Abstract:
The illumination apparatus includes a first light source and a second light source configured to generate light in wavelength bands required for at least two illumination modes; a dichroic mirror configured to transmit light in a predetermined band from the first light source, to reflect light from the second light source outside the predetermined band in the direction of the optical axis of light from the first light source, and to combine the light from the first light source and the light from the second light source; and a control unit configured to control the illumination states of the first light source and the second light source.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an illumination apparatus and an examination system including the same. 
       BACKGROUND ART 
       [0002]    There is a known illumination apparatus that is provided with a movable filter, which is constituted of a filter having at least two different spectral characteristics, interposed between a white light source and an illuminated area and that moves the filter depending on an illumination mode to mechanically switch the light to be transmitted through the illuminated part, from the white light (for example, refer to PTL 1). 
         [0003]    Another known illumination apparatus has a brightness priority mode and color priority mode and outputs a mode setting signal to electrically switch between the brightness priority mode and the color priority mode (for example, refer to PTL 2). 
         [0004]    Another known illumination apparatus partially replaces main illumination light from a lamp, etc., which is substantially white, with sub-illumination light from a laser light source, etc. and enhances the emission spectrum of the main illumination light with the sub-illumination light to generates illumination light (for example, see PTL 3). 
       CITATION LIST 
     Patent Literature 
     {PTL 1} 
       [0000]    
       
         Japanese Unexamined Patent Application, Publication No. 2001-314370 
       
     
       {PTL 2} 
       [0000]    
       
         Japanese Unexamined Patent Application, Publication No. 2006-349731 
       
     
       {PTL 3} 
       [0000]    
       
         Japanese Unexamined Patent Application, Publication No. 2002-296680 
       
     
       SUMMARY OF INVENTION 
     Solution to Problem 
       [0008]    A first aspect of the present invention is an illumination apparatus configured to illuminate an illumination area in a plurality of illumination modes constituted of light in different predetermined bands, having bands in which a first band required by one illumination mode of the plurality of illumination modes is narrower than a second band required by another illumination mode, the apparatus including a first light source configured to emit illumination light in a band substantially the same as the first band; a second light source configured to emit illumination light in at least the second band; a light combining unit configured to transmit light in the first band, among the illumination light emitted from the first light source, in the direction of the illumination area as transmitted light while reflecting light outside the first band, among the illumination light emitted from the second light sources, in the direction of the illumination area as reflected light and to optically combine the transmitted light and the reflected light; an illumination-mode selecting unit configured to select an illumination mode from the plurality of illumination modes; and a control unit configured to control the light intensity of light emitted from the first light source and the second light source on the basis of the selected illumination mode, wherein the one illumination mode is a first illumination mode for lighting only the first light source, and the other illumination mode is a second illumination mode for lighting both the first light source and the second light source. 
         [0009]    A second aspect, which is described below and differs from the first aspect in that the positions of the light sources with respect to the light combining unit differ, may be employed. 
         [0010]    A second aspect of the present invention is an illumination apparatus configured to illuminate an illumination area in a plurality of illumination modes constituted of light in different predetermined bands, having bands in which a first band required by one illumination mode of the plurality of illumination modes is narrower than a second band required by another illumination mode, the apparatus including a first light source configured to emit illumination light in a band substantially the same as the first band; a second light source configured to emit illumination light in at least the second band; a light combining unit configured to reflect light in the first band, among the illumination light emitted from the first light source, in the direction of the illumination area as reflected light while transmitting light outside the first band, among the illumination light emitted from the second light sources, in the direction of the illumination area as transmitted light and to optically combine the transmitted light and the reflected light; an illumination-mode selecting unit configured to select an illumination mode from the plurality of illumination modes; and a control unit configured to control the light intensity of light emitted from the first light source and the second light source on the basis of the selected illumination mode, wherein the one illumination mode is a first illumination mode for lighting only the first light source, and the other illumination mode is a second illumination mode for lighting both the first light source and the second light source. 
         [0011]    A third embodiment of the present invention in examination system including one of the illumination apparatus described above; an irradiation optical system configured to irradiate a subject with light combined at the light combining unit; and a light receiving unit configured to receive light reflected at the subject, wherein the control unit controls the emission light intensity of the first light source and the second light source on the basis of the intensity of the reflected light received by the light receiving unit. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0012]      FIG. 1  is a schematic configuration diagram of an examination system according to embodiments of the present invention. 
