Abstract:
A transmissive display device. The transmissive display device comprises a transmissive display panel positionable in a viewing position by a user and including a viewing front surface and a light-receiving rear surface, a reflective surface that is positionable by a user to receive ambient light and reflect it toward the rear surface and though the transmissive display panel, and an un-grooved transmissive ambient light diffuser, without annular rings, positionable by a user so that ambient light is transmitted through the diffuser to thereby cooperate with the reflective surface to provide diffuse ambient light to the rear surface of the transmissive display panel.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a divisional application of U.S. patent application Ser. No. 10/902,962, filed Jul. 30, 2004 which is a continuation of U.S. Pat. No. 6,795,137, filed Apr. 26, 1999. This application is also related to co-pending divisional U.S. patent application Ser. No. (attorney docket number 116617.04), filed Dec. 13, 2004. This application is related to co-pending U.S. patent application Ser. No. 10/870,235 filed Jun. 16, 2004, which is a divisional application of U.S. Pat. No. 6,795,137. This application is also related to co-pending U.S. patent application LCD WITH POWER SAVING FEATURES Ser. No. 09/299,522, filed Apr. 26, 1999. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to methods and apparatus for implementing display devices and, more particularly, to methods and apparatus for reducing the amount of electrical power required by display devices, e.g., transmissive and/or transreflective liquid crystal display (LCD) devices.  
       BACKGROUND OF THE INVENTION  
       [0003]     Displays are found in numerous commercial and consumer devices. Because of various physical characteristics, flat panel displays tend to be favored over cathode ray tube (CRT) displays in many applications where size, weight and/or power consumption is of concern.  
         [0004]     Flat panel displays, including e.g., liquid crystal display (LCD) devices come in many different sizes. Small LCD devices are used in applications ranging from calculators and wristwatches to point-of-sale terminals and gas pumps. Larger LCD devices are found in portable computers, desktop computer displays, and numerous other devices.  
         [0005]     Known LCDs are frequently implemented as reflective, transmissive, or transflective devices. A reflective LCD, as the name implies, uses reflection to illuminate the display.  FIG. 1  illustrates a known reflective LCD  102 . The reflective LCD  102  includes a closed housing  109  which contains a liquid crystal cell  104  and a reflector  110 . A screen  105  made of, e.g., glass, is used to seal the front of the closed housing  109 . Light from an external light source  106  passes through the screen  105 , liquid crystal cell  104  and is then reflected back towards the eye  108  by the reflector  110  located behind the liquid crystal cell  104 . The liquid crystal cell includes, for example, front and rear polarizers with a layer of liquid crystal material sandwiched there between. The light absorptive characteristics of the liquid crystal cell are varied by changing an electric field applied to the layer of liquid crystal material. Thus, by varying an electric field images may be displayed on the LCD  102  and perceived by a viewer represented by the eye  108 .  
         [0006]     Reflective LCDs are generally the least expensive type of LCD and use the least amount of power. Reflective LCDs rely on ambient, e.g., external natural or artificial light sources for illumination. Accordingly, reflective LCDs do not include a backlight. Such displays operate satisfactory in well lit locations. However, because they lack an internal light source they are difficult to read in low light conditions which are often encountered indoors. For this reason, reflective displays have not found wide spread use in portable computers or other devices which may need to be used in low light conditions.  
         [0007]     Transmissive LCDs such as transmissive LCD  103 , illustrated in  FIG. 2 , use an internal light source  107 , referred to as a backlight, for illumination. In the transmissive LCD  103 , the backlight  107  is enclosed in an opaque housing  110  behind the liquid crystal cell  104  and display screen  105 . Light from the backlight  107  passes through the liquid crystal cell  104  and display screen  105  before being perceived by a viewer, represented by the eye  108 . Since the housing  110  is opaque, natural and/or ambient light from behind the housing is prevented from entering the liquid crystal cell from the rear of the housing.  
         [0008]     Transmissive displays are well suited for use indoors under artificial lighting. For this reason, transmissive LCDs are frequently used in, e.g., portable computers and lab instruments. One drawback to transmissive displays is that they consume a relatively high amount of power due to the use of the backlight. In portable devices such as battery powered notebook computers, minimizing power consumption is important. Power consumption by the backlight is a major factor in determining the amount of time portable computers can be used between recharges.  
