Abstract:
A light for a curing instrument includes a plurality of light sources, each producing an incident light beam. The incident light beams are combined to produce a single output beam, which exhibits a broader spectral width than any of the incident light beams. In one embodiment of the invention, the output beam exhibits an intensity over a spectral range defined by a first characteristic wavelength of a first of the plurality of light sources and a second characteristic wavelength of a second of the plurality of lights sources such that the intensity varies by no more than 25 percent over the range. In another embodiment of the invention including a one or more blue LED light sources among the plurality of light sources, at least one white LED is included in the plurality of light sources in order to generate an output light beam having a component portion that is characterized as green. In a third embodiment of the invention, a plurality of fiber optic bundles receive the incident light beams, and are arranged at a transmitting end so that individual fibers from the plurality of bundles are randomly combined to form a single output surface for transmitting the output beam.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a light used for curing light-activated compound materials. In particular, the present invention relates to a curing light comprising two or more light sources whose outputs are integrally combined to produce a light spectrum suitable for curing a variety of light-activated compounds. 
   BACKGROUND OF THE INVENTION 
   Light-activated compounds are well known and used in a variety of commercial applications. For example, such compounds are widely used in a variety of dental procedures including restoration work and teeth filling after root canals and other procedures requiring drilling. Several well-known dental compounds have been sold, for example, under the trade names of BRILLIANT LINE, Z-100, TPH, CHARISMA and HERCULITE &amp; BRODIGY. 
   Dental compounds typically comprise liquid and powder components mixed together to form a paste. Curing of the compound requires the liquid component to evaporate, causing the composite to harden. In the past, curing has been accomplished by air drying, which has had the disadvantage of requiring significant time. This time can greatly inconvenience the patient. More recently, use of composite materials containing light-activated accelerators has become popular in the field of dentistry as a means for decreasing curing times. According to this trend, curing lights have been developed for dental curing applications. An example of such a curing light is illustrated by U.S. Pat. No. 5,975,895, issued Nov. 2, 1999 to Sullivan, which is hereby incorporated by reference. 
   Conventional dental curing lights generally employ tungsten filament halogen lamps that incorporate a filament for generating light, a reflector for directing light and often a filter for limiting transmitted wavelengths. For example, a blue filter may be used to limit transmitted light to wavelengths in the region of 400 to 500 nanometers (nm). Light is typically directed from the filtered lamp to a light guide, which directs the light emanating from an application end of the guide to a position adjacent to the material to be cured. 
   Filters are generally selected in accordance with the light activation properties of selected composite compound materials. For example, blue light may be found to be effective to excite composite accelerators such as camphoroquinine, which has a blue light absorption peak of approximately 470 nanometers (nm). Once excited, the camphoroquinine accelerator in turn stimulates the production of free radicals in a tertiary amine component of the composite, causing polymerization and hardening. 
   An increasing number of light activated compounds are being developed using a variety of photo initiators with different light properties For example, orthodontic adhesives have been produced with a phenol propanedione accelerator that undergoes free radical production in the presence of green light having a light absorption peak of approximately 440 nm. In order to be effectively used with a variety of compounds, it would therefore be desirable to have a curing light capable of delivering light of several colors. 
   As halogen lamps typically produce a broad light spectrum, these lights would seem to provide some advantage over other more monochromatic light sources, such as light emitting diodes (LEDs) and laser diodes (LDs). However, a problem with conventional halogen-based lights is that the lamp, filter and reflector degrade over time. This degradation is particularly accelerated, for example, by the significant heat generated by the halogen lamp. For example, this heat may cause filters to blister and cause reflectors to discolor, leading to reductions in light output and curing effectiveness. While heat may be dissipated by adding a fan unit to the light, the fan may cause other undesired effects (for example, undesirably dispersing a bacterial aerosol that may have been applied by the dentist to the patient&#39;s mouth). Alternate lamp technologies using Xenon and laser light sources have been investigated, but these technologies have tended to be costly, consumed large amounts of power and generated significant heat. Laser technologies have also required stringent safety precautions. 
   LEDs and LDs appear to be good alternates to halogen curing light sources, having excellent cost and life characteristics. Generating little heat, they also present less risk of irritation or discomfort to the patient. However, LEDs and LDs individually tend to produce relatively monochromatic light energy. 