           [0013]      FIG. 2  is a schematic configuration diagram of an illumination apparatus according to a first embodiment of the present invention. 
           [0014]      FIG. 3  is a graph illustrating the spectral characteristic of a first light source in  FIG. 2 . 
           [0015]      FIG. 4  is a graph illustrating the spectral characteristic of a second light source in  FIG. 2 . 
           [0016]      FIG. 5  is a graph illustrating the reflection characteristic of a dichroic mirror in  FIG. 2 . 
           [0017]      FIG. 6  illustrates the illumination state of each light source in each illumination mode of the illumination apparatus in  FIG. 2 . 
           [0018]      FIG. 7  is a graph illustrating the spectral characteristic of illumination light emitted from the illumination apparatus in  FIG. 2  in a white light mode. 
           [0019]      FIG. 8  is a graph illustrating the spectral characteristic of illumination light emitted from the illumination apparatus in  FIG. 2  in a special light mode. 
           [0020]      FIG. 9  is a schematic configuration diagram of an illumination apparatus according to a second embodiment of the present invention. 
           [0021]      FIG. 10  is a graph illustrating the spectral characteristic of a first light source in  FIG. 9 . 
           [0022]      FIG. 11  is a graph illustrating the spectral characteristic of a second light source in  FIG. 9 . 
           [0023]      FIG. 12  is a graph illustrating the reflection characteristic of a dichroic mirror in  FIG. 9 . 
           [0024]      FIG. 13  is a diagram illustrating the illumination state of each light source in each illumination mode of the illumination apparatus in  FIG. 9 . 
           [0025]      FIG. 14  is a graph illustrating the spectral characteristic of illumination light emitted from the illumination apparatus in  FIG. 9  in a white light mode. 
           [0026]      FIG. 15  is a graph illustrating the spectral characteristic of illumination light emitted from the illumination apparatus in  FIG. 9  in a special light mode. 
           [0027]      FIG. 16  is a schematic configuration diagram of an illumination apparatus according to a third embodiment of the present invention. 
           [0028]      FIG. 17  is a graph illustrating the spectral characteristic of a first light source in  FIG. 16 . 
           [0029]      FIG. 18  is a graph illustrating the spectral characteristic of a second light source in  FIG. 16 . 
           [0030]      FIG. 19  is a graph illustrating the reflection characteristic of a first dichroic mirror in  FIG. 16 . 
           [0031]      FIG. 20  is a graph illustrating the reflection characteristics of second and third dichroic mirrors in  FIG. 16 . 
           [0032]      FIG. 21  is a graph illustrating the reflection characteristic of a fourth dichroic mirror in  FIG. 16 . 
           [0033]      FIG. 22  is a graph illustrating the spectral characteristic of light traveling along an optical path A in the illumination apparatus in  FIG. 16 . 
           [0034]      FIG. 23  is a graph illustrating the spectral characteristic of light traveling along an optical path B in the illumination apparatus in  FIG. 16 . 
           [0035]      FIG. 24  is a graph illustrating the spectral characteristic of light traveling along an optical path C in the illumination apparatus in  FIG. 16 . 
           [0036]      FIG. 25  is a graph illustrating the spectral characteristic of light traveling along an optical path D in the illumination apparatus in  FIG. 16 . 
           [0037]      FIG. 26  is a graph illustrating the spectral characteristic of illumination light emitted from the illumination apparatus in  FIG. 16  in a white light mode. 
           [0038]      FIG. 27  is a graph illustrating the spectral characteristic of illumination light emitted from the illumination apparatus in  FIG. 16  in a special light mode. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
       [0039]    An illumination apparatus according to a first embodiment of the present invention will be described below with reference to the drawings. 
         [0040]      FIG. 1  is a configuration diagram illustrating, in outline, an examination system  100  including an illumination apparatus according to this embodiment. 
