Abstract:
An adjustable color-temperature projecting device includes a light source for providing light beams, and a filtering means. The filtering means includes red, green and blue filtering sections. The blue filtering section has coatings with different transmissivitys. The intensity of blue primary color light is varied due to the different transmissivitys of the blue filtering section, so that the ratio of blue primary color light in the hybrid light is modified to cause change in color temperature with reduced loss of brightness. Then, the filtering means is moved so that the light beam is projected onto a predetermined location to obtain the desired color temperature.

Description:
BACKGROUND OF INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to a projecting device, and more particularly to an adjustable color-temperature projecting device.  
           [0003]    2. Description of the Prior Art  
           [0004]    Color temperature brings different visual impressions. For example, a color of low color temperature gives warm feeling, while a color of high color temperature gives cool feeling. Therefore, the color temperature of a projecting device can be adjusted to satisfy the consumer&#39;s demands or visual requirement for different occasions such as presentation in conferences or movie shows.  
           [0005]    Referring to FIG. 1, a conventional projecting device  10  includes a light source  11 , a color wheel  12 , an integrated rod  13 , a light valve  14  and a projection lens  15 . The color wheel  12  includes red, green and blue color light filters, or alternatively red, green, blue and white color light filters arranged in circle. After a light beam emitting from the light source  11  travels through the color wheel  12 , red, green and blue color lights are subsequently generated and then subjected to uniformization via the integrated rod  13 . Thereafter, the color lights are projected on the light valve  14 . Under control of digital signals from the light valve  14 , the continuous color lights are converted into gray scales to form an image on a screen  16  via the projection lens  15 . In order to adjust the color temperature, a filtering sheet  17  is further mounted in front of the projection lens  15 . On the filtering sheet  17  is applied a coating which removes the color lights of a certain wavelength range. The filtering sheet  17  may be mutually rotated to attach on or dispatch from the projection lens  15  for change in color temperature. When the filtering sheet  17  is attached on the projection lens  15 , color lights from the respective filters of the color wheel  12  are processed by the optical valve  14 , then projected on the projection lens  15 , and pass through the filtering sheet  17 . The filtering sheet  17  removes a part of the color light of a certain wavelength range to alter the spectrum distribution of the red, green and blue color lights, and thus to cause change in color temperature. Thereby, the image is displayed on the screen  16 . Since all the color lights pass through the filtering sheet  17  for a further filtering process, a part of the color lights from the red, green and white filters are removed, which results in reduced brightness.  
         SUMMARY OF INVENTION  
         [0006]    One object of the invention is to provide a projecting device with adjustable color temperature, in which the color temperature is adjusted by controlling the light beam passing through a coating with different predetermined transmissivities on a blue filtering section.  
           [0007]    Another object of the invention is to provide a projecting device with adjustable color temperature, in which only the transmittance of the blue filtering section is changeable to reduce adverse effect on the brightness of the projecting device.  
           [0008]    In order to achieve the above and other objectives, the projecting device of the invention includes a light source for providing alight beam, and a filtering means. The filtering means includes red, green and blue filtering sections. The blue filtering section has coatings of different transmittances. The intensity of blue primary color light is varied due to the different transmissivities of the blue filtering section, so that the ratio of blue primary color light in a hybrid light is modified to cause change in color temperature with a reduced loss of brightness. Then, the filtering means is moved so that the light beam is projected at a predetermined location to obtain the desired color temperature. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0009]    The drawings included herein provide a further understanding of the invention. A brief introduction of the drawings is as follows:  
         [0010]    [0010]FIG. 1 is a schematic view of a conventional projecting device;  
         [0011]    [0011]FIG. 2 is a schematic view of a projecting device with adjustable color temperature according to one embodiment of the invention;  
         [0012]    [0012]FIG. 3 is a front view of a filtering means according to a first embodiment of the invention;  
         [0013]    [0013]FIG. 4 is a graph illustrating the relationship between the transmissivity and the location of the blue filtering section according to one embodiment of the invention;  
         [0014]    [0014]FIG. 5 is a front view of a filtering means having a white filtering section according to one embodiment of the invention;  
         [0015]    [0015]FIG. 6 is a graph illustrating the relationship between the wavelength and visual sensitivity; and  
         [0016]    [0016]FIG. 7 is a front view of a filtering means according to a second embodiment of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0017]    To provide a further understanding of the invention, the following detailed description illustrates embodiments and examples of the invention, this detailed description being provided only for illustration of the invention.  
         [0018]    Referring to FIG. 2, a projecting device  20  with adjustable color temperature according to the invention includes a light source  21 , a filtering means  22 , a light valve  23  and a projection lens  24 . The light source  21  generates a light beam which passes through the filtering means  22  to subsequently generate primary color lights of red (R), green (G) and blue (B) colors. The primary color lights then are projected to the light valve  23 . Under control of digital signals of the light valve  23 , red, green and blue color lights are converted into gray scales and then projected on a screen  25  via the projection lens  24 .  