   U.S. Pat. No. 6,331,111 to Cao discloses a curing light system incorporating a plurality of LEDs or LDs in a single curing light. The plurality of LEDs or LDs are located on a single heat sink to facilitate heat dissipation, and radiate light through a transparent focus dome or window toward a curing target. Cao notes that LEDs and LDs may be selected having different characteristic wavelengths in order to cure a variety of composite materials having photo initiators sensitive to these different characteristic wavelengths. However, Cao falls short of disclosing an efficient means for combining light energy from monochromatic light sources of a few colors in order to produce a broad, continuous spectrum of light energy for curing a variety of composite materials. 
   SUMMARY OF THE INVENTION 
   Limitations of the prior art are overcome by a novel curing light comprising a plurality of light sources each producing an incident light beam, and means for integrating the plurality of incident light beams into a single output light beam. In a first embodiment of the present invention, at least a first one of the light sources has a first characteristic wavelength and at least a second one of the light sources has a second characteristic wavelength, selected so that the output light beam exhibits an intensity that varies by no more than 25 percent over a range defined by the first and second characteristic wavelengths. This result may be achieved, for example, where the first one of the light sources has a first spectral width ending at an uppermost wavelength and the second one of the light sources has a second spectral width ending at a lowermost wavelength, by selecting the first and second light so that the uppermost wavelength of the first light source and the lowermost wavelength of the second light source are approximately coincident. 
   In a second embodiment of the present invention, where at least one of the at least one of the light sources is a light emitting diode (LED) that produces an incident light beam characterized as blue, another light source is selected to be an LED that produces an incident light beam characterized as white, so that the output light beam contains a light component that is characterized as green. 
   In a third embodiment of the present invention, the means for integrating the incident light beams comprises a plurality of fiber optic bundles, wherein a receiving end of each fiber optic bundle is arranged to receive an incident light beam from one of the plurality of light sources, and transmitting ends of fibers in each of the plurality of fiber optic bundles are randomly combined to form a single output surface for transmitting the output beam. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete understanding of the invention may be obtained by reading the following description of specific illustrative embodiments of the invention in conjunction with the appended drawing in which: 
       FIG. 1  shows a typical spectral line for a conventional light source; 
       FIG. 2  shows a typical spectral line for a conventional light emitting diode (LED); 
       FIGS. 3 ,  4  illustrate the effects of using an LED light to cure a composite resin, when the composite resin includes an accelerator activated by light energy at a wavelength outside of the spectral width region of the LED. 
       FIGS. 5 ,  7  and  7   a  illustrate principles and embodiments of the present invention relating to an engineered light spectrum; 
       FIGS. 6   a ,  6   b ,  8   a ,  8   b  and  9  illustrate apparatus embodying principles of the present invention; and 
       FIG. 10  illustrated a dental curing light that incorporates the inventive apparatus of  FIGS. 6   a ,  6   b ,  8   a , and  8   b.    
   

   In the various figures, like reference numerals wherever possible designate like or similar elements of the invention. 
   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The following detailed description includes a description of the best mode or modes of the invention presently contemplated. Such description is not intended to be understood in a limiting sense, but to be an example of the invention presented solely for illustration thereof, and by reference to which in connection with the following description and the accompanying drawing one skilled in the art may be advised of the advantages and construction of the invention. 
     FIG. 1  illustrates a typical spectral line for a light source. Light energy concentrates near a peak (central) wavelength  1  (λ p ,), where a relative light power reaches a maximum relative value  3  of 1.0 at the peak wavelength  1 . Here, power may be measured, for example, as an electrical output from a photodetector that is indicative of the light intensity. 
   The further a wavelength deviates from the peak wavelength, λ p , the lower its light power amplitude. An important characteristic of this spectral line is its spectral width  2  (Δλ), which is conveniently defined to be the width in nanometers (nm) of the spectral line between wavelengths producing a power that is half of maximum relative power value  3 . With increased spectral width, more colors are effectively emitted by the light source. As previously suggested, an unfiltered halogen light may effectively transmit light over a bandwidth (spectral width) of 100 nm. By way of contrast, an LED&#39;s spectral width may be on the order of tens of nm, while a LD&#39;s typical width may be 1 nm or less. 
     FIG. 2  illustrates a spectral line  6  for a typical LED having a central wavelength  1  of 470 nm. An operating range  4  is defined by the spectral width  2 , and is shown in  FIG. 2  as a grayed region under spectral line  6  with boundaries at lower limit wavelength  7  and upper limit wavelength  8 . Within this range, light power is produced at a minimum level  5  no less that 50 percent of the maximum power produced at central wavelength  1 . 
