CA2110532C - Liquid-crystal display unit for electronic display - Google Patents

Abstract

LIQUID-CRYSTAL DISPLAY UNIT FOR ELECTRONIC DIRECTORY

ABSTRACT OF THE DISCLOSURE

A liquid-crystal display, preferably eighteen lines of forty characters each, is mounted in a case. The temperature of the display medium is held within operating limits for the display -- notwithstanding ambient temperature and humidity variations over generally normal ranges for at least the tem-perate zones, and even if the display unit receives direct sunlight. The unit works outdoors, at temperatures to at least 46 °C (115 °F) as well as in buildings with no temperature control. This is accomplished by use of a shading hood, and a window (preferably unperforated polycarbonate, curved, upward-and-outward-concave, and cylindrical-segment) that reflects to a viewer only light from the hood underside. No ventilating fan, plenum or other ventilating opening is needed. A circuit-board-mounted temperature sensor controls the contrast-adjust-ing voltage of the display -- using data in a digital-memory "look up" table. A heater is preferably provided, also temper-ature-controlled. The entire unit can be flush-mounted in a wall without disrupting operation. Visible glare arising in reflection at the window is reduced by the hood-and-window combination, without need for any antireflection coating on the window.

Description

BACKGROUND
1. FIELD OF THE INVENTION
This invention relates generally to practical display units for electronic directories and like electronic tabulations for public viewing; and more particularly to a display unit for an electronically controlled directory that employs a liquid-crystal display.

2. PRIOR ART
Directories are commonly posted in the public lobbies of business buildings, apartment houses, multiple-building condo-r~ilG~»2 t' minimum complexes, and other multiple-occupant facilities. In 2 secured facilities, the entries in such directories often include room or suite numbers, or other numbers for use With an 4 adjacent telephone or intercom in contacting individual occu-pants to gain admission.
In a few large facilities, in recent years, hand-lettered or movable-letter directories have given way to electronic systems that are much easier to revise. Such systeAS eliminate tedious manual reshuffling of placards or letters to keep entries in alphabetical order and to accommodate subdivision or 11 consolidation of occupant suites.
12 Although they are an enormous improvement over manual 13 directories, the electronic systems have suffered from a major 14 limitation in their use of cathode-ray-tube (CRT) display units. Such video display units, in the forms currently t6~ encountered in commercial practice, have several well-known drawbacks.
The drawbacks of CRT displays include image instability, poor resolution and (particularly in bright light) poor con-trast. Instability of the image, ranging from minor flicker to 21 , vertical roll, can make reading the information on the screen 22 difficult.
23 Poor resolution severely limits the number of entries that 24 can be displayed simultaneously on a screen of moderate size.

;, , ; . - . , .4 ~ ., f S ~~z This strategy sometimes leads to very large screens that 2 visually dominate a lobby.

tive, because the CRT or video colors inject an incongruously gaudy element into a fine decor.
CRT displays are particularly troublesome in brightly lit environments such as outdoors and in lobbies surrounded by large windows that admit brilliant sunlight. In these circumstances, contrast can be so inadequate that the displays are almost completely unreadable.
Moreover, CRT displays are relatively expensive. In large formats they are too deep (front to back) for straightforward mounting in a wall -- and so require provision of a free-standing or recessed support structure enclosure two or three feet deep. Because of their evacuated-chamber construction, they are also relatively fragile and inordinately subject to vandalism.
Other display types -- light-emitting diode (LED) and liquid-crystal displays (LCD) -- are known for use with electronic information processors. Before introduction of our directories disclosed earlier, LCD displays were not effective or in common use for directories or other large electronic tabulations for public viewing; we shall explain some reasons for this shortly.
Most LEDs require relatively bulky apparatus for each character to be displayed. Furthermore LEDs are quite dim, and in the few very-small-screen outdoor applications where they have been used (such as some automatic-teller machines) f r ~~lt~~~~
they are extremely hard to read -- even when elaborately 2 shaded. A larger LED array such as required for a directory 3 would be prohibitively difficult to shade effectively and would be inordinately expensive.
Under ideal conditions, liquid-crystal displays are capa-6 ble of excellent contrast and resolution, are plainly readable even in the brightest light, and are readily backlighted for nighttime use. Their use also results in a far less expensive and much more compact product package. LCDs are accordingly excellent for directories and the like, and the LCD directories 11 disclosed in the above-mentioned parent applications have been 12 very successful; but LCDs do have important limitations.
13 An LCD has a display medium -- the liquid-crystal fluid 14 itself -- and a structure which contains the fluid. Tn at least some commercial LCDs this structure typically includes 16~ two planar pieces of material with the medium sandwiched between them. At least the piece on the viewing side of the sandwich, which in this document we will call the LCD "face,"
19 ordinarily is transparent glass or plastic.
Electrodes are formedon the opposed interior surfaces of 21, this sandwich. These electrodes too are ordinarily transparent 22 on at least the a a side. One elecErode material is intrinsic 23 tin oxide.

24 Both the fluid glass are very sensitive to temper-and the ature. (It may be recalledthat the early applications of I S . ~ , ' :. : . " ..

~~1~~~~z 1 liquid-crystal displays were as novelty items, particularly including thermometers.) 3 If the temperature of the glass rises beyond certain 4 relatively narrow limits, the display develops dark spots, or the entire display may actually turn dark. As we understand 6 it, this darkening is due to an expansion of the cell gap 7 within the glass. The black characters or other symbols then 8 fail to stand out well against the darkening background.
On the other hand, if the temperature falls too much, the changing of characters begins to be very slow, an effect which 11 is said to be related to increasing viscosity of the medium.
12 As temperature decreases further the display blushes a differ-13 ent color (e-, pink) -- this time due to contraction of the 14 cell gap -- and again becomes unreadable.
Directory applications would call for use of the larger 16~ graphic LCDs, and also for a type of medium known as "super-17 twist" fluid. This kind of fluid provides far superior con-18 trast and hence significantly better readability. The large 19 LCDs, however, and especially those using supertwist fluid, are particularly sensitive to temperature.

