Abstract:
A vehicle occupant is illuminated with infrared light by an apparatus including a display apparatus illuminated with visible light for displaying information to the occupant and an infrared illuminator hidden behind the display apparatus for illuminating the occupant through the display apparatus. In a preferred embodiment, the display apparatus is a liquid crystal display (LCD) mounted in the vehicle instrument panel for displaying images and data to the driver, and infrared light emitted by the infrared illuminator is transmitted through the LCD to illuminate the occupant.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to infrared illumination of a vehicle occupant, and more particularly to apparatus for unobtrusively mounting an illuminator in a vehicle instrument panel. 
       BACKGROUND OF THE INVENTION 
       [0002]    Infrared lighting is generally used in vehicle systems that produce digital images of the vehicle occupants. For example, a digital image of the vehicle driver can be analyzed to determine a direction of the driver&#39;s gaze, or to detect eye or head movement characteristic of a drowsy driver. Infrared lighting is used for these systems because it is imperceptible to the occupant, and provides consistent illumination of the occupant under various ambient lighting conditions. One of the implementation issues concerns how and where to install the illuminator and imager such that the occupant is adequately illuminated without unduly disturbing the aesthetics of the vehicle or occluding portions of the instrument panel. For example, the illuminator and imager for a driver may be mounted at the base of the instrument cluster or on a stationary portion of the steering column, but it is difficult to do so in a way that does not detract from the vehicle aesthetics or partially occlude the instrument cluster. Accordingly, what is needed is a way of illuminating an occupant with infrared light that provides adequate illumination without affecting the vehicle aesthetics or occluding the instrument panel. 
       SUMMARY OF THE INVENTION 
       [0003]    The present invention is directed to an improved apparatus for illuminating a vehicle occupant with infrared light, including a display apparatus illuminated with visible light for displaying information to the occupant and an infrared illuminator hidden from occupant view for illuminating the occupant through the display apparatus. In a preferred embodiment, the display apparatus is a liquid crystal display (LCD) mounted in the vehicle instrument panel for displaying images and data to the driver, and infrared light produced by the infrared illuminator is transmitted through the LCD to illuminate the occupant. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]      FIG. 1  depicts a vehicle occupant, instrument panel and steering wheel, and a panel-mounted display apparatus according to this invention; 
           [0005]      FIG. 2  is a diagram of a preferred embodiment of the panel-mounted display apparatus of  FIG. 1 , including a panel-mounted LCD illuminated with visible light and an infrared illuminator disposed in the instrument panel behind the LCD; 
           [0006]      FIG. 3  is a graph depicting infrared light transmissivity of the LCD of  FIG. 2  for different display settings of the LCD; and 
           [0007]      FIG. 4  is a diagram of an alternate embodiment of this invention including a panel-mounted graphic applique illuminated with visible light and an infrared illuminator disposed in the instrument panel behind the graphic applique. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0008]    Referring to  FIG. 1 , the reference numeral  10  generally designates the cabin portion of a vehicle, including a seat  12 , an instrument panel  14 , a steering column  16  and steering wheel  18 , and a display apparatus  20  mounted in the instrument panel  14  for viewing by an occupant  22  of seat  12 . The occupant  22  can be the vehicle driver as shown, but the apparatus of this invention is also applicable to other vehicle occupants. 
         [0009]    It will be understood that the illustrated vehicle is equipped with an occupant monitoring system in which the occupant  22  is illuminated with infrared light and a video imaging system responsive to the infrared light reflected from occupant  22  captures and processes video images of occupant  22 . An example of such an occupant monitoring system is described in the U.S. Pat. No. 7,253,739 to Hammoud et al., assigned to the assignee of the present invention, and incorporated herein by reference. The monitoring system of Hammoud et al. is designed to detect driver eye closure, and includes one or more infrared LEDs for illuminating the driver&#39;s face, and a video imaging camera mounted on the steering column or in the instrument panel forward of the driver. The present invention is not directed to a driver monitoring system per se, but to infrared vision systems in general, and in particular to an apparatus for illuminating a vehicle occupant  22  with infrared light in a way that provides adequate illumination of the occupant  22  without affecting the vehicle aesthetics, occluding the instrument cluster of instrument panel  14 , or taking up space on the instrument panel  14 . Moreover, the apparatus of the present invention may be installed in connection with a display apparatus located in a panel other than instrument panel  14 , such as in a console, or center-stack navigation or entertainment unit, or a seat back or headrest. 
