CA2059848A1 - Liquid crystal display and reflective diffuser therefor - Google Patents
Liquid crystal display and reflective diffuser thereforInfo
- Publication number
- CA2059848A1 CA2059848A1 CA002059848A CA2059848A CA2059848A1 CA 2059848 A1 CA2059848 A1 CA 2059848A1 CA 002059848 A CA002059848 A CA 002059848A CA 2059848 A CA2059848 A CA 2059848A CA 2059848 A1 CA2059848 A1 CA 2059848A1
- Authority
- CA
- Canada
- Prior art keywords
- cavity
- liquid crystal
- crystal display
- diffuser
- light
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
- G02B6/0011—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form
- G02B6/0033—Means for improving the coupling-out of light from the light guide
- G02B6/005—Means for improving the coupling-out of light from the light guide provided by one optical element, or plurality thereof, placed on the light output side of the light guide
- G02B6/0055—Reflecting element, sheet or layer
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
- G02B6/0096—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the lights guides being of the hollow type
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
- G02F1/1336—Illuminating devices
- G02F1/133615—Edge-illuminating devices, i.e. illuminating from the side
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M1/00—Substation equipment, e.g. for use by subscribers
- H04M1/02—Constructional features of telephone sets
- H04M1/22—Illumination; Arrangements for improving the visibility of characters on dials
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
- G02B6/0011—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form
- G02B6/0033—Means for improving the coupling-out of light from the light guide
- G02B6/0035—Means for improving the coupling-out of light from the light guide provided on the surface of the light guide or in the bulk of it
- G02B6/0045—Means for improving the coupling-out of light from the light guide provided on the surface of the light guide or in the bulk of it by shaping at least a portion of the light guide
- G02B6/0046—Tapered light guide, e.g. wedge-shaped light guide
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Nonlinear Science (AREA)
- Engineering & Computer Science (AREA)
- Signal Processing (AREA)
- Mathematical Physics (AREA)
- Chemical & Material Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Devices For Indicating Variable Information By Combining Individual Elements (AREA)
- Liquid Crystal (AREA)
Abstract
ABSTRACT
A diffuser for backlighting a display panel consists of a shell having a flat surface for positioning against the backside of the panel. A reflection cavity extending into the shell from the flat surface has highly reflective walls one of which opposite the mouth of the cavity defines a ramp. An illumination cavity extending into the shell intercepts the reflection cavity at an aperture near the foot of the ramp.
When light propagates from the illumination cavity into the reflection cavity, the walls of the latter cavity distribute that light by reflection and the ramp redirects that light to the mouth of the reflection cavity from which the light propagates to the display panel as a uniform diffuse emanation.
A diffuser for backlighting a display panel consists of a shell having a flat surface for positioning against the backside of the panel. A reflection cavity extending into the shell from the flat surface has highly reflective walls one of which opposite the mouth of the cavity defines a ramp. An illumination cavity extending into the shell intercepts the reflection cavity at an aperture near the foot of the ramp.
When light propagates from the illumination cavity into the reflection cavity, the walls of the latter cavity distribute that light by reflection and the ramp redirects that light to the mouth of the reflection cavity from which the light propagates to the display panel as a uniform diffuse emanation.
Description
2t~5~$
Liguid Cry~tal Di~play and Reflective Diffu~er Therefor FIELD OF THE INVENTION
This invention relates to liquid crystal display. It relates especially to a reflective diffuser which takes light emitted from concentrated light sources and distributes that light evenly over a given surface area, typically onto the backlighting area of the liquid crystal display.
BACKGROUND OF THE INVENTION
Diffusers find wide-spread application in many products made by the electronics industry, for example, calculators, cellular telephones, and stereos, just to name a few.
Pre~ently, manufacturing co~t and degree of reflectivity determine the commercial success of a diffuser.
Figur~;5 shows a cross section of a conventional, so-called transflective diffuser 2. This diffuser 2 is a solid, generally rectangular, clear plastic block which has a cylindrical aperture 4 formed adjacent to a front face 6 and a cavity in the underside of the block defining a ramped surf~ce a extending between the aperture 4 and a back face 10. A
portion of the top surface 12 located over the aperture 4 has a reflective coating 13a to prevent light emitted by light sources 16 ~Figure 5) in aperture 4 from propagating through that portion of the top surface. The ramped surface 8 is also coated with a reflective coating 13b; this coating reflects emitted light through the top surface 12 not covere~ by coating 13a.