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temperature-sensitive. LCD wristwatches also take advantage of 2 the wearer's limited temperature tolerance, and heat conduction 3 to and from the wearer's body, to limit the severity of temper-4 atures to which the display is exposed.
Even under such relatively protected conditions, fading 6 and blushing of wristwatch displays is well known to athletes and workers whose activities reach the anticipated design 8 limits of the watches.
LCDs are also used for many usually indoor applications such as calculators and laptop,computers. Here too they are 11 typically used in temperature-controlled environments, or if 12 they are found to malfunction can generally be moved into such 13 environments.
14 Operation of large LCDs is subject. to temperature problems in lobbies and other indoor entryways, as well as outdoors, if 16~ the locations receive intense sunlight. Temperature rise in 11 such areas sometimes outstrips the capabilities of a building 18 air-conditioning system, and can be severe enough to degrade 19 the performance of an LCD.
If the LCD is inside a case, and protected from vandals by 21, an unbreakable window, as is desirable in our application, the 22 temperature problem can be aggravated much further. This is 23 due to a "greenhouse" effect, in which air trapped between the 24 window and the LCD becomes extremely hot, much like the interi-or of a car left shut on a hot day.

A related problem of LCD temperature sensitivity involves a voltage that is applied to the display medium to control the contrast of the characters relative to the background screen. The necessary voltage for proper contrast varies very strongly and nonlinearly with temperature.
Thus, as the temperature to which the LCD is exposed changes (e-q., between day and night), the LCD contrast requires constant adjustment to prevent characters from disappearing or otherwise becoming illegible. A very nonlinear relationship between the voltage and the temperature renders the problem of automatic contrast-control technique far from straightforward.
For whatever reason, LCDs were not used in sizable directory-type displays before introduction of our own earlier units. Those units in fact dealt very effectively with all the problems described above, and those described in the following paragraphs of this section as well; and were accorded a most favorable commercial reception.
They have, however, left some room for further refinement in that they require cooling fans and power to drive the fans. Our earlier units also require relatively expensive case construction to provide effective ventilation fans, plena and holes while deterring vandalism and theft.
_ g _ n .a ~,.tiu::~~2 1 The use of ventilation fans also draws dirt into the case with the ventilating air. Flow of dirty air through the unit produces an objectionable accumulation of dirt on the inside 4 surface of the window and on the LCD face, a particular annoy-ence near construction sites.
Moreover, because of significant temperature gradients 7 within the case, in our earlier units, we found it necessary to position in the LCD-face region -- just inside the window --9 the temperature sensor needed to develop a temperature-compen-sating voltage for contrast control. This required relatively 11 costly and awkward cabling to the sensor from the circuit board ~2 at the rear of the display-unit case.
14 We will return now to more general discussion of electron-is directories and the like.
16~ Another problem arises in configuration of such devices 11 when outdoor or bright-lobby applications are involved. That 18 is the problem of controlling reflections at glass or plastic , 19 surfaces of the display unit.
Such reflections of the viewing person -- and of objects 21. around. and behind that person, become confused with the dis-22 played characters, making the display very hard to read. When 23 sufficiently bright, these reflections actually obscure the 24 displayed characters.

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1 ' As a verbal shorthand we shall refer to these confusing 2 and obscuring reflections collectively as "glare." Such glare 3 can be controlled to a certain extent by providing a matte 4 finish on the screen itself, provided that the electronic display screen (such as a CRT screen) is directly exposed to 6 the viewing person. Direct exposure of the display screen is 7 accordingly a conventional teaching of the prior art.
This conventional teaching, however, severely limits the 9 use of electronic directories since it makes them susceptible to vandalism. Direct exposure of the display screen makes it 11 easy for a vandal to break the screen or damage the display 12 unit.
13 Hence there is a conflict between the direct exposure that is reflected at a glass or plastic surface, however, is light not used to develop visible LCD characters -- and, in fact, is light that creates reflections which compete with the already diminished LCD characters.
Thus, again, even if there had been a suggestion of LCD use in electronic directories, such a suggestion would have been particularly likely to meet with immediate rejection in view of the relatively adverse glare-related properties of LCDs.
Our own earlier units, resolved glare problems satisfactorily by use of coatings applied to the window as well as the face of the LCD display. Again, this solution to the glare problem was found entirely satisfactory except for the cost of the coatings.
Finally, even though the electronic directory systems currently available are far more convenient in terms of entering and deleting names than the movable-letter or placard directories, before introduction of our units they still required local procedures for entries or revisions --either at the system itself or through a computer close by.
This arrangement was very inconvenient for buildings with off-site property management, especially when tenant turnover was high and frequent directory changes required.

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All of the above limitations resulted in the relatively limited use of electronic directories before the advent of commercial units corresponding to our inventions. As can now 4 be seen, the prior art failed to provide an adequate display system for directories and the like, particularly for use out 6 of doors and in lobbies or other entryways subject to intense sunlight.

