Patent Publication Number: US-8992042-B2

Title: Illumination devices using natural light LEDs

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application hereby claims priority under 35 U.S.C. §119(e) to Provisional U.S. Application No. 61/559,385 filed Nov. 14, 2011, entitled “Illumination Devices and Methods of Using the Same.” 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to apparatus and methods of using an illumination device comprising one or more white lights for medical diagnostic illumination or examination illumination. 
     SUMMARY 
     An illumination device is disclosed with at least one light emitting diode emitting electromagnetic radiation with a wavelength from about 200 nanometers to about 440 nanometers. The electromagnetic radiation is emitted along a path. A composition of phosphors coat the at least one light emitting diode. The composition of phosphors may comprise a red phosphor, yellow phosphor, a blue phosphor, a green phosphor, an orange phosphor, a violet phosphor, or combinations thereof. At least one wavelength selection device positioned in the path to selectively permit electromagnetic radiation of a particular range of wavelengths to pass through. A mirror to change a direction of the path and at least one lens to diverge the electromagnetic radiation are included where the at least one wavelength selection device, the minor, and the at least one lens are disposed in the path. The at least one light emitting diode, the wavelength selection device, the minor, and the at least one lens are attached to and within a housing. 
     A method of illuminating a specimen is disclosed, which includes emitting electromagnetic radiation along a path with a wavelength from about 200 nanometers to about 440 nanometers using at least one light emitting diode, selectively permitting electromagnetic radiation of a particular range of wavelengths to pass through a wavelength selection device disposed in the path, changing the direction of the path using a mirror, and diverging the electromagnetic radiation using a lens, wherein the wavelength selection device, the minor, and the lens are disposed in the path. The at least one light emitting diode is coated with a composition of phosphors comprising a red phosphor, yellow phosphor, a blue phosphor, a green phosphor, an orange phosphor, a violet phosphor, or combinations thereof. 
     A method of producing electromagnetic radiation is disclosed, including illuminating a specimen using an illumination device and actuating a second adjustment wheel to change the particular range of wavelengths permitted by the at least one wavelength selection device, wherein the illumination device comprises at least one light emitting diode emitting electromagnetic radiation with a wavelength from about 200 nanometers to about 440 nanometers along a path, a composition of phosphors coat the at least one light emitting diode, at least one wavelength selection device positioned in the path to selectively permit electromagnetic radiation of a particular range of wavelengths to pass through, a mirror to change a direction of the path, a lens to diverge the electromagnetic radiation, and a housing, wherein the composition of phosphors may comprise a red phosphor, yellow phosphor, a blue phosphor, a green phosphor, an orange phosphor, a violet phosphor, or combinations thereof, wherein the at least one wavelength selection device, the mirror, and the at least one lens are disposed in the path, and wherein the at least one light emitting diode, the wavelength selection device, the minor, and the at least one lens are attached to and within a housing. 
     These and additional features provided by the embodiments described herein will be more fully understood in view of the following detailed description, in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments set forth in the drawings are illustrative in nature and not intended to limit the subject matter defined by the claims. The following detailed description of the illustrative embodiments can be understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which: 
         FIG. 1 : An illustration depicting the CRI scoring of a UV/NUV pumped illumination device according to one or more embodiments herein; 
         FIG. 2 : A perspective view of an illustrative ophthalmoscope according to one or more embodiments herein; 
         FIG. 3 : A schematic diagram of the ophthalmoscope of  FIG. 1 ; 
         FIG. 4 : A perspective view of an otoscope according to one or more embodiments herein; 
         FIG. 5 : A schematic diagram of an illustrative illumination device according to one or more embodiments herein; 
         FIG. 6 : A schematic diagram of an illustrative illumination device according to one or more embodiments herein; 
         FIG. 7 : A schematic diagram of an illustrative illumination device according to one or more embodiments herein; 
         FIG. 8 : A schematic diagram of an illustrative indirect binocular ophthalmoscope according to one or more embodiments herein; 
         FIG. 9 : A plot graphically the electromagnetic spectrum of several different NUV pumped LEDs coated with a composition of phosphors; and 
         FIG. 10 : A plot graphically illustrates the electromagnetic spectrum of a single composition of phosphors on a NUV pumped LED at varying electrical currents. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure includes an illumination device that includes a light source that emits approximately white light (wavelengths from about 380 nanometers to about 780 nanometers) and may be used in medical diagnostic or examination procedures. More particularly, the present disclosure describes an illumination device comprising one or more light sources such as, for example, light emitting diodes (“LED”) pumped with electromagnetic radiation generally within the ultraviolet (“UV”) range and/or near the ultraviolet range (“NUV”) of the electromagnetic spectrum used in medical diagnostic illumination or examination illumination. 