Figure 4 shows a liquid crystal display assembly that employs the transflective diffuser 2 shown in Figure 5. The diffuser 2 is disposed on the surface of a substrate 14 so that the aperture 4 receives a pair of incandescent bulbs 16 hand soldered to the substrate surface. A color filter 18 is positioned on the diffuser top surface 12, a liquid crystal display panel 20 rests on top of the filter 18, and a cover 22 overlies the liquid crystal display panel 20. Electrical , ~ -2~98~ ~
interconnects 24 and 26, which bracket diffuser 42, stand on electrical contact areas 28 on the substrate surface and provide electrical interconnections between substrate 14 and registering contacts on the underside of the liquid crystal display panel 20. Barbed tabs 29 on the cover 22 can be snapped into corresponding slots 30 in the substrate 14 to mechanically secure the components of this assembly to the substrate 14.
The light from bulbs 16 is transmitted through transflective diffuser 2 to the reflective coating 13b on the ramped surface 8 where it is reflected up to the liquid crystal display panel 20. This reflected light provides background illumination for the liquid crystal display so that the human eye can read the alphanumeric characters on the display whe,n there is li,ttle or no ambient light present. The coating l~a, of transflective diffuser 2 prevents co~centrated areas of reflected light, called "hot spots", from appearing in the background of the liquid crystal display. Such hot spots, being easily dis~ernible by the human eye, would degrade the quality of the backlighting.
The coatings ~3a and 13b of diffuser 2 have largely determined the efficiency of this diffuser. That is, the degree of reflectivity of the coating is directly dependent on the quality of the coatings. The more reflective the coatings, the greater the portion of the emitted light that the diffuser will reflect up to the display panel 20, rather thàn refract through the walls of the diffuser. Unfortunately, the cost of coating the surfaces of the diffuser is also directly proportional to the coating reflectivity. Consequently, manufacturers have compromised by painting coatings onto the surfaces 8 and 12 which have both moderate reflectivity and cost.
The illustrated display assembly is disadvantaged also because it requires relatively intense incandescent bulbs because of light losses incurred in the transflective diffuser.
2 ~
In accordance with present day practice, the bulbs are soldered manually to the substrate 14. Also, since such bulbs are clear, a color filter 18 must be included to produce the required backlighting color. Both of these factors add appreciably to the overall cost of the assembly.
8UNNARY OF T~E INVENTION
With the foregoing in mind, it is an object of the present invention to provide a diffuser for a liquid crystal display which has a lower manufacturing cost and higher efficiency than those of presently available diffusers.
Another object of the present invention is to provide a diffuser for a liquid crystal display which provides the display with high quality ~acklighting devoid of hot spots.
:' , ,, A further obiect is t,o provide a li,quid crystal dis~lay, assembly incorporating such a diffuser.
Yet another object of the present invention is to lower the cost to manufacture the liquid crystal display assemblies by eliminatinq the need for manually soldered incandescent bulbs and color filters in such assemblies.
These and other objects of the present invention are obtained from a so-called reflective diffuser formed as a shell of opaque material whose surfaces can be made highly reflective. At least one surface is flat 50 that the shell can be placed against the back side of a display panel. A so-called illumination cavity extends into the shell from the flat surface thereof, the mouth of the cavity having an areal extent comparable to that of the display area in the display panel.
The walls of the cavity are highly reflective and the bottom wall extends from the flat surface toward the opposite surface of the shell to define a ramp.
The shel1 also includes a second cavity, denominated an illumination cavity, which intercepts the first or reflection cavity near the foot of the ramp at an aperture whose nominal plane may be more or less perpendicular to the flat surface of ': '. ~:'` ;
2 ~
the shell. The illumination cavity is arranged to receive one or more light sources, preferably light emitting diodes (LEDs) which emit light of a desired color or colors.
The walls of the illumination cavity, like those of the reflection cavity, are made highly reflective and preferably the wall facing the reflection cavity is ramped to reflect light emitted by the light source(s) through the aperture onto the ramped wall of the reflection cavity. When the diffuser with its light source is in operation, the walls of the reflection cavity distribute by reflection substantially all of the light entering that cavity and the ramped wall of the latter cavity redirects that light to the mouth of the reflection cavity from which the light propagates as a uniform and inte~se diffuse emanation to.the backside of the display panel-to.provide high quality.backlighting.. therefor. . . .. . -Preferably, to maximize the light-emitting efficiency of the diffuser, the ramped walls of the reflection and illumination cavitie~ have parabolic curvature, with the focus of the former being located outside the shell opposite the mouth of the reflection cavity and that of the latter being positioned in the shell near the aperture between the two cavities.