concave instrument-panel window, with a small overhang of the instrument panel that shades the window from steeply inclined rays of direct sunlight. If the driver's eyes are in a relatively narrow range of positions evidently contemplated by the system designers, such a window reflects the inside of the overhang, rather than the driver's own image, into the driver's eyes.
In practice, however, as used in automotive applications the curved window works only if the driver's eyes are in rather exactly the design position -- as to both height and fore/aft distance -- behind the steering wheel. If the driver sits too far forward or sits too tall, relative to design expectations, the driver's view of the instruments is confused by superimposed parts of the driver's own image, or light from the sky or objects behind the driver.
viewers of directories are not subject to standing or sitting in such a constrained fashion. Accordingly the glare-elimination problem is substantially more severe in relation to directories.
SUMMARY OF THE INVENTION
The invention provides a display unit for an electronic directory that is exposed to sunlight; said display unit comprising: a case including a front wall; a liquid-crystal display mounted within the case and comprising a face for displaying directory information in the form of a directory; an aperture defined in the front wall for viewing the display face; a hood mounted to the front wall of the case, extending outward therefrom at the aperture and dimensioned to shade substantially the entire aperture from sunlight at midday; said hood having an undersurface; an external window mounted to the case to protect the liquid-crystal display; said window being shaped, disposed and oriented to reflect into a viewer's eyes substantially only the undersurface of the hood, if the viewer looks at the LCD
from in front of the LCD; and solid-state digital electronic circuitry, electrically interconnected with the liquid-crystal display, for electronically storing directory information and for controlling the liquid-crystal display unit to automatically exhibit stored directory information in the form of a directory having multiple listings in an alphabetical or like order or in classified groupings.
The invention also provides a display unit for an electronic directory that is exposed to sunlight; said display unit comprising: a case including a front wall; a liquid-crystal display mounted within the case and comprising a face for displaying directory information in the form of a directory; an aperture defined in the front wall for viewing the display face; a substantially cylindrical window mounted to the case at the aperture to protect the liquid-crystal display; a hood mounted to the front wall of the case, extending outward from the front wall of the case beyond the center of curvature of the substantially cylindrical window;
and solid-state digital electronic circuitry, electrically interconnected with the liquid-crystal display, for electronically storing directory information and for controlling the liquid-crystal display unit to automatically exhibit stored directory information in the form of a directory having multiple listings in an alphabetical or like order or in classified groupings.
The invention further provides a vandalism-resistant display unit for an electronic directory, comprising: a substantially vandalism-resistant case including a front wall;
a liquid-crystal display, mounted within the case, and having a display medium and a structure for containing the display medium; the liquid-crystal display structure comprising a face disposed in front of the medium, for displaying directory information outdoors in the form of a directory; means for protecting the liquid-crystal display against vandalism and for maintaining the temperature of the liquid-crystal display medium and structure between practical operating limits for the display, notwithstanding ambient temperature and humidity variations over generally normal ranges for at least the temperature zones, and even if the display unit is placed to receive direct sunlight when the sun is out; the protecting and temperature-maintaining means comprising: an external window mounted to the case in the front wall to protect the liquid-crystal display, and means for reducing glare from the window and reducing solar heat loading into the case through the window, said glare-and-heat-loading reducing means comprising: (i) a hood mounted to the front wall of the case, extending outward therefrom above the window, and dimensioned to shade substantially the entire window from sunlight at least at mid-day, said hood having an underside, (ii) configuration of the window in a curved shape, generally concave upward and outward, to reflect into a viewer's eyes only light from the underside of the hood, if the viewer looks at the LCD from in front of the LCD; and solid-state digital -15a-electronic circuitry, electrically interconnected with the liquid-crystal display, for electronically storing directory information and for controlling the liquid-crystal display unit to automatically exhibit stored directory information in the form of a directory having multiple listings in an alphabetical or like order or in classified groupings.
Generally throughout this document including the appended claims we intend such phrases as "shade from sunlight", "reflect all sunlight", "receives no reflected sunlight" etc. to refer only to rays of sunlight received directly from the sun in primary straight-line paths.
Further, by phrases such as "reflect all sunlight" and "reflected sunlight" we refer only to specular reflection of that directly received sunlight.
Of course sunlight approaches our apparatus not only directly but also by reflection from the ground and from nearby buildings, plants and people -- and even from the sky.
Furthermore the transmissive window of our apparatus, like every surface (even a mirror surface) scatters much light as well as reflecting specularly. Except where otherwise clear from the context: (1) from our references to sunlight we explicitly exclude light thus approaching indirectly; and (2) from our references to directions of reflection we explicitly exclude -15b- '<~i:i.~~~~
1 We regard these two properties of the window as mutually 2 independent, in accordance with correspondingly independent claims appended hereto. As will become clear, however,Ithese 4 two aspects of the invention are amenable to being practiced together, and we do prefer to practice the invention with both.

The foregoing may be a description or definition of the present invention in its broadest or most general terms. Even in such general or broad forms, however, as can now be seen the invention resolves the previously outlined problems of the 11 prior art.
12 In particular heat loading is substantially eliminated 13 because the direct rays of the sun are entirely deterred from 14 striking the window at least at midday when heat loading is of primary significance. At those times, the window directly 16~ receives substantially no sunlight to reflect.
At other times, direct sunlight can strike the window, but 18 at those times sunlight is not as intense. Moreover, much of it is reflected outward from the window rather than being admitted to the case.
21 We have tested units in accordance with our invention in 22 desert temperatures up to 46 'C (115' F), and with no ventila-23 tion fans or even ventilation holes. Remarkably, in these 24 tests there was no blush of the LCD display.

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In addition we have found that with this system the temperature distribution within the case is more homogenous, to such an extent that we can reposition -- onto the circuit board 4 at the rear of the case -- the temperature sensor that is used to develop a temperature-compensated voltage to control the 6 LCD. This repositioning allows us to eliminate the previously required costly and awkward cabling between the circuit board and the LCD-face region.

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images. Using a substantially cylindrical-form window has at 2 least one and possibly two further advantages:
First, it can be shown geometrically that with a suitably 4 oriented cylindrical-segmental window it is possible to virtu-ally guarantee -- subject to some qualifications that will be 6 presented in a later section of this document -- that a viewer 7 who looks at the LCD from in front of the LCD can see only one 8 reflection: that of the undersurface of the top section of the 9 hood.
To obtain this condition, if the window at its top edge is 11 substantially tangent to the front wall of the case: (1) the '12 top section of the hood should be made to extend outward from 13 the front wall of the case beyond the center of curvature of ~4 the cylindrical segment that is the window -- or in other words, the hood top section should extend from the front wall of the case by a distance just greater than the radius of curvature of the window -- and (2) that radius should be equal to the sum of the squares of the viewing-aperture height a_ and bottom hood-section length b, divided by twice the latter length: (as+ bs)/2_b.
(By "suitably oriented", however, we do not mean to imply 22 that the window at its top edge must be substantially tangent 23 to the front wall of the case. To the contrary, the desired 24 effect can be obtained with a shorter hood if the upper edge of the window is canted back to a nonvertical orientation; howev-Gv .
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er, this solution does tend to restrict viewing from lower 2 angles.) We do prefer that the hood extend outward by at least the 4 window radius, and as will be recalled this is part of the second independent major aspect of the invention. This condi-tion optimizes the efficacy of glare reduction by intercepting at the hood undersurface rays corresponding to the reflection of the viewer's line of sight.
Although this condition is easily satisfied, we have discovered that the limitations of the glare-reducing curved 11 window in automotive applications are due to failure to observe 12 this requirement. When the hood is not long enough, light from 13 the sky above the viewer's head is more readily reflected into ~4 the viewer's eyes if the viewer's head is not precisely in the ~5 design position; and this is just what happens in the automo-tive situation.
The second, or possible second, advantage of cylindrical windows relates to another geometrical property: very general-ly speaking, a cylindrical window tends to reflect sunlight 20 incident on the window to certain portions of the hood under-2~ surface, and tends to reflect the viewer's gaze to different 22 portions of the hood undersurface. As will be shown later, 23 this selectivity is not absolute, rather being variable with 24 time of day, height and position of the viewer, and portion of 25 the LCD display being viewed.