         [0041]    As illustrated in  FIG. 1 , the examination system  100  according to this embodiment includes an illumination apparatus  10  constituted of a light source unit (irradiation optical system)  11 , a light-source driving unit  12 , and an illumination control unit (control unit)  13 ; an image acquisition unit (light receiving unit)  21 ; an image processing unit  22 ; and an image monitor  23 . 
         [0042]    The light source unit  11  has a plurality of light sources and emits illumination light toward a subject S. The detailed configuration of the light source unit  11  will be described below. 
         [0043]    The image acquisition unit  21  is, for example, an image acquisition element, such as a CCD, and detects ight reflected at the subject S. That is, the image acquisition unit  21  functions as light-receiving means for receiving light reflected at the subject S. Moreover, the image acquisition unit  21  acquires an image of the subject S by detecting the light reflected at the subject S and outputting an image acquisition signal to the image processing unit  22 . 
         [0044]    The image processing unit  22  processes the image acquisition signal output from the image acquisition unit  21  to generate an image of the subject S. The image processing unit  22  outputs the generated image of the subject S to the image monitor  23  as an image display signal and outputs the brightness of the image of the subject S to the illumination control unit  13  as a screen brightness signal. 
         [0045]    The image monitor  23  displays the image of the subject S on a monitor screen on the basis of the image display signal output from the image processing unit  22 . 
         [0046]    The illumination control unit  13  receives a screen brightness signal output from the image processing unit  22 , as well as an illumination-mode instruction signal output from the illumination-mode selecting unit  29 , such as, for example, a switch. Here, the illumination-mode instruction signal is a signal that instructs the switching of illumination light to be emitted from the light source unit  11  toward the subject S to, for example, white light or special light. 
         [0047]    The illumination-mode instruction signal is also sent to the image processing unit  22 , where an image may be generated by switching to an image processing method optimal for each illumination mode. For example, in an examination method of forming a clear image of blood vessels by irradiating them with only light near 415 nm and near 540 nm, which are easily absorbed by hemoglobin in blood, reflected light near 415 nm is generated as B (blue) and G (green) channel signals of the displayed image, and reflected light near 540 nm is generated as an R (red) channel signal of the displayed image, and these signals are output to the image monitor  23 . 
         [0048]    The illumination control unit  13  generates a light-source control signal on the basis of the screen brightness signal output from the image processing unit  22  and outputs this signal to the light-source driving unit  12 . Specifically, the illumination control unit  13  calculates the light intensity of the illumination light emitted from the light source unit  11  such that the brightness of the image of the subject S generated by the image processing unit  22  is constant and outputs this to the light-source driving unit  12  as a light-source control signal. Moreover, in response to the selected illumination mode, the illumination control unit  13  outputs to the light-source driving unit  12  a light-source control signal indicating which light source, among the multiple light sources in the light source unit  11 , is to be lit. 
         [0049]    When the brightness of the subject S cannot be set constant by controlling it with the light-source driving unit  12 , the display gain may be set at the image processing unit  22  such that the brightness of the image of the subject S becomes constant when the image of the subject S is displayed on the image monitor  23 . 
         [0050]    The light-source driving unit  12  drives multiple light sources in the light source unit  11  on the basis of the light-source control signal output from the illumination control unit  13 . 
         [0051]    As illustrated in  FIG. 2 , the light source unit  11  includes a light source (first light source)  1  and a light source (second light source)  2 , which are disposed such that optical axes thereof are orthogonal to each other, and a dichroic mirror (light combining unit)  5  disposed at the intersection of the optical axis of the light source  1  and the optical axis of the light source  2 . 
         [0052]    As illustrated in  FIG. 3 , the light source  1  is a light source that emits white light L 1  in a wide wavelength band. 
         [0053]    As illustrated in  FIG. 4 , the light source  2  is a light source that emits light L 2  in a narrow wavelength band, such as a laser beam, and emits light having substantially all components in an extremely limited wavelength band (wavelength band of wavelengths λ 1  to λ 2  illustrated in  FIG. 5 ) compared with the light L 1 . 
         [0054]    As illustrated in  FIG. 5 , the dichroic mirror  5  has a reflection characteristic in which light in the wavelength bands smaller than wavelength λ 1  and larger than or equal to wavelength λ 2  is transmitted, white light in the wavelength band between wavelengths λ 1  to λ 2  is reflected. 