     Color rendering refers to the way that a lamp or other light source affects the way that an object&#39;s color is seen. The characteristics of the light source are called color rendering properties. Generally, when a light source has good color rendering properties, it means that it can illuminate objects without changing their natural colors. A more technical description of color rendering is defined as the “effect of an illuminant on the color appearance of objects by conscious or subconscious comparison with their color appearance under a reference illuminant”. 
     The CIE Color Rendering Index (CRI) is the only internationally-accepted metric for assessing the color rendering performance of light sources. In the calculation of the CRI, the color appearance of 14 reflective samples is simulated when illuminated by a reference source and the test source. The reference source is a Planckian radiator (if below 5000 Kelvin) or a CIE Daylight source (if at or above 5000 Kelvin), matched to the correlated color temperature (CCT) of the test source. After accounting for chromatic adaptation with a Von Kries correction, the difference in color appearance ΔE for each sample between the two light sources is computed in CIE 1964 W*U*V* uniform color space. The special color rendering index (R i ) is calculated for each reflective sample by:
 
 R   i =100−4.6 ΔEi   (1)
 
     The general color rendering index (R a ) is simply the average of R for the first eight samples, all of which have low to moderate chromatic saturation: 
     
       
         
           
             
               
                 
                   
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     A perfect score of 100 represents no color differences in any of the eight samples under the test and reference sources. For the visible spectrum, a score of 100 indicates a spectral distribution of wavelengths from about 380 nanometers to about 780 nanometers. 
     The CRI method specifies that the CCT of the reference source be matched to that of the test source, which assumes complete chromatic adaptation to the chromaticity of the light source. This assumption fails at extreme CCTs, however. For example, a 2000 K (very reddish) blackbody source achieves R a =100, as does a daylight spectrum of 20,000 K (very bluish). However, neither of these sources renders colors well. None of the eight reflective samples used in the computation of R a  are highly saturated. This is problematic, especially for the peaked spectra of white LEDs. Color rendering of saturated colors can be very poor even when the R a  value is good. Further, by optimization of lamps&#39; spectra to the CRI, R a  values can be made very high while actual color rendering is much poorer. This is because the eight color samples used in the calculation of R a  are all of medium saturation and the number of samples is too few. 
     The eight special color rendering indices are combined by a simple averaging to obtain the general color rendering index. This makes it possible for a lamp to score quite well, even when it renders one or two colors very poorly. Standard white LEDs are at an increased risk of being affected by this problem, as their peaked spectra are more vulnerable to poor rendering in certain areas of color space. Finally, the very definition of color rendering is flawed for many applications. Color rendering is a measure of only the fidelity of object colors under the illuminant of interest and any deviations of object color appearance from under a blackbody source is considered bad. Due to this constraint, all shifts in perceived object hue and saturation result in equal decrements in CRI score. In practical application, however, increases in chromatic saturation, observed when certain sources illuminate certain surfaces, is considered desirable. Increases in saturation yield better visual clarity and enhance perceived brightness. 
     As discussed above the current CRI metric is based on only eight reflective samples, all of which are low to medium chromatic saturation. These colors do not adequately span the range of normal object colors. Some lights that are able to accurately render colors of low saturation perform poorly with highly saturated colors. This is particularly prominent with light sources with peaked spectral distributions as realized by solid-state lighting. Additionally, the CRI penalizes lamps for showing increases in object chromatic saturation compared to reference lights, which is actually desirable for many applications. 
     Rather than assess only color fidelity, this improved metric is intended to assess overall color quality of light sources and is aptly named Color Quality Scale (CQS) to avoid confusion with the CRI. One of the most serious problems with the CRI is that color rendering of saturated colors can be very poor even when the Ra value is good. For the CQS, the eight samples used in the calculation of R have been replaced with 15 samples of high chromatic saturation spanning the entire hue circle.  FIG. 1  illustrates a UV and/or NUV pumped LED with a CRI score of R a =98 (R1−R8). A score of R a =97 (R1−R15) (not shown) is achieved using the CQS standard. 
