Patent Publication Number: US-2023134505-A1

Title: Illumination system, projection device, and projection control method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of China application serial no. 202111297969.6 filed on Nov. 4, 2021. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to an optical system, an optical device including the optical system, and a control method, and more particularly to an illumination system, a projection device, and a projection control method. 
     Description of Related Art 
     In recent years, a projection device based on a solid-state light source such as a light-emitting diode (LED) and a laser diode has gradually earned a place in the market. An existing projection device uses an independent light source of a light-emitting diode with three primary colors as the source of the illumination light beams thereof, and these illumination light beams are then modulated by a light valve to project image light beams to the outside. 
     However, because the current light source efficiency of green light-emitting diodes is insufficient, when there is a need for higher brightness, blue light-emitting diodes are used to excite yellow-green phosphors to obtain higher-efficiency green light, and the blue light-emitting diodes and the yellow-green phosphors are together used as another projection device model of green light source. However, the relative spectral green purity of the green light generated by excitation is not pure enough, thus causing the issue that the color point of the white light formed by mixing light at the end has a yellowish color shift. As a result, the color gamut of the resulting illumination light beam is smaller, and the color gamut requirements of the display market may not be met. 
     The information disclosed in this Background section is only for enhancement of understanding of the background of the described technology and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Further, the information disclosed in the Background section does not mean that one or more problems to be resolved by one or more embodiments of the invention was acknowledged by a person of ordinary skill in the art. 
     SUMMARY OF THE INVENTION 
     The invention provides an illumination system and a projection device that have good reliability and produce an output light beam with good color performance. 
     The invention provides a projection control method that may readily adjust an illumination light beam and produce a final output image light beam with good color performance. 
     Other objects and advantages of the invention may be further understood from the technical features disclosed in the invention. 
     In order to achieve one or part or all of the above objectives or other objectives, an embodiment of the invention provides an illumination system. The illumination system includes a first light-emitting unit, a second light-emitting unit, a third light-emitting unit, a first dichroic element, a second dichroic element, and a control unit. The first light-emitting unit includes a first light-emitting element and a second light-emitting element. The first light-emitting element provides a first sub-light beam, and the second light-emitting element provides a second sub-light beam. A main light emission wavelength range of the first sub-light beam falls within a main light emission wavelength range of the second sub-light beam, and the main light emission wavelength range of the second sub-light beam is greater than the main light emission wavelength range of the first sub-light beam. The second light-emitting unit is configured to provide a second light beam. The third light-emitting unit is configured to provide a third light beam. The first dichroic element is located on a transmission path of the second light beam and the third light beam. The second dichroic element is located on a transmission path of the first sub-light beam, the second sub-light beam, the second light beam, and the third light beam. The second light beam is transmitted to the second dichroic element after being reflected by the first dichroic element, the third light beam is transmitted to the second dichroic element after passing through the first dichroic element. The second light beam and the third light beam are reflected by the second dichroic element to form a portion of an illumination light beam, and at least one of the first sub-light beam and the second sub-light beam is reflected by the second dichroic element or passes through the second dichroic element to form another portion of the illumination light beam. The control unit is electrically connected to the first light-emitting unit and configured to switch the illumination system between a high-performance mode and a high-chroma mode. When the illumination system is in the high-performance mode, the control unit controls a current ratio of the second light-emitting element to be greater than a current ratio of the first light-emitting element, and when the illumination system is in the high-chroma mode, the control unit controls the current ratio of the second light-emitting element to be less than the current ratio of the first light-emitting element. 
     In order to achieve one or part of or all of the above objectives or other objectives, an embodiment of the invention provides a projection device. The projection device includes the illumination system above, at least one light valve, and a projection lens. The light valve is located on a transmission path of an illumination light beam and is adapted to convert the illumination light beam into an image light beam. The projection lens is located on a transmission path of the image light beam, and is adapted to project the image light beam out of the projection device. 