         [0055]    By having such a reflection characteristic, the dichroic mirror  5  transmits light in the wavelength bands smaller than wavelength λ 1  and greater than or equal to λ 2 , among the light L 1  emitted from the light source  1 . Meanwhile, the dichroic mirror  5  reflects light in the wavelength band of wavelengths λ 1  to λ 2 , among the light L 1  emitted from the light source  1 . 
         [0056]    Moreover, the dichroic mirror  5  transmits light in the wavelength bands smaller than wavelength λ 1  and greater than or equal to wavelength λ 2 , among the light L 2  emitted from the light source  2 . Meanwhile, the dichroic mirror  5  reflects, in the direction of the optical axis of the light L 1  emitted from the light source  1 , light in the wavelength band of wavelengths λ 1  to λ 2 , among the light L 2  emitted from the light source  2 . Here, as described above, since the light L 2  has substantially all components in the wavelength band of wavelengths λ 1  to λ 2 , the dichroic mirror  5  reflects substantially all components of the light L 2  in the direction of the optical axis of the light L 1 . 
         [0057]    Now, in a white light mode in which the subject S is irradiated with white light, the light source  1  and the light source  2  are illuminated as illustrated in  FIG. 6 . 
         [0058]    In such a case, the dichroic mirror  5  combines the light transmitted through the dichroic mirror  5 , among the light L 1  emitted from the light source  1 , and light reflected at the dichroic mirror  5 , among the light L 2  emitted from the light source  2 , and emits this combined light L 5  in the direction of the optical axis of the light L 1 . As illustrated in  FIG. 7 , the combined light L 5  has a spectral characteristic resulting from superimposing the light in the wavelength bands smaller than wavelength λ 1  and greater than or equal to wavelength λ 2 , among the light L 1  emitted from the light source  1 , and light in the wavelength band of wavelengths λ 1  to λ 2 , among the light L 2  emitted from the light source  2 . 
         [0059]    As illustrated in  FIG. 6 , in a special light mode in which the subject S is irradiated with special light, for example, the light source  1  is turned off, and only the light source  2  is illuminated. 
         [0060]    In such a case, the dichroic mirror  5  reflects and emits light in the wavelength band of wavelengths λ 1  to λ 2 , among the light L 2  emitted from the light source  2 , in the direction of the optical axis of the light L 1 . In such a case, the spectral characteristic of the light emitted in the direction of the optical axis of the light L 1  is as illustrated in  FIG. 8 . 
         [0061]    The operation of the examination system  100  having the above-described configuration will be described below. 
         [0062]    First, for example, a user selects an illumination mode from a plurality of illumination modes, and an illumination-mode instruction signal for driving the illumination apparatus  10  in the selected illumination mode is sent from the illumination-mode selecting unit  29 , which is not shown. 
         [0063]    When the selected illumination mode is the white light mode, the light source  1  and the light source  2  are both driven. In such a case, the dichroic mirror  5  combines the light in the wavelength bands smaller than wavelength λ 1  and greater than or equal to wavelength λ 2 , among the light L 1  emitted from the light source  1 , and the light of wavelengths λ 1  to λ 2 , among the light L 2  emitted from the light source  2 , and emits the combined light L 5  in the direction of the optical axis of the light L 1 . As illustrated in  FIG. 7 , the combined light L 5  is white light having a wide wavelength band. 
         [0064]    On the other hand, when the selected illumination mode is a special light mode, the light source  1  is turned off, and only the light source  2  is driven. In such a case, the dichroic mirror  5  emits, in the direction of the optical axis of the light L 1  emitted from the light source  1 , light in the wavelength band of wavelengths λ 1  to λ 2 , among the light L 2  emitted from the light source  2 . In such a case, as illustrated in  FIG. 8 , the light emitted in the direction of the optical axis of the light L 1  is special light having a narrow wavelength band. 
         [0065]    In either illumination mode described above, the light intensity of the illumination light emitted from the light source unit  11  is controlled by the illumination control unit  13  such that the brightness of the image of the subject S is constant. Such control of the light intensity of the illumination light will be described below. 
