Patent Publication Number: US-2012032880-A1

Title: Pointing device and display apparatus having the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from Korean Patent Application No. 10-2010-0074964, filed on Aug. 3, 2010 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Field 
     Apparatuses and devices consistent with the exemplary embodiments relate to a pointing device which projects light beams on a screen and a display apparatus having the same, and more particularly, to a pointing device with a light emission structure to allow an image to be effectively displayed on a screen based on a trace of light beams projected on the screen, and a display apparatus having the same. 
     2. Description of the Related Art 
     A display apparatus for processing an image signal or image data which is input externally or stored therein through various processes and displaying an image on a panel or a screen based on the processed image signal or image data, may be implemented in various ways including a television (TV), a monitor, a portable media player or the like depending on its usage. Such a display apparatus may be implemented as an electronic board (“E-board”) which detects a trace formed on a screen and displays an image on the screen based on the detected trace. 
     An E-board type display apparatus may be a resistive type which detects a pressure on a resistive touch screen, an infrared type which detects imaging of an infrared beam projected on a screen, and so on. 
     However, the resistive type display apparatus detecting a trace by a touch on the screen has to employ the entire screen as a touch-enabled screen, which may result in an increase in production costs and difficulty in a user writing on a portion of the screen which is hard to be accessed by the user. Accordingly, such a resistive type display apparatus is not easy to implement in a large-sized screen. In addition, the infrared type display apparatus having the diffusion property of the infrared beam may provide an unclear trace of the infrared beam imaged on the screen when it is projected over a long distance depending on scattering of the infrared beam and the amount of infrared beam used in certain environments. 
     SUMMARY 
     One or more exemplary embodiments provide a pointing device with an improved light emission structure to allow an image to be effectively displayed on a screen based on a trace of light beams projected on the screen, and a display apparatus having the same. 
     According to an exemplary embodiment, there is provided a display apparatus including: a pointing device which generates a light beam and projects the light beam on a screen; a camera which detects a trace of the light beam imaged on the screen; and an image processing unit which processes an image corresponding to the trace of the light beam detected by the camera to display the image on the screen, the pointing device including: a first light source unit which generates and emits the light beam having a first wavelength range, a second light source unit which generates and emits the light beam having a second wavelength range different from the first wavelength range, and a switching circuit which selectively applies power to one of the first light source unit and the second light source unit depending on a distance between the screen and the pointing device, so that the light beam of one of the first wavelength range and the second wavelength range is selectively projected. 
     The first wavelength range may be a range of infrared wavelength, and the second wavelength range may be a range of visible wavelength. 
     The display apparatus may further include a filter which is placed on a path of light input to and detected by the camera and passes an amount of the light beam of the range of visible wavelength reduced by a predetermined rate. 
     The switching circuit may apply the power to the first light source unit if the distance between the screen and the pointing device is smaller than a predetermined reference distance and apply the power to the second light source unit if the distance between the screen and the pointing device is larger than the predetermined reference distance. 
     The pointing device may further include a detecting unit which detects the distance between the screen and the pointing device and transfers a result of the detection to the switching circuit. 
     The pointing device may further include a user input unit which is configured to designate selective power application by the switching circuit. 
     The pointing device may further include a housing which has a user holdable rod-like shape and includes a first end portion in which the first and second light source units are placed. 
     The first light source unit may further include: a first light source which generates the light beam having the first wavelength range; and a hemispherical diffusing lens which diffuses the light beam input from the first light source. 
     The diffusing lens may be supported to the housing to move between a first position closer to the housing and a second position farther from the housing, and the pointing device may further include: an elastic member which elastically biases the diffusing lens toward the second position; and an electrode unit which makes electrical conduction to allow the switching circuit to apply power to the first light source unit when the diffusing lens is located in the first position due to an external pressure. 
     The second light source unit may include: a second light source which generates the light beam having the second wavelength range; and an optical duct member which guides the light beam input from the second light source to go straight in parallel. 
     The second light source may be located in the central region within the diffusing lens at the first end portion of the housing, and the optical duct member may extend to the outer side of the diffusing lens through a hole formed in the diffusing lens. 