     In order to achieve one or part of or all of the above objectives or other objectives, an embodiment of the invention provides a projection control method. The projection control method is configured to switch a projection device between a high-performance mode and a high-chroma mode, wherein the projection device includes a first light-emitting unit, a second light-emitting unit, a third light-emitting unit, a first dichroic element, a second dichroic element, and a control unit, the first light-emitting unit includes a first light-emitting element and a second light-emitting element, the first light-emitting element provides a first sub-light beam, the second light-emitting element provides a second sub-light beam, a main light emission wavelength range of the first sub-light beam falls within a main light emission wavelength range of the second sub-light beam, the main light emission wavelength range of the second sub-light beam is greater than the main light emission wavelength range of the first sub-light beam, the second light-emitting unit is configured to provide a second light beam, the third light-emitting unit is configured to provide a third light beam, the first dichroic element is located on a transmission path of the second light beam and the third light beam, and the second dichroic element is located on a transmission path of the first sub-light beam, the second sub-light beam, the second light beam, and the third light beam. The second light beam is transmitted to the second dichroic element after being reflected by the first dichroic element, the third light beam is transmitted to the second dichroic element after passing through the first dichroic element, the second light beam and the third light beam are reflected by the second dichroic element to form a portion of an illumination light beam, at least one of the first sub-light beam and the second sub-light beam is reflected by the second dichroic element or passes through the second dichroic element to form another portion of the illumination light beam, and the projection control method includes the following steps. When the projection device is in the high-performance mode, a current ratio of the second light-emitting element is controlled to be greater than a current ratio of the first light-emitting element. When the projection device is in the high-chroma mode, the current ratio of the second light-emitting element is controlled to be less than the current ratio of the first light-emitting element. 
     Based on the above, the embodiments of the invention have at least one of the following advantages or efficacies. In an embodiment of the invention, the illumination system and the projection device may control the different current ratios of the first light-emitting element and the second light-emitting element via the control unit, so as to adjust the composition of the green light portion in the illumination light beam. In turn, the illumination system and the projection device may meet the requirements of both efficacy and color performance. Moreover, the projection control method of the present embodiment may readily switch the illumination system and the projection device between the high-performance mode and the high-chroma mode. Therefore, the efficacy and color performance requirements of the illumination system and the projection device may both be met. 
     Other objectives, features and advantages of the present invention will be further understood from the further technological features disclosed by the embodiments of the present invention wherein there are shown and described preferred embodiments of this invention, simply by way of illustration of modes best suited to carry out the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG.  1    is a block diagram of a projection device of an embodiment of the invention. 
         FIG.  2 A  is a schematic diagram of the optical path architecture of an illumination system of  FIG.  1   . 
         FIG.  2 B  is a schematic front view of the first light-emitting element and the second light-emitting element of  FIG.  2 A . 
         FIG.  2 C  is a graph of the light emission wavelength spectrum and brightness of the first sub-light beam and the second sub-light beam of  FIG.  2 A . 
         FIG.  3    is a flowchart of a projection control method of an embodiment of the invention. 
         FIG.  4 A  is a schematic diagram of the optical path architecture of another illumination system of  FIG.  1   . 
         FIG.  4 B  and  FIG.  4 C  are respectively schematic front views of the first light-emitting element and the second light-emitting element of  FIG.  4 A . 
         FIG.  5    is a schematic diagram of the optical path architecture of yet another illumination system of  FIG.  1   . 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top”, “bottom”, “front”, “back”, etc., is used with reference to the orientation of the Figure(s) being described. The components of the invention may be positioned in a number of different orientations. As such, the directional terminology is used for purposes of illustration and is in no way limiting. On the other hand, the drawings are only schematic and the sizes of components may be exaggerated for clarity. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the invention. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including”, “comprising”, or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms “connected,” “coupled,” and “mounted” and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings. Similarly, the terms “facing,” “faces” and variations thereof herein are used broadly and encompass direct and indirect facing, and “adjacent to” and variations thereof herein are used broadly and encompass directly and indirectly “adjacent to”. Therefore, the description of “A” component facing “B” component herein may contain the situations that “A” component directly faces “B” component or one or more additional components are between “A” component and “B” component. Also, the description of “A” component “adjacent to” “B” component herein may contain the situations that “A” component is directly “adjacent to” “B” component or one or more additional components are between “A” component and “B” component. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive. 