         [0066]    First, the subject S is irradiated with illumination light from the light source unit  11 , and the light reflected at the subject S is detected by the image acquisition unit  21 . 
         [0067]    Next, the image processing unit  22  processes an image acquisition signal output from the image acquisition unit  21  to generate an image of the subject S, and this image of the subject S is displayed on the image monitor  23 . Also, the brightness of the image of the subject S is output to the illumination control unit  13  as a screen brightness signal. 
         [0068]    At the illumination control unit  13 , the light intensity of the illumination light emitted from the light source unit  11  is controlled on the basis of the screen brightness signal from the image processing unit  22  such that the brightness of the image of the subject S is constant. Two cases of intensity control of the illumination light, which is mentioned above, for simply switching the illumination mode and for alternating between two illumination modes in short periods of time will be described below. 
         [0069]    When the illumination mode is simply switched, in the white light mode, the light source  1  and the light source  2  are illuminated, and the light intensity of the two light sources is controlled to maintain the color balance while maintaining a constant light intensity ratio of the two light sources such that the brightness of the screen is constant. 
         [0070]    In the special light mode, only the light source  2  is illuminated, and the light intensity of the light source  2  is controlled such that the brightness of the screen is constant. 
         [0071]    As described above, by controlling the light source  1  and the light source  2 , in either the white light mode or the special light mode, the brightness of the image of the subject S displayed on the image monitor  23  can be maintained constant. 
         [0072]    When examining an area emitting fluorescence as a result of being excited by a specific wavelength, it is difficult to determine the position of a specific area by examining only a fluorescence image. Thus, the image acquired by using the special light as illumination and an image for comparison acquired by using other illumination light are acquired by alternately switching between the illumination modes in a short period of time, and the two images are displayed side by side or in superimposition. 
         [0073]    In the examination system  100  according to this embodiment, the illumination mode is switched every one frame (for example, 1/60 s), and the light emission intensity of the light sources is controlled such that the screen brightness in each illumination mode is constant every time the illumination mode is switched. That is, light intensity control is not performed within a frame, but light intensity control of the light sources is performed on the basis of information about the previous image acquisition screen in the same illumination mode. In this way, the brightness of the image of the subject S displayed on the image monitor  23  can be maintained constant. 
         [0074]    As described above, in the illumination apparatus  10  and the examination system  100  according to this embodiment, among the light L 1  emitted from the light source  1 , light in a predetermined band is transmitted through the dichroic mirror  5 . Among the light L 2  emitted from the light source  2 , substantially all light beams are reflected in the optical axis direction of the light L 1  by the dichroic mirror  5 . In this way, the light L 1  emitted from the light source  1  and the light L 2  emitted from the light source  2  are combined and emitted as the combined light L 5 . 
         [0075]    In this way, normal examination can be performed by, for example, lighting the light source  1  and the light source  2  and irradiating the subject S with light in a wide band (for example, white light). Moreover, special examination can be performed by, for example, lighting only the light source  2  and irradiating the subject S with light in a narrow band (for example, blue light). 
         [0076]    In this embodiment, it is described that, in the special light mode, the light source  1  is turned off and only the light source  2  is lit; instead, the light source  2  may be turned off and only the light source  1  may be lit. 
         [0077]    By switching between the white light mode, the special light mode, etc. with the illumination-mode selecting unit  29 , the illumination state of the light sources can be controlled to irradiate the subject S with light corresponding to the examination mode. In this case, since the switching between the two illumination modes having different spectral characteristics can be performed by merely controlling the lighting of the two light sources, the illumination mode switching can be performed instantaneously, and reliability can be improved because movable parts are not included. 
         [0078]    Moreover, by acquiring an image of the subject S with the image acquisition unit  21  and controlling the light intensities of the light sources such that the brightness of the image is constant, the light intensity of the light emitted onto the subject S is controlled in response to the intensity of the light reflected at the subject S, and the examination precision of the subject S can be improved. Also, since the illumination light intensity of the light source unit  11  is controlled such that the brightness of the subject S acquired by the image acquisition unit  21  is constant, appropriate screen brightness can be maintained even when the illumination mode is switched. 
       Second Embodiment 
       [0079]    Next, an illumination apparatus according to a second embodiment of the present invention will be described mainly with reference to  FIGS. 9 to 15 . 