         [0019]    Referring to FIG. 3, the filtering means  22  has at least one red filtering section  221 , one green filtering section  222  and one blue filtering section  223  to respectively separate red, green and blue color lights from the light beam. The red filtering section  221  and the green filtering section  222  respectively have constant transmissivity. The blue filtering section  223  has gradually changing transmissivities. Referring to FIG. 4, the transmissivity decreases from the inside to the outside. Furthermore, the filtering means  22  is a color wheel connected to a moving device (not shown) to allow linear movement of the filtering means  22 . The filtering means  22  is moved to a predetermined location by means of the moving device to change the location where the light beam passes through the blue filtering section  223 , thereby changing the transmissivity and the intensity of blue primary color light through the blue filtering section  223  to achieve change in color temperature. For example, when the light beam passes through part A of the blue filtering section  223  with high transmissivity, a blue primary light with high intensity is generated. The blue primary color light is mixed with red and green primary lights that respectively come from the red and green filtering sections  221 ,  222  and have constant intensities so as to obtain a hybrid light of high color temperature, i.e. cool hybrid light. When the light beam passes through part B of the blue filtering section with low transmissivity, a blue primary light of low intensity is generated. The blue primary color light is mixed with the red and green primary color lights, respectively coming from the red and green filtering sections  221 ,  222  and having constant intensities, to obtain a hybrid light of low color temperature, i.e. warm hybrid light.  
         [0020]    The transmissivitys vary according to different locations of the blue filtering section  223 . The filtering means  22  is moved by the moving device to change the location where the light beam is projected on the filtering means  22  to generate blue primary light of different intensities. Blue color light of different intensities is mixed with red and green color lights respectively having constant transmissivity to achieve adjustment of the color temperature. Referring to FIG. 5, the filtering means  22  further has a white filtering section  224  to increase the brightness, while the transmissivity of other color light filtering sections is kept constant. When the location where the light beam is projected on the filtering means  22  is changed, the intensity of the colored light passing through the white filtering section  224  is not affected, thereby achieving the adjustment of color temperature with reduced loss of brightness.  
         [0021]    Furthermore, each part of the red and green filtering sections  221 ,  222  has constant transmissivity. Therefore, when the moving device changes the location where the light beam is projected on the filtering means  22 , only the intensity of blue primary blue primary light is changeable, while the transmissivity of other color lights such as green primary light and red primary light remains unchanged. Therefore, the loss of brightness is reduced.  
         [0022]    The brightness of color light is the product of irradiancy with visual sensitivity. FIG. 6 illustrates a relationship between the wavelength and the visual sensitivity. Referring to FIG. 6, blue light of wavelength of 380 nm-490 nm has a visual sensitivity lower than green and red lights. Among the different color lights, blue light has minimal influence on the brightness. Therefore, changing the sensitivity of blue primary color light for adjusting the color temperature is achieved with a reduced loss of brightness. In other words, the change in color temperature rarely affects the brightness of an illuminating device.  
         [0023]    Since the transmissivity gradually changes across the blue filtering section  223 , non-uniform color lights therefore are generated all over the blue filtering section  223 . In order to render the color lights uniform, an uniformization element  26  such as an integrated rod is further mounted at a rear end of the filtering means  22  to project a uniform light on the light valve  23 .  
         [0024]    Referring to FIG. 7, a filtering means  32  in another embodiment of the invention includes at least one red filtering section  321 , one green filtering section  322  and one blue filtering section  323  to separate red, green and blue primary color lights from the light beam. The red filtering section  321  and the green filtering section  322  are coatings respectively with constant transmissivitys. The blue filtering section  323  is divided into a plurality of regions  3231 ,  3232  each of which has coatings with different transmissivities. The region  3231  has a transmissivity higher than the region  3232 . The filtering means  32  is further connected to a moving device (not shown) to drive the filtering means  32  to linearly move along the regions  3231 ,  3232 .  
         [0025]    The moving device enables to change the location where the light beam passes through the blue filtering section  323  to modify the transmissivity, so that the intensity of blue primary color light is changed and the color temperature of the hybrid light is changed. When the light beam passes through the high-transmissivity region  3231  of the blue filtering section  323 , as indicated by C in FIG. 7, high-intensity blue primary color light is generated. Blue primary color light then is mixed with red and green primary color lights, respectively coming from the red and green filtering sections  321 ,  322  and having constant intensities, to generate a hybrid light of high color temperature TH. When the light beam passes through the low-transmissivity region  3232  of the blue filtering section  323 , as indicated by D in FIG. 7, low-intensity blue primary color light is generated. The obtained blue light then is mixed with red and green primary color lights, respectively coming from the red and green filtering sections  321 ,  322  and having constant intensities, to generate a hybrid light of low color temperature TL. When the light beam passes between the high-transmissivity region  3231  and the low-transmissivity region  3132 , as indicated by E in FIG. 7, a hybrid light of color temperature ranging form TH to TL is generated according to the transmission of the light beam between the high-transmissivity region  3231  and the low-transmissivity region  3132 .  
         [0026]    It should be apparent to those skilled in the art that the above description is only illustrative of specific embodiments and examples of the invention. The invention should therefore cover various modifications and variations made to the herein-described structure and operations of the invention, provided they fall within the scope of the invention as defined in the following appended claims.