Due to its unique construction, my reflective type diffuser directs a substantially greater portion of the light emitted by the associated light source(s) to the liquid crystal display panel than does the prior transflective-typ`e diffuser described above. Yet, even though this reflective diffuser is more efficient than the prior diffuser, it is less expensive to make because it can be molded as a unitary part using relatively little material and it requires no secondary reflective coating~
A liquid crystal display assembly employing my reflective diffuser is advantaged also in that it can use low intensity LEDs to produce the same or better backlighting intensity than is obtained from transflective diffusers. LEDs 2~98d~
are surface mounted components which can be machine soldered, rather than hand soldered, to the substrate and they come in a variety of different colors. Therefore, their use significantly reduces the cost associated with mounting the light sources to the substrate and completely eliminates the cost of the color filters required in conventional display assemblies. The LEDs also have a significantly longer luminou~
life than the incandescent bulbs used heretofore in transflective diffusers which, therefore, increases the useful life of my entire liquid crystal display assembly.
~RIEF DE8CRIPTION OF T~B DRAWING8 The above and further advantages of the invention may be better understood by referring to the following description in coh~unction with the accompa~yin~ drawings, in which:
Figure 1 is a side view of a telephone handset incorporating my liquid crystal display assembly;
Figure 2 is an exploded perspective view of the liquid crystal display assembly in the telephone handset shown in Figure 1;
Figure 3 is a sectional view taken along line 3-3 of Figure 2;
Figure 4, already described, is an exploded perspective view of a conventional transflective liquid crystal display assembly, and Figure 5, already described, is a sectional vi`ew taken along line 5-5 of Figure 4.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENT
Figure 1 shows a telephone handset 32. ~he housing for this telephone handset 32 consists of an upper shell 34 and a lower shell 36. A printed circuit board or substrate 38 lies within the lower shell 36 of the telephone handset 32 and a liquid crystal display assembly 40 incorporating a reflective diffuser 42 ~Figure 2) is securely mounted to the printed 2 ~ g circuit: board or substrate 38. Assembly 40 produces a display which is visible through an aperture 34a in the upper shell 34.
Referring to Figure 2, assembly 40 comprises the reflective diffuser 42 disposed over a segment of substrate 38.
A row of light-emitting diodes (LEDs) 46 machine-soldered to the substrate project up into the under~ide of diffuser 42 and a liquid crystal display panel 48, having a display area 48a, q rests on top of the reflective diffuser 42 under aperture 34a in the handset 32. A pair of electrical interconnects 52 and 54 extend up from substrate 38 fore and aft diffuser 42, establishing electrical contacts between rows of electrical contacts 56 on the substrate surface and corresponding rows of registering contacts on the underside of liquid crystal display panel 48. Assembly 4~ is topped off by an apertured cover 50 overlying panel.48 and forming a frame o~ ~ezel around display area 48a. Barbed tabs 58 projecting down from the edges of the cover 50 can be snapped into corresponding slots 60 in the substrate 38 to mechanically secure the components of this assembly to the ~,ubstrate 38.
Thus, the liquid crystal display assembly 40 in Figure 2 is quite similar to the conventional one depicted in Figures 4 and 5, except that the assembly 40 employs the novel reflective diffuser 42 which enables the use of machine-soldered LEDs 46 instead of manually-soldered incandescent bulbs. And, since the LEDs can be made with a wide variety of different colors, the assembly 40 no longer requires a color filter. `
Referring to Figures 2 and 3, diffuser 42 comprises a relatively thin, generally rectangular shell 80 having front and rear walls 82 and 84, a pair of side walls 86 and 88, and top and bottom surfaces 92 and 94. A generally rectangular illumination cavity 96 is present in the bottom surface 94 of the shell. This cavity extends between the side walls 86 and 88 of the shell with its mouth 96a being close to, and generally parallel to, the shell front wall 82 and the cavity is relatively narrow in the front-to-back direction. Cavity 96 2 ~ 8 has a wall 98 adjacent to the shell front wall 82 which is upwardly-rearwardly curved forming a relatively wide ramped surface that extends between the side walls of the shell and faces the rear wall thereof.
A second, much larger, generally rectangular reflection cavity 102 is formed in shell 80 just rearwardly of cavity 96.
The mouth 102a of cavity 102 is located at the flat top surface 92 of the shell and its areal extent is comparable to th~t of the display area 48a of display panel 48. Thi~ reflection cavity 102 has highly reflective walls, one vf which, namely wall 104, extends downwardly and forwardly defining a curved ramp which extends from the rear edge of the reflection cavity mouth 102a to the rear edge of the illumination cavity mouth 96a at the underside of the shell so that the two cavities are next t~ one another in the shell. .In the illustrated diffuser, the front edge of the reflection cavity mouth 102a is located more or less directly above, and extends parallel to, the rear edge of the illumination cavity mouth 96a. Thus, the two cavities intercept at a more or less vertical, generally xectangular aperture 1~6 at the foot of the ramped wall 104.
The nominal plane of aperture 106 is more or less parallel to shell front and rear walls 82 and 84 and perpendicular to top and bottom surfaces 92 and 94. Also, the ramped wall 98 of the illumination cavity faces the reflection cavity 102 through the aperture.