     It should be understood that the scoring of the LED spectral distribution properties are not limited by the CRI/CQS scoring standards. Any scoring standard may be used to rate the electromagnetic spectrum of the LED. Those LEDs that produce near to or reproduce blackbody incandescent light or sunlight are the subject of this disclosure. For example, the illumination devices and methods shown and disclosed herein using UV and/or NUV pumped LED&#39;s are operable to produce a CRI score of about greater than 80%, about greater than 90%, about greater than 95%, greater than about 96%, greater than about 97%, greater than about 98%, greater than about 99%, from about 97% to about 99%, or about 100%. This high color rendering achieves subtle color expressions that were considered impossible with conventional LED&#39;s. The medical evaluations would thus be enhanced by the UV and/or NUV LED illumination devices and methods using the same of the present disclosure. 
       FIGS. 2 and 3  illustrate an illumination device  5  housed in an ophthalmoscope  10 . The ophthalmoscope  10  comprises a base housing  11 , a head  13 , a first adjustment wheel  15 , and a second adjustment wheel  17 . The base housing  11  may house a battery (e.g., power source  12 ,  FIG. 3 ). The illumination device  5  may include a power source  12 , a LED  14 , a wavelength selective device  16 , a mirror  18 , and/or a lens  19 . The first adjustment wheel  15  may be operable to switch to a different lens of the lens  19  and the second adjustment wheel  17  may be for adjusting or changing the particular range of wavelengths permitted by the wavelength selection device  16 . The ophthalmoscope  10  may be used to observe and diagnose a retina (not shown) of a patient. It is understood that in this illustrative embodiment and/or in any other embodiments shown and described herein, the illumination device  5  may include one or more of the lens  19 , the wavelength selection device  16 , mirros, and/or any other components. 
     The illumination device  5  may have a housing  25  wherein the LED  14 , the wavelength selection device  16 , the mirror  18 , and the lens  19  may be attached to and/or within.  FIG. 3  is illustrative of the illumination device  5  and one embodiment of the attachment configuration within the housing  25  but it should not be viewed as limiting. The LED  14  may emit electromagnetic radiation, along a path  20 . The mirror  18  maybe used to change a direction of the path  20  to better optimize the path  20  within the housing  25 . It should be understood that more than one minor  18  may be used. The lens  19  may be used to diverge the electromagnetic radiation from the LED  14  onto the specimen that is being observed. It should be understood that more than one lens  19  and more than the wavelength selection device  16  may be used. The wavelength selection device  16 , the mirror  18 , and the lens  19  are disposed in the path  20 . 
     The LED  14  of the illumination device  5  may be an UV and/or NUV pumped LED and may emit electromagnetic radiation with a wavelength from about 200 nanometers to about 440 nanometers, particularly from about 300 nm to about 440 nm, particularly from about 300 nm to about 430 nm, more particularly, from about 300 nm to about 425 nm, more particularly, from about 325 nm to about 415 nm, more particularly from about 370 nm to about 410 nm, more particularly from about 370 nm to about 405 nm, or even more particularly at about 405 nm. 
     A composition of phosphors may coat the LED  14  either inside or outside of the LED housing. The composition of phosphors may comprise a red phosphor, yellow phosphor, a blue phosphor, a green phosphor, an orange phosphor, a violet phosphor, or combinations thereof. Depending on the color (i.e. wavelength) of the LED  14 , phosphors of different colors may be applied to or coat the LED  14  to modify the emitted electromagnetic radiation spectrum which is reflected in the spectrum and CRI value. If several phosphor materials of distinct colors are mixed and applied such as, for example, red (e.g. (Sr,Ca)AlSiN 3 :Eu 2+ ), and green (e.g. Ba 3 Si 6 O 12 N 2 :Eu 2+ ) and/or yellow, the emitted electromagnetic radiation spectrum is broadened, effectively raising the CRI value of the given LED  14  to much greater levels than possible with only the emitted electromagnetic radiation spectrum of the given LED  14  alone. 