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Nevertheless these phenomena are present and significant 2 -- and tend to make the viewer's lines of sight congruent, by reflection at the window surface, with portions of the hood 4 undersurface that are not strongly illuminated. The less strongly illuminated are superimposed reflections from a 6 window, in general, the less confusion with objects viewed 7 directly by transmission through the window.
As a practical matter, we are not certain just how much advantage is conferred in this way, because our invention works very well even without this effect. More specifically, at least if the hood undersurface is a dark color and not reflec-12 tive, even brightly illuminated portions do not ordinarily 13 cause significant -- or usually even noticeable -- confusing ~4 reflections.
~5 It is possible, however, that under special circumstances a further important improvement in glare reduction may result from this differentiation between areas of the hood that are strongly illuminated and areas that are reflected into the 19 viewer's line of sight. In particular the benefits of this effect may be important if the hood undersurface becomes very 21. dusty (particularly if the dust is light in color), or if the 22 site is subject to incidence of sunlight at very shallow angles 23 (as when no building, tree etc. is present to block the light 24 from the rising or setting sun).

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-., 1 We are not scientists and cannot fully assess the practi-2 cal significance of all the theoretically available benefits of our invention. We have found, however, that it works and it 4 works well.
Although the invention in its broad general forms as 7 described above thus provides very significant advances rela-8 tive to the prior art, nevertheless for greatest enjoyment of 9 the benefits of the invention it is preferably practiced in conjunction with certain other features or characteristics 11 which enhance its benefits. For example, we prefer that the 12 display unit further comprise a glare-reducing material applied 13 on the liquid-crystal display (but not on the window).
14 With respect to the invention in its above-mentioned " ' st aspect" -- which is to say, characterizing the invention 16~ simply in terms of reflecting to the viewer only portions of the underside of the hood -- we also consider it preferable 18 that the window be curved. A planar window can be used, but a 19 curved window is preferred because the hood length can be relatively shorter, the window itself is mechanically stronger, 21 , and more importantly the readability of the display unit is 22 extended to lower viewing angles.

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window be substantially vertical, in otherwordssubstan-or 2 tially tangent to the front wall the case.The bottom of of 3 the window is thus projected outwardfrom planeof the the 4 front wall.
Preferably the hood structure too is extended outward from 6 the bottom of the aperture (or if preferred from some point below the bottom of the aperture) to meet and support the 8 bottom of the window. Side panels of the hood structure interconnect and stabilize the top and bottom hood sections, and also provide surfaces for holding the window in place.
For best resistance to vandals, we prefer to configure the ~2 hood in a strengthening folded rectangular form, using stain-13 less steel, with an internal curved track or retainer on each ~4 of the inward-facing lateral panels to hold the window. We prefer to make the window of Lexan'" -- a brand of extremely 16~ tough polycarbonate -- heat-formed to the desired curvature described above. The folded steel hood and curved Lexan window 18 mechanically reinforce each other very effectively.
Whether the window is cylindrical or not, we consider it preferable that the window reflect:

22 - substantially all directly received sunlight upward and outward to the hood, and ~1 ~ .~ '~ ,.. ~
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1 - a viewer's own image upward and outward to the underside 2 of the hood (rather than back toward the viewer), and 4 - outward to a viewer only light from a portion of the hood that receives no reflected sunlight near midday.
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In addition, preferably the underside of the hood -- what the viewer sees due to reflection at the window -- is a very dark color, ideally black, and has a matte finish or is other-1U wise given minimum reflectance. The surface in any event 11 should not be not bright enough to make its reflection at the 12 window noticeable, in comparison with the LCD characters seen 13 through the window.
14 As already suggested, we prefer to retain the use of a 15 temperature sensor, as in our earlier units, for monitoring the temperature of the LCD medium to permit automatic adjustment of the LCD contrast-control voltage. Because temperature varia-tion within the case is greatly reduced by our present inven-tion, however, as mentioned above the sensor now can be located 20 directly on the electronics circuit board, thereby rendering 21. the apparatus simpler and less costly.
22 The sensor controls the contrast-control voltage through a r"a' 23 voltage-adjusting circuit that includes an analog-to-digital 24 ("A/D") temperature-conversion stage and a digital electronic ,.. .:, ;:_ .. .;:. . , ,..' _,.:~~ .. : - ,:... , _.... .. .. ' .
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memory. This memory holds a lookup table for establishing 2 desired contrast-control voltages for various temperatures.
3 After some experimentation we have come to prefer this system because the voltage requirement varies strongly with temperature, particularly toward the extremes of the tempera-6 ture operating range, and is difficult to represent in closed form as by a formula. We prefer to include A/D conversion of temperature because representing the voltage-temperature relationship with an analog circuit is relatively difficult and expensive.
» Because that relationship is difficult to represent in ~2 closed form as by a formula, we prefer to use a look-up table.
~3 This approach has the added benefit of allowing us to easily change the relationship to account for differences in display ~5 lots or even different displays we might subsequently use.
We also prefer to provide a heater for raising the LCD
temperature, and to provide "heater-controlling means" for operating the heater only when needed. The heater-controlling means are also responsive to temperature.
20 The LCD face may be guarded against glare by either a 2~ matte finish or an antireflection coating as suggested in our 22 previous applications. For this purpose we now prefer a matte-23 surfaced film with a multilayer antireflection coating, avail-24 able from Optical Coating Laboratories Inc., Santa Rosa, Cali-25 fornia as its type HEA2000.
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1 Fig. Z is an interior side elevation, partly in section, 2 of the Fig. 1 embodiment of the invention;
3 Fig. 2A is a like elevation showing geometrical construc-4 tion lines representing various light rays related to the glare-reduction and heat-load-reduction characteristics of the invention;
7 Fig. 3 is a front elevation of the same embodiment;
Fig. 4 is a block diagram of the programming processing flow for the system and shows the different programming devices that can be used along with the major electronic components 11 used to process their input'; and 12 Fig. 5 is a picture of our handheld programmer -- one of 13 the devices used to program the system manually at the system.

