LED luminance-enhancement and color-mixing by rotationally multiplexed beam-combining

This application is a Continuation of International Patent Application No. PCT/US07/75780 filed Aug. 13, 2007, entitled LED LUMINANCE-ENHANCEMENT AND COLOR-MIXING BY ROTATIONALLY MULTIPLEXED BEAM-COMBINING, which claims the benefit of U.S. Provisional Application No. 60/822,209, filed Aug. 11, 2006, entitled LED LUMINANCE-ENHANCEMENT AND COLOR-MIXING BY ROTATIONALLY MULTIPLEXED BEAM-COMBINING, both of which are incorporated herein by reference in their entireties.

The present invention relates to enhancing luminance, and more particularly to luminance enhancement and color mixing.

The use of light emitting diodes (LED) has increased dramatically over the last few decades. Numerous applications for LEDs have been identified and continue to be identified.

LEDs alone typically emitted relatively low light emissions as compared with many other types of light sources. As a result, the use of LEDs for some implementations has been limited.

The present invention advantageously addresses the needs above as well as other needs through the provision of the methods and systems for use in providing enhanced illumination. Some embodiments provide lighting systems. These systems comprises at least two light sources and one or more smoothly rotating wheels, said one or more wheels comprising at least one mirror sector, the circumferential portion of said mirror sector being the inverse of the number of said sources, a first source of said at least two sources is so disposed that said mirror sector reflects light from the first source into a common output path, said first source pulsing such that a duty cycle of the first source corresponds to a time said mirror sector reflects light from the first source into said common output path.

A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description of the invention and accompanying drawings which set forth an illustrative embodiment in which the principles of the invention are utilized.

The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein:

FIG. 1 shows a simplified schematic view of a light system with sectored mirror that alternates two light sources onto a receiver.

FIG. 2 graphically shows non-overlapping LED spectra.

FIG. 3 shows a dichroic-mirror design for overlaying spectra, such as the spectra of FIG. 2 .

FIG. 4 graphically shows overlapping LED spectra.

FIG. 5 shows a simplified schematic view of a light system that overlays spectra.

FIG. 6 shows a perspective view of a triconic color wheel.

FIG. 7 shows a nonimaging relay lens.

FIG. 8A is a side view of a multi-wheel 4-LED system.

FIG. 8B is a perspective view of the multi-wheel system of FIG. 8A .

FIG. 9 is a perspective view of a two-color variation of a multi-wheel system according to some embodiments.

FIG. 10 is a perspective view of a three-color view of a multi-wheel system according to some embodiments.

FIG. 11 is a side view of a more compact version of a multi-wheel system according to some embodiments.

Corresponding reference characters indicate corresponding components throughout the several views of the drawings.

In spite of decades of progress in making LEDs brighter, there are still light sources that greatly outshine them, such as HID filaments and arc lamps. LED luminance is typically limited by the LED chip's maximum operating temperature, which often will be exceeded unless cooling means match the chip's heat load. When input current is pulsed and heat load is intermittent, higher luminance can be temporarily attained. This effect is limited in many blue and green chips to only about a 50-100% increase. Some present embodiments provide methods to in part pulse multiple chips out of phase, to have their output combined into a temporally constant light with enhanced luminance.

Another problem with LEDs is color mixing while retaining the high luminance of the individual chips. The typical RGB LED configuration has three LED chips situated side-by-side in a diffusive medium that mixes the colors over a much larger emission area than that of the three chips. Some present embodiments in part overlay the separate chips into a common output. Conventional dichroic mirrors can do this, but generally only for collimated light and only for LEDs having spectra without substantial overlap. This typically precludes the addition of more colors to an illuminant to improve its gamut and its color rendering over the standard three.

Some systems utilize a rotating fold mirror to reflect successive radially ingoing collimated beams, down a rotational axis to a single receiver. One potential drawback with this approach is the requirement for a very rapid stepper motor to quickly rotate between the different incoming beams and then stop rotating for the on-time each is allotted. An ordinary rotating mirror is typically not possible because of the very short dwell time of each input beam to fully occupy the output beam.