         [0009]     Many portable computers include a brightness control which allows the intensity of the backlight used in a transmissive display to be manually adjusted by a system user. While manually adjusting the display brightness to the minimum setting which is acceptable to the user for a particular set of room conditions can maximize the time before the computer needs recharging, users are not accustomed to adjusting the brightness of their displays each time they move to a different room or ambient lighting conditions change. To allow for a transmissive display to be used in a wide range of conditions, the brightness of the display is normally set to a value which exceeds the brightness required for normal room conditions, e.g., so that the display can be used in higher than normal lighting conditions without having to adjust the brightness. Unfortunately, such intensity settings tend to waste power which, as discussed above, is a limited resource in the context of most portable devices.  
         [0010]     Since the amount of power delivered by batteries is often a function of their size and thus weight, it is desirable to minimize power consumption requirements in portable devices to allow for longer periods of use between battery recharges and/or the use of smaller, lighter, batteries. It is desirable that any methods and apparatus directed to power conservation be at least partially automated so that a user need not make display adjustments each time lighting conditions change.  
         [0011]     In addition to relatively high power consumption, another disadvantage of the known transmissive LCD  103  is that such displays are usually hard to read in direct sunlight. The difficulty in reading such displays in direct sunlight arises from the fact that incident sunlight reflected from the display screen  105  can be quite bright compared to the intensity of the light, originating from the backlight  107 .  
         [0012]     While some manufacturers of transmissive LCDs have incorporated high output backlight to enable out of doors use of transmissive displays, the relatively high power consumption of such devices renders them unsuitable for most battery powered applications.  
         [0013]     Another type of known LCD device is the transflective LCD  111  illustrated in  FIG. 3 . Transflective LCD  111  combines features of the reflective and transmissive LCDs discussed above. As illustrated, a transflective LCD  111  includes a liquid crystal cell  104 , partially transmissive reflector  116  and a backlight  107 . The transflective display components are enclosed in an opaque housing  114  which is sealed in the front with a screen  105 . Behind the screen  105  is the liquid crystal cell  104 , transmissive reflector  116  and backlight  107 . Because the housing  114  is opaque, it prevents external, e.g., natural or ambient light from entering from the rear of the housing.  
         [0014]     In the transmissive display  111 , the reflector is normally a white or silver translucent material that reflects some of the ambient light entering from the front, i.e., viewing side or surface, of the display  106  while still allowing light from the backlight  107  to pass through. Transflective LCD  111  is useful in a wide range of lighting conditions. For this reason, LCD  111  is frequently used where a display must function in both day and night light conditions, e.g., in gas station pump displays. Transflective displays suffer from some of the same power consumption problems, associated with the use of a backlight, discussed above in regard to transmissive displays. In addition, transflective displays tend to have relatively poor contrast ratios since partially transmissive reflector  116  must be partially transparent to let light from the backlight through.  
         [0015]     In view of the above discussion it is apparent that there is a need for improved displays, e.g., LCD displays, which can be viewed easily in a wide range of light conditions. It is desirable that at least some of the new displays be capable of implementation without a backlight and the power consumption associated therewith.  
         [0016]     From the above discussion, it is also apparent that there is a need for methods and apparatus directed to reducing the amount of power utilized by displays which incorporate backlights.  
       SUMMARY OF THE PRESENT INVENTION  
       [0017]     The present invention therefore provides a transmissive display device, comprising a transmissive display panel positionable in a viewing position by a user and including a viewing front surface and a light-receiving rear surface; a reflective surface that is positionable by a user to receive ambient light and reflect it toward the rear surface and though the transmissive display panel, and an un-grooved transmissive ambient light diffuser, without annular rings, positionable by a user so that ambient light is transmitted through the diffuser to thereby cooperate with the reflective surface to provide diffuse ambient light to the rear surface of the transmissive display panel.  
         [0018]     In accordance with a further aspect of the present invention a transmissive display device, comprising a transmissive display panel positioned in a viewing position and including a viewing front surface and a light-receiving rear surface, a reflective surface that receives ambient light and reflects it toward the rear surface and though the transmissive display panel, and an un-grooved transmissive ambient light diffuser, without annular rings secured directly to the light receiving rear surface, through which ambient light is transmitted, the diffuser cooperating with the reflective surface to provide diffuse ambient light to the rear surface of the transmissive display panel is provided.  
         [0019]     In accordance with another aspect of the present invention a portable computer comprising a base portion, a lid portion, including, a first panel assembly, a second panel assembly, and a hinge coupling the lid portion to the base portion, whereby the hinge allows the lid portion to be raised when the device is in use and lowered when the device is not in use is provided.  