16~ DETAILED DESCRIPTION OF TfIE PREFERRED EMBODIMENTS

18 As seen in Figs. 1 and 2, the preferred embodiment of our 19 display unit has a case 101 that includes a front panel 107.
The case 101 also includes a rear wall 103, left and right side 21 walls 104, 105, a ceiling 106, and a floor 107. We prefer to 22 make the front panel stainless steel and the case painted cold-23 rolled steel.
24 The front panel 102 is hinged to the right wall 105, and provided with a keyed lock 107 that engages a strike groove c= .a ., ~,.~i.~l~~a~
1 formed in the left wall 104 to secure the front panel firmly 2 against the rear parts 103-106 of the case. Formed in the 3 front panel 102 are a viewing port 111, louvres 112 and an 4 array of twelve small square access holes 113, a small hole 114 and a larger hole 115.
The louvres 112 are provided for transmission of sound from an audio speaker 203 (Fig. 2) that is mounted behind the 8 front panel 102. The square access holes 113 accommodate 9 twelve pushbuttons of a standard telephone-type pushbutton array 116. The small hole 114 allows for transmission of sound 11 to a microphone 204 (Fig. Z) that is mounted directly behind 12 the hole. The larger hole 115 is for installation of a post-13 office key lock. If this lock is not used, a plug fills the 14 hole.
The hood structure 131 projects forward (from the front "' 16~ wall 102 of the case) at the bottom of the window aperture 139, 17 as well as at the top. Fig. 1 shows that the top and bottom 18 hood sections 132, 133 are interconnected by tapered side 1,9 panels 134, 135 for strength and some exclusion of laterally approaching ambient light.
21 . Securely mounted in tracks 136 carried on inward-facing 22 lateral surfaces 134, 135 of the hood 131 is the polycarbonate 23 viewing window 117, which carries no antireflection coating.
24 Behind the window 117 is an LCD 120, preferably six to eighteen rows of twenty-six to forty characters each. A bezel 137 ', ~
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~~ a ., r r' 'rl r~iil~~a2 1 inside the case, within the boundary of the viewing aperture 2 139, guards the edges of the LCD face 120. The bezel, integral 3 with the LCD, wraps around the top, bottom and sides of the LCD
4 and accordingly is seen face-on in Fig. 2 as well as Fig. 1.
As previously explained, the window 117 is preferably 6 curved -- and more specifically concave upward and outward, and 7 preferably substantially cylindrical -- to reduce "glare" (as 8 defined above) sufficiently that the LCD 120 can be read. The 9 latter function is particularly important when the LCD is facing away from the incident sunlight.
11 When that is so, the person attempting to read the LCD is 12 facing into the sun, and is brightly illuminated. Under these 13 circumstances the reflected image of the person's own face and 14 surroundings, as would be seen in a generally an window, could be extremely bright and could almost.totally obscure the 16~ LCD. (In our earlier units this problem was overcome by 17 provision of an antireflection coating.) 18 As to the detailed geometry of the hood (and window), our 19 research revealed a family of different solutions. These can be described using the assumption that the window 117 should be 21 substantially vertical at its top edge 119. We believe that 22 this assumption tends to minimize the size of the window and 23 the hood.
24 As one extreme solution (not illustrated), the top section of the hood can be minimized in length by making the top and ~~a.~~~z 1 bottom sections (corresponding to 132, 133 in the illustrated 2 embodiment) equal in length, and selecting a window curvature 3 that brings the outward bottom edge of the window into tangency 4 with the bottom section of the hood. This solution is objec-tionable in that the bottom characters of the display would not 6 be readily visible to people whose eyes would be at a low level 7 relative to the display.
That includes not only children and other relatively short people, but also wheelchair users, automobile drive-up directo ry users, etc. Furthermore, even for users who would be able 11 to look directly into the device -- for example, along an ;;.<
12 essentially horizontal line of sight -- the equal lengths of 13 top and bottom sections would produce a sort of tunnel effect 14 that would be unpleasant.
At the other extreme, in purest mathematical principle the 16~ window would be entirely flat (radius of curvature infinite), the bottom section of the hood zero length, and the top section 18 accordingly of infinite length. Of course a hood of great length would be impractical or at least very uneconomic.
An intermediate solution of optimum economics can be 21, selected using certain other needed input parameters: (1) the 22 aperture height a of the display to be used, (2) the vertical 23 and horizontal distances from the bottom edge of the case 24 aperture to the bottom line of characters of the display, and (3) the assumed vertical and horizontal distances from that ~~ii~~3~
1 line of characters to the lowest eye position which is to be 2 accommodated.
3 Items (2) and (3) suffice to permit straightforward 4 calculation of the greatest permissible bottom-section length _b of the hood. That distance _b in conjunction with item (1), the aperture height a_ -- and the assumption of window verticality at the top of the aperture -- permit similar calculation of the 8 radius of curvature of the window using the formula presented 9 earlier.
That radius in turn yields the forward extension of the 11 top section of the hood: the hood length should be just 12 greater than the radius, or to put it another way the top 13 section 132 of the hood extends just beyond the center of 14 curvature 118 (Fig. 2A). As will now be clear, different display sizes and different installation arrangements call for 16~ different window curvatures and thus different hood configura tions and sizes.

19 We shall offer next a discussion of the selective reflec-tion effects mentioned earlier in this document. As stated in 21 . that discussion, we are not yet certain how important these 22 effects are in practical operation of our invention.
23 Fig. ZA shows that very steeply angled rays 141 of direct 24 midday sunlight either are captured by the hood top section 132 or miss the apparatus entirely. Rays 142 incident near midday ", . ~ - , :<; .. ;.
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lv .L l 1 rays from the LCD (but not necessarily through the topmost part 2 of the window from the bezel) will be confused only with light 3 reflected from relatively rearward regions 154 of the hood 4 underside 132. We give that surface a black matte finish so that most of the illumination that does reach those rearward regions 154 is absorbed, and much of the small residual is scattered omnidirectionally -- so that very little light is 8 scattered from area 149 within the pencil 153, 152 to compete 9 with rays 151 from the LCD.
Thus for a viewer looking horizontally at the center of 11 the LCD, glare is substantially eliminated. It is also readily 12 seen from study of the drawing that there is no angle of view, 13 for any eye position outside the hood, Lhat allows specular 14 reflection at the window into the viewer's eyes from the sky or any other background source 16~ It remains to consider whether there is any angle of view at which information in rays from the LCD can be confused by 18 light reflected from the most intensely illuminated forward 19 portions 145 of the hood undersurface 132. Because the hood 24 top section 132 extends just beyond the window center of curva-21 , ture 118, and in specular reflection the incident and reflected 22 rays form equal angles about the radius to the point (or in 23 this case line) of reflection, the brightest reflected illumi-24 nation -- ordinarily occurring at midday -- strikes the under-side of the hood just behind the center of curvature.