Some present embodiments utilize a smoothly rotating mirror that generally limit and in some instances substantially alleviate inevitable vibrations produced by the rapid and intermittent rotations of a stepper motor and a scan mirror.

Another problem in putting the light onto a rotational axis of a scanning mirror makes the system sensitive to errors in its tilt or centering relative to the axis, which could occur during assembly and/or develop over time due to the inherently high vibration levels from stepper motors. Also, a stepper motor typically has very high torque, increasing its size and the weight of the support structure. Some present embodiments alleviate these shortcomings utilizing rotation of a sectored mirror, array of lenses, and/or combinations thereof.

Further, some present embodiments provide temporal mixing of the light from multiple light-emitting diodes that are intermittently pulsing with out-of-phase duty cycles. These duty cycles can be short enough to take advantage of initially high efficacy that some LEDs have immediately after power-on. Additionally, some embodiments use smoothly rotating mirror-wheels to interleave beams from different LEDs with sufficiently short on-duration as to have enhanced luminance.

Light emitting diodes typically suffer from rapid non-radiative recombination of electron-hole pairs in the active layer, but millisecond-scale pulses can be used that are short enough that this is not fully in effect. Instead, high transient currents are rewarded with up to double the luminance of steady-state operation. A duty cycle of approximately 25% enables this high luminance to be achieved about a fourth of the time. Some present embodiments enable four such sources to be interleaved into a steady luminance-doubled output.

FIG. 1 shows a light system 10 the utilizes a sectored mirror 13 M that alternately directs light from two light sources 11 and 12 onto a receiver 15 , according to some embodiments. Luminance-enhanced light system 10 comprises first collimated light source 11 and second collimated light source 12 . Source 11 , in some instances, is boresighted directly onto receiver 15 , while source 12 is positioned to reflect off of semicircular mirror 13 M, which rotates about axis 14 . Semicircular transparent sector 13 T allows first source 11 to illuminate receiver 15 during half the rotational period of wheel 13 . Mirror 13 M enables second source 12 to take over for the other half of the period.

FIG. 2 depicts a graphical representation of how a dichroic mirror can act upon spectrally separate light beams. Graph 20 has horizontal axis for wavelength λ and vertical axis L R for normalized spectral intensity. Curves L 1 and L 2 represent the separate spectra of two LEDs. Curve F T is the normal-incidence transmittance of a suitable selective filter.

FIG. 3 shows color mixer 30 comprising first LED 31 and second LED 33 , with respective spectra L 1 and L 2 of FIG. 2 . They are optically coupled to collimators 32 and 34 , respectively. Dichroic filter 35 , with curve F T of FIG. 2 , enables second beam 39 to be overlaid on first beam 38 . This method is typically inapplicable in the case of two LEDs with overlapping spectra.

FIG. 4 shows graph 40 of relative spectral intensity S as a function of wavelength λ for four overlapping LEDs L 1 , L 2 , L 3 , & L 4 . The use of dichroic filters would in this case typically entail substantial losses.

FIG. 5 shows four-LED system 50 with LEDs L 1 , L 2 , L 3 , & L 4 having the overlapping spectra shown in FIG. 4 . The LEDs are configured as in FIG. 3 , with a mirror arrangement including mirror 53 M that is the same as the mirror arrangement in FIG. 1 .

FIG. 6 shows an alternative mirror wheel design that is multi-conic with multiple sectors that in some embodiments correspond to a number of light sources. System 60 comprises trisectored mirror-wheel 61 , and LEDs 62 , 63 , & 64 , each with a collimator as 64 c . The three sectors are differently inclined along a perimeter so as to reflect in turn each of the collimator outputs into common output path 66 . The mirrors profiles can have many shapes such as flat, spherical or even aspheric to correct the astigmatism caused to the reflected beam. Since those profiles are rotationally symmetric, they remain invariant with the rotation. In some embodiments that may enhance performance, the collimators 64 c concentrate the light into a small spot inside the sector, thereby reducing the transition time between outputs from one LED to the next. In some implementations, for example, the system 60 could be the basis for an RGB television illuminator for a digital micromirror device.

