Reflector for a lighting device and illumination system of a projection apparatus

A reflector for the lighting device and an illumination system of the projection apparatus are provided. The reflector comprises a first reflecting structure and a second reflecting structure disposed on the portion of the first reflecting structure. The reflecting surfaces of the first and second reflecting structures are formed with a distance therebetween. After the first portion of the light is reflected from the first reflecting surface and the second portion of the light is reflected from the second reflecting surface, the second portion of the light is adapted to remove the centrally dimmed area at the opening of the lighting device. Thus, the luminance performance can be improved.

This application claims the benefits of the priority based on Taiwan Patent Application No. 096125590 filed on Jul. 13, 2007; the disclosures of which are incorporated by reference herein in their entirety.

CROSS-REFERENCES TO RELATED APPLICATIONS

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a reflector for a lighting device and an illumination system for use in a projection apparatus. In particular, the invention relates to a reflector that can effectively eliminate a centrally dimmed area generated from the opening of the lighting device in an illumination system of a projection apparatus.

2. Descriptions of the Related Art

The projection apparatus, which is widely used in offices, homes, conference rooms or the like, typically comprises a light source and other optical components such as prisms and imaging lens. Because uniform light rays are pertinent for the imaging quality of the projection apparatus, the light source is one of the critical components in the projection apparatus.

Among various types of projection apparatuses, the digital light processing (DLP) projection apparatus, which can generate a sequence of digital light pulses in response to a digital signal, has been popular on the market. An internal arrangement of a conventional DLP projection apparatus is depicted inFIG. 1A. The projection apparatus10comprises a light source11, a light integration rod12, a color wheel13, a light-coupling device14, a digital micro-mirror device (DMD)15, and a lens16. Here, only a single DMD15and a single light source11are shown as an example. The ultra high-pressure (UHP) lamp, which costs less and has a high light emitting efficiency, is the preferred light source11.

In the configuration depicted inFIG. 1A, the color wheel13is adapted to convert light emitted from the light source11into light of the three primary colors. Specifically, when the light passes through the light integration rod12, it is preliminarily turned into images. Then, the color wheel13, typically disposed at the entrance of the light integration rod12, generates the three primary colors selectively. Subsequently, upon entering the light coupling device14, the light is reflected and modulated by individual micro-mirror structures of the DMD15and is finally projected by the projection lens16.

To improve the luminance of the illumination system, a multi-light-source arrangement may be considered so that light from multiple light sources are projected into the light integration rod12together for light integration before being used in other back-end optical elements. However, due to the restriction imposed by the étendue conservation law in the DMD15, a simply addition of light sources will not result in an equivalent improvement of the luminance as desired. Consequently, the configuration of the light sources to achieve an optimal effect has become one of the greatest challenges posed to the designers of illumination systems.

In consideration of the restriction imposed by the étendue conservation law, a conventional way for improvement is to design the optical path as a retro-reflect system. As an example, two parabolic lighting devices11a,11bthat can emit parallel light are illustrated inFIG. 1B. With the two parabolic lighting devices11a,11bdisposed opposite of each other, a portion of the parallel light projected from the parabolic lighting devices11a,11bis outwardly reflected by a reflecting prism17directly, while the remaining portion is first reflected inside the opposite lighting device and then guided to reflect from the reflecting prism17. As a result, a portion of the light may be reclaimed before being reflected, thus meeting the restriction imposed by the étendue conservation law on the system.

However, some drawbacks still exist with the retro-reflect system. For example, if a lighting device with a bulb (e.g. an UHP lamp) is employed, limitations of the structure may lead to a centrally dimmed area in the light projected from the opening of the lighting device. For example, if an elliptical lighting device11cis used, as shown inFIG. 1C, a dim area will occur in the center115of the projection plane113formed by the light projected from the opening since the lighting device11ccomprises a bulb111. The dimmed area decreases the overall luminance.

In view of this, it is highly desirable to provide a reflector that can effectively eliminate the occurrence of a centrally dimmed area in an illumination system of a projection apparatus.

SUMMARY OF THE INVENTION

One objective of this invention is to provide an illumination system for use in a projection apparatus and a reflector for a lighting device. In the present invention, an additional reflecting surface with a different thickness is locally disposed on the original reflecting surface of the reflector, leading to a local shift of the light after reflection. The centrally dimmed area is thus removed. In consideration of the étendue conservation law, light at the fringe portion of a lighting device will not be used for projection in practice, so even a locally dimmed portion generated at the edge of the projection surface after shift will not influence the overall luminance.