     In some embodiments, the composition of phosphors may be modified to absorb electromagnetic radiation instead of produce electromagnetic radiation to narrow the spectrum of emitted light. The composition of phosphors may allow filtering of the UV and/or NUV electromagnetic spectrum without the need for a dedicated wavelength selection device  16 . The compositions of phosphors may absorb electromagnetic radiation with a wavelength of from about 300 nanometers to about 440 nanometers, preferably from about 200 nanometers to about 300 nanometers, and more preferably from about 200 nanometers to about 440 nanometers. 
     In another embodiment, the composition of phosphors may be added to shift the electromagnetic spectrum to a CRI value of around 100% or natural sunlight which is ideally suited to provide maximum color representations of the specimens being illuminated for medical diagnosis or examination. The composition of phosphors types and amounts used in the UV and/or NUV LED&#39;s may be manipulated (by adding and/or subtracting the phosphor and/or different types of phosphors) to optimize the contrast of the specimen illuminated by the LED and/or to customize the spectrum (i.e., a non-uniform spectrum) to meet a specific need. For example, a diseased area on a specimen may be more apparent when illuminated with an electromagnetic spectrum emphasizing specific wavelengths. In another example, the composition of phosphors may be optimized for maximum visualization of the specimen (e.g. retina) and provide maximum contrast. 
     Still referring to  FIG. 3 , the wavelength selection device  16  positioned in the path  20  to selectively permit electromagnetic radiation of a particular range of wavelengths to pass through. The particular range of wavelengths may be from about 200 nanometers to about 380 nanometers and/or from about 380 nanometers to about 750 nanometers. Illustrative wavelength selective devices  16  include, but are not limited to, dichroic filters, dichroic mirrors, dichroic reflectors, reflective filters, thin film filters, interference filters, gel film filters, band pass filters, interference bandpass filters (e.g., exciter filters, barrier filters, etc.), any other optical, color filtering, or interference devices, or combinations thereof. The wavelength selective device  16  is optionally a very accurate color filter used to selectively pass light of certain wavelengths (e.g., visible light), while reflecting or absorbing light of other wavelengths (e.g., UV and/or NUV light). Additionally, wavelength selective devices  16  may be a part of, optically connected to, or used with the illumination device  5 . 
     Furthermore, the LED  14  may be arranged in an array (not shown). The array may be chosen from a linear array, a stagger array, a herringbone array, a honeycomb array, a triangular array, a hexagonal array, or a circular array. Further embodiments could feature high brightness white LED&#39;s, high power white LED&#39;s, cold white LED&#39;s or a plurality of white LED&#39;s. 
     Referring to  FIG. 4 , illustrates an otoscope  60  comprising the illumination device  5  (e.g., shown in  FIGS. 2-6 ) that includes the LED  14  pumped with UV and/or NUV and the composition of phosphors e.g., red, green, and blue phosphor as described above. The otoscope  60  may comprise a head assembly  70  and a body assembly  80 . The head assembly  70  may further comprise a lens assembly  72  and a speculum component  74 . It is understood that the otoscope  60  may include one or more components of conventional otoscopes without departing from the present disclosure. 
     Referring to  FIGS. 5 ,  6  and  7 , additional examples of illumination device  5  are shown and described. The illumination device  5  may be optically connected to, or be used in conjunction with the wavelength selective devices  16  to selectively transmit electromagnetic radiation in a particular range of wavelengths such as, for example, visible light, while blocking certain other wavelengths such as, for example UV and/or NUV. Such wavelength selective device  16  when optionally being used with a medical diagnostic and examination illumination devices  5  and instruments of the present disclosure may permit the transmittance of visible light while preventing the transmittance of the UV and/or NUV light from the illumination device  5  to a specimen  57 . Alternatively, the wavelength selection device  16  may also be designed to transmit or pass through only or a portion of the UV and/or NUV light from the LED  14 , while blocking the emission of all or a portion of the visible light, to stimulate the auto-fluorescence and measure such auto-fluorescence in the skin, eye, or ear to assist in medical diagnostics. 