The walls of both cavities are quite smooth an~ highly reflective. Preferably the ramped walls 98 and 104 of those cavities have parabolic curvature, with the focus of the reflection cavity wall 104 being located on an imaginary li~e located above the mouth of that cavity and extending parallel to the front and rear edges of that cavity and that of the wall 98 of the illumination cavity extending in the same direction between the top and bottom surfaces of the shell near the aperture 106 between the two cavities. A void 108 may be formed in the underside of shell 80 below cavity wall 104 to .~ .
.
2~5~
reduce the weight and material cost of the diffuser.
When light sources 46 are present in the illumination cavity 96 of the diffuser, a major portion of the light is beamed directly through the aperture 106 between the two cavities to the hi~hly reflective walls of the reflection cavity 102. Those walls distribute that incident light by reflection and the curved wall 104 reflects the light upward to the mouth 102a of the illumination cavity. The remaining light from the light sources 46 is distributed by reflection from the curved front wall 98 of the illumination cavity 96 through the aperture 106 to the curved wall 104 of the reflection cavity 102 where it is reflected upward to the mouth 102a of that cavity. No light at all is transmitted through the walls of the shell 80. Therefore, substantially all of the light from the light sources 46 leaves ~hq diffus~r 42 as an upwardly directed, uniformly intense diffuse emanation from the mouth 102a of the illumination cavity 102. Thus when the diffuser is positioned against the backside of liquid crystal display panel 48, it provides high ~uality backlighting that is intense and uniform over the entire display area 48a of the panel.
The reflective diffuser 42 can be fabricated out of any opa~ue material capable of having highly reflective surfaces but, in this embodiment, it is made of a white polycarbonate plastic material. This diffuser is also preferably a unitary structure fabrica~ed by a molding process.
Reflective diffuser 42 operates very simply. ~Light from the LEDs 46 passes directly,or is reflected by the walls of illumination cavity 96, through the aperture 106 into reflection cavity 102. The walls of the latter cavity distribute and redirect substantially all of that light upwards to the underside of display area 48a of display panel 48 thereby providing relatively intense and uniform background illumination for the characters being displayed by the li~uid crystal display panel 48. Since the diffuser 42 is made of an opaque material, none of the light from LEDs 46 can propagate 2 a ~ 8 directly to display panel 48; it must first pass through aperture 106 into reflection cavity 102 for redirection toward the display panel. This eliminates the possibility of there being hot spots in the backlighting for the display or light loss by transmission through the sides and bottom of the diffuser.
The foregoing description has been limited to a specific embodiment of this invention. It will be apparent, however, that variations and modifications may be made to that embodiment, with the attainment of some or all of the advantages of the invention. Therefore, it is the object of the appended claims to cover all such variations and modifications as come within the true spirit and scope of the invention.
. . .
'~
Liguid Cry~tal Di~play and Reflective Diffu~er Therefor FIELD OF THE INVENTION
This invention relates to liquid crystal display. It relates especially to a reflective diffuser which takes light emitted from concentrated light sources and distributes that light evenly over a given surface area, typically onto the backlighting area of the liquid crystal display.
BACKGROUND OF THE INVENTION
Diffusers find wide-spread application in many products made by the electronics industry, for example, calculators, cellular telephones, and stereos, just to name a few.
Pre~ently, manufacturing co~t and degree of reflectivity determine the commercial success of a diffuser.
Figur~;5 shows a cross section of a conventional, so-called transflective diffuser 2. This diffuser 2 is a solid, generally rectangular, clear plastic block which has a cylindrical aperture 4 formed adjacent to a front face 6 and a cavity in the underside of the block defining a ramped surf~ce a extending between the aperture 4 and a back face 10. A
portion of the top surface 12 located over the aperture 4 has a reflective coating 13a to prevent light emitted by light sources 16 ~Figure 5) in aperture 4 from propagating through that portion of the top surface. The ramped surface 8 is also coated with a reflective coating 13b; this coating reflects emitted light through the top surface 12 not covere~ by coating 13a.
Figure 4 shows a liquid crystal display assembly that employs the transflective diffuser 2 shown in Figure 5. The diffuser 2 is disposed on the surface of a substrate 14 so that the aperture 4 receives a pair of incandescent bulbs 16 hand soldered to the substrate surface. A color filter 18 is positioned on the diffuser top surface 12, a liquid crystal display panel 20 rests on top of the filter 18, and a cover 22 overlies the liquid crystal display panel 20. Electrical , ~ -2~98~ ~
interconnects 24 and 26, which bracket diffuser 42, stand on electrical contact areas 28 on the substrate surface and provide electrical interconnections between substrate 14 and registering contacts on the underside of the liquid crystal display panel 20. Barbed tabs 29 on the cover 22 can be snapped into corresponding slots 30 in the substrate 14 to mechanically secure the components of this assembly to the substrate 14.