         [0020]     In accordance with a further aspect of the present invention a portable computer comprising, a base including a CPU and a keyboard coupled to the CPU, a transmissive display coupled to the CPU, in which the transmissive display is part of a first panel assembly, and the transmissive display has a first viewing surface, and a second surface, an outer diffuser panel coupled to the second surface of the transmissive display to form the first panel assembly, an inner diffuse reflector that is part of a second panel assembly, having a first reflecting surface, and a second surface, an outer protective layer disposed on the second surface of the inner diffuse reflector that is part of the second assembly, and a hinge coupling the first panel assembly between the base and the second panel assembly is provided.  
         [0021]     In accordance with still another aspect of the present invention a method of controlling the backlighting of a transmissive display comprising the steps of measuring a viewed surface light intensity at a viewing surface of a transmissive display, measuring a backlight light intensity at a backlit surface of the transmissive display, comparing the viewed surface light intensity to the backlight light intensity, and adjusting a backlight to maintain a viewed backlight light intensity greater than the viewing surface light intensity is provided.  
         [0022]     Many of the attendant features of this invention will be more readily appreciated as the same becomes better understood by reference to the following detailed description considered in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]      FIG. 1  illustrates a known reflective LCD device.  
         [0024]      FIG. 2  illustrates a known transmissive LCD device.  
         [0025]      FIG. 3  illustrates a known transreflective LCD device.  
         [0026]      FIGS. 4-6  illustrate transmissive displays implemented in accordance with the present invention.  
         [0027]      FIG. 7  illustrates a transmissive display of the present invention which incorporates a backlight.  
         [0028]      FIG. 8  illustrates a transreflective display implemented in accordance with another exemplary embodiment of the present invention.  
         [0029]      FIGS. 9 through 11  illustrate a portable computer incorporating a display implemented in accordance with the present invention.  
         [0030]      FIG. 12  illustrates a portable computer including a light sensor and intensity control circuit implemented in accordance with another embodiment of the present invention.  
         [0031]      FIG. 13  illustrates a transmissive display device of the present invention which includes a plurality of light sensors and an intensity control circuit.  
         [0032]      FIG. 14  illustrates a portable computer implemented using a plurality of light sensors and an intensity control circuit.  
         [0033]      FIG. 15  is a frontal view of the portable computer illustrated in  FIG. 14 . 
     
    
     DETAILED DESCRIPTION  
       [0034]     As discussed above, the present invention is directed to methods and apparatus for reducing the amount of electrical power required by display devices, e.g., LCDs.  
         [0035]     In the description which follows, for the purposes of brevity, elements which are the same as, or similar to one another, will be identified using the same reference numerals. In addition, arrows will be used to illustrate rays of light which may be emitted by, e.g., a natural or artificial light source.  
         [0036]      FIG. 4  illustrates a transmissive display device  200  implemented in accordance with one embodiment of the present invention. The display  200  comprises, e.g., a transmissive display panel  206  which comprises a protective outer layer, i.e., the screen  105 , and an inner layer, implemented as a liquid crystal cell  104 . A translucent diffuser  208  and diffuse reflector  210  are positioned behind the display panel  206  in an angular arrangement to form a back portion and a bottom portion, respectively, of the display  200 . Sides (not shown) coated with a reflective material may be used to seal the remaining rear portion of the display  200  positioned behind the liquid crystal display  206 . Note that in use, a viewer represented by the eye  108  is positioned in front of the display panel  206 . The rear of the display  200  is positioned facing the highest intensity ambient light source present, e.g., the sun  202 . In such an arrangement, ambient light is allowed to pass through the translucent diffuser  208  and is reflected by the diffuse reflector  210  onto the non-viewing side, e.g., rear, of the display panel  206 .  
         [0037]     In such an arrangement, the high intensity ambient light passing through the display panel  206  from the rear should be greater than the amount of ambient light reflected from the viewing side, e.g., front, of the display panel  206 . Such an embodiment allows for viewing of the display in high intensity sunlight and other high intensity ambient light conditions without the need for a powered backlight. The use of the translucent diffuser  208  and diffuse reflector  210  help to eliminate bright spots by diffusing the ambient light before it passes through the display panel  206 .  
         [0038]     It is contemplated that a wide variety of plastic and non-plastic materials may be used to implement the translucent diffuser  208  and diffuse reflector  210 . In one embodiment, a translucent plastic material was used as the translucent diffuser  208  while a white sheet of paper was used as the diffuse reflector  210 .  