       FIG.  1    is a block diagram of a projection device of an embodiment of the invention.  FIG.  2 A  is a schematic diagram of the optical path architecture of an illumination system of  FIG.  1   .  FIG.  2 B  is a schematic front view of the first light-emitting element and the second light-emitting element of  FIG.  2 A .  FIG.  2 C  is a graph of the light emission wavelength spectrum and brightness of the first sub-light beam and the second sub-light beam of  FIG.  2 A . Referring to  FIG.  1   , in the embodiment, a projection device  200  includes an illumination system  100 , at least one light valve  210 , and a projection lens  220 . The light valve  210  is located on the transmission path of an illumination light beam  70  and is adapted to convert the illumination light beam  70  into image light beam  80 . The projection lens is located on the transmission path of the image light beam  80 , and is adapted to project the image light beam  80  out of the projection device. In the embodiment, the number of the light valve  210  is one, but the invention is not limited thereto. In other embodiments, the number of the light valve  210  may also be a plurality. When the number of the light valve  210  is three, the illumination light beam may be output to the light valves  210  at the same time. When the number of the light valve  210  is less than three, the illumination light beam may sequentially output a portion of different colors of light in a sequential rotation output manner. Moreover, in the embodiment, the light valve  210  may be a digital micro-mirror device (DMD) or a liquid-crystal-on-silicon (LCOS) panel. However, in other embodiments, the light valve  210  may also be a transmissive liquid-crystal panel or other light beam modulators. 
     Specifically, as shown in  FIG.  1    and  FIG.  2 A , in the embodiment, the illumination system  100  is adapted to emit the illumination light beam  70 . The illumination system  100  includes a first light-emitting unit  110 , a second light-emitting unit  120 , a third light-emitting unit  130 , a first dichroic element  140 , a second dichroic element  150 , and a control unit  160 . Moreover, an optical lens group CL may respectively be disposed on the respective light-emitting beam transmission paths of the first light-emitting unit  110 , the second light-emitting unit  120 , and the third light-emitting unit  130 , so that the light beams emitted by the first light-emitting unit  110 , the second light-emitting unit  120 , and the third light-emitting unit  130  are collimated. 
     Please refer further to  FIG.  2 A  and  FIG.  2 B , in the embodiment, the first light-emitting unit  110  includes a first light-emitting element  111  and a second light-emitting element  112 , and the first light-emitting element  111  and the second light-emitting element  112  are packaged on a same substrate SB. The first light-emitting element  111  and the second light-emitting element  112  respectively provide a first sub-light beam  51 G and a second sub-light beam  52 G. Moreover, the second light-emitting unit  120  and the third light-emitting unit  130  are respectively configured to provide a second light beam  50 R and a third light beam  50 B. In the embodiment, the first light-emitting element  111  is a green light-emitting diode, the second light-emitting unit  120  is a red light-emitting diode, and the third light-emitting unit  130  is a blue light-emitting diode. In other words, in the embodiment, the first sub-light beam  51 G is pure green light, the second light beam  50 R is pure red light, and the third light beam  50 B is pure blue light. 
     Moreover, as shown in  FIG.  2 B , in the embodiment, the second light-emitting element  112  is a structure in which the blue light-emitting diode is covered with a yellow-green phosphor. In this way, when the second light-emitting element  112  emits light, the yellow-green phosphor may be excited by the pure blue light to form the second sub-light beam  52 G of yellow-green light. In addition, the second light-emitting element  112  of this structure has higher optical efficiency than the first light-emitting element  111 , but has a relatively broader light emission spectrum. More specifically, in the embodiment, as shown in  FIG.  2 C , the main light emission wavelength range of the first sub-light beam  51 G falls within the main light emission wavelength range of the second sub-light beam  52 G, the main light emission wavelength range of the second sub-light beam  52 G is greater than the main light emission wavelength range of the first sub-light beam  51 G, and the main emission wavelength range is, for example, the FWHM range of the main light emission wavelength brightness (peak value), but is not limited thereto. The main light emission wavelength of the first sub-light beam  51 G is, for example, greater than the main light emission wavelength of the second sub-light beam  52 G. For example, in the embodiment, the main light emission wavelength range of the first sub-light beam  51 G is between 570 nm and 585 nm (the main light emission wavelength range is 15 nm), and the main light emission wavelength range of the second sub-light beam  52 G is between 490 nm and 590 nm (the main light emission wavelength range is 100 nm). 