The light from bulbs 16 is transmitted through transflective diffuser 2 to the reflective coating 13b on the ramped surface 8 where it is reflected up to the liquid crystal display panel 20. This reflected light provides background illumination for the liquid crystal display so that the human eye can read the alphanumeric characters on the display whe,n there is li,ttle or no ambient light present. The coating l~a, of transflective diffuser 2 prevents co~centrated areas of reflected light, called "hot spots", from appearing in the background of the liquid crystal display. Such hot spots, being easily dis~ernible by the human eye, would degrade the quality of the backlighting.
The coatings ~3a and 13b of diffuser 2 have largely determined the efficiency of this diffuser. That is, the degree of reflectivity of the coating is directly dependent on the quality of the coatings. The more reflective the coatings, the greater the portion of the emitted light that the diffuser will reflect up to the display panel 20, rather thàn refract through the walls of the diffuser. Unfortunately, the cost of coating the surfaces of the diffuser is also directly proportional to the coating reflectivity. Consequently, manufacturers have compromised by painting coatings onto the surfaces 8 and 12 which have both moderate reflectivity and cost.
The illustrated display assembly is disadvantaged also because it requires relatively intense incandescent bulbs because of light losses incurred in the transflective diffuser.
2 ~
In accordance with present day practice, the bulbs are soldered manually to the substrate 14. Also, since such bulbs are clear, a color filter 18 must be included to produce the required backlighting color. Both of these factors add appreciably to the overall cost of the assembly.
8UNNARY OF T~E INVENTION
With the foregoing in mind, it is an object of the present invention to provide a diffuser for a liquid crystal display which has a lower manufacturing cost and higher efficiency than those of presently available diffusers.
Another object of the present invention is to provide a diffuser for a liquid crystal display which provides the display with high quality ~acklighting devoid of hot spots.
:' , ,, A further obiect is t,o provide a li,quid crystal dis~lay, assembly incorporating such a diffuser.
Yet another object of the present invention is to lower the cost to manufacture the liquid crystal display assemblies by eliminatinq the need for manually soldered incandescent bulbs and color filters in such assemblies.
These and other objects of the present invention are obtained from a so-called reflective diffuser formed as a shell of opaque material whose surfaces can be made highly reflective. At least one surface is flat 50 that the shell can be placed against the back side of a display panel. A so-called illumination cavity extends into the shell from the flat surface thereof, the mouth of the cavity having an areal extent comparable to that of the display area in the display panel.
The walls of the cavity are highly reflective and the bottom wall extends from the flat surface toward the opposite surface of the shell to define a ramp.
The shel1 also includes a second cavity, denominated an illumination cavity, which intercepts the first or reflection cavity near the foot of the ramp at an aperture whose nominal plane may be more or less perpendicular to the flat surface of ': '. ~:'` ;
2 ~
the shell. The illumination cavity is arranged to receive one or more light sources, preferably light emitting diodes (LEDs) which emit light of a desired color or colors.
The walls of the illumination cavity, like those of the reflection cavity, are made highly reflective and preferably the wall facing the reflection cavity is ramped to reflect light emitted by the light source(s) through the aperture onto the ramped wall of the reflection cavity. When the diffuser with its light source is in operation, the walls of the reflection cavity distribute by reflection substantially all of the light entering that cavity and the ramped wall of the latter cavity redirects that light to the mouth of the reflection cavity from which the light propagates as a uniform and inte~se diffuse emanation to.the backside of the display panel-to.provide high quality.backlighting.. therefor. . . .. . -Preferably, to maximize the light-emitting efficiency of the diffuser, the ramped walls of the reflection and illumination cavitie~ have parabolic curvature, with the focus of the former being located outside the shell opposite the mouth of the reflection cavity and that of the latter being positioned in the shell near the aperture between the two cavities.
Due to its unique construction, my reflective type diffuser directs a substantially greater portion of the light emitted by the associated light source(s) to the liquid crystal display panel than does the prior transflective-typ`e diffuser described above. Yet, even though this reflective diffuser is more efficient than the prior diffuser, it is less expensive to make because it can be molded as a unitary part using relatively little material and it requires no secondary reflective coating~
A liquid crystal display assembly employing my reflective diffuser is advantaged also in that it can use low intensity LEDs to produce the same or better backlighting intensity than is obtained from transflective diffusers. LEDs 2~98d~
are surface mounted components which can be machine soldered, rather than hand soldered, to the substrate and they come in a variety of different colors. Therefore, their use significantly reduces the cost associated with mounting the light sources to the substrate and completely eliminates the cost of the color filters required in conventional display assemblies. The LEDs also have a significantly longer luminou~
life than the incandescent bulbs used heretofore in transflective diffusers which, therefore, increases the useful life of my entire liquid crystal display assembly.