   Composite compound material manufacturers typically quote standard cure times for a light source operating at a minimum of 50 percent of a maximum power output level. As a result, outside of operating range  4 , the relative power of the LED it typically too low to polymerize a composite material within the standard cure times quoted by a material&#39;s manufacturer. Conversely, any composite material having a light activated component sensitive to a wavelength within operating range  4  can generally be cured by the light source within the manufacturer&#39;s quoted times. 
   LEDs are often considered to produce light that is effectively monochromatic, or consisting of one color. As illustrated by  FIG. 2 , even the monochromatic light of an LED is however composed of a range of wavelengths. Visible light (“white light”) ranges approximately from 400 nm to 700 nm (in other words, white light has a spectral width of about 300 nm). An LED typically appears to produce one color because the spectral width of an LED&#39;s visible radiation is relatively narrow at approximately 30 nm. As spectral width narrows, light appears to be increasingly monochromatic. 
   Light-activated composite materials are used in a variety of commercial applications. For example, light-activated composite materials are widely used as adhesives (for example, in the semiconductor industry) and as fillers (for example, in the dental industry). Dental resins are very well known in the dental industry for the restoration of primary teeth. They are available in a variety of shades, and typically polymerize with a dental curing lamp producing visible light in a range between 400 to 500 nm. Within this range, manufacturers may produce as many as 10 to 15 different shades of composite resins for various applications, each activated by light emanating at a different wavelength in the visible range. As a result, no single LED light source is effective to activate each of these composite resins. 
     FIG. 3  shows the spectral line  6  of  FIG. 2  with relation to a composite resin having a polymerizing wavelength  9  of 455 nm. As shown in  FIG. 3 , polymerizing wavelength  9  lies outside of the spectral width  2  of LED  10  having a central wavelength  1  of 470 nm. Thus, a curing light based on LED  10  would be ineffective for curing the resin activated at wavelength  9 . Note that LED  10  produces a diminished power level  11  representing only 30% of its maximum light intensity at wavelength  9 . 
   As shown in  FIG. 4 , alternately, for a composite resin that polymerizes at wavelength  12  of 470 nm, wavelength  12  would lie outside of the spectral width  2  of LED  13  having a central wavelength  1  of 455 nm. In this case, LED  13  produces a diminished power level  14  representing only 15% of its maximum light intensity at wavelength  12 . 
   By way of contrast, the present invention operates to integrate light supplied by several carefully-selected monchromatic light sources in order, for example, to produce light having a spectral width encompassing wavelengths for the more popular light-activated dental compounds. The development of this “engineered” light spectrum will now be explained with reference to  FIGS. 5 ,  7  and  7   a.    
     FIG. 5  provides a composite graph illustrating principles of the present invention. In  FIG. 5 , spectral performance characteristics are illustrated for an engineered light source comprising combined outputs from 4 LED light sources. Accordingly,  FIG. 5  shows spectral lines for a “Royal Blue” LED  15  centered at 460 nm (for example, Nichia Corporation part number NSPB500SV), a “Blue” LED  16  centered at 470 nm (for example, Nichia Corporation part number NSPB500SW470), and an “Aqua Blue” LED  17  centered at 480 nm (for example, Nichia Corporation part number NSPB500SX), and a “White” LED  18  (for example, Nichia Corporation part number NSPW500BS). LED  18  is introduced for the following reason. There are a small percentage of accelerators used in dental composites that do not chemically react with visible blue light wavelengths. Through a number of experiments, we determined that a splash of white light added to a blue light source is effective to stimulate such accelerators, in particular those that require a splash of green spectral light. One skilled in the art will readily recognize that white LED  18  may also be added with a similar effect to other groups of LEDs selected to produce one of the other visible colors (for example, red, orange, yellow, indigo and violet). For example, three “red” LEDs could be selected to produce each producing outputs centered at one of 625 nm, 660 nm and 700 nm. This and all other such single color/white light source combinations are fully contemplated by the present invention. 