     In addition, as shown in  FIG.  2 A , in the embodiment, the first dichroic element  140  is located on the transmission path of the second light beam  50 R and the third light beam  50 B. The second dichroic element  150  is located on the transmission path of the first sub-light beam  51 G, the second sub-light beam  52 G, the second light beam  50 R, and the third light beam  50 B. The second light beam  50 R and the third light beam  50 B are transmitted from the first dichroic element  140  to the second dichroic element  150 , and the first dichroic element  140  is not on the transmission path of the first sub-light beam  51 G and the second sub-light beam  52 G. The second light-emitting unit  120  and the third light-emitting unit  130  are respectively located at two sides of the first dichroic element  140  (the light beams from the second light-emitting unit  120  and the third light-emitting unit  130  are respectively incident on different side surfaces of the first dichroic element  140 ). The first dichroic element  140  and the first light-emitting unit  110  are respectively located at two sides of the second dichroic element  150 . Moreover, in the embodiment, the first dichroic element  140  is, for example, a dichroic mirror reflecting red light and letting light beams of other colors (such as blue light) pass through (in other embodiments, the first dichroic element  140  may be a dichroic mirror reflecting blue light and letting light beams of other colors pass through), and the second dichroic element  150  is, for example, a dichroic mirror reflecting red light and blue light and letting light beams of other colors (such as yellow-green light) pass through. In this way, as shown in  FIG.  2 A , the first sub-light beam  51 G and the second sub-light beam  52 G are formed into a first light beam  50 G and transmitted to the second dichroic element  150 , the second light beam  50 R is transmitted to the second dichroic element  150  after being reflected by the first dichroic element  140 , the third light beam  50 B is transmitted to the second dichroic element  150  after passing through the first dichroic element  140 , and the second dichroic element  150  reflects the second light beam  50 R and the third light beam  50 B to form the red and blue portions of the illumination light beam  70  and lets the first light beam  50 G pass through to form the green portion of the illumination light beam  70 . In other words, the illumination light beam  70  includes at least one of the first light beam  50 G, the second light beam  50 R, and the third light beam  50 B. Moreover, as shown in  FIG.  2 A , in the embodiment, the exit directions of the first light beam  50 G, the second light beam  50 R, and the third light beam  50 B leaving the illumination system  100  are the same, and the first light beam  50 G, the second light beam  50 R, and the third light beam  50 B leave along a first direction Dl. For example, in an embodiment not shown, the illumination system  100  may further include a light-homogenizing element. The incident directions of the first light beam  50 G, the second light beam  50 R, and the third light beam  50 B transmitted to the light-incident surface of the light-homogenizing element are the same (incident angles are substantially the same), and after the light passing through the light-homogenizing element is homogenized, the light travels toward the same direction from the light exit surface of the light-homogenizing element to leaves the illumination system  100 . 
     In the embodiment, since the illumination system  100  may form the three primary colors of the illumination light beam  70  via the first sub-light beam  51 G and the second sub-light beam  52 G of the first light beam  50 G, the second light beam  50 R, and the third light beam  50 B, there is no need to provide a color filter module. In other words, the main light emission wavelength range of the second sub-light beam  52 G transmitted to the second dichroic element  150  is substantially the same as the main light emission wavelength range of the second sub-light beam  52 G transmitted to the at least one light valve. Here, “substantially the same” means that the difference in the main light emission wavelength range is less than  5 %. 
     Moreover, as shown in  FIG.  2 A , in the embodiment, the illumination system  100  may optionally be provided with an auxiliary light-emitting unit  170 . The auxiliary light-emitting unit  170  is, for example, a blue light-emitting diode emitting short-wavelength blue light, and may be configured to provide an auxiliary light beam AL. The auxiliary light-emitting unit  170  and the first light-emitting unit  110  are located at the same side of the second dichroic element  150  (the light beams from the auxiliary light-emitting unit  170  and the first light-emitting unit  110  are respectively incident on the same side surface of the second dichroic element  150 ) and face the first dichroic element  140  and the second dichroic element  150 . Moreover, the auxiliary light beam AL is transmitted to the second light-emitting element  112  of the first light-emitting unit  110  after being reflected by the second dichroic element  150 . In the embodiment, the auxiliary light beam AL provided by the auxiliary light-emitting unit  170  may make the yellow-green phosphor of the second light-emitting element  112  be excited by more blue light, thereby increasing the light quantity of the second sub-light beam  52 G. That is, the second sub-light beam  52 G may include a light beam formed by the blue light-emitting diode of the second light-emitting element  112  and the auxiliary light-emitting unit  170  irradiating the yellow-green phosphor of the second light-emitting element  112 . 