         [0080]    The illumination apparatus according to this embodiment differs from the embodiment described above in that two dichroic mirrors are provided. In the following, descriptions of the commonalities with the first embodiment are omitted, and mainly the differences are described. 
         [0081]    As illustrated in  FIG. 9 , a light source unit  11  includes a light source (first light source)  1  and a light source (second light source)  2 , which are disposed such that the optical axes thereof are orthogonal to each other, a second dichroic mirror (light combining unit)  6  disposed at the intersection of the optical axis of the light source  1  and the optical axis of the light source  2 , and a first dichroic mirror  5  interposed between the light source  1  and the second dichroic mirror  6 . 
         [0082]    As illustrated in  FIG. 10 , the light source  1  is a light source that emits white light L 1  in a wide wavelength band. 
         [0083]    As illustrated in  FIG. 11 , the light source  2  is a light source that emits light L 2  in a narrow wavelength band, such as a laser beam, and emits narrow-band light having substantially all components in an extremely limited wavelength band (wavelength band smaller than wavelength λ 1  illustrated in  FIG. 12 ) compared with the light L 1 . 
         [0084]    As illustrated in  FIG. 12 , the first dichroic mirror  5  and the second dichroic mirror  6  have a reflection characteristic in which light in the wavelength band larger than or equal to wavelength λ 1  is transmitted and light in the wavelength band smaller than wavelength λ 1  is reflected. 
         [0085]    By having such a reflection characteristic, the dichroic mirror  5  transmits light in the wavelength band larger than or equal to wavelength λ 1 , among the light L 1  emitted from the light source  1 . Meanwhile, the dichroic mirror  5  reflects light in the wavelength band smaller than wavelength λ 1 , among the light L 1  emitted from the light source  1 . 
         [0086]    Similar to the dichroic mirror  5 , the dichroic mirror  6  transmits light in the wavelength band larger than or equal to wavelength λ 1 , among the light L 1  emitted from the light source  1 . 
         [0087]    Meanwhile, the dichroic mirror  6  reflects light in the wavelength band smaller than wavelength λ 1 , among the light L 2  emitted from the light source  2 , in the direction of the optical axis of the light L 1  emitted from the light source  1 . 
         [0088]    Here, in the white light mode in which the subject S is irradiated with white light, for example, as illustrated in  FIG. 13 , the light source  1  is lit with 100% intensity, and the light source  2  is lit with 80% intensity. 
         [0089]    In such a case, the dichroic mirror  6  combines the light L 5  transmitted through the dichroic mirror  5 , among the light L 1  emitted from the light source  1 , and the light reflected at the dichroic mirror  6 , among the light L 2  emitted from the light source  2 , and emits this combined light L 6  in the direction of the optical axis of the light L 1 . As illustrated in  FIG. 14 , the combined light L 6  has a spectral characteristic resulting from superimposing the light in the wavelength band larger than or equal to wavelength λ 1 , among the light L 1  emitted from the light source  1 , and light in the wavelength band smaller than wavelength λ 1 , among the light L 2  emitted from the light source  2 . 
         [0090]    In a special light mode  1  in which the subject S is irradiated with special light, for example, as illustrated in  FIG. 13 , the light source  1  is turned off, and the only the light source  2  is lit with 100% intensity. 
         [0091]    In such a case, the dichroic mirror  6  reflects and emits light in the wavelength band smaller than wavelength λ 1 , among the light L 2  emitted from the light source  2 , in the direction of the optical axis of the light L 1 . In such a case, the spectral characteristic of the light emitted in the direction of the optical axis of the light L 1  is as illustrated in  FIG. 15 . 
         [0092]    In a special light mode  2  in which the subject S is irradiated with special light, for example, as illustrated in  FIG. 13 , the light source  1  is lit with 30% intensity, and the light source  2  is lit with 100% intensity. 
         [0093]    In such a case, the dichroic mirror  6  combines the light L 5  transmitted through the dichroic mirror  5 , among the light L 1  emitted from the light source  1 , and the light reflected at the dichroic mirror  6 , among the light L 2  emitted from the light source  2 , and emits this combined light L 6  in the direction of the optical axis of the light L 1 . 