   As shown in  FIG. 5 , light output from LEDs  15 – 18  may be combined to produce spectral line  19 , which exhibits a spectral width  20  that is much broader than the spectral widths of the individual LEDs  15 – 18 . In addition, the maximum relative power  21  for the combined spectral line  19  is substantially higher than the maximum relative power individually produced by each of the four LEDs  15 – 18  (shown in  FIG. 5  each at a reference level of 100 perecent). In the example of  FIG. 5 , the maximum relative power  21  of spectral line  19  is about 3 times higher than the reference level. 
     FIG. 7  illustrates the spectral performance of an embodiment of an inventive engineered light source comprising a 470 nm “Blue” LED  16  (Luxeon part number LXHL-BB0I Blue), a 460 nm “Royal Blue” LED  15  (Luxeon part number LXHL-BR02), and a “White” LED  18  (Luxeon part number LXHL-BW0I).  FIG. 7   a  illustrates the spectral performance of an alternate light source to the light source of  FIG. 7 , replacing the 470 nm “Blue” LED  16  of  FIG. 7  with a 505 nm “Cyan” LED  17   a  (Luxeon part number LXHL-BE01). 
   In the engineered light source of  FIG. 7 , the center spectral wavelengths for the blue LEDs  15 ,  16  are positioned approximately 14 nm apart, producing a spectral width  52  as shown in the spectral line  53  for the combined light source of 37 nm. Spectral line  53  over spectral width  52  exhibits a relative power that is nearly at or above the maximum power levels of the individual LEDs over this range. With the selected LEDs  15 ,  16  and  18 , for example, a maximum power output of approximately 1200 milliwatts per centimeter square (mw/cm 2 ) output may be achieved by the emgineered light source of  FIG. 7 . 
   In  FIG. 7   a , the center spectral wavelengths for LEDs  15 ,  17   a  are more widely separated at approximately 32 nm apart, producing a spectral width  54  as shown in the spectral line  55  for the combined light source of 69 nm. While relative power drops to a diminished level  56  near the center of the spectral width  54  due to the increased separation, even at its lowest level, relative power remains nearly at the maximum relative power levels shown for individual LEDs  15 ,  17   a.    
   In the example of  FIG. 7 , output power can be substantially increased by replacing the LED  16  with a more powerful 470 nm LED (Luxeon part number LXHL-LB5C), replacing LED  15  with a more powerful 460 nm LED (Luxeon part number LXHL-LR5C), and replacing LED  18  with a more powerful white LED (Luxeon part number LXHL-LW5C), or their equivalent. This combination produces a combined power output in excess of 4000 mw/cm 2 . 
   FIGS.  6  and  8 – 10  illustrate novel apparatus embodying principles of the present invention.  FIGS. 8   a,b  show an embodiment of the present invention employing a fiber optic cable assembly  26  that receives light produced by individual LEDs  22  at input surfaces  33 , and conducts light to a transmitting surface  34 , to be re-directed to input surface  35  of fiber optic light guide  37 . Light is directed by conventional light guide  37  to transmitting surface  36  for application, for example, to polymerize a dental composite resin. Assembly  26  may be preferably constructed with optical fibers having a numerical aperture (NA) of approximately 0.66, and arranged such that individual fibers directed from input surfaces  33  are randomly ordered within the area defined by transmitting surface  34 . 
     FIGS. 6   a  and  6   b  illustrate aspects of a carrier  57  for physically packaging the LEDs  22 . By way of example, carrier  57  comprises four surface mount LEDs  22  (available, as described above, as LUMILED LEDs from Luxeon), a printed circuit board  23 , a heat sink  24  for dissipating heat away from the base of the LEDs  22 , and thermal conductive compound  25  to assist in the transfer of heat from the base of each LED  22  to the surface of the heat sink  24 . 
   As shown in  FIGS. 8   a, b , circuit board  23  and heat sink  24  of carrier  57  of  FIGS. 6   a ,  6   b  are fixedly positioned abutting a lip surrounding rearward recess  60  in a light housing  58 . Each LED  22  is further fitted to a collimator lens  27  (for example, Luxeon part number LXHL-NXO5) for directing light rays  28  received from LED  22  toward an input surface  33 . Such collimator lenses are known to have light transmission efficiencies of up to 90%, and to deliver a concentrated light beam of about 10 mm in diameter, with some minor losses due to stray output beams. 