         [0039]     As will be appreciated, in portable applications it is desirable that a display be capable of being stored in a relatively small space. Specifically, in portable computer applications it is generally desirable that a display be relatively thin, e.g., no more than a few inches in thickness, and be capable of being folded down flat, e.g., over a computer keyboard.  
         [0040]      FIGS. 5 and 6 , illustrate embodiments wherein displays  203  and  205  of the present invention, are implemented using hinged panels capable of being folded to form a flat assembly for storage and transport purposes.  
         [0041]     In the  FIG. 5  embodiment, the diffuse reflector  210  is attached to the bottom of the display screen  206  via a first hinge  212  while the rear translucent diffuser  208  is attached to the top of the display panel  206  via a second, e.g., top, hinge  214 .  FIG. 5  illustrates the display  203  deployed for use. When deployed, the display  203  assumes, when viewed from the side, a triangular shape similar to that of the display  200 . In order to make the display  203  easy to deploy, sides which would otherwise be used to close off the cavity formed by the diffuser  208 , diffuse reflector  210  and display panel  206  are omitted. When not in use, the translucent diffuser  208  may be folded back on top of the display panel  206  which can then lie flat against the diffuse reflector  210 . Alternatively, the translucent diffuser  214  can be positioned between the display  206  and the diffuse reflector  210  to form a flat assembly with the diffuse reflector  210  on the bottom, diffuser  208  in the middle and the display panel  206  on top.  
         [0042]      FIG. 6  illustrates another display  205  which can be folded flat. In this embodiment, the second hinge  214  is eliminated and the translucent diffuser  208  is secured directly to the back of the display panel  206 . A first hinge  212  is located at the intersection of the bottom of the combined display panel/diffuser assembly and the diffuse reflector  210 . The first hinge  212  is used to allow the folding down of the display panel assembly to form a flat display for storage and/or transportation purposes.  
         [0043]     The displays illustrated in  FIGS. 4, 5  and  6  eliminate the need for a backlight through the use of ambient light for illumination purposes. However, in low light conditions, or in conditions where light is generally of uniform intensity in all directions, use of a supplemental light source, e.g., a backlight, may be desirable. Accordingly, the use of a backlight to supplement ambient lighting is contemplated and employed in various embodiments of the present invention.  
         [0044]     In various embodiments, the display panels  206  used in the  FIG. 4-6  embodiments are mounted in housings which support the display panel  206  and provide a point of attachment for the first hinge  212 . In such an embodiment, the housing may be considered part of the display panel  206 .  
         [0045]      FIG. 7  illustrates a back lit transmissive display  302  implemented in accordance with one embodiment of the present invention. The display  302  includes a display panel  206  behind which a backlight  207  is located. The backlight  207  is located in a housing which utilizes diffuse reflectors  210  for sidewalls and a translucent diffuser  208  to close the rear of the housing. The diffuse reflectors  210  act as a light pipe and serve to direct ambient light entering through the rear translucent diffuser  208  so that it passes out through the display panel  206 . While the translucent diffuser  208  is illustrated directly behind the liquid crystal display, use of the light pipe formed by the diffuse reflectors  210  allows for the translucent diffuser to be positioned at various locations that are not necessarily located directly behind the display panel  206 . For example, the translucent diffuser  208  may be positioned at the top of a device incorporating the display  302  or at a position off-set from the display panel  206 .  
         [0046]     The techniques of the present invention involving the use of ambient light can be applied to virtually any type of device which uses a backlight.  FIG. 8  illustrates a transreflective display  304  implemented in accordance with the present invention. Note how in the  FIG. 8  embodiment, the solid (non-translucent) rear of the known transreflective display  111  is replaced with translucent material  208  to produce the display  304 . In the  FIG. 8  embodiment, the translucent material  208  allows natural or artificial ambient light to supplement or replace the light produced by the backlight  207 .  
         [0047]      FIG. 9  illustrates a portable computer device  400  implemented in accordance with the present invention. The computer device includes a base portion  406  for housing a CPU, memory, a keyboard, etc, and a lid portion including first and second panel assemblies  402 ,  404 . A hinge  408  is used to connect the lid portion of the computer  400 , to the base portion  406 . The hinge  408  allows the lid portion to be raised, e.g., when the computer is in use, and lowered e.g., for storage and/or during transport.  