Another objective of this invention is to provide an illumination system for use in a projection apparatus and a reflector for a lighting device. In the structure disclosed in this invention, the optical couplings are accomplished mostly in traditional optical manners to avoid light loss during the light coupling process.

Yet a further objective of this invention is to provide a reflector for a lighting device and an illumination system for use in a projection apparatus. The reflector may be associated with other illumination systems such as a retro-reflect system. The reflector may also partially shift the reflected light to compensate and eliminate the centrally dimmed area generated at the lighting device opening.

To achieve the abovementioned objectives, a reflector for a lighting device is provided in this invention. The lighting device comprises a luminous portion and a reflecting portion, wherein the luminous portion is adapted to emit light and the reflecting portion is adapted to project the light towards the reflector. The reflector comprises a first reflecting structure and a second reflecting structure. The first reflecting structure has a first reflecting surface. The first portion of the light reflected by the first reflecting surface forms the first bright area and dim area on the projection surface. The second reflecting structure is locally disposed on the first reflecting surface, and has a second reflecting surface formed a certain distance from the first reflecting surface. The second portion of the light reflected by the second reflecting surface forms a second bright area on the projection surface to at least partially cover the dim area, thus, eliminating the conventional centrally dimmed area on the projection surface. Additionally, this invention further provides an illumination system for use in a projection apparatus, which comprises the lighting device and the reflector described above.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The first embodiment of the reflector of this invention is depicted inFIGS. 2A and 2B. The reflector21is associated with a lighting device23, which comprises a luminous portion231and a reflecting portion233. Light emitting from the luminous portion231is reflected by the reflecting portion233and projected towards the reflector21. In this embodiment, the reflecting portion233is elliptical in shape to converge the light emitted from the luminous portion231.

More specifically, the reflector21comprises a first reflecting structure211and a second reflecting structure213. The first reflecting structure211has a first reflecting surface2110, while the second reflecting structure213has a second reflecting surface2130, both of which may be concave surfaces. The first reflecting surface2110and the second reflecting surface2130should preferably have an adequate curvature so that both surfaces have the same focus point. The first reflecting surface2110and the second reflecting surface2130may either be parallel or unparallel to each other. Variations may be readily made on the reflecting surfaces by those skilled in the art.

The second reflecting structure213is locally disposed on the first reflecting surface2110at a certain distance from the second reflecting surface2130and the first reflecting surface2110. A perspective view of the second reflecting structure213is depicted inFIG. 2B. In this embodiment, the second reflecting structure213is disposed so that it protrudes from the first reflecting surface2110and strip-like in shape. However, the shape of the second reflecting structure213may be varied depending on specific design requirements, and is not just limited thereto.

Conceivably, light emitting from the luminous portion231, after being projected by the reflecting portion233and reflected by the reflector21, is adapted to form a bright area on a projection surface25. For convenience of description, the light emitting from the luminous portion231may be divided into a first portion A and a second portion B. The first portion A is reflected by the first reflecting surface2110to project towards the projection surface25, while the second portion B is reflected by the second reflecting surface2130to project towards the projection surface25. In this embodiment, since the second portion B is reflected by the second reflecting surface2130instead, it appears to have a shift on the projection surface25as compared to the conventional projection approach, thus compensating for the centrally dimmed area.

More specifically,FIG. 2Cis a schematic view illustrating the projection of only the first portion A onto the projection surface25. The first portion A projected onto the projection surface25forms the first bright area251and dim area (as shown by a hatched portion inFIG. 2C). The dim area may be further divided into a first dim portion253and a second dim portion255. The first dim portion253is substantially located at the center of the first bright area251, and at least covers the central dim area that tends to occur in the prior art (as shown by a dashed circle inFIG. 2C). The second dim portion255is substantially defined between the first dim portion253and the border250of the bright area251. As shown inFIG. 2D, it is clear that the second portion B of the light is exactly reflected by the second reflecting surface2130of the second reflecting structure213, and forms a second bright area257on the projection surface25which covers at least a portion of the dim area described above, particularly the first dim portion253. In this way, the second portion B of the light reflected by the second reflecting structure213shifts on the second bright area257on the projection surface, thus compensating for the conventional centrally dimmed area. More specifically, the second bright area257that was conventionally projected onto the second dim portion255is now shifted to at least cover the first dim portion253.