     It should be mentioned that, in the embodiment above, although the second dichroic element  150  is exemplified by a dichroic mirror reflecting red light and blue light and letting yellow-green light beam pass through, the invention is not limited thereto. In other embodiments, the second dichroic element  150  may also be a dichroic mirror reflecting yellow-green light and letting red and blue light beams pass through. In the embodiment, the exit directions of the first light beam  50 G, the second light beam  50 R, and the third light beam  50 B leaving the illumination system  100  are also the same, but leave along a second direction D 2 . Moreover, since the second dichroic element  150  is configured to reflect one of the auxiliary light beam AL and the first light beam  50 G and let the other of the auxiliary light beam AL and the first light beam  50 G pass through; in the embodiment, the auxiliary light-emitting unit  170  and the first light-emitting unit  110  are located at two sides of the second dichroic element  150 , and the auxiliary light beam AL is transmitted to the second light-emitting element  112  of the first light-emitting unit  110  after passing through the second dichroic element  150 . Those having ordinary skill in the art may make appropriate changes to the optical path configuration thereof after referring to the invention to achieve similar effects and advantages as the embodiment of  FIG.  2 A , which should still fall within the scope of the invention, and are not repeated herein. 
     In the following, how the illumination system  100  forms various colors of the illumination light beam  70  in different modes is further explained with reference to  FIG.  1   ,  FIG.  2 A ,  FIG.  2 B , and  FIG.  3   . 
     Specifically, in the embodiment, the illumination system  100  has a high-performance mode and a high-chroma mode, and as shown in  FIG.  2 A , the control unit  160  is electrically connected to the first light-emitting unit  110  and configured to switch the illumination system  100  between the high-performance mode and the high-chroma mode. For example, the illumination system  100  and the projection device  200  shown in  FIG.  1    and  FIG.  2 A  may be configured to execute the projection control method of  FIG.  3   , so that when the illumination system  100  is in the high-performance mode, the control unit  160  controls the current ratio of the second light-emitting element  112  to be greater than the current ratio of the first light-emitting element  111 , and when the illumination system  100  is in the high-chroma mode, the control unit  160  controls the current ratio of the second light-emitting element  112  to be less than the current ratio of the first light-emitting element  111 , and the composition of the green portion in the illumination light beam  70  may be adjusted, so as to meet the requirements of both efficacy and color performance thereof. Here, the meaning of the current ratio is the ratio of the current passing through the first light-emitting element  111  (or the second light-emitting element  112 ) in the first light-emitting unit  110  to the overall current (that is, the total current passing through the first light-emitting unit  110 ). 
     In the invention, when the projection device  200  is in one of the high-performance mode and the high-chroma mode, whether the projection device  200  needs to be switched to the other of the high-performance mode and the high-chroma mode is determined. If yes, the projection device  200  is switched to the other of the high-performance mode and the high-chroma mode, and if not, the projection device  200  is kept in the original mode. For example, as shown in  FIG.  3   , when the projection device  200  is preset in the high-performance mode (the projection device  200  is in the high-performance mode), the control unit  160  may control the current ratio of the second light-emitting element  112  to be 90% to 95%, and control the current ratio of the first light-emitting element  111  to be 5% to 10%. At this time, since the current ratio of the second light-emitting element  112  is higher, the second sub-light beam  52 G provided by the second light-emitting element  112  with higher light efficiency may provide most of the green light. In this way, the first light-emitting unit  110  may have a relatively higher light efficiency, but the relative spectral purity of the resulting first light beam  50 G is lower, and the illumination light beam  70  formed thereby has a smaller color gamut, but the requirements of high brightness may be met. 
     Next, when the user determines that the use situation requires the projection device  200  to have a higher color performance (for example, the user acts to switch the mode), step S 110  may be performed to switch the projection device  200  to the high-chroma mode. Specifically, when the projection device  200  is in the high-chroma mode, the control unit  160  controls the current ratio of the second light-emitting element  112  to be 5% to 10%, and controls the current ratio of the first light-emitting element  111  to be 90% to 95%. At this time, since the current ratio of the first light-emitting element  111  is higher, the first sub-light beam  51 G with higher spectral purity may be used as most of the green light. The resulting first light beam  50 G has a higher relative spectral purity, and may form an illumination light beam  70  with a larger color gamut to meet the requirements of a wide color gamut. Conversely, when the user determines that the use situation does not require the projection device  200  to have a higher color performance (for example, the user does not act to switch the mode), step S 120  may be performed to keep the projection device  200  in the high-performance mode. Moreover, as shown in  FIG.  3   , when the projection device  200  is in the high-chroma mode, the user may also determine whether the projection device  200  needs to have a higher brightness performance. When the user determines that the projection device  200  needs to have a higher brightness performance, step S 130  may be performed to switch the projection device  200  to the high-performance mode. When the user determines that the projection device  200  does not need to have a higher brightness performance, step S 140  may be performed to keep the projection device  200  in the high-chroma mode. 
     In this way, the illumination system  100  and the projection device  200  may control the different current ratios of the first light-emitting element  111  and the second light-emitting element  112  via the control unit  160 , so as to adjust the composition of the green light portion in the illumination light beam  70 . In turn, the illumination system  100  and the projection device  200  may meet the requirements of both efficacy and color performance. Moreover, the projection control method of the embodiment may readily switch the illumination system  100  and the projection device  200  between the high-performance mode and the high-chroma mode. Therefore, the efficacy and color performance requirements of the illumination system  100  and the projection device  200  may both be met. It should be mentioned that, in other embodiments of the invention, the steps for the user to determine the use situation may be executed by the control unit  160 . For example, the control unit  160  may automatically switch (or keep) to the high-chroma mode or the high-performance mode by comprehensively determining factors such as environmental brightness, projection content (video or presentation), and/or user settings, etc., thus further improving the convenience of using the projection device. 
       FIG.  4 A  is a schematic diagram of the optical path architecture of another illumination system of  FIG.  1   .  FIG.  4 B  and  FIG.  4 C  are respectively schematic front views of the first light-emitting element and the second light-emitting element of  FIG.  4 A . Please refer to  FIG.  4 A  to  FIG.  4 C . An illumination system  400  of  FIG.  4 A  is similar to the illumination system  100  of  FIG.  2 A , and the differences are as follows. In the embodiment, the first light-emitting element  411  and the second light-emitting element  412  of the first light-emitting unit  410  are packaged on different substrates SB 1  and SB 2 , and the transmission directions of the first sub-light beam  51 G and the second sub-light beam  52 G to the second dichroic element  150  are the same. In other words, in the embodiment, the first light-emitting element  411  and the second light-emitting element  412  of the first light-emitting unit  410  may be disposed side by side in a third direction D 3 , for example. In this way, the light-receiving area of the first sub-light beam  51 G and the second sub-light beam  52 G is increased, and the optical efficiency thereof may be further improved. In addition, when the auxiliary light-emitting unit  170  is provided, the optical paths of the auxiliary light-emitting unit  170  and the second light-emitting element  412  need to be aligned, so that the auxiliary light beam AL is transmitted to the second light-emitting element  412 . 
     In this way, the illumination system  400  may also be configured to execute the projection control method of  FIG.  3   . Moreover, the control unit  160  is configured to control the ratios of different currents passing through the first light-emitting element  411  and the second light-emitting element  412 , so that the composition of the green light in the illumination light beam  70  may be adjusted, so that the illumination system  400  may meet the requirements of efficacy and color performance, and may achieve similar effects and advantages to the above illumination system  100 , which are not repeated herein. Moreover, when the illumination system  400  is applied to the projection device  200 , the projection device  200  may also achieve the above effects and advantages, which are not repeated herein. 
       FIG.  5    is a schematic diagram of the optical path architecture of yet another illumination system of  FIG.  1   . Please refer to  FIG.  5   . An illumination system  500  of  FIG.  5    is similar to the illumination system  400  of  FIG.  4 A , and the differences are as follows. In the embodiment, the second dichroic element  550  is an X-type dichroic mirror, and includes a first sub-dichroic element  551  and a second sub-dichroic element  552  not disposed side-by-side (for example, perpendicular and intersected in the middle of the element), wherein the first sub-dichroic element  551  has the same optical function and arrangement position as the second dichroic element  150  of  FIG.  2 A , and may reflect the second light beam  50 R and the third light beam  50 B and let the first light beam  50 G pass through. 