         [0048]      FIG. 10  illustrates the computer system  400 , with the lid portion in the raised position. In this position, the keyboard  407  included in the base portion  406  is both visible and accessible to a user of the computer  400 .  
         [0049]      FIG. 11  illustrates the computer system  400  arranged for use. In the  FIG. 11  arrangement the upper portion of the lid  402  has been lowered to a fully open position. The upper portion  402  is positioned in  FIG. 11  so that it extends parallel to the base portion  402 . The upper lid panel  402  includes an inner diffuse reflector  210  and an outer protective layer  212  made of an opaque material. The lower panel  404  of the lid comprises an outer diffuser panel  208  which is secured to an inner display panel  206 .  
         [0050]     The upper panel  402  of the lid is positioned at an angle relative to the upper lid panel  402  so that ambient light falling on the upper lid panel will be reflected by the diffuse reflector  210  through the diffuser panel  208 .  
         [0051]     In order to supplement the natural illumination supplied to the rear of the display panel  206 , in the  FIG. 11  embodiment, an optional backlight  410  is incorporated into the diffuser panel  208 . The backlight is positioned so that its light output is directed through the display panel  206  as opposed to being directed out the back.  
         [0052]     As discussed above, minimizing power consumption by a backlight is important in order to prolong the amount of time a battery powered device can operate before the battery needs to be charged or replaced.  
         [0053]     In most portable computer devices, backlight intensity is controlled by a user accessible control, e.g., a potentiometer. In most known computer devices, the brightness of the backlight is fixed at the intensity determined by the user. As ambient light conditions change, e.g., the intensity of light impinging on the front of the display screen decreases, it may be possible to decrease the intensity of the backlight, and thus save power, without having a substantial negative impact on the readability of the displayed images. Unfortunately, most portable computer users are unwilling to manually adjust the brightness of the display each time ambient light conditions change resulting in the wastage of power. Power wastage occurs from setting the brightness control higher than is required so that frequent adjustments to a display&#39;s brightness need not be made.  
         [0054]     The inventors of the present application recognized that by automating all or part of the backlight intensity adjustment process, to take into consideration changes in ambient light conditions, power savings could be achieved. In accordance with one power saving feature of the present invention a photo-sensor is used to measure the intensity of light impinging on at least a portion of the front of a display screen. The result of this light measurement is then used to control backlight intensity. By measuring ambient light conditions and adjusting backlight intensity, e.g., at power up and/or periodically during use, the intensity of the backlight is adjusted so that it does not significantly exceed a level required to display images in a manner deemed suitable by a user of the system. A user may indicate the desired degree of contrast between the incident light and the light output by a display by manually adjusting a brightness control. By automatically adjusting backlight intensity as a function of ambient light conditions, power savings can be achieved. User selectable normal and power saving modes of operation are easily supported. In the power saving mode a minimal backlight intensity is maintained as a function of detected light conditions. During normal mode operation a somewhat brighter screen appearance is maintained.  
         [0055]      FIG. 12  illustrates a portable computer  500  implemented in accordance with one exemplary embodiment of the present invention. The portable computer  500  comprises a base portion  506 , keyboard  507  and a hinge  508 . The hinge  508  attaches a display comprising a backlight  510 , diffuser  509 , transmissive display panel  206  and a photo-sensor  502 . The photo-sensor  502  is mounted on the front of the display panel  206  so that the intensity of light falling on the front of the display panel  206  can be measured.  
         [0056]     The portable computer  500 , further comprises a backlight intensity control circuit  503  and a brightness control circuit  504  which are used to control the amount of power supplied to the backlight  510  and thus the intensity of light supplied to the rear of the display panel  206 . The intensity control circuit may be implemented using software routines executed by a CPU included in the base portion  506 . The brightness control circuit  504  may be implemented as a potentiometer which has one terminal coupled to a power supply represented by the symbol PS and another terminal coupled to the intensity control circuit  503 . A user may adjust the potentiometer, e.g., by turning a knob, thereby adjusting the brightness control signal supplied to the intensity control circuit  503 .  
         [0057]     The intensity control circuit  503  determines the amount of power supplied to the backlight  510  as a function of the output of the photo-sensor  502  and the received brightness control signal. The intensity of the backlight  510 , as a function of the photo-sensors and brightness control outputs, is adjusted so that the perceived brightness of the display will remain generally constant despite changes in ambient light conditions. Accordingly, when the output of the photo-sensor  502  indicates an increase in the intensity of the ambient light striking the screen  206 , the power to the backlight  510  will be increased. As the intensity of the ambient light striking the screen  206  decreases, the intensity control circuit decreases the power supplied to the backlight  510  and thus the intensity of the light output therefrom. A minimum power level is set, e.g., pre-programmed, for the backlight  510  to insure that the display will be readable in low light conditions.  