   To improve upon the effectiveness of collimator lens  27 , the present invention also comprises planar-convex, anti-reflective lens  29  for further focusing and concentrating light rays produced by lens  27  towards input surface  33  (illustrated in  FIG. 8   a  as light rays  31 ). A suitable lens may be found, for example, as Edmund Industrial Optics part number L45-238, selected to have a diameter approximately equal to a maximum diameter of collimator lens  27 . An output curvature (thickness)  30  of the lens  29  may be selected for directing light beams  31  along a proper focal distance  32 . 
   Lens  29  is preferably anti-reflection coated, to improve upon a total transmission of only 92% characteristic for uncoated lenses, and to reduce hazards caused, for example, by reflections traveling backwards through the system (ghost images). A ¼λ thick Magnesium Fluoride broadband coating (400–750 nm typical) is preferably used for substrates with an index of refraction ranging from 1.45 to 2.40. This coating is less sensitive to angular and spectral variations than multi-layer dielectric coatings. The performance of the coating will increase as the index of refraction of the substrate increases. 
   Each lens unit  27 ,  29  is fixedly positioned and aligned in one of a plurality of cavities  59  in housing  58 , using conventional means. Each cavity  59  is in communication with recess  60 , so that, when carrier  57  is positioned adjacent to recess  60 , each of the plurality of LEDs  22  are received in an appropriated position in relation to a lens  27 . Each of a plurality of bores  61  is in communication with a cavity  59  at an opposing end of the cavity  59  in order to fixedly receive an input end  62  of fiber optic assembly  26 , so that each input surface  33  of the fiber optic assembly  26  is positioned at a proper focal length  32  and orientation with respect to an associated lens unit  27 ,  29 . 
   Chamber  38  of housing  58  provides a space for orienting fiber optic assembly  26  so that an output end  63  of fiber optic assembly  26  can be fixedly positioned at an opposing end of chamber  38 . Transmitting surface  34  of fiber optic assembly  26  is thereby effectively positioned with respect to input-surface  35  of light guide  37  in order to facilitate transmittance of light energy from fiber optic assembly  26  to light guide  37 . Output end  63  of fiber optic assembly  26  may be fixedly positioned in chamber  38  by a variety of conventional means such as, for example, insert  64  which interferingly rests at a desired position in chamber  38 . Light guide  37  is fixedly mounted in forward recess  65  of housing  58 , having for example a conventional geometry and employing conventional means for fixedly mounting light guide  37  to housing  58 . 
     FIG. 9  illustrates an alternate embodiment to the inventive apparatus illustrated in  FIGS. 8   a, b . In  FIG. 9 , each LED  22  is mounted is mounted on one of a plurality of carriers  57 , each carrier  57  being installed abutting one of a plurality of rearward recesses  60  in light housing  58 . Each recess  60  communicates with a cavity  59 , and each cavity  59  fixedly holds a lens unit  27 ,  29  for focusing and condensing light emitted by the LED  22  on input surface  35  of light guide  37 . Cavities  59  communicate with chamber  38  so that light transmitted via lens unit  27 ,  29  travels directly through cavity  38  to input surface  35  without a need, for example, to be directed by the fiber optic assembly  26  of  FIGS. 8   a, b.    
     FIG. 10  illustrates the embodiment of  FIG. 8   a, b  packaged for use, for example, in a dental curing light. In  FIG. 10 , housing  58   a  houses lens units  27 ,  29  and carrier  57 , which mounts LEDs  22 . Housing  58   a  also contains bores  61  for locating input ends  62  of fiber optic assembly  26  in their desired position relative to lens units  27 ,  29 . Carrier  57 , after assembly in housing  58   a , is positioned against locating surface  58   b  in order to locate the assembly  58   a ,  57  within chamber  38  of exterior housing  58   c . At a forward end of exterior housing  58   c , transmitting surface  34  of fiber optic assembly  26  is held in a desired position with respect to input surface  35  of light guide  37  by retainer  64 . Exterior housing  58   c  includes a handle portion  58   e  for convenient gripping and accommodation of a trigger (not shown) for operating the curing light. Housing  58   c  also includes slots  58   d  in proximity to carrier  57  to assist in dissipating heat generated by carrier  57 . For clarity in illustrating the present invention, other conventional elements of the curing light that may be located, for example, within the handle portion  58   e , are not shown in  FIG. 9 . 
   The foregoing describes the invention in terms of embodiments foreseen by the inventor for which an enabling description was available, notwithstanding that insubstantial modifications of the invention, not presently foreseen, may nonetheless represent equivalents thereto.