~RIEF DE8CRIPTION OF T~B DRAWING8 The above and further advantages of the invention may be better understood by referring to the following description in coh~unction with the accompa~yin~ drawings, in which:
Figure 1 is a side view of a telephone handset incorporating my liquid crystal display assembly;
Figure 2 is an exploded perspective view of the liquid crystal display assembly in the telephone handset shown in Figure 1;
Figure 3 is a sectional view taken along line 3-3 of Figure 2;
Figure 4, already described, is an exploded perspective view of a conventional transflective liquid crystal display assembly, and Figure 5, already described, is a sectional vi`ew taken along line 5-5 of Figure 4.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENT
Figure 1 shows a telephone handset 32. ~he housing for this telephone handset 32 consists of an upper shell 34 and a lower shell 36. A printed circuit board or substrate 38 lies within the lower shell 36 of the telephone handset 32 and a liquid crystal display assembly 40 incorporating a reflective diffuser 42 ~Figure 2) is securely mounted to the printed 2 ~ g circuit: board or substrate 38. Assembly 40 produces a display which is visible through an aperture 34a in the upper shell 34.
Referring to Figure 2, assembly 40 comprises the reflective diffuser 42 disposed over a segment of substrate 38.
A row of light-emitting diodes (LEDs) 46 machine-soldered to the substrate project up into the under~ide of diffuser 42 and a liquid crystal display panel 48, having a display area 48a, q rests on top of the reflective diffuser 42 under aperture 34a in the handset 32. A pair of electrical interconnects 52 and 54 extend up from substrate 38 fore and aft diffuser 42, establishing electrical contacts between rows of electrical contacts 56 on the substrate surface and corresponding rows of registering contacts on the underside of liquid crystal display panel 48. Assembly 4~ is topped off by an apertured cover 50 overlying panel.48 and forming a frame o~ ~ezel around display area 48a. Barbed tabs 58 projecting down from the edges of the cover 50 can be snapped into corresponding slots 60 in the substrate 38 to mechanically secure the components of this assembly to the ~,ubstrate 38.
Thus, the liquid crystal display assembly 40 in Figure 2 is quite similar to the conventional one depicted in Figures 4 and 5, except that the assembly 40 employs the novel reflective diffuser 42 which enables the use of machine-soldered LEDs 46 instead of manually-soldered incandescent bulbs. And, since the LEDs can be made with a wide variety of different colors, the assembly 40 no longer requires a color filter. `
Referring to Figures 2 and 3, diffuser 42 comprises a relatively thin, generally rectangular shell 80 having front and rear walls 82 and 84, a pair of side walls 86 and 88, and top and bottom surfaces 92 and 94. A generally rectangular illumination cavity 96 is present in the bottom surface 94 of the shell. This cavity extends between the side walls 86 and 88 of the shell with its mouth 96a being close to, and generally parallel to, the shell front wall 82 and the cavity is relatively narrow in the front-to-back direction. Cavity 96 2 ~ 8 has a wall 98 adjacent to the shell front wall 82 which is upwardly-rearwardly curved forming a relatively wide ramped surface that extends between the side walls of the shell and faces the rear wall thereof.
A second, much larger, generally rectangular reflection cavity 102 is formed in shell 80 just rearwardly of cavity 96.
The mouth 102a of cavity 102 is located at the flat top surface 92 of the shell and its areal extent is comparable to th~t of the display area 48a of display panel 48. Thi~ reflection cavity 102 has highly reflective walls, one vf which, namely wall 104, extends downwardly and forwardly defining a curved ramp which extends from the rear edge of the reflection cavity mouth 102a to the rear edge of the illumination cavity mouth 96a at the underside of the shell so that the two cavities are next t~ one another in the shell. .In the illustrated diffuser, the front edge of the reflection cavity mouth 102a is located more or less directly above, and extends parallel to, the rear edge of the illumination cavity mouth 96a. Thus, the two cavities intercept at a more or less vertical, generally xectangular aperture 1~6 at the foot of the ramped wall 104.
The nominal plane of aperture 106 is more or less parallel to shell front and rear walls 82 and 84 and perpendicular to top and bottom surfaces 92 and 94. Also, the ramped wall 98 of the illumination cavity faces the reflection cavity 102 through the aperture.
