Illumination – Light modifier – Refractor
Reexamination Certificate
2000-12-22
2003-04-15
O'Shea, Sandra (Department: 2875)
Illumination
Light modifier
Refractor
C362S326000, C362S327000, C362S328000, C362S334000, C362S335000, C362S336000, C362S350000, C362S364000, C362S255000
Reexamination Certificate
active
06547423
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an LED module comprising an LED (light-emitting diode) and a rotationally symmetrical, bowl-shaped collimator lens which is provided with a recess in which the LED is situated, and which collimator lens is also provided with a flat surface from which light generated by the LED emerges, the normal to the surface extending substantially parallel to the axis of symmetry of the lens. The invention also relates to a luminaire provided with a number of said LED modules.
BACKGROUND OF THE INVENTION
An LED module of the type mentioned in the opening paragraph is known per se. For example in the English-language abstract of Japanese patent application JP 61-147.585, a description is given of such an LED module. This LED module comprises an LED which is secured onto a substrate and which is positioned in the recess of a bowl-shaped collimator lens. This lens is rotationally symmetrical in shape and has an associated axis of symmetry. The position of the LED and the shape of the lens are attuned to each other in such a manner that a large part of the light generated by the LED is converted via refraction and reflection into a parallel light beam which leaves the lens via a flat surface. The lens and the substrate are secured in a metal housing.
This known LED module has an important drawback. The emerging light leaves the lens in a direction that is substantially parallel to the axis of symmetry of the lens. Under certain conditions it is desirable for the parallel beam to leave the lens at a certain angle, viewed relative to the axis of symmetry.
Copending application Ser. No. 09/415,833 filed Oct. 12, 1999 of Keuper and Pashley, the disclosure of which is incorporated herein by this reference thereto, aims at providing an LED module of the above-mentioned type, in which the light emerges at a specific angle relative to the axis of symmetry of the lens, the proposed LED module is additionally compact, the said LED module has a simple structure, and its manufacture is inexpensive. The LED module comprises a LED and a rotationally symmetrical, bowl-shaped collimator lens which is provided with a recess in which the LED is situated and which collimator lens is also provided with a flat surface from which light generated by the LED emerges, the normal to the surface extending substantially parallel to the axis of symmetry of the lens, which LED module in accordance with the invention is characterized in that the surface is provided with a sawtooth-like structure for deflecting the emerging light.
The invention in said co-pending application is based on the recognition that such a sawtooth-like structure offers a good solution to the deflection of the parallel beam leaving the lens. Since the maximum dimensions of the teeth are very small (below 1 mm), such a sawtooth-like structure can be provided in a relatively thin layer (thickness below 1 mm). By virtue thereof, also the maximum dimensions of the LED module remain limited. In comparison to alternative solutions in which a separate prism is arranged in front of the emergent face of the lens, or the lens is beveled, said co-pending application offers compact, inexpensive LED modules which can be readily manufactured. Such a collimator is referred to as the “flat top tulip” collimator. In its preferred embodiments, it is preferably a solid plastic piece with an air-filled indentation at the entrance aperture. The wall of the indentation is a section of a circular cone (of cone angle typically about 2°), and the indentation terminates in a lens shape. The LED (in an appropriate package) injects its light into the entrance aperture indentation, and that light follows one of two general paths. On one path it impinges on the inner (conic) wall of the solid collimator where it is refracted to the outer wall and subsequently reflected (typically by TIR) to the exit aperture. On the other path, it impinges on the refractive lens structure, and is then refracted towards the exit aperture. This is illustrated schematically in
FIGS. 1A and 1B
. The collimator is designed to produce perfectly collimated light from an ideal point source at the focus. When it is used with a real extended source of appreciable surface area (such as an LED chip), the collimation is incomplete (nor can it ever be complete for any design, for functional reasons). Instead it is directed into a diverging conic beam of cone angle &thgr;. Improving (i.e. reducing) this angle &thgr; is a primary purpose of the present invention.
SUMMARY OF THE INVENTION
This invention represents an improvement in the performance of the Flat top Tulip Collimator disclosed and claimed in our co-pending application Ser. No. 09/415,833 referred to above in terms of reduced size, beam divergence, beam uniformity, and to some degree efficiency. Moreover, it allows a wider variety of choices in optimizing various performance characteristics at the expense of others. This in turn allows more flexibility in the design process, leading to improvements in the various applications that employ the LEDs and collimation optics.
According to the invention, the various optical surfaces of the collimation optics are defined according to one or more constructive rules in order to reduce the angular errors, which result from the finite (i.e. non-infinitesimal) LED source size.
The advantages of the present invention are described in the description that follows in terms of five main characteristics: (1) the beam divergence angle, (2) the exit aperture diameter d
e
, (3) the overall height h, (4) the spatial uniformity of the exit beam, and (5) the efficiency &eegr;. Since &thgr; and d
e
are ultimately related by a fundamental theorem—the conservation of etendue, the initial description is geared to one fixed value of d
e
, namely 30 mm. This is arbitrary and for illustrative convenience only, and in no way limits the generality of possible design choices. In the discussion that follows, performance will be described in relation to a 30 mm flat top tulip collimator with a 1 mm square LED chip in the standard LED package with a 2.75 mm radius hemispheric dome lens. This will be referred to hereinafter as the “Reference Collimator 20” and is illustrated in FIG.
1
A. Additionally, we take as the “beam divergence angle” the cone half-angle that envelopes 90% of the beam, and we refer to this angle hereinafter as angle &thgr;
90
%.
An object of this invention is to gain improvements in one or more desirable characteristics of a flat top tulip collimator without sacrificing performance in other areas. Such areas for improvement are discussed herein in terms of several distinct applications including high-performance white light illumination, Projection Displays, and Light Generators for signing and illumination.
For high performance white light illumination, especially involving the color mixing of red, green, and blue (“RGB” LEDs), all of the above characteristics are important. In particular, for the deterministic color-mixing schemes such as the Beam Splitter Mixer as claimed in our U.S. Pat. No. 6,139,166 issued Oct. 31, 2000 and assigned to the same assignee as this application, or dichroic mixing, the sine qua non is the beam uniformity. This is the case because in these schemes, the various RGB beams are superposed, and if those beams are not uniform (e.g. if they contain imaging information) then that will result in unacceptable color error. Specifically, the lens of the Reference Collimator forms an image of the actual LED chip, which in addition to being generally square has bond-wire attachments, contact electrodes, and possibly other undesirable spatial non-uniformities- and thus directly leads to poor performance in such applications. Adding a diffusive surface property to the lens can disrupt the imaging, but in the Reference Collimator, this also increases &thgr;
90%
, which is undesirable.
Another object of the invention is to modify the flat top tulip collimator such that the beam divergence angle of the (smooth) lens portion is less than that of the re
Marshall Thomas
Pashley Michael
Koninklijke Phillips Electronics N.V.
O'Shea Sandra
Zeade Bertrand
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