~.s ., ~~3~
r ~ .t 1 In order for the viewer's eye to receive, by reflection 2 from the same surface, light from that most-intensely illumi-3 nated region, the viewer's eye would have to be positioned 4 along the path of incidence -- which is to say, with the ..;,4,..w viewer's head partially within the hood. If the viewer is in that position, the viewer's head will obstruct much or all (depending on the width of ,the display) of the incoming sun- , -light under'consideration; and to the extent that any incoming sunlight remains troublesome the viewer will perceive that this situation can be eliminated by moving just slightly away from 11 the apparatus.
12 At times ear midday, when incoming sunlight is intermedi-13 ate between the illustrated steep and shallow paths 142 and 14 146, that light is reflected to generally forward-to-intermedi-ate regions of the hood. If the viewer in position 161 of Fig.
16~ 2A looks at the forwardmost lower edge of the window, the 17 viewer may be able to see some of those regions'; however, that part of the window will appear to be be ow the bottom edge of the LCD, and therefore will not make any part of the LCD hard to read.
21 As the viewer in position 161 looks instead at the bottom 22 edge of the LCD, through the point marked 155 in the drawing, 23 the point along the hood which is imaged in confusion with the 24 LCD is shifted rearward of the area that is illuminated by reflected sunlight. If the viewer looks at any portion of the .. . : v - '.~ . '-. : .: :'. ,>:: : : :r ' . , . ; :, :. , , .. . : ;, ;
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~~.:~~ ~~2 1 Resulting dimensions for our most highly preferred embodi-ment, which we believe makes an ideal working tradeoff for various field applications, appear in a tabulation several 4 paragraphs below.
Our earlier units employed six metal extenders, spaced along the top and bottom edges of the viewing port, to stand the LCD off from the rear surface of the front panel and 9 thereby define an air space between the viewing window and the LCD. This provision was satisfactory except for the relatively 11 small additional or differential cost of, making the case deep 12 enough (ie., large enough in the front-to-back direction) to 13 accommodate this space -- and the corresponding cost of accom-14 modating the case with this added depth. If desired the case may be made shallower to exploit the potential saving that 16~ results from eliminating the air-space requirement in accor-dance with the present invention.

~;1=ii~~~~
1 we believe that an LCD with a different bezel or no bezel could 2 serve as well.
3 The display can be operated from a microprocessor or even 4 a personal computer or other microcomputer, in very generally conventional fashion. We prefer, however, to use novel elec-6 tronics and software which we have developed. These additional subsystems optimize the performance of the display as part of a 8 novel programmable electronic directory system, as will be 9 described shortly.
Mounted to the system circuit board (rather than immedi-11 ately behind the window as in prior forms of our apparatus) is 12 a thermistor element 123. As in our earlier apparatus, this 13 thermistor is excited and monitored by portions of the elec-14 tropic circuitry 211 within the case 101, and the resulting temperature information is used to control the LCD contrast 16' voltage.
A small strip.heater 212 is advantageously mounted behind 18 the LCD 120. Also as in our earlier units, this heater too is 19 temperature-controlled but need not be made responsive to the thermistor 123. The heater element itself is self regulating:
21. its resistance increases with temperature, tending to reduce 22 heat output. The heater can be a twelve-volt d. c. model CDH
23 00310 commercially available from Midwest Components, Inc. of 24 Muskegon, Michigan.

n .r .f ~ ' ~'~ ~) ~,.1.~~J~~, Approximate dimensions of the apparatus are collected 2 below.

3 ~m nches case 101 height 53~ 21 width 42 16.5 7 depth 11 4.3 port 111 height 17~ 6.9 ' width 27,~ 10.8 12 window 117 height (when 13 flat) 18 7.1 14 radius of curvature 21 g,3 16~ width 27 10.6 17 thickness 0.3 0.13 19 hood width 27 10.7 height 17~' 6.8 21 depth 21 8.3 23 Thus our inve ntion encompasses several important innova-24 tions relating provision of a high-resolution, to high-con-trast, essentiallyglare-free display electronic directo-for ;< ,. r .;:,:- .::: . ,: .:. ,~' .; -: , _;;:. ;. -;
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ries and the like. It is particularly advantageous in outdoor installations, and in building entries or lobbies where temper-ature and brightness of illumination are not well controlled.

Our invention further encompasses important innovations in a programmable electronic directory system. These innovations will be described herebelow.

s;._I..1 ~~cl~
1 Figure 4 gives an overview of the programming processing 2 flow and shows the different programming devices that can be 3 used along with the major electronic components used to process 4 their input. Local programming is generally done using a handheld programmer of our own design (pictured in Fig, 5) 6 which plugs directly into the system electronics via ribbon cable. The programmer is an alphanumeric membrane keypad that 8 simply provides contact closure output. As a result, it is 9 extremely rugged, very thin, small sized, and very inexpensive.
As can be seen from the graphics on the keypad, it as well 11 as our system can do substantially more than provide for an 12 electronic directory. In one of its forms, the system can be a 13 complete access control system providing for both occupant and 14 visitor access control, using card or code entry for occupants and telephone entry for visitors. In this system configuration, 16~ the electronic directory would normally be part of the tele-phone entry function for visitor access control. The microphone 18 and the speaker are for communications between the visitor and 19 the person being contacted in the building whose name is listed on the electronic directory. This system configuration is, 21 however, only one form in which the electronic directory could 22 be used and in no way is intended to limit the scope of our 23 claims.
24 The 12-button keypad, which also provides simple contact closure output, can also be used to program the system locally.