The walls of both cavities are quite smooth an~ highly reflective. Preferably the ramped walls 98 and 104 of those cavities have parabolic curvature, with the focus of the reflection cavity wall 104 being located on an imaginary li~e located above the mouth of that cavity and extending parallel to the front and rear edges of that cavity and that of the wall 98 of the illumination cavity extending in the same direction between the top and bottom surfaces of the shell near the aperture 106 between the two cavities. A void 108 may be formed in the underside of shell 80 below cavity wall 104 to .~ .
.
2~5~
reduce the weight and material cost of the diffuser.
When light sources 46 are present in the illumination cavity 96 of the diffuser, a major portion of the light is beamed directly through the aperture 106 between the two cavities to the hi~hly reflective walls of the reflection cavity 102. Those walls distribute that incident light by reflection and the curved wall 104 reflects the light upward to the mouth 102a of the illumination cavity. The remaining light from the light sources 46 is distributed by reflection from the curved front wall 98 of the illumination cavity 96 through the aperture 106 to the curved wall 104 of the reflection cavity 102 where it is reflected upward to the mouth 102a of that cavity. No light at all is transmitted through the walls of the shell 80. Therefore, substantially all of the light from the light sources 46 leaves ~hq diffus~r 42 as an upwardly directed, uniformly intense diffuse emanation from the mouth 102a of the illumination cavity 102. Thus when the diffuser is positioned against the backside of liquid crystal display panel 48, it provides high ~uality backlighting that is intense and uniform over the entire display area 48a of the panel.
The reflective diffuser 42 can be fabricated out of any opa~ue material capable of having highly reflective surfaces but, in this embodiment, it is made of a white polycarbonate plastic material. This diffuser is also preferably a unitary structure fabrica~ed by a molding process.
Reflective diffuser 42 operates very simply. ~Light from the LEDs 46 passes directly,or is reflected by the walls of illumination cavity 96, through the aperture 106 into reflection cavity 102. The walls of the latter cavity distribute and redirect substantially all of that light upwards to the underside of display area 48a of display panel 48 thereby providing relatively intense and uniform background illumination for the characters being displayed by the li~uid crystal display panel 48. Since the diffuser 42 is made of an opaque material, none of the light from LEDs 46 can propagate 2 a ~ 8 directly to display panel 48; it must first pass through aperture 106 into reflection cavity 102 for redirection toward the display panel. This eliminates the possibility of there being hot spots in the backlighting for the display or light loss by transmission through the sides and bottom of the diffuser.
The foregoing description has been limited to a specific embodiment of this invention. It will be apparent, however, that variations and modifications may be made to that embodiment, with the attainment of some or all of the advantages of the invention. Therefore, it is the object of the appended claims to cover all such variations and modifications as come within the true spirit and scope of the invention.
. . .
'~
Claims (19)
1. A diffuser for backlighting a display panel with a selected display area, said diffuser comprising:
a body of opaque material having a relatively flat surface for positioning adjacent to a display panel and an opposite surface;
means defining a first cavity in said body, said cavity having a mouth at said flat surface whose areal extent is comparable to that of the display area, and highly reflective walls, at least one of which walls extends from said flat surface toward said opposite surface to define a ramp, and means defining a second cavity in said body, said second cavity intercepting said first cavity near the foot of said ramp so that when light propagates from the second cavity into the first cavity, the walls of the first cavity distribute by reflection substantially all of that light and said ramp redirects that light to the mouth of the first cavity from which the light propagates as a uniformly intense diffuse emanation.
a body of opaque material having a relatively flat surface for positioning adjacent to a display panel and an opposite surface;
means defining a first cavity in said body, said cavity having a mouth at said flat surface whose areal extent is comparable to that of the display area, and highly reflective walls, at least one of which walls extends from said flat surface toward said opposite surface to define a ramp, and means defining a second cavity in said body, said second cavity intercepting said first cavity near the foot of said ramp so that when light propagates from the second cavity into the first cavity, the walls of the first cavity distribute by reflection substantially all of that light and said ramp redirects that light to the mouth of the first cavity from which the light propagates as a uniformly intense diffuse emanation.
2. The diffuser defined in claim 1 wherein the body is white polycarbonate plastic shell.
3. The diffuser defined in claim 1 wherein said body is generally rectangular with said flat and opposite surfaces constituting said top and bottom surfaces of the body;
said second cavity has a generally rectangular mouth at said body bottom surface, and said first and second cavities are next to one another in said body and intercept at a planar aperture which is generally rectangular and extends between the mouths of said first and second cavities.
said second cavity has a generally rectangular mouth at said body bottom surface, and said first and second cavities are next to one another in said body and intercept at a planar aperture which is generally rectangular and extends between the mouths of said first and second cavities.
4. The diffuser defined in claim 3 wherein said first cavity one wall has parabolic curvature with the focus of the curve overlying the mouth of the first cavity.
5. The diffuser defined in claim 3 wherein said second cavity has walls which are highly reflective, and one wall facing said first cavity which curves upwardly-inwardly from the mouth of said second cavity to said aperture.
