn couples power to power supply  323 . Power supply  323  powers fans  325 ,  327 ,  329 , and  335 .  
         [0067]     The various parts of the inventive light source  310  are contained in a housing  332 . Numerous vent holes, including vent holes  331  and  333  are provided in housing  332 .  
         [0068]     Filters may be provided in the system as described in connection with the embodiments of  FIGS. 1-3 , and as discussed above.  
         [0069]     While an illustrative embodiment of the invention has been described, it is, of course, understood that various modifications will be apparent to those of ordinary skill in the art. Such modifications are within the spirit and scope of the invention which is defined and limited only by the appended claims.