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 . fig1 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 . fig2 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 fig2 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 fig2 , 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 . fig3 shows the spectral line 6 of fig2 with relation to a composite resin having a polymerizing wavelength 9 of 455 nm . as shown in fig3 , 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 fig4 , 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 fig5 , 7 and 7 a . fig5 provides a composite graph illustrating principles of the present invention . in fig5 , spectral performance characteristics are illustrated for an engineered light source comprising combined outputs from 4 led light sources . accordingly , fig5 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 fig5 , 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 fig5 each at a reference level of 100 perecent ). in the example of fig5 , the maximum relative power 21 of spectral line 19 is about 3 times higher than the reference level . fig7 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 ). fig7 a illustrates the spectral performance of an alternate light source to the light source of fig7 , replacing the 470 nm “ blue ” led 16 of fig7 with a 505 nm “ cyan ” led 17 a ( luxeon part number lxhl - be01 ). in the engineered light source of fig7 , 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 fig7 . in fig7 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 fig7 , 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 . fig6 and 8 – 10 illustrate novel apparatus embodying principles of the present invention . fig8 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 . fig6 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 fig8 a , b , circuit board 23 and heat sink 24 of carrier 57 of fig6 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 fig8 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 . fig9 illustrates an alternate embodiment to the inventive apparatus illustrated in fig8 a , b . in fig9 , 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 fig8 a , b . fig1 illustrates the embodiment of fig8 a , b packaged for use , for example , in a dental curing light . in fig1 , 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 fig9 . 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 .
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 .