         [0094]    The light intensity ratio of the light sources may be arbitrarily changed in accordance with the subject to be examined, the brightness of the screen, etc. 
         [0095]    With the illumination apparatus according to this embodiment, in addition to the advantages achieved by the first embodiment described above, sharp band catting is possible by transmitting the light L 1 , which is emitted from the light source  1 , through two dichroic mirrors. In this way, sufficient band separation is possible even with a filter with few dielectric layers (i.e., inexpensive filter). 
       Third Embodiment 
       [0096]    Next, an illumination apparatus according to a third embodiment of the present invention will be described mainly with reference to  FIGS. 16 to 27 . 
         [0097]    The illumination apparatus according to this embodiment differs from the embodiments described above in that light from the light sources are first separated and then recombined. For the illumination apparatus according to this embodiment, descriptions of the commonalities with the first embodiment are omitted, and mainly the differences are described below. 
         [0098]    As illustrated in  FIG. 16 , a light source unit  11  includes a light source (first light source)  1  and a light source (second light source)  2 , which are disposed such that the optical axes thereof are orthogonal to each other, dichroic mirrors  4 ,  5 ,  6 , and  7  disposed on the optical axis of the light source  1 , and mirrors  8  and  9  disposed on a branching optical path branched by the dichroic mirror  4 . 
         [0099]    As illustrated in  FIG. 17 , the light source  1  is a light source that emits white light L 1  in a wide wavelength band. 
         [0100]    As illustrated in  FIG. 18 , the light source  2  is a light source that emits light L 2  in a narrow wavelength band, such as a laser beam, and emits narrow-band light having substantially all components in an extremely limited wavelength band (wavelength band of wavelengths λ 1  to λ 2  illustrated in  FIGS. 19 and 20 ) compared with the light L 1 . 
         [0101]    The dichroic mirrors  4 ,  5 ,  6 , and  7  are disposed along the optical axis of the light source  1  in this order from near the light source  1 . 
         [0102]    As illustrated in  FIG. 19 , the first dichroic mirror  4  has a reflection characteristic in which light in a wavelength band larger than or equal to wavelength λ 1  is transmitted, and light in the wavelength band smaller than wavelength λ 1  is reflected. 
         [0103]    As illustrated in  FIG. 20 , the second dichroic mirror  5  and the third dichroic mirror  6  have a reflection characteristic in which light in the wavelength band larger than or equal to wavelength (c)λ2 is transmitted, and light in the wavelength band smaller than wavelength λ 2  is reflected. 
         [0104]    As illustrated in  FIG. 21 , the fourth dichroic mirror  7  has a reflection characteristic in which light in a wavelength band larger than or equal to wavelength λ 1  is transmitted, and light in the wavelength band smaller than wavelength (c)λ1 is reflected. 
         [0105]    With the illumination apparatus having the above-described configuration, the light source  1  and the light source  2  are lit in the white light mode in which the subject S is irradiated with white light. 
         [0106]    In such a case, the first dichroic mirror  4  transmits light L 4  of wavelength (c)λ1 or larger (optical path A), among the light L 1  emitted from the light source  1 , and emits light L 1 ′ below wavelength λ 1  toward the mirror  9  (optical path B). 
         [0107]    As illustrated in  FIG. 22 , the light L 4  traveling along through the optical path A is light in a wavelength band larger than or equal to wavelength λ 1 , among the light L 1  emitted from the light source  1 . 
         [0108]    As illustrated in  FIG. 23 , the light L 1 ′ traveling along the optical path B is light in a wavelength band smaller than wavelength λ 1 , among the light L 1  emitted from the light source  1 . The light L 1 ′ traveling along the optical path B is reflected to the fourth dichroic mirror  7  by the mirror  9  and the mirror  8 . 
         [0109]    The second dichroic mirror  5  transmits light L 5  of wavelength λ 2  or larger (optical path C), among the light L 4  transmitted through the first dichroic mirror  4 , and reflects light smaller than wavelength λ 2  away from the optical path. 
         [0110]    As illustrated in  FIG. 24 , the light L 5  traveling along the optical path C is light in the wavelength band larger than or equal to λ 2 , among the light L 4  transmitted through the first dichroic mirror  4 . 