The system 60 of FIG. 6 could comprise a different number of sectors (two, four or more) to produce the multiplexing of the corresponding number of light sources.

Alternatively, instead of the mirrors of the system 60 in FIG. 6 , a sectored lens-wheel could be used, so the light is transmitted instead of reflected. Another embodiment comprises the combination or refractive and reflective sectors.

FIG. 7 shows aperture 71 admitting edge rays 71 r that are such as to form a tube entirely illuminating nonimaging relay lens 72 , which in turn sends the edge rays through second aperture 73 . Such a lens enables multiple light sources to be temporally interleaved.

FIG. 8A is a schematic side view of multi-wheel system 80 , showing LEDs 81 L, 82 L, 83 L, & 84 L coupled to their respective nonimaging collimators 81 C, 82 C, 83 C, & 84 C and sectored mirror-wheels 81 M, 82 M, and 83 M, and fixed mirror 84 M. The mirror-wheels 81 M, 82 M, and 83 M rotate about common axis 85 .

FIG. 8B is a perspective view of system 80 showing how the rotation of the sectored mirror-wheels 81 M, 82 M, and 83 M gives the overlaid output. LED 81 L is on when mirrored sector 81 M is under it. Likewise for LED 82 L and mirrored sector 82 M, on the next 90° of wheel rotation, and LED 83 L and mirrored sector 83 M. On the final 90° of rotation, the transparent sectors 81 T, 82 T, & 83 T allow LED 84 L to reflect off stationary mirror 84 M and pass up through the transparent sectors 81 T, 82 T, & 83 T and the lenses 81 N, 82 N, 83 N and 84 N to provide the output beam 86 .

FIG. 9 is a perspective view of multi-wheel two-color system 90 , according to some embodiments, with color sectored mirror-wheels that are substantially the same as those of FIG. 8B that have mirror sections (e.g., 93 M) and the transparent sections (e.g., 93 T) and rotate about an axis 95 . The two-color system 90 includes a first bank, set or system of LEDs 91 -L 1 , 92 -L 1 , 93 -L 1 and 94 -L 1 with an associated system of lenses, a second bank, set or system of LEDs 91 -L 2 , 92 -L 2 , 93 -L 2 and 94 -L 2 with an associated system of lenses. The two systems of LEDs and lenses operate 180° out of phase and are overlaid by dichroic mirror 97 . The light from both stacks of LEDs comes out as a combined output 96 .

FIG. 10 shows three-color system 100 . The three-color system 100 includes three sectored mirror-wheels each with mirrored sections (e.g., 100 M) and optically transparent sections (e.g., 100 T) at least for the wavelengths of light emitted from the respective LEDs. The three-color system 100 further includes dual dichroic mirrors 107 forming common output beam 106 from three LEDs and associated lens systems 101 , 102 and 103 .

FIG. 11 shows a side view of a multi-wheel system according to some embodiments that is more compact than the system of, for example, FIGS. 8A and 8B . The system includes LED sources 11 L, 112 L, 113 L and 114 L with associated lenses 114 C, and sectored mirror-wheels that rotate about an axis 115 . The system of FIG. 11 , in part, shows how the larger wheels of, for example, FIGS. 8A and 8B can be made smaller, utilizing more compact collimators having a different optical architecture.

The present embodiments provide methods, systems and apparatuses for use in enhancing light and/or mixing light. Some embodiments provide multiple LED systems that interleave phased pulses through the use of a sectored mirror wheel that is smoothly rotating. Rapid rotational rates are utilized in at least some embodiments that give short pulse times that enable enhanced luminance to be attained. Multiple wavelengths can also be interleaved. Further, some embodiments provide spot-focusing that can minimize the transition time between phases. Some embodiments provide color mixing, enhanced luminance and/or both color mixing and enhanced doubled luminance are attained. For example, some embodiments provide a doubling of luminance.

While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.