     The illumination device  5  may be configured to produce digital images or digital imaging of the specimen  57 . The illumination device  5  may be coupled to an imager  30 . The coupling may be optically and/or electrically coupling or the illumination device  5  may be used in conjunction with the imager  30 . Examples of the imager  30  may include digital imaging devices such as a digital camera and/or other image sensors. In some embodiments, the imager  30  (e.g., digital camera) may include a charge-coupled device (“CCD”) and/or a complimentary metal-oxide semiconductor (“CMOS”). In another embodiment, the illumination device  5  may be optically and/or electrically connected to one CCD and/or CMOS sensors. It is understood that the imager  30  as shown in  FIGS. 4 ,  5 , and  6  may be the human eye, a camera, digital camera, digital sensors (e.g., CCD, CMOS), projector, film, display, other imaging device, and/or combinations thereof. Furthermore, it should be understood that more than one of the imager  30  may be coupled to the illumination device  5  as for example where an image is projected and produced on film. 
       FIG. 7  depicts the illumination device  5  may comprise the wavelength selective device  16  disposed before and/or after the specimen  57  where each wavelength selection device  16  may permit different particular range of wavelengths to pass through. Such an illumination device  5  would be operable to change the color of the electromagnetic radiation emitted from the LED  14  and/or to block visible light to measure auto-fluorescence. For example the first wavelength selection device  16  may filter harmful UV electromagnetic radiation and illuminate the specimen  57  with the remaining spectrum and the second wavelength selection device  16  may filter part of the visible spectrum to emphasize certain wavelengths for the imager  30 . 
     In another embodiment, one or more of the illumination device  5  may be used to perform a fluorescein angiography or fluorescent angiography. Fluorescein angiography or fluorescent angiography is a technique for examining the circulation of the retina using the dye tracing method. It involves injection of sodium fluorescein into the systemic circulation, and then an angiogram is obtained by photographing the fluorescence emitted after illumination of the retina with blue light at a specific wavelength, e.g., 490 nanometers. In one example, the illumination device  5  may comprise the composition of phosphor coated on the UV and/or NUV LED (, e.g., LED  14 ) of the illumination device  5  tuned through the composition of phosphors to emit electromagnetic radiation in order to perform the fluorescein angiography procedure. In another example, the illumination device  5  may comprise the composition of a phosphor coating on the UV and/or NUV LED, wherein the electromagnetic radiation emitted is across a much broader range of the electromagnetic spectrum of wavelengths than just the specific wavelength necessary to perform the procedure, but may includes the wavelength selection device  16  in the form of an interference bandpass filter (e.g., exciter filter or barrier filter) that blocks out all electromagnetic radiation but a specific wavelength such as, for example, 490 nm, which is necessary to perform the fluorescein angiography procedure. Exciter filters allow only blue light to illuminate the retina. Depending on the specific filter or the wavelength selection device  16 , the excitation wavelength hitting the retina will be from about 465 to about 490 nm. Many exciter filters may only allow light through at a wavelength of 490 nm. Barrier filters allow only yellow-green light (from the fluorescence) to reach the imager  30  (e.g., camera, eye), skin, ear, etc. Barrier filters generally only allow light from about 520 nm to about 530 nm, but many only allow light with a wavelength of about 525 nm. It should be understood that more than one imager  30  may be used. 
     Referring to  FIG. 8 , a binocular indirect ophthalmoscope  85  is shown. The binocular indirect ophthalmoscope  85  includes an adjustable head assembly  90 , which may be worn on the head of a doctor using the binocular indirect ophthalmoscope  85  in a manner similar to a conventional indirect ophthalmoscope. The adjustable head assembly  90  may have a head band  95  for encircling the head, a strap  100  integral with head band  95  adapted to fit on top of the head, and a semi-circular band  105  pivotally attached to the sides of the head band  95  and extending toward the front end thereof. The viewing assembly  110  below an illumination assembly  115  may be secured to the forward part of semi-circular band  105  by a coupling attachment  117  or other suitable means. Although the semi-circular band  105  is rigidly secured, it may be pivoted up or down with reference to head band  95  so as to adjust the vertical position of the viewing assembly  110 . 
     The housing of illumination assembly  115  has a tube  120  or other similar means extending downwardly therefrom into the viewing assembly  110  which is provided with means therein for permitting binocular vision when the observer&#39;s eyes are optically aligned with the viewing assembly  110 . The illumination assembly  115  may include elements of the illumination device  5 , such as, for example, LED  14  pumped with UV and/or NUV electromagnetic radiation as shown and described above, emitting in a predetermined electromagnetic radiation spectrum. It is understood that multiple LED&#39;s  14  may be used, depending on the desired application. 