     The image processing unit may be implemented as a projection type unit. 
     According to another aspect of an exemplary embodiment, there is provided a pointing device of a display apparatus, which generates a light beam and projects the light beam on a screen, including: a first light source unit which generates and emits the light beam having a first wavelength range; a second light source unit which generates and emits the light beam having a second wavelength range different from the first wavelength range; and a switching circuit which selectively applies power to one of the first light source unit and the second light source unit depending on a distance between the screen and the pointing device, so that the light beam of one of the first wavelength range and the second wavelength range is selectively projected. 
     The first wavelength range may be a range of infrared wavelength, and the second wavelength range may be a range of visible wavelength. 
     The switching circuit may apply the power to the first light source unit if the distance between the screen and the pointing device is smaller than a predetermined reference distance and apply the power to the second light source unit if the distance between the screen and the pointing device is larger than the predetermined reference distance. 
     The pointing device may further include a detecting unit which detects the distance between the screen and the pointing device and transfers a result of the detection to the switching circuit. 
     The pointing device may further include a user input unit which is configured to designate selective power application by the switching circuit. 
     The pointing device may further include a housing which has a user holdable rod-like shape and includes a first end portion in which the first and second light source units are placed. 
     The first light source unit may include: a first light source which generates the light beam having the first wavelength range; and a hemispherical diffusing lens which diffuses the light beam input from the first light source. 
     The diffusing lens may be supported to the housing to move between a first position closer to the housing and a second position farther from the housing, and the pointing device may further include: an elastic member which elastically biases the diffusing lens toward the second position; and an electrode unit which makes electrical conduction to allow the switching circuit to apply power to the first light source unit when the diffusing lens is located in the first position due to an external pressure. 
     The second light source unit may include: a second light source which generates the light beam having the second wavelength range; and an optical duct member which guides the light beam input from the second light source to go straight in parallel. 
     The second light source may be located in the central region within the diffusing lens at the first end portion of the housing, and the optical duct member may extend to the outer side of the diffusing lens through a hole formed in the diffusing lens. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and/or other aspects will become apparent and more readily appreciated from the following description of exemplary embodiments, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a view showing an exemplary display apparatus according to a first exemplary embodiment; 
         FIG. 2  is a view showing a configuration of an image processing unit in the display apparatus shown in  FIG. 1 ; 
         FIG. 3  is a graph showing a relative comparison of an amount of a visible light beam detectable by a camera depending on whether or not a filter is used in the display apparatus shown in  FIG. 1 ; 
         FIG. 4  is a sectional side view showing a general structure of a pointing device in the display apparatus shown in  FIG. 1 ; 
         FIG. 5  is a sectional side view showing a general structure of a pointing device according to a second exemplary embodiment; and 
         FIG. 6  is a view showing a configuration of a pointing device according to a third exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Below, exemplary embodiments will be described in detail with reference to accompanying drawings so as to be easily realized by a person having ordinary knowledge in the art. The exemplary embodiments may be embodied in various forms without being limited to the exemplary embodiments set forth herein. Descriptions of well-known parts are omitted for clarity, and like reference numerals refer to like elements throughout. However, it is appreciated that it is not meant to exclude such omitted components from a display apparatus  1  of the exemplary embodiments. 
       FIG. 1  is a view showing an exemplary display apparatus  1  according to a first exemplary embodiment. 
     Referring to  FIG. 1 , a display apparatus  1  according to the first exemplary embodiment includes a screen  100 , a pointing device  200  which generates and projects a light beam L on the screen  100 , a camera  300  which detects a trace T of the light beam imaged on the screen  100  by the pointing device  200 , and an image processing unit  400  which processes an image corresponding to the trace T of the light beam L detected by the camera  300  so that the image can be displayed on the screen  100 . 
     In the display apparatus  1 , one of a light beam L having a first range of wavelength and a light beam L having a second range of wavelength different from the first range of wavelength is selectively projected on the screen  100  from the pointing device  200  in correspondence to a distance between the screen  100  and the pointing device  200 . In this exemplary embodiment, the first range of wavelength corresponds to a range of infrared wavelength and the second range of wavelength corresponds to a range of visible wavelength. 