UJ
date a wide range of devices. The serial ASCII data that enter 2 through the RS-232 connection proceed to a UART (Universal 3 Asynchronous Receiver Transmitter), which converts the serial 4 data to parallel data -- and also has a hardware interrupt to alert the microprocessor that it has data. We use Exar 88C681 6 UART. The microprocessor handles these data in the same way as those from the handheld programmer and keypad, except that it 8 displays these data on the device connected to the RS-232 port (~. the video screen that is part of the terminal).
The RS-232 port also provides a means of remote program-ming in that a modem can be connected to the RS-232 port and '12 thus allow communications with the system over the telephone 13 lines from a remote location having a modem and terminal. Our ~4 system also has an onboard modem chip (Rockwell RC224AT), which eliminates the need for an outboard modem. An outboard modem 16~ would be used only if a baud data transmission rate faster than » 2400 were desired. A "dumb" terminal, as opposed to a personal ~8 computer (PC), can be used in either instance, since all the necessary intelligence resides in our system.
The serial ASCII data from the onboard modem is sent to a 2~ UART and then to the microprocessor. Data entries and system 22 prompts are sent back to the modem -- which then transmits them 23 over the telephone line to the modem and terminal at the remote 24 location, where they are displayed on the video screen.

~' .l .l ~~ ~~i~~
1 from a common input source -- in this case the unknown type of 2 telephone call being answered.
We accomplish this by using an active hybrid circuit. The 4 hybrid is an analog three-port circuit design having an input port, an output port, and an input/output port that enables 6 concurrent testing for either an incoming modem signal or a DTMF signal. Outputs of the modem transmitter and voice chip are fed to the input port and both the modem receiver and the DTMF receiver inputs are connected to the output port of the hybrid. The telephone-line interface feeds signals both into 11 and out of the input/output port of the active hybrid.
12 When the system is called, it senses the ring signal on 13 the line and integrates these occurrences over a period of time 14 to avoid spuriously answering on noise pulses. The system then answers by seizing the line and, after a 2.2 second delay, 16~ answers in English speech by saying, "Hello."
The system then presents the modem answering tone and listens concurrently for either an origination tone from a possible modem originating station or a DTMF tone. If an origination tone from a modem is detected, the unit will ignore 21 subsequent DTMF tones during the same session. Conversely, if 22 a DTMF tone is detected, the unit turns off its modem answering 23 tone, ignores any subsequent modem frequencies, and obeys only 24 the incoming DTMF commands.

..x~~) Another feature of the active hybrid is cancellation of leakage between the input port (transmitter output) and the output port (receiver input). This is accomplished by mathe-4 matical relationships that are inherent in the design.

i :i0~~2 Our system allows these data to be retrieved when the 2 system is in the programming mode, either locally or remotely, 3 by display on the system LCD, a printer, or a terminal, depend-4 ing on the programming mode as discussed earlier. The chip we use for the transaction buffer memory is an RCA 6264 eight-h thousand byte RAM or a RCA 62256 thirty-two thousand byte RAM.
The size depends on the maximum number of transactions to be retained.
We have also created a software program on floppy disc that allows the data in the transaction buffer to be sorted 11 after it is retrieved. Sorting can be by date, time, source 12 and type of transaction; and by code used, name, and action 13 taken. Thus, a user can focus in more narrowly on the specific 14 transactions he wishes to review.
The program also allows the programmed information stored 16~ in the system EEPROM memory (e-R., names on the directory, codes, telephone numbers, etc.) to be downloaded to a floppy 18 disc. Thus, a backup disc file of the system memory can be maintained.
This is a particularly attractive feature with directory 21 , units having the capacity for a large number of names, where 22 loss of the system memory (e-R.~,, due to lightning strike) 23 would necessitate reprogramming many names. With this floppy-24 disc program, the names on the backup disc file can simply be uploaded to the affected system once it is back in commission.

'<~~s~a3~
This floppy-disc program can be used in any IBM-compatible 2 PC with DOS 2.0 or higher. The PC can be connected directly to 3 the system via RS-232 connection or can communicate with the system via modem -- since the floppy-disc program includes the terminal-emulation and communications software necessary for a PC to be able to communicate via modem.
It will be understood that the foregoing disclosure is intended to be merely exemplary, and not to limit the scope of the invention -- which is to be determined by reference to the f0 appended claims.

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Claims (30)

1. A display unit for an electronic directory that is expose to sunlight; said display unit comprising:
a case including a front wall;
a liquid-crystal display mounted within the case and com-prising a face for displaying directory information in the for of a directory;
an aperture defined in the front wall for viewing the display face;
a hood mounted to the front wall of the case, extending outward therefrom at the aperture and dimensioned to shade sub-stantially the entire aperture from sunlight at midday; said hood having an undersurface;
an external window mounted to the case to protect the liquid-crystal display; said window being shaped, disposed and oriented to reflect into a viewer's eyes substantially only the undersurface of the hood, if the viewer looks at the LCD from in front of the LCD; and solid-state digital electronic circuitry, electrically interconnected with the liquid-crystal display, for electroni-cally storing directory information and for controlling the liquid-crystal display unit to automatically exhibit stored directory information in the form of a directory having multi-ple listings in an alphabetical or like order or in classified groupings.

2. The display unit of claim 1, wherein:
the window reflects substantially all directly received sunlight upward and outward to the hood.

3. The display unit of claim 2, wherein:
the window reflects light from a viewer's own image upward and outward to the hood, if the viewer looks at the LCD from in front of the LCD.

4. The display unit of claim 3, wherein:
the window reflects outward to a viewer substantially only light from a portion of the hood that receives no reflected sunlight near midday, if the viewer looks at the LCD from in front of the LCD.

5. The display unit of claim 1, further comprising:
a glare-reducing material applied on the liquid-crystal display.

6. The display unit of claim 1, wherein:
the window is curved.

7. The display unit of claim 6, wherein:
the curved window is upward- and outward-concave.

8. The display unit of claim 6, wherein:
the curved window is substantially cylindrical; and the hood extends outward from the front wall of the case beyond the center of curvature of the cylindrical window.

9. The display unit of claim 6, wherein:
the hood also has a lower section that extends outward from generally a bottom edge of the aperture, to generally meet the window at the bottom edge of the window.

10. The display unit of 1, wherein:
the aperture has a height a;
the lower section extends outward by a distance b relative to the front wall of the case; and the window is cylindrical and has a radius of curvature approximately equal to (a2 + b2)/2b.

11. The display unit of claim 10, wherein:
the underside of the hood is very dark in color.

12. The display unit of claim 11, wherein:
the hood also has lateral interconnecting panels that carry tracks for securing the window.

13. The display unit of claim 12, further comprising:
a glare-reducing material applied on the liquid-crystal display.

14. The display unit of claim 8, further comprising:
a glare-reducing material applied on the liquid-crystal display.

15. A display unit for an electronic directory that is exposed to sunlight; said display unit comprising:
a case including a front wall;
a liquid-crystal display mounted within the case and com-prising a face for displaying directory information in the form of a directory;
an aperture defined in the front wall for viewing the display face;
a substantially cylindrical window mounted to the case at the aperture to protect the liquid-crystal display;
a hood mounted to the front wall of the case, extending outward from the front wall of the case beyond the center of curvature of the substantially cylindrical window; and solid-state digital electronic circuitry, electrically interconnected with the liquid-crystal display, for electroni-cally storing directory information and for controlling the liquid-crystal display unit to automatically exhibit stored directory information in the form of a directory having multi-ple listings in an alphabetical or like order or in classified groupings.

16. The display unit of claim 15, wherein:
the substantially cylindrical window is concave upward and outward.

17. The display unit of claim 15, wherein:
the window is substantially tangent to the front wall of the case near the top of the aperture.

18. The display unit of claim 16, wherein:
the window is concave outward and upward, and substantial-ly tangent to the front wall of the case near the top of the aperture.

19. The display unit of claim 17, wherein:
the window reflects light from a viewer's own image in a direction other than back toward the viewer.

20. A vandalism-resistant display unit for an electronic directory, comprising:
a substantially vandalism-resistant case including a front wall;
a liquid-crystal display, mounted within the case, and having a display medium and a structure for containing the display medium;
the liquid-crystal display structure comprising a face disposed in front of the medium, for displaying directory information outdoors in the form of a directory;
means for protecting the liquid-crystal display against vandalism and for maintaining the temperature of the liquid-crystal display medium and structure betwen practical operating limits for the display, notwithstanding ambient temperature and humidity variations over generally normal ranges for at least the temperate zones, and even if the display unit is placed to receive direct sunlight when the sun is out; the protecting and temperature-maintaining means comprising:

an external window mounted to the case in the front wall to protect the liquid-crystal display, and means for reducing glare from the window and reducing solar heat loading into the case through the window, said glare-and-heat-loading reducing means comprising:

(i) a hood mounted to the front wall of the case, extending outward therefrom above the window, and dimensioned to shade substantially the entire window from sunlight at least at mid-day, said hood having an underside, (ii) configuration of the window in a curved shape, generally concave upward and outward, to re-flect into a viewer's eyes only light from the underside of the hood, if the viewer looks at the LCD from in front of the LCD; and solid-state digital electronic circuitry, electrically interconnected with the liquid-crystal display, for electroni-cally storing directory information and for controlling the liquid-crystal display unit to automatically exhibit stored directory information in the form of a directory having multi-ple listings in an alphabetical or like order or in classified groupings.

21. The display unit of claim 20, wherein:
the curved shape of the window is substantially cylindri-cal; and the hood extends outward from the front wall of the case beyond the center of curvature of the cylindrical window.

22. The display unit of claim 20, wherein:
the window reflects substantially all received sunlight upward and outward to the hood, and light from a viewer's own image upward and outward to the hood, if the viewer looks at the LCD from in front of the LCD.

23. The display unit of claim 20, wherein:
the window reflects outward to a viewer only light from a portion of the hood that receives no reflected sunlight near midday, if the viewer looks at the LCD from in front of the LCD.

24. The display unit of claim 20, wherein:
the glare-and-heat-loading reducing means further comprise a glare-reducing material applied on the liquid-crystal display.

25. A vandalism-resistant and weather-resistant display unit for an outdoor-installed electronic directory, comprising:
a substantially vandalism-resistant and weather-resistant case for outdoor installation, said case including a front wall, side-wall structure, and a bottom wall;
a liquid-crystal display, mounted within the case, and having a display medium and a structure for containing the display medium;
the liquid-crystal display structure comprising a face disposed in front of the medium, for displaying directory information outdoors in the form of a directory;
means for protecting the liquid-crystal display against vandalism and rainwater and for maintaining the temperature of the liquid-crystal display medium and structure between practi-cal operating limits for the display, notwithstanding ambient temperature and humidity variations over generally normal ranges for at least the temperate zones, and even if the display unit is placed to receive direct sunlight when the sun is out; the protecting and temperature-maintaining means comprising:

an external window mounted to the case in the front wall to protect the liquid-crystal display, and means for reducing glare from the window and reducing solar heat loading into the case through the window, said glare-and-heat-loading reducing means comprising:

(i) a hood mounted to the front wall of the case, extending outward therefrom above the window, and dimensioned to shade substantially the entire window from sunlight at midday, said hood having an underside, (ii) configuration of the window in a curved shape, generally concave upward and outward, to re-flect into a viewer's eyes substantially only light from the underside of the hood, if the viewer looks at the LCD from in front of the LCD; and solid-state digital electronic circuitry, electrically interconnected with the liquid-crystal display, for electroni-cally storing directory information and for controlling the liquid-crystal display unit to automatically exhibit stored directory information in the form of a directory having multi-ple listings in an alphabetical or like order or in classified groupings.

26. The display unit of claim 25, wherein:
the glare-and-heat-loading reducing means further comprise a glare-reducing material applied on the liquid-crystal display.

27. The display unit of claim 26, wherein:
the curved shape of the window is substantially cylindri-cal; and the hood extends outward from the front wall of the case beyond the center of curvature of the cylindrical window.

28. The display unit of claim 26, wherein:
the window reflects substantially all received sunlight upward and outward to the hood

29. The display unit of claim 26, wherein:
the window reflects light from a viewer's own image upward and outward to the hood, if the viewer looks at the LCD from in front of the LCD.

30. The display unit of claim 26, wherein:
the window reflects outward to a viewer only light from a portion of the hood that receives no reflected sunlight near midday, if the viewer looks at the LCD from in front of the LCD.