         [0058]     In one embodiment, even if the output of the photo-sensor  502  indicates little or no incident light, the intensity control circuit  503  does not lower the power output to the backlight  510  below a preselected threshold to insure that in dark or dimly lit conditions, images on the display panel  206  will remain visible. In such an embodiment, intensity control circuit  503  maintains backlight light output between a minimum threshold level and full intensity as a function of the output of the photo-sensor  502  and the brightness control circuit  504 .  
         [0059]      FIG. 13  illustrates a transmissive display  501  which uses natural or ambient light, in accordance with the present invention, to supplement light provided, when required, by a backlight  207 . The structure of the display  501  is similar to that of the display  302 . However, to insure energy efficient control of the backlight  207 , the display  501  includes a front photo-sensor  502 , a rear photo-sensor  512 , an intensity control circuit  505  and a manual brightness control device  504 . In the  FIG. 13  embodiment, the intensity control circuit  505  receives signals indicating the amount of light shining on the rear of the display panel  206  from the rear photo-sensor  512  and the amount of light shining on the front of the display panel  502 . In order to maintain the brightness at the user selected level, indicated by the output of the control device  504 , the intensity control circuit adjusts the amount of power supplied to the backlight  207  so that the difference between the signals generated by the front and rear photo-sensors  502 ,  512  remains constant, or relatively constant, despite changes in ambient light conditions.  
         [0060]     While the rear photo-sensor is shown inside the display housing so that it measures the light, including the light from the backlight  207 , impinging on the rear of the display panel  206 , it is contemplated that the intensity control may be performed as a function of a measurement of light impinging on the exterior rear of the housing, e.g., on or near the diffuser  208 . In one particular embodiment, backlight control is achieved using signals received from a front photo-sensor  502  and a rear photo-sensor  512  positioned on the exterior of the display  501 . Such an embodiment is possible since the amount of light which will be generated by the backlight  207 , given a particular power input, can be predicted with reasonable certainty in most monitors.  
         [0061]      FIG. 14  illustrates a portable computer system  503  which is similar in construction to the previously described computer system  400 . Unlike the computer system  400 , the computer system  503  includes front and rear display panel sensors  502 ,  512 , a backlight intensity control circuit  505  and a manual brightness control circuit  504 . The various components operate as described above to adjust backlight intensity as a function of the measured intensity of ambient light incident on the rear of the display panel and the measured intensity of ambient light on the front of the display panel. In the  FIG. 14  embodiment, the photo-sensor  512  is mounted on an exterior portion of transmissive diffuser  208  or on a portion of a display housing  504  (see  FIG. 15 ) used to mount the panels  206 ,  208 . Accordingly, in such an embodiment, the photo-sensor  512  detects ambient light reflected by the reflector  210  towards the rear of the display panel  206 .  
         [0062]      FIG. 15  is a frontal view of the computer system  503  illustrated in  FIG. 14 . From this view, a display housing  504  used to mount the panels  206 ,  208  and photo-sensor  502 , is visible. In the  FIG. 15  embodiment, the display housing  504  is used to mount the front photo-sensor  502 .  
         [0063]     While the photo-sensors  502 ,  512  have been illustrated in some figures as protruding from the surfaces on which they are mounted, it is to be understood that they may be flush mounted to facilitate folding and storage of the display device into which they are incorporated. In addition, it is to be understood that the intensity control circuit  505  and brightness control circuit  504  may be located internal to the housing  406 .  
         [0064]     It should also be noted that the computer system  503  may include a central processing unit (CPU), a memory device and various software routines which are stored in the memory device and executed by the CPU. The intensity control circuit  505  may be implemented using software which controls the intensity of the backlight  510  as a function of the various input signals which are shown as being supplied to the intensity control circuit  505 . In fact, the intensity control function may be incorporated into, and/or be implemented as, operating system routines executed by the CPU included in the computer  500 .  
         [0065]     While numerous exemplary embodiments of the methods and apparatus of the present invention have been described above, it will be apparent to one of ordinary skill in the art, in view of the above description of the invention, that numerous additional embodiments are possible without varying from the scope of the invention.