In other words, the concept of the present invention is to eliminate the dim light of the centrally dimmed area by projecting adequate light that would be conventionally projected elsewhere onto the central area. Referring again toFIG. 2A, a portion of the light that would project onto the central dim area in the prior art will not be utilized in this embodiment, i.e. will not be reflected onto the projection surface25. The resulting dim area will be compensated by adequate light shifted from other portions. It should be noted that, although this may lead to a local dimmed area at the fringe (as shown by the hatched portion inFIG. 2D), the fringe area is not used for projection due to the restriction imposed by the étendue conservation law, and therefore will not impact the overall performance.

The second embodiment of this invention is depicted inFIG. 3A, in which the inventive concept of the first embodiment is used with two lighting devices. As illustrated inFIG. 3B, the reflector31comprises two concave reflecting surfaces of a particular curvature, which correspond to lighting devices33,34respectively. Specifically, the reflector31comprises a first reflecting structure311and a second reflecting structure313. The first reflecting structure311has two reflecting surfaces adjacently disposed facing the same direction. The second reflecting structure311is locally formed outwards on the first reflecting structure311, and also has two concave reflecting surfaces adjacently disposed facing the same direction. The reflecting surfaces of the first reflecting structure311and second reflecting structures313should have the same focus point as that of the first reflecting structure311. The reflecting surfaces of the first reflecting structure311and of the second reflecting structure313are separated a certain distance from each other, and may be either parallel or unparallel to each other. The details of which will not be further described in detail herein. As depicted in this figure, the second reflecting structure313may be shaped like a strip and arranged in the center of the first reflecting structure311. This strip-like shape of the second reflecting structure313is only intended to illustrate rather than to limit the shape thereof.

After being reflected by the first reflecting structure311and the second reflecting structure313, the respective portions of light generated from the lighting devices33,34will shift on the projection surface to compensate for the centrally dimmed area. Thereafter, the conditioned light will be gathered into a light integration rod39, where the light is uniformed for use in subsequent optical components.

The third embodiment of this invention is associated with four lighting devices, as depicted inFIG. 4. A reflector41, which is similar to that of the second embodiment in structure, comprises two concave reflecting structures of a particular curvature, i.e. a first reflecting structure411and a second reflecting structure413. The second reflecting structure413is locally disposed on the first reflecting structure411and has the same focus point as the first reflecting structure411. The reflecting structures are spaced a certain distance from each other and may either be parallel or unparallel to each other.

Light generated from the lighting devices43,44are guided by a reflecting prism47to project onto the reflector41. Similarly, light generated from the lighting devices45,46are guided by the reflecting prism48to project onto the reflector41. After being reflected by the first reflecting structure411and the second reflecting structure413, light in the centrally dimmed area is eliminated, and by means of the second reflecting structure413, a second portion of light is shifted to project onto the dim area formed by the first portion to at least compensate for the centrally dimmed area. Thereafter, the conditioned light will be gathered into a light integration rod49, where the light is uniformed for use in subsequent optical components.

The reflector disclosed in this invention may also be applied to a parabolic lighting device that emits parallel light to constitute a retro-reflect system. The fourth embodiment of this invention is depicted inFIG. 5A, where a reflector51is associated with two parabolic lighting devices53,54emitting parallel light. The reflector51comprises a first reflecting structure511and a second reflecting structure513, which have a first reflecting surface and a second reflecting surface respectively for projecting the light generated from the lighting devices53,54to a bright area on the projection surface.FIG. 5Billustrates the perspective view of the reflector51. In this embodiment, both the first and second reflecting surfaces are flat surfaces. More specifically, the first reflecting structure511may be a triangular prism with two inclined planes, which have an angle, included therebetween and define the first reflecting surface. The second reflecting structure513has two recesses55locally disposed on the first reflecting surface of the first reflecting structure511. The bottom surfaces of the recesses55are recessed a certain distance from the first reflecting surface to define the second reflecting surface.

As shown inFIG. 5A, the two lighting devices53,54disposed opposite from each other can define a space therebetween, through which light emitted from both lighting devices53,54propagates before being projected outside by the reflector51. That is, the straight line connecting the two luminous portions531,541of the lighting devices53,54may be used to divide the space into a first half portion56and a second half portion57, in which the first half portion56is proximate to the projection surface (not shown), while the second half portion57is distal from the projection surface. In this embodiment, the reflector51is located inside the second half portion57.

FIGS. 5C and 5Dshow only the left half of the projection surface, while the right half thereof is symmetric and will not be described in detail herein. The first portion of light reflected by the first reflecting surface of the first reflecting structure511propagates along the original path to project a first bright area251and a dim area (as shown by the hatched portion inFIG. 5C). The dim area may be divided into a first dim portion253and a second dim portion255, wherein the first dim portion253may be defined at the center of the first bright area251, and at least covers the conventional centrally dimmed area. The second dim portion255is substantially located between the first dim portion253and a border of the bright area251. With the structure of this embodiment, light in the conventional centrally dimmed area is eliminated and is compensated for the second portion of light after shift.

On the other hand, the second portion of light reflected by the second reflecting surface of the second reflecting structure513will travel on an altered path. Due to the second reflecting structure513of this embodiment, light traveling along the light path L1, L2as shown inFIG. 5Awill be reflected with a delay, following the light path L1′, L2′ instead. Therefore, when the second portion of light is projected onto the projection surface, the second bright area257shown inFIG. 5Dwill partially cover the dim area, and preferably cover the first dim portion253and a part of the second dim portion255. Likewise, a symmetric result will occur in the right half of the projection surface to completely cover the area of the conventional dimmed area.

Similarly, although this approach may lead to a local dim area at the fringe (as shown by the hatched portion inFIG. 5D), in consideration of the restriction imposed by the étendue conservation law on the projection system, such the fringe area will not be used for projection and therefore will not impact the overall performance.

Due to the “retro-reflection” phenomenon, it should be further noted that the light propagating in the first half portion56of the space will first be projected into the opposite lighting device where it is subjected to an internal reflection, then projected towards the second half portion57, and finally projected onto the projection surface, as shown by the light path L3inFIG. 5A. The output light may further propagate through a light gathering device, a light integration rod (not shown) or the like to be gathered and uniformed therein for use in other subsequent optical components.

The fifth embodiment of this invention does not utilize a retro-reflect system, as depicted inFIGS. 6A and 6B. In this embodiment, a reflector61and two oppositely disposed lighting devices63,64are included. The lighting devices63,64have luminous portions631,641respectively. Likewise, for convenience of description, a straight line connecting the two luminous portions631,641may be defined to divide the space between the lighting devices63,64into a first half portion66proximate to the projection surface (not shown) and a second half portion67distal from the projection surface.

The reflector61comprises a first reflecting structure611and a second reflecting structure613for projecting the light emitted from the lighting devices63,64onto the projection surface to form a bright area. The first reflecting structure611may be a triangular prism consisting of two inclined planes with an angle between them to define the first reflecting surface. The second reflecting structure613comprises two protrusions65disposed on the first reflecting surface of the first reflecting structure611respectively. In this embodiment, the protrusions65are formed inside the first half portion66, and the top surface of the protrusions65defines the second reflecting surface.

With the protrusions65of the second reflecting structure613, the first portion of light reflected by the first reflecting surface of the first reflecting structure611still travels along the original path, as shown by the light path L4inFIG. 6A. As shown inFIG. 6C, the first portion of light will form a first bright area251, a first dim portion253and a second dim portion255on the projection surface. On the other hand, the second portion of light reflected by the second reflecting surface of the second reflecting structure613would travel along another path, as shown inFIG. 6A. Specifically, the light as shown along the light paths L5, L6will be reflected in advance and travel along the light paths L5′, L6′ instead. Therefore, when the light is finally projected onto the projection surface, a local shift of the bright area will occur.

In other words, the second bright area257generated by the second portion of light passing through the second reflecting structure613will compensate for the local dim area (i.e. the first dim portion253and a portion of the second dim portion255) caused by the first portion of light. Likewise, a similar result will occur in the right half of the projection surface, thereby completely compensating for the conventional centrally dimmed area. Further, because some diffusions tend to occur after light is projected; an intersection area will be observed between the projection surfaces depicted inFIG. 6CandFIG. 6D. Conceivably, such diffusion may also serve to compensate for the dim areas on the fringe.

The output light may further be gathered and uniformed by a light gathering device, a light integration rod (not shown) or the like for subsequent use in other optical components.

In accordance with the disclosure of this invention, to compensate for the centrally dimmed area, a shift of light is intentionally introduced. Consequently, a local fringe dim area may be formed between the shifting area and a fringe of the projection surface. However, in consideration of the restriction imposed by the étendue conservation law, such a fringe area will not be used for other optical components in practice and therefore will not impact the overall performance.

It follows from the above description that, this invention introduces a local shift of the reflected light by making a local variation to the reflector, thereby to compensate for the centrally dimmed area with a portion of the bright area, thus, achieving a better imaging quality.