         [0111]    The third dichroic mirror  6  transmits light of wavelength λ 2  or larger, among the light L 5  transmitted through the second dichroic mirror  5 , and reflects the light smaller than wavelength λ 2 , among the light L 2  emitted from the light source  2 . In this way, the third dichroic mirror  6  combines the light of wavelength λ 2  or larger, among the light L 5 , and the light smaller than wavelength λ 2 , among the light L 2 , and emits the combined light L 6  in the direction of the optical axis of the light source  1  (optical path D). The light L 6  traveling along the optical path D is light having a spectral characteristic such as that illustrated in  FIG. 25 . 
         [0112]    The fourth dichroic mirror  7  transmits light of wavelength λ1 or larger, among the light L 6  transmitted through the third dichroic mirror  6 , and reflects the light smaller than wavelength λ 1 , among the light L 1 ′ reflected at the mirror  9 , in the direction of the optical axis of the light source  1 . In this way, the fourth dichroic mirror  7  combines the light of wavelength λ 1  or larger, among the light L 6 , and the light smaller than wavelength λ 1 , among the light L 1 ′, and emits the combined light L 7  in the direction of the optical axis of the light source  1 . In this way, the combined light L 7  emitted from the fourth dichroic mirror  7  is light having a spectral characteristic such as that illustrated in  FIG. 26 . 
         [0113]    In a special light mode in which the subject S is irradiated with special light, for example, the light source  1  is turned off, and only the light source  2  is lit. 
         [0114]    In such a case, the light L 6  traveling along the optical path D is light in a wavelength band smaller than wavelength λ 2 , among the light L 2  emitted from the light source  2 . The combined light L 7  emitted from the fourth dichroic mirror  7  is light in a wavelength band larger than or equal to wavelength λ 1 , among the light L 6  traveling along the optical path D. That is, as illustrated in  FIG. 27 , the combined light L 7  emitted from the fourth dichroic mirror  7  is light in a wavelength band of wavelengths λ 1  to λ 2 , among the light L 2  emitted from the light source  2 . 
         [0115]    With the illumination apparatus according to this embodiment, in addition to the advantages achieved by the first embodiment described above, for example, light of an intermediate wavelength, such as green, can be cut with a low-pass filter and a high-pass filter, not a band-pass filter. In this way, the wavelength where folding of the a reflection characteristic occurs in the infrared region and ultraviolet region can be extended more than a band-pass filter, and thus, near-ultraviolet rays, near-infrared rays, etc., can be used as special light. 
         [0116]    In this embodiment, it is described that, in the special light mode, the light source  1  is turned off and only the light source  2  is lit; instead, the light source  2  may be turned off and only the light source  1  may be lit. Moreover, similar to the second embodiment, the light intensity ratio of the light sources may be changed. 
         [0117]    The embodiments of the present invention have been described above in detail with reference to the drawings. The detailed configuration, however, is not limited to the embodiments, and design changes etc., may also be included so long as they do not depart from the scope of the invention. 
         [0118]    For example, in the first embodiment, an example in which the illumination apparatus according to the present invention is applied to an examination system has been described. Examples of the systems to which such an illumination apparatus can be applied include an endoscope system using special light (infrared light examination or chemical fluoroscopy) or a microscope system performing fluoroscopy. 
         [0119]    Moreover, in the embodiments, an illumination apparatus including two light sources is described; instead, three or more light sources may be provided. Furthermore, a combination of multiple light sources emitting light of different wavelengths may be used as one light source. In this way, by using a combination of multiple light sources as one light source, illumination light having a desired wavelength can be easily provided. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1  light source (first light source) 
           2  light source (second light source) 
           4  dichroic mirror 
           5  dichroic mirror (light combining unit) 
           6  dichroic mirror (light combining unit) 
           7  dichroic mirror (light combining unit) 
           10  illumination apparatus 
           11  light source unit (irradiation optical system) 
           12  light-source driving unit 
           13  illumination control unit (control unit) 
           21  image acquisition unit (light receiving unit) 
           22  image processing unit 
           23  image monitor 
           29  illumination-mode selecting unit 
           100  examination system 
         S subject