     Since the light beams L having the different ranges of wavelength have different optical properties, the image processing unit  400  may normally display an image corresponding to the trace T of the light beam L in correspondence to variation of the distance between the screen  100  and the pointing device  200  as the pointing device  200  projects a light beam L having an appropriate range of wavelength on the screen depending on the distance between the screen  100  and the pointing device  200 . 
     The screen  100  is installed on an installation plane such as a wall for image display. The screen  100  may be implemented with various different sizes, colors and so on within a range in which an image V projected from the image processing unit  400  can be displayed. For example, the screen may have a white color which allows the image V to be more clearly displayed and the trace T of the light beam L to be easily detected by the camera  300 . 
     The screen  100  may include, but is not limited to, flexible material for facilitation of attachment/detachment to/from the installation plane, solid material fixedly attached to the installation plane, or the like. 
     A configuration of the camera  300  and the image processing unit  400  will be now described with reference to  FIG. 2 .  FIG. 2  is a view showing a configuration of the camera  300  and the image processing unit  400  in the display apparatus  1 . 
     Referring to  FIG. 2 , the camera  300  detects the trace T of the light beam L imaged on the screen  100  and transfers the detected trace T to the image processing unit  400 . The camera  300  may be separated communicatively from or incorporated into the image processing unit  400 . 
     When the light beam L is imaged on the screen  100 , the camera  300  receives light reflected from the screen and calculates a relative coordinate of the trace T of the light beam L on the screen  100 . For this purpose, the camera  300  includes a lens system (not shown) for light receipt and a complementary metal oxide semiconductor (CMOS) or charge-coupled device (CCD) image sensor (not shown) for detection of light input through the lens system. 
     A filter  310  is disposed on a path of the light received in the camera  300 . The filter  310  may be disposed with no restriction on its position as long as it can filter the light received in the camera  300 . For example, the filter  310  may be combined with the lens system (not shown) for light receipt in the camera  300 . 
     The filter  310  passes an amount of visible light reduced by a preset rate. In contrast, the filter  310  passes infrared light substantially without any reduction. 
     Hereinafter, the reason for application of the filter  310  to the camera  300  will be described with reference to  FIG. 3 .  FIG. 3  is a graph showing a relative comparison of an amount of a visible light beam detectable by the camera  300  depending on whether or not a filter is used. 
     In the graph of  FIG. 3 , a horizontal axis represents relative numerical values of luminance of light input to the camera  300  and a vertical axis represents relative numerical values of luminance of light output from the camera  300 . The relative numerical values on the horizontal and vertical axes are dimensionless, and a lower value indicates a lower luminance, whereas a higher value indicates a higher luminance. 
     A curve C 1  involves non-application of the filter  310 , i.e., the light received in the camera  300  does not pass through the filter  310 . A curve C 2  involves application of the filter  310 , i.e., the light received in the camera  300  passes through the filter  310 . A curve C 3  involves recognition by a human&#39;s field of view. 
     As can be seen from the curve C 1 , the luminance of the light output from the camera  300  is in direct proportion to the luminance of the light input to the camera  300 , which increases from 0 to about 190. However, if the luminance of the light input to the camera  300  exceeds 190, a section S occurs in which the luminance of the light output from the camera  300  does not increase but remains unchanged even with increase in the luminance of the light input to the camera. 
     This section S occurs when the light received in the camera  300  is out of a dynamic range which is a range of luminance of light recognizable by the camera  300 . Specifically, an image sensor (not shown) in the camera  300  is saturated if it detects light having high luminance which exceeds the upper limit of the dynamic range. For example, when an image and the trace T of the light beam L are together displayed, the camera  300  may not recognize the trace T of the light beam L due to such a saturation effect although the trace T of the light beam L has a luminance higher than that of the image. 
     To avoid this problem, the filter  310  passes an amount of the light received in the camera  300  by a preset rate, for example, 15% to 20%, and transfers the resultant amount of the light to the camera  300 . Accordingly, the dynamic range of the camera  300  is adjusted as shown in curve C 2 . 