     Moreover, as shown in  FIG.  5   , in the embodiment, the first sub-light beam  51 G of the first light-emitting element  411  and the second sub-light beam  52 G of the second light-emitting element  412  of the first light-emitting unit  410  are incident on the second dichroic element  550  (the second sub-dichroic element  552 ) in different transmission directions, and the second sub-dichroic element  552  of the second dichroic element  550  reflects one of the first sub-light beam  51 G and the second sub-light beam  52 G and lets the other of the first sub-light beam  51 G and the second sub-light beam  52 G pass through. More specifically, in the embodiment, the first light-emitting element  411  and the second light-emitting element  412  are located at different sides of the second sub-dichroic element  552  of the second dichroic element  550 , and are for example, respectively located at two sides of the normal line of the surface of the first sub-dichroic element  551  of the second dichroic element  550  facing the first light-emitting element  411  and the second light-emitting element  412  (the first light-emitting element  411  and the second light-emitting element  412  are located at the same side of the first sub-dichroic element  551  of the second dichroic element  550 ). In this way, the first sub-light beam  51 G and the second sub-light beam  52 G may be incident on the second sub-dichroic element  552  of the second dichroic element  550  along the opposite directions of the first direction D 1  and the second direction D 2 , respectively. Moreover, in the embodiment, the second sub-dichroic element  552  of the second dichroic element  550  reflects the first sub-light beam  51 G and lets the second sub-light beam  52 G pass through. 
     Moreover, it should be mentioned that, due to the limitation of the above optical path configuration, in the embodiment, the auxiliary light-emitting unit  170  is not provided. Therefore, the performance is slightly lower than the model of the illumination system  100  including the auxiliary light-emitting unit  170 , but the illumination system  500  may still be configured to implement the projection control method of  FIG.  3   . Moreover, the different current ratios of the first light-emitting element  411  and the second light-emitting element  412  are controlled via the control unit  160 , so that the composition of the green light portion in the illumination light beam  70  may be adjusted. Therefore, the illumination system  500  may meet the requirements of both efficacy and color performance, and may achieve similar effects and advantages to the illumination system  400 , which are not repeated herein. Moreover, when the illumination system  500  is applied to the projection device  200 , the projection device  200  may also achieve the above effects and advantages, which are not repeated herein. 
     Based on the above, the embodiments of the invention have at least one of the following advantages or efficacies. In an embodiment of the invention, the illumination system and the projection device may control the different current ratios of the first light-emitting element and the second light-emitting element via the control unit, so as to adjust the composition of the green light portion in the illumination light beam. In turn, the illumination system and the projection device may meet the requirements of both efficacy and color performance. Moreover, the projection control method of the embodiment may readily switch the illumination system and the projection device between the high-performance mode and the high-chroma mode. Therefore, the efficacy and color performance requirements of the illumination system and the projection device may both be met. 
     The foregoing description of the preferred embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form or to exemplary embodiments disclosed. Accordingly, the foregoing description should be regarded as illustrative rather than restrictive. Obviously, many modifications and variations will be apparent to practitioners skilled in this art. The embodiments are chosen and described in order to best explain the principles of the invention and its best mode practical application, thereby to enable persons skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use or implementation contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents in which all terms are meant in their broadest reasonable sense unless otherwise indicated. Therefore, the term “the invention”, “the present invention” or the like does not necessarily limit the claim scope to a specific embodiment, and the reference to particularly preferred exemplary embodiments of the invention does not imply a limitation on the invention, and no such limitation is to be inferred. The invention is limited only by the spirit and scope of the appended claims. Moreover, these claims may refer to use “first”, “second”, etc. following with noun or element. Such terms should be understood as a nomenclature and should not be construed as giving the limitation on the number of the elements modified by such nomenclature unless specific number has been given. The abstract of the disclosure is provided to comply with the rules requiring an abstract, which will allow a searcher to quickly ascertain the subject matter of the technical disclosure of any patent issued from this disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Any advantages and benefits described may not apply to all embodiments of the invention. It should be appreciated that variations may be made in the embodiments described by persons skilled in the art without departing from the scope of the present invention as defined by the following claims. Moreover, no element and component in the present disclosure is intended to be dedicated to the public regardless of whether the element or component is explicitly recited in the following claims.