       FIG. 9  graphically illustrates the electromagnetic spectrum of several different NUV pumped LEDs coated with different compositions of red, green, and blue phosphor. The composition of phosphors and mixtures were different in “NUV Pumped LED  1 ” (circle marker), “NUV Pumped LED  2 ” (triangle marker), and “NUV Pumped LED  3 ” (no marker), illustrating how different electromagnetic wavelength characteristics could be achieved by changing the phosphor characteristics to achieve different color temperatures and/or to enhance or change the contrast for various medical devices. “NUV Pumped LED  3 ” illustrates a relatively “flat” distribution of electromagnetic radiation across the visible spectrum. A peak  140  is illustrative of the NUV wavelength used to pump the LED  14 . A weak peak  145  is also illustrative of the filtering properties of the wavelength selection device  16 . As described above, the NUV wavelength could be filtered to produce the weak peak  145  by the mixture of the composition of phosphors of “NUV Pumped LED  1 ” or as a separate device. 
       FIG. 10  graphically illustrates the electromagnetic spectrum of a single composition of phosphors on a NUV pumped LED at varying electrical currents. If more optical power is needed, then more UV and/or NUV LED&#39;s  14  of  FIG. 3  may be added and/or more electrical current may be provided to the illumination device  5 . At 150 milliamps (closed circle marker), the electromagnetic spectrum is relatively flat for the compositions of phosphors across the visible spectrum. As the current is increased from 150 milliamps to 300 milliamps (no marker), the electromagnetic spectrum starts to emphasize the wavelengths of the dominant phosphors in the composition of phosphors on the LED  14 . The intermediate currents at 200 milliamps (square marker) and 250 milliamps (closed triangle marker) illustrate the shift from the relatively flat electromagnetic spectrum at 150 milliamps to the emphasized wavelengths at 300 milliamps. The current of the LED  14  is a consideration for medical diagnostic equipment and the resulting electromagnetic spectrum. As described in  FIG. 9 , the peak  140  of  FIG. 10  is indicative of the NUV wavelength used to pump the LED  14 . 
     As set for herein, the UV and/or NUV pumped LED&#39;s or lasers may act as a light source for a variety of equipment, instruments, and/or medical diagnostic and/or examination procedures, including but not limited to general medical lighting (e.g., surgical lights, examination room lighting, focused examination lighting, etc.), retinal imaging devices, otoscopes, ophthalmoscopes (e.g., manual ophthalmoscopes, slit lamps, stereo ophthalmoscopes, direct ophthalmoscopes, indirect ophthalmoscopes, combinations thereof, etc.), and dermascopes. 
     It should be understood that in any of the illustrative examples of the illumination device  5  shown and described above herein, the LED  14  may comprise blue light rather than UV and/or NUV as, for example, electromagnetic energy having wavelength from about 440 nm to about 490 nm. The composition of phosphors coating the blue pumped LED  14  may be adjusted to achieve the desired CRI, R9, CQS, and/or other illumination properties. The blue pumped LED  14  may be combined with any of the other components as shown and described herein to perform the illumination methods as shown and described herein. The illustrative embodiments of the illumination device  5  shown and described herein may include one or more of the LED  14  comprising blue light. 
     In certain illustrative examples of the illumination device  5 , conventional illumination devices may be fitted or retrofitted with the UV and/or NUV LED&#39;s as shown and described herein without modification or with use of simple adaptors. In other embodiments, conventional instruments may also be slightly modified or redesigned to incorporate the UV and/or NUV LED&#39;s if needed as well. If UV and/or NUV LED adaptors or retrofitting of existing instruments is impractical, designs of new instruments utilizing the UV and/or NUV LED or UV and/or NUV laser are envisioned. 
     It is noted that the terms “substantially” and “about” may be utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. These terms are also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue. 
     While particular embodiments have been illustrated and described herein, it should be understood that various other changes and modifications may be made without departing from the spirit and scope of the claimed subject matter. Moreover, although various aspects of the claimed subject matter have been described herein, such aspects need not be utilized in combination. It is therefore intended that the appended claims cover all such changes and modifications that are within the scope of the claimed subject matter.