     As shown in the curve C 2 , the luminance of the light output from the camera  300  is in direct proportion to the luminance of the light input to the camera  300  over the entire section without a section such as the section S in the curve C 1 . Namely, the application of the filter  310  to the camera  300  allows the camera  300  to clearly recognize the trace T of the light beam L even under light-intensive use environments. 
     Referring again to  FIG. 2 , the image processing unit  400  subjects the externally input image signal or image data to various processes and displays an image on the screen  100  based on the processed image signal or image data. In this exemplary embodiment, the image processing unit  400  may be implemented as a projection type unit although it may be implemented by any other type. 
     The image processing unit  400  includes an illumination optical unit  410  which generates and emits light, a display device  420  which displays an image on a plate based on the light emitted from the illumination optical unit  410 , and a projection optical unit  430  which enlarges and projects the image displayed on the plate of the display device  420  on the screen  100 . The image processing unit  400  further includes a controller  440  which controls operation of other elements  410 ,  420  and  430  of the image processing unit  400  so that the image based on information regarding coordinates of the trace T of the light beam L transferred from the camera  300  can be displayed on the screen  100 . 
     The illumination optical unit  410  includes a light source (not shown) which generates light, and at least one optical lens (not shown) which adjusts various optical properties, such as collimation, equalization, polarization, condensation and so on, of the light from the light source (not shown). A plurality of optical lens (not shown) may be placed along an optical path for aberration correction. 
     The display device  420  forms an image by selectively transmitting or reflecting the light emitted from the illumination optical unit  410 . The display device  420  may be implemented as a reflective display device which forms an image by selectively reflecting incident light in the unit of a pixel, or a transmissive liquid crystal display which selectively transmits incident light in the unit of a pixel. Examples of the reflective display device may include a digital micro-mirror device (DMD), a reflective liquid crystal on silicon (LOCOS) device, and other devices known in the art. 
     The projection optical unit  430  enlarges and displays the image formed on the display device  420  by enlarging and projecting the image formed on the display device  420  on the screen  100  using various lens configurations placed along the optical path. 
     Upon receiving the coordinate information of the trace T of the light beam L from the camera  300 , the controller  440  controls the illumination optical unit  410  and the display device  420  such that an image corresponding to the received coordinate information can be displayed on the display device  420 . That is, when the trace T of the light beam L projected from the pointing device  200  appears on the screen  100 , the camera  300  detects the trace T and its coordinate information and transfers the detected coordinate information to the controller  440 . Then, the controller  440  displays the image on the display device  420  based on the transferred coordinate information and the displayed image is projected onto the projection optical unit  430  and then is displayed on the screen  100 . 
     Accordingly, when the trace T of the light beam L is formed on the screen  100  by the pointing device  200 , the image corresponding to the trace T is displayed on the screen  100 . 
     Hereinafter, the pointing device  200  will be described with reference to  FIG. 4 .  FIG. 4  is a sectional side view showing a general structure of the pointing device  200  according to this exemplary embodiment. 
     Referring to  FIG. 4 , the pointing device  200  may selectively project one of a light beam L 1  having a range of infrared wavelength and a light beam L 2  having a range of visible wavelength, depending on a distance between the screen  100  and the pointing device  200 . 
     Such selective projection is attributed to a difference in optical characteristics between diffusive infrared light and paralleling visible light. Thus, if the distance between the screen  100  and the pointing device  200  is smaller than a predetermined reference distance, the camera  300  can easily detect the trace T on the screen for the diffusive infrared light rather than for the paralleling visible light. In contrast, if the distance between the screen  100  and the pointing device  200  is larger than the reference distance, the camera  300  can easily detect the trace T on the screen for the paralleling visible light rather than for the diffusive infrared light since the infrared light is diffusive to make it difficult to form an image on the screen  100 . 
     Accordingly, in this exemplary embodiment, depending on the distance between the screen  100  and the pointing device  200 , the pointing device  200  is configured to project the light beam L 1  having the range of infrared wavelength if the distance is relatively small and project the light beam L 2  having the range of visible wavelength if the distance is relatively large. This allows the camera  300  to easily detect the trace T of one of the light beams L 1  and L 2  on the screen  100  even when the distance between the screen  100  and the pointing device  200  varies. 
     Here, the reference distance is a reference for distinguishing between a short distance where the light beam L 1  having the infrared wavelength range is used and a long distance where the light beam L 2  having the visible wavelength range is used. The reference distance may be variously determined depending on a use environment of the pointing device  200  such as light intensity of a surrounding environment, reflectivity of a screen, etc. Thus, the reference distance is not limited to a specific value or range. 
     As shown in  FIG. 4 , the pointing device  200  includes a housing  210 , a first light source unit  221  and  223  which is placed at one end portion of the housing  210  and generates and emits the light beam L 1  having a range of infrared wavelength, a second light source unit  231  and  233  which is placed at the one end portion of the housing  210  in a manner to be separated from the first light source unit  221  and  223  and generates and emits the light beam L 2  having a range of visible wavelength, a power supply unit  240  which supplies power, a switching circuit  250  which switches to selectively provide power from the power supply unit  240  to one of the first light source unit  221  and  223  and the second light source  231  and  233 , and a user input unit  260  which is provided to designate a switching operation of the switching circuit  250  with a user&#39;s manipulation. 
     The housing  210  is not limited in its shape, size and material but is preferably of a bar shape, which facilitates a user&#39;s holding of the pointing device  200  to project the light beams L 1  and L 2  on a desired site of the screen  100 . In this exemplary embodiment, the housing  210  has a cylindrical rod-like shape and contains the power supply unit  240  and the switching circuit  250 . In addition, the first light source unit  221  and  223  and the second light source unit  231  and  233  are disposed at the first end portion of the housing  210  and the user input portion  260  is disposed at an outer side to be held by the user. 
     The first light source unit  221  and  223  includes a first light source  221  which is electrically connected to the switching circuit  250  and generates and emits the light beam L 1  having the range of infrared wavelength, and a diffusing lens  223  which diffuses the light beam L 1  emitted from the first light source  221 . 
     In response to application of power by the power supply unit  240  through the switching circuit  250 , the first light source  221  generates the light beam L 1  having the range of infrared wavelength, i.e., 780 nm to 1200 nm, and emits the generated light beam L 1  to the diffusing lens  223 . In this exemplary embodiment, the first light source  221  is disposed in an edge region at the first end portion of the housing  210 . 
     The diffusing lens  223  has a circular or elliptical hemispherical shape and is configured to cover the first end portion of the housing  210 . The diffusing lens  223  is disposed to project externally and convexedly from the first end portion of the housing  210 , with an end portion of the diffusing lens  223  being supported on the edge region of the first end portion of the housing  210 . 
     In this case, since the first light source  221  is disposed in the edge region at the first end portion of the housing  210 , the light beam L 1  emitted from the first light source  221  is incident into the end portion of the diffusing lens  223 . The incident light beam L 1  is externally output after being diffused over the entire diffusing lens  223  of the hemispherical shape, thereby increasing a size of optical spot imaged by the light beam L 1 . 
     In addition, the diffusing lens  223  is supported on the first end portion of the housing  210  in such a manner that the diffusing lens  223  can move between a first position A closer to the housing  210  and a second position B farther from the housing  210 . In this case, an elastic member  227  to elastically bias the diffusing lens  223  toward the second position B is interposed between the diffusing lens  223  and the housing  210 . 
     In addition, a first electrode  271  is coupled to the diffusing lens  223  and a second electrode  272  is coupled to the first end portion of the housing  210 . The first and second electrodes  271  and  272  are electrically connected to the switching circuit  250 . When the diffusing lens  223  is in the first position A, the first and second electrodes  271  and  272  make electrical conduction by mutual contact, thereby applying power to the first light source  221 . A wiring structure of applying power to the first light source  221  by means of the switching circuit  250  upon making electrical conduction between the first and second electrodes  271  and  272  may be changed in its design by those skilled in the art without departing from the spirit and scope of the exemplary embodiment. 
     On the other hand, when the diffusing lens  223  is in the second position, the first and second electrodes  271  and  272  are separated and electrically isolated from each other. Even under this condition, it is to be understood that the switching circuit  250  may cause power to be applied to the first light source  221  by means of the user input unit  260 . 
     In addition, since the second light source unit  231  and  233  is placed in the central area of the first end portion of the housing  210 , the first and second electrodes  271  and  272  may be configured to have a ring-like shape surrounding the second light source unit  231  and  233  for the purpose of avoiding mutual interference. 
     For example, if a user is handwriting by pressing the tip of the pointing device  200  against the screen  100  formed of rigid material, the diffusing lens  223  is pressed in contact with the screen  100  and moves to the first position A against an elastic force of the elastic member  227 . Accordingly, the first and second electrodes  271  and  272  make electrical conduction therebetween, thereby generating the light beam L 1  from the first light source  221  and projecting it on the screen  100  through the diffusing lens  223 . 
     If the user stops the handwriting with the pointing device  200  on the screen  100  and separates the pointing device  200  from the screen  100 , the first and second electrodes  271  and  272  are separated from each other to stop the generation of the light beam L 1  from the first light source  221 . In this manner, when the user presses the pointing device  200  against the screen  100  for handwriting, the light beam L 1  can be projected on the screen  100  without any user&#39;s manipulation through the user input unit  260 . 
     The second light source unit  231  and  233  includes a second light source  231  which is electrically connected to the switching circuit  250  and generates and emits the laser light beam L 2  having the range of visible wavelength, and an optical duct member  233  which guides the light beam L 2  from the second light source  231  such that the light beam L 2  goes straight in parallel. 
     The second light source  231  generates the light beam L 2  having the range of visible wavelength, i.e., 400 nm to 780 nm. The second light source  231  is disposed in the central region of the first end portion of the housing  210  in an inner side of the diffusing lens  223 . 
     The optical duct member  233  has a rod-like shape having one end portion coupled to or disposed adjacent to the second light source  231  and the other end portion extending to the outer side of the diffusing lens  223  through a hole  225  formed in the diffusing lens  223 . When the light beam L 2  from the second light source  231  is incident into the one end portion, the optical duct member  233  guides the light beam L 2  to go straight without being diffused toward the diffusing lens  223  such that the light beam L 2  exits through the other end portion in the outer side of the diffusing lens  223 . 
     If the optical duct member  233  is not present, the light beam L 2  is diffused by the diffusing lens  223  since the second light source  231  is inside the diffusing lens  223 , which may make it difficult to form a trace T by the light beam L 2  on the screen  100  at a long distance. Thus, by employing the optical duct member  233  which guides the light beam L 2  from the second light source  231  to the outer side of the diffusing lens  223 , it is possible to minimize the diffusion of the light beam L 2  by the diffusing lens  223 . 
     The power supply unit  240  may be implemented by a replaceable battery or rechargeable battery built in the housing  210  for supply of DC power. 
     The switching circuit  250  selectively provides power from the power supply unit  240  for one of the first light source  221  and the second light source  231 . Such an operation of the switching circuit  250  may be controlled by the user input unit  260  or depending on whether or not electrical conduction is made between the first and second electrodes  271  and  272 . The switching circuit  250  may be configured in different ways without departing from the spirit and scope of the exemplary embodiment. 
     The user input unit  260  is disposed at the outer side of the housing  210  such that a user can manipulate it to control the operation of the switching circuit  250 . That is, the user may manipulate the user input unit  260  so that the light beam L 1  having the range of infrared wavelength or the light beam L 2  having the range of visible wavelength can be generated. 
     A pointing device  600  according to a second exemplary embodiment, having a structure different from that of the first exemplary embodiment, will be hereinafter described with reference to  FIG. 5 . 
       FIG. 5  is a sectional side view showing a general structure of a pointing device  600  according to the second exemplary embodiment. 
     Referring to  FIG. 5 , the pointing device  600  according to the second exemplary embodiment includes a housing  610 , a first light source unit  621  and  623  which is placed at a first end portion of the housing  610  and generates and emits a light beam L 1  having a range of infrared wavelength, a second light source unit  631  and  633  which is placed at the first end portion of the housing  610  in a manner to be separated from the first light source unit  621  and  623  and generates and emits a light beam L 2  having a range of visible wavelength, a power supply unit  640 , a switching circuit  650 , and a user input unit  660 . 
     The first light source unit  621  and  623  includes a first light source  621  which generates the light beam L 1 , and a first light source lens  623  which adjusts the light beam L 1  to have predetermined optical properties. The second light source unit  631  and  633  includes a second light source  631  which generates the light beam L 2 , and a second light source lens  633  which adjusts the light beam L 2  to have predetermined optical properties. The first light source lens  623  and the second light source lens  633  may be implemented in various ways including diffusion, collimation, condensation and so on depending on optical properties to be adjusted. 
     Unlike the first exemplary embodiment, the second exemplary embodiment does not require the optical duct member  233  and the hole  225  of the first exemplary embodiment since the present exemplary embodiment has no structure to interfere with the light beam L 2 . 
     Various elements of the second exemplary embodiment are analogous to elements of the first exemplary embodiment, and therefore, an explanation of such elements will not be repeated for the purpose of brevity of the description. 
     Although it is illustrated in the first and second exemplary embodiments that the switching operation of the switching circuits  250  and  650  is controlled by a user&#39;s manipulation through the user input units  260  and  660 , the exemplary embodiments are not limited thereto. For example, a switching operation of a switching circuit  750  may be automatically performed without requiring a user&#39;s separate manipulation, as will be described below with reference to  FIG. 6 . 
       FIG. 6  is a view showing a configuration of a pointing device  700  according to a third exemplary embodiment. 
     Referring to  FIG. 6 , the pointing device  700  according to the third exemplary embodiment includes a first light source unit  720  which generates and emits a light beam L 1  having a range of infrared wavelength, a second light source unit  730  which generates and emits a light beam L 2  having a range of visible wavelength, a power supply unit  740  which supplies power, a switching circuit  750  which selectively applies the power from the power supply unit  740  for one of the first light source unit  720  and the second light source unit  730 , and a detecting unit  760  which detects a distance between the screen  100  and the pointing device  700  and transfers a result of the detection to the switching circuit  750 . 
     Configuration of the first light source  720 , the second light source  730  and the power supply unit  740  may be analogous to corresponding elements of the first and second exemplary embodiments, and therefore, explanation of such configuration will not be repeated for the purpose of brevity of the description. 
     The detecting unit  760  which detects the distance between the screen  100  and the pointing device  700 , may be implemented in various ways including, but is not limited to, ultrasonography. In addition, the detecting unit  760  may be configured in various ways, such as by installing in the pointing device  700  as in this exemplary embodiment, installing in the screen  100 , installing in both in a corresponding manner, or installing in a separate third position such that a result of detection by the detecting unit  760  can be wirelessly transferred to the switching circuit  750 . 
     Based on the result of detection transferred from the detecting unit  760 , the switching circuit  750  applies power from the power supply unit  740  to one of the first and second light sources  720  and  730 . For this purpose, the switching circuit  750  may further include a separate microcontroller. 
     For example, the detecting unit  760  may transfer a low signal to the switching circuit  750  if a detected distance is smaller than a predetermined reference distance and transfer a high signal to the switching circuit  750  if the detected distance is larger than the predetermined reference distance. The switching circuit  750  applies power from the power supply unit  740  to the first light source  720  upon receiving the low signal from the detecting unit  760  and applies power from the power supply unit  740  to the second light source  730  upon receiving the high signal from the detecting unit  760 . 
     Accordingly, the light beam L 1  having the range of infrared wavelength and the light beam L 2  having the range of visible wavelength may be automatically and selectively projected on the screen  100  depending on the distance between the screen  100  and the pointing device  700  without requiring a user&#39;s separate manipulation. 
     Further, this exemplary embodiment may additionally include a separate user input unit (not shown) for turning the power supply unit  740  on/off. 
     Although a few exemplary embodiments have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these exemplary embodiments without departing from the principles and spirit of the inventive concept, the scope of which is defined in the appended claims and their equivalents.