         [0010]    As shown more clearly in  FIG. 2 , the display apparatus  20  includes an LCD assembly  24 , a long-pass filter  26  that transmits infrared light but reflects visible light, a set of IR LEDs  28 , and optionally a digital imaging chip  30 . The LCD assembly  24  comprises a color LCD  32  and a primary color lighting apparatus  34  for illuminating LCD  32  with visible light. In the illustrated embodiment, the lighting apparatus  34  comprises an acrylic lightpipe  36  that is side-lit with visible light by a set of red, blue and green LEDs  38 . The lightpipe  36  diffuses the visible light emitted by LEDs  38 , and projects it forward toward LCD  32  by internal reflection as illustrated in  FIG. 2 . Visible light emitted rearward of the lightpipe  36  is reflected forward by long-pass filter  26 . Finally, the IR LEDs  28  (and optionally, the imaging chip  30 ) is mounted on a circuit board  40  disposed rearward of the long-pass filter  26 . Infrared light emitted from the IR LEDs  28  passes through the long-pass filter  26 , the light pipe  36  and the LCD  32  as indicated to illuminate the occupant  22  for imaging purposes. 
         [0011]    Although it would seem that the LCD  32  would not transmit infrared light very well, or that its infrared transmissivity would vary markedly depending on what is the LCD is displaying, we have found that an LCD transmits infrared light surprisingly well, and that its infrared transmissivity is substantially independent of what the LCD is displaying. This phenomenon is graphically illustrated in  FIG. 3 , where traces  42 ,  44  and  46  depict the radiance of light transmitted through an LCD when backlit by an infrared LED as shown in  FIGS. 1-2 . Trace  42  represents the radiance when the LCD is off, trace  44  represents the radiance when the LCD is activated to display a solid white image, and trace  46  represents the radiance when the LCD is activated to display a solid black image. In the typical near-infrared range of 800 nm-1,000 nm, there is essentially no difference in radiance, the import of which is that the infrared light emitted by IR LEDs  28  will adequately and equivalently illuminate occupant  22  regardless of what is displayed by LCD  32 . 
         [0012]    The imager chip  30  may be co-located with IR LEDs  28  as shown, or alternately may be separately mounted in the instrument panel  14 , as indicated in phantom by the reference numeral  30 ′. In applications where low to medium resolution imaging is sufficient, co-locating imager chip  30  with IR LEDs  28  is practical. However, in applications where high resolution imaging is required, we have found that it is best to mount the imager chip separately, as shown in phantom for example. 
         [0013]    Referring to  FIG. 4 , the reference numeral  20 ′ depicts an alternate display apparatus in which the LCD  32  of  FIGS. 1-2  is replaced by an applique  50  in which an opaque coating  52  on a transparent or translucent panel  54  is selectively removed to define a window  56 . The window  56  may be in the shape of a graphic symbol, or alpha-numeric character, or simply a circular or rectangular marker such as in the face of a gauge. The visible light produced by lighting apparatus  34  is transmitted through the applique window  56  to display the symbol, character or indicia to the occupant  22 , and the infrared light produced IR LEDs  28  passes through the long-pass filter  26 , the light pipe  36  and the applique window  56  as indicated to illuminate the occupant  22  for imaging purposes. In an alternate mechanization, the color LEDs  38  may be mounted with IR LEDs  28  on circuit board  40 ; this eliminates the need for lightpipe  36  and long-pass filter  26 . In any case, the apparatus of the present invention may be installed in connection with an applique located in a panel other than instrument panel  14 , such as in steering wheel  18 , a console, a or center-stack navigation or entertainment unit, or a seat back or headrest, for example. 
         [0014]    In summary, the present invention provides an improved way of illuminating a vehicle occupant with infrared light. The aesthetics of the instrument panel are unaffected by the lighting apparatus, the illumination is independent of the tilt angle of the steering column  16 , and the driver&#39;s view of the instrument cluster remains unobstructed. While the present invention has been described with respect to the illustrated embodiments, it is recognized that numerous modifications and variations in addition to those mentioned herein will occur to those skilled in the art. For example, the visible lighting apparatus  34  may be different than shown, and so forth. Accordingly, it is intended that the invention not be limited to the disclosed embodiment, but that it have the full scope permitted by the language of the following claims.