6. The diffuser defined in claim 5 wherein said second cavity one wall has parabolic curvature, with the focus of the curve being positioned between the top and bottom surfaces of the body near said aperture.
7. The diffuser defined in claim 3 wherein said aperture is defined by walls of said cavities and adjacent edges of said cavity mouths.
8. The diffuser defined in claim 1 and further including lighting means received in said second cavity.
9. The diffuser defined in claim 8 where said lighting means comprise one or more light-emitting diodes.
10. A liquid crystal display assembly comprising a substrate having lighting means mounted thereon;
the diffuser defined in claim 1 positioned with its said opposite surface overlying the substrate and its said second cavity receiving the lighting means, and a display panel having a display area overlying said diffuser so that said display area is in register with the mouth of said body first cavity.
the diffuser defined in claim 1 positioned with its said opposite surface overlying the substrate and its said second cavity receiving the lighting means, and a display panel having a display area overlying said diffuser so that said display area is in register with the mouth of said body first cavity.
11. A liquid crystal display assembly comprising:
a circuit board having a plurality of light sources mounted thereon, and overlying the circuit board and the light sources, a shell of opaque material, means defining a reflection cavity in the top of the shell, the reflection cavity having a mouth at the top of the shell and a highly reflective inclined bottom surface opposite said mouth, means defining in the bottom of the shell an illumination cavity for receiving the light sources, the illumination cavity having a highly reflective surface facing the reflection cavity and means defining an aperture between the two cavities at the foot of said inclined bottom surface.
a circuit board having a plurality of light sources mounted thereon, and overlying the circuit board and the light sources, a shell of opaque material, means defining a reflection cavity in the top of the shell, the reflection cavity having a mouth at the top of the shell and a highly reflective inclined bottom surface opposite said mouth, means defining in the bottom of the shell an illumination cavity for receiving the light sources, the illumination cavity having a highly reflective surface facing the reflection cavity and means defining an aperture between the two cavities at the foot of said inclined bottom surface.
12. The liquid crystal display assembly of claim 11 and further including a liquid crystal display panel overlying the mouth of the reflection cavity.
13. The liquid crystal display assembly of claim 11 wherein the light sources are light-emitting diodes.
14. The liquid crystal display assembly of claim 11 wherein said inclined bottom surface is curved.
15. The liquid crystal display assembly of claim 11 wherein said shell is of a white polycarbonate plastic.
16. A liquid crystal display assembly comprising:
a substrate having a light sources disposed on a substrate face;
a liquid crystal display panel disposed over the substrate;
positioned between the substrate and the display, a body of opaque material, said body incorporating means defining in the top of the body a reflection cavity having a highly reflective inclined bottom surface, means defining in the bottom of the body an illumination cavity receiving the light sources, the illumination cavity having a highly reflective surface facing the reflection cavity and means defining an aperture between the two cavities, and housing means protectively enclosing the body and the liquid crystal display, the housing having an aperture disposed to expose at least a portion of the liquid crystal display panel, and means for mechanically securing the housing to the substrate to secure the body and liquid crystal display panel to the substrate.
a substrate having a light sources disposed on a substrate face;
a liquid crystal display panel disposed over the substrate;
positioned between the substrate and the display, a body of opaque material, said body incorporating means defining in the top of the body a reflection cavity having a highly reflective inclined bottom surface, means defining in the bottom of the body an illumination cavity receiving the light sources, the illumination cavity having a highly reflective surface facing the reflection cavity and means defining an aperture between the two cavities, and housing means protectively enclosing the body and the liquid crystal display, the housing having an aperture disposed to expose at least a portion of the liquid crystal display panel, and means for mechanically securing the housing to the substrate to secure the body and liquid crystal display panel to the substrate.
17. The liquid crystal display assembly of claim 16 wherein the light sources are light-emitting diodes.
18. The liquid crystal display assembly of claim 16 wherein the body is of a polycarbonate plastic.
19. The liquid crystal display assembly of claim 16 wherein the bottom surface of the reflection cavity is curved.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/662,257 US5166815A (en) | 1991-02-28 | 1991-02-28 | Liquid crystal display and reflective diffuser therefor including a reflection cavity section and an illumination cavity section |
| US07/662,257 | 1991-02-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2059848A1 true CA2059848A1 (en) | 1992-08-29 |
Family
ID=24657026
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002059848A Abandoned CA2059848A1 (en) | 1991-02-28 | 1992-01-22 | Liquid crystal display and reflective diffuser therefor |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US5166815A (en) |
| CA (1) | CA2059848A1 (en) |
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| Publication number | Publication date |
|---|---|
| US5166815A (en) | 1992-11-24 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |