Patent Publication Number: US-2005141222-A1

Title: Lighting device and temperature detection method thereof

Description:
BACKGROUND  
      The invention relates to an image projection apparatus, a lighting device, and a temperature detection method thereof, and in particular, to a temperature detection method that can accurately detect the temperature of a light source of the lighting device.  
      In a conventional image projection apparatus such as a projector, the temperature of a lighting device, such as a discharge lamp, is detected at several predetermined positions therein (ex: on the housing, the light source, the post, and etc.) to make sure that the lighting device can operate within a predetermined range of the temperature.  
      To detect the temperature, a thermally-sensitive detection device such as a thermal couple or an infra-ray (IR) detector is utilized. When the thermal couple is utilized, it is adhered to the lighting device at several positions and connected to a cable. If the number of the thermal couple exceeds a predetermined number or the cable is placed in an incorrect position, the cooling flow field in the lighting device may be disturbed by the cable so that the temperature cannot be detected accurately.  
      Additionally, referring to  FIG. 1   a , an invisible-light filter  12   a  is disposed in front of a light source  11  in a lighting device  10   a  of a projector, such as a DLP projector, to separate UV and IR. When a light beam from the light source  11  passes through the invisible-light filter  12   a , it transmits and reflects simultaneously. The reflected light beam is focused around a post  13  and the light source  11  so that the detected temperature exceeds the actual temperature.  
      Furthermore, as shown in  FIG. 1   b , U.S. pat. appli. Ser. No. 10/604,722 discloses an image projection apparatus  10   b  with a slanted invisible-light filter  12   a . In the image projection apparatus  10   b , the invisible-light filter  120   b  is disposed in a manner such that an actuate angle is formed between a normal thereof and an optical path. Due to such an arrangement, the reflected light beam may be focused on a cathode cable  14  of the lighting device  10  so that the detected temperature exceeds the actual temperature.  
     SUMMARY  
      In view of this, an embodiment of the invention provides a lighting device and temperature detection method thereof that can accurately detect the temperature of a light source.  
      Another object of an embodiment of the invention is to provide an image projection apparatus that can accurately detect the temperature of a light source.  
      Accordingly, an embodiment of the invention provides a temperature detection method for a lighting device. The temperature detection method comprises the following steps. The lighting device is provided, comprising an invisible-light filter deposed slantwise in front of the lighting device. The invisible-light filter reflects part of an invisible light of a light beam, generated by the lighting device, back to the lighting device to form a first beam. A thermally-sensitive detection device is provided in the lighting device outside a propagation path of the first beam to avoid the heat thereof. The temperature in the lighting device is detected by the thermally-sensitive detection device.  
      It is noted that the invisible-light filter is preferably deposed slantwise in front of the lighting device to avoid the first beam overlapping the light source of the lighting device.  
      It is understood that the thermally-sensitive detection device may be a thermal couple or be made of thermally-sensitive paint.  
      In an embodiment of the invention, a lighting device is provided, comprising a light source, a reflective housing, a cathode cable, and an invisible-light filter. The light source generates a light beam. The reflective housing comprises an opening and receiving space. The light source is disposed in the receiving space so that the light beam propagates along an optical path from the receiving space via the opening. The cathode cable is electrically connected to the light source, and disposed in the reflective housing. The invisible-light filter is disposed outside the reflective housing to reflect part of an invisible light of the light beam back to the reflective housing to form a first beam. Neither the light source nor the cathode cable is disposed on a propagation path of the first beam. That is, the propagation path of the first beam does not overlap the cathode cable or the light source.  
      In a preferred embodiment, an angle between a normal of the invisible-light filter and the optical path exceeds zero degrees so that neither the light source nor the cathode cable is disposed in the propagation path of the first beam.  
      In another preferred embodiment, the reflective housing is elliptical. The light source is disposed on a focus of the elliptical reflective housing. The optical path is a major axis of the elliptical reflective housing. The invisible-light filter is disposed near the opening. The lighting device further comprises a post electrically connected to the light source.  
      In an embodiment of the invention, an image projection apparatus is provided, comprising a light source, a reflective housing, a cathode cable, an invisible-light filter, and an image module. The light source generates a light beam. The reflective housing comprises an opening and receiving space. The light source is disposed in the receiving space so that the light beam propagates along an optical path from the receiving space via the opening. The cathode cable is coupled to the light source, and disposed in the reflective housing. The invisible-light filter is disposed outside the reflective housing to reflect part of an invisible light of the light beam back to the reflective housing to form a first beam. The image module comprises a plurality of controllable optical reflective surfaces to adjust the light beam and generate a projected beam with optical images. Neither the light source nor the cathode cable is disposed in a propagation path of the first beam. That is, the propagation path of the first beam does not overlap the cathode cable and the light source.  
      It is noted that the image module may be a digital micro-mirror device or a liquid crystal display panel, and the image projection apparatus may be a projector. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      An embodiment of the present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:  
       FIG. 1   a  is a schematic view of a conventional lighting device;  
       FIG. 1   b  is a schematic view of an image projection apparatus as disclosed in U.S. pat. appli. Ser. No. 10/604,722;  
       FIG. 2  is a schematic view of an image projection apparatus as disclosed in an embodiment the invention;  
       FIG. 3  is a front view of a lighting device in  FIG. 2 ; and  
       FIG. 4  is a flowchart of a temperature detection method as disclosed in an embodiment of the invention. 
    
    
     DETAILED DESCRIPTION  
       FIG. 2  shows an image projection apparatus  26  of an embodiment of the invention. The image projection apparatus  26  comprises a light source  21 , a reflective housing  22 , a cathode cable  23 , an invisible-light filter  24 , an image module  25 , and a post  27 . The post  27  is electrically connected to the light source  21 . The light source  21 , the reflective housing  22 , the cathode cable  23 , the invisible-light filter  24 , and the post  27  constitute a lighting device  20  of the invention.  
      The light source  21  generates a light beam B, and is disposed in receiving space  212  of the reflective housing  22 . The reflective housing  22  comprises an opening  211  and the receiving space  212  therein. The reflective housing  22  reflects the light beam B to substantially propagate along an optical path P from the receiving space  212  via the opening  211 . In  FIG. 2 , the reflective housing  22  is elliptical. The light source  21  is disposed on one of focuses of the elliptical reflective housing  22 . The optical path P is a major axis of the elliptical reflective housing  22 . Furthermore, it is noted that the type of the reflective housing is not limited, and the invisible-light filter  24  can be disposed on a type of housing other than the reflective housing.  
      The cathode cable  23  is a cable for a cathode (not shown) of the image projection apparatus  26 . The cathode cable  23  is electrically connected to the light source  21  and disposed in the reflective housing  22 . The image module  25  comprises a plurality of controllable optical reflective surfaces (not shown) to adjust the light beam B and generate a projected beam projecting optical images. It is understood that the image module  25  may be a digital micro-mirror device or a liquid crystal display panel  
      The invisible-light filter  24  is disposed outside the reflective housing  22  near the opening  211  to reflect part of an invisible light of the light beam B back to the reflective housing  22  to form a first beam U. Due to the arrangement of the invisible-light filter  24 , neither the light source  21  nor the cathode cable  23  is disposed in a propagation path of the first beam U. That is, the cathode cable  23  and the light source  21  are disposed in the reflective housing  22  in a manner such that they and the propagation path of the first beam U do not overlap.  
      In  FIG. 2 , an angle θ exceeding zero degree is formed between a normal N of the invisible-light filter  24  and the optical path P so that neither the light source  21  nor the cathode cable  23  is disposed in the propagation path of the first beam U.  
      It is understood that the image projection apparatus  26  may be a projector.  
      Referring to  FIG. 3 , since the cathode cable  23  and the light source  21  are disposed in the reflective housing  22  in a manner such that they do not overlap the propagation path of the first beam U, thus, the cathode cable  23  and the light source  21  will not be heated up or even burned down by the first beam U, and the temperature of the light source  21  can be accurately detected.  
      Similarly, the thermally-sensitive detection device (not shown) is deposed in the lighting device  20  outside a propagation path of the first beam U to avoid the heat thereof during temperature detection.  
       FIG. 4  shows a temperature detection method for a lighting device as disclosed in an embodiment of the invention. The temperature detection method comprises the following steps. In step S 11 , the lighting device  20  as shown in  FIG. 2  is provided, comprising the invisible-light filter  24  for reflecting part of the invisible light of the light beam B back to the reflective housing  22  of the lighting device  20  to form the first beam U. In step S 12 , a thermally-sensitive detection device is disposed in the lighting device  20  in a manner such that it is out of the propagation path of the first beam U. In step S 13 , the temperature in the lighting device  20  is detected by the thermally-sensitive detection device.  
      It is understood that the thermally-sensitive detection device may be a thermal couple or be made of thermally-sensitive paint.  
      It is noted that to avoid affecting the cooling flow field during temperature detection, few thermally-sensitive detection devices in the lighting device  20  are preferred.  
      It is also noted that the invisible-light filter  24  is preferably deposed slantwise in front of the lighting device to avoid the first beam U overlapping the light source  21 , or the cathode cable  23 .  
      As stated above, since the number of the thermally-sensitive detection device adhered to the lighting device is as few as possible, the temperature of the light source can be accurately detected.  
      While the invention has been described by way of example and in terms of the preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiment. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.