United States Patent [19]
`Lenko et al.
`
`[11] Patent Number:
`[45] Date of Patent:
`
`4,915,478
`Apr. 10, 1990
`
`[75]
`
`[54] LOW POWER LIQUID CRYSTAL DISPLAY
`BACKLIGHT
`Inventors: DanielS. Lenlm, Monrovia; Wayne
`R. Grine, Crownsville, both of Md.
`[73] Assignee: The United States of America as
`represented by the Secretary of the
`Navjr, Washington, D.C.
`[21] Appl. No.: 254,552
`[22] Filed:
`Oct. 5, 1988
`Int. Cl,4 .............................................. G02F 1/133
`[51]
`[52] U.S. Cl •............................... 350/338; 350/339 D;
`350/345
`[58] Field of Search ................... 350/345, 338, 339 D;
`362/800
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`4,059,916 11/1977 Tachihara eta!. ............. 350/345 X
`4,329,625 5/1982 Nishizawa et a! .............. 362/800 X
`4,415,236 11/1983 Perregaux ....................... 350/339 D
`4,451,871 5/1984 Kirkley eta!. .................. 362/800 X
`4,487,481 12/1984 Suzawa ............................... 350/345
`4,630,895 12/1986 Abdala, Jr. et a! ................. 350/345
`4,641,925 2/1987 Gasparaitis et a! ................. 350/345
`4,659,183 4/1987 Suzawa · ............................... 350/345
`
`FOREIGN PATENT DOCUMENTS
`83/03013 9/1983 PCT Int'1 Appl. ................. 350/345
`Primary Examiner-Stanley D. Miller
`Assistant Examiner-Anita Pellman Gross
`Attorney, Agent, or Firm-Kenneth E. Walden; Jacob
`Shuster
`ABSTRACf
`[57]
`A liquid crystal display panel having a backlight for
`providing high brightness, uniformity of illumination
`intensity, high ·efficiency, and long battery life, and
`which can be manufactured at a low cost. The display
`device includes a liquid crystal display panel, a light
`source for illuminating the liquid crystal panel, a light
`passage member which can be formed of a transparent
`material disposed between the liquid crystal panel and
`the light source. The light source inlet side of the light
`passage member is formed with a recess with the thick(cid:173)
`ness being reduced at the region diametrically opposed
`to the light source. A light reflecting member reflects
`light fr-om the light source. Within the photoconductor,
`two or more of the wedged shaped photo conductor
`can be used for increased area of coverage.
`
`1_ Claim, 1 Drawing Sheet
`
`10
`
`10
`
`12
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`12
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`LG Display Ex. 1023
`
`LGD_001795
`
`

`

`U.S. Patent
`
`Apr. 10, 1990
`
`4,915,478
`
`Fl G.1 A
`
`FIG. 18
`
`I
`
`I
`
`30
`
`FIG. 2
`
`LGD_001796
`
`

`

`1
`
`4,915,478
`
`LOW POWER LIQUID CRYSTAL DISPLAY
`BACKLIGHT
`
`2
`wedge shaped so that the length of the light path be(cid:173)
`tween the light source and the exposed surface portion
`is uniform throughout the light passage member.
`The light passage member can be made of a transpar-
`5 ent plastic and the reflecting member can be a matted
`material which is highly reflecting, but diffused, such as
`paper, plastic or paint adhered to the appropriate sur(cid:173)
`face portions of the light passage member. In one em-
`bodiment, all surfaces except for the light output surface
`are covered with the diffused reflecting material.
`Accordingly, it is an object of the invention to pro(cid:173)
`vide an improved backlighting device for a liquid crys(cid:173)
`tal display.
`It is a further object of the invention to provide an
`improved liquid crystal display device including a back(cid:173)
`lighting unit.
`It is another object of the invention to provide a
`liquid crystal display device with an improved back(cid:173)
`light unit for providing uniform illumination intensity
`and long battery life.
`Further objects and advantages of the present inven(cid:173)
`tion will become apparent as the following description
`proceeds and features of novelty characterizing the
`invention will be pointed out with particularity in the
`claims annexed to and forming a part of this specifica(cid:173)
`tion.
`
`BACKGROUND OF THE INVENTION
`The present invention relates to a liquid crystal dis(cid:173)
`play device (LCD) and more particularly, to a backlight
`illumination unit for the LCD.
`In a liquid crystal display, a light is applied to a dis(cid:173)
`play member from the back side of the display member 10
`where there is not sufficient ambient light impinging
`onto the front for viewing the display on the device. An
`observer sees the transmitted through light as displayed
`information.
`For backlighting, a luminous member is located be- IS
`hind the liquid crystal display member. The luminous
`member generates light which is applied to the back of
`liquid crystal display member and an observer sees the
`displayed information as bright and dark regions illumi(cid:173)
`nated by light transmitted through liquid crystal display 20
`member. The liquid crystal display inember selectively
`allows portions of display member to transmit light
`whereas other portions of display member are opaque
`and prevent transmission of light. When liquid crystal
`display devices are used in toys, watches, and other 25
`portable battery powered devices, it is necessary to
`provide an illumination device which is operable for
`long periods of time, which has a relatively large panel
`area, and which is electrically power efficient.
`A liquid crystal display device having a backlight 30
`unit with a small lamp has been employed for wrist(cid:173)
`watches. The backlight for such a wristwatch display is
`used to illuminate the face of the watch to make it possi(cid:173)
`ble to read the time at night. Conventional types of
`backlights for liquid crystal display devices are not fully 35
`satisfactory in brightness, illumination intensity unifor(cid:173)
`mity, and long battery life.
`A relatively large amount of electrical power is
`needed to provide energy to the luminous member, at
`least a much larger amount than necessary to power the 40
`LCD itself. Thus the power needed to drive a luminous
`member is of considerable importance. Even if this
`power consumption is reduced to less than 1 watt, the
`power used to backlight liquid crystal display member
`is not neglegible, especially where dry cell batteries are 45
`used as the power source, battery life is significantly
`shortened as a result of the power used to drive the
`luminous member.
`Accordingly, there is a need to increase the battery
`life of a portable liquid crystal displays using backlight- 50
`ing for viewing situations where there is insufficient
`ambient light to produce a viewable display. It is also
`desirable to improve the efficiency of the backlight as
`well as the uniformity of the illumination in order to
`reduce battery drain.
`
`55
`
`SUMMARY OF THE INVENTION
`A liquid crystal display device includes a liquid crys-
`tal display panel, a light source for illuminating the
`liquid crystal panel, a light passage member made of one 60
`of transparent material with the light passage member
`being disposed between the liquid crystal panel and the
`light source, and a light reflecting member with the
`light passage member having an opening facing the
`liquid crystal panel to direct light to the rear side of the 65
`LCD panel. The light reflecting member is disposed on
`a surface of the light passage member to scatter light
`passing therethrough. The light passage member is
`
`DESCRIPTION OF THE DRAWINGS
`For a better understanding of the present invention
`reference may be had to the accompanying drawings
`wherein:
`FIG. 1 shows a representative side and top view of
`the backlight device of the present invention.
`FIG. 2 is a schematic of the electrical circuit used in
`connection with the backlight device of FIG. 1.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`One embodiment of a liquid crystal display device
`including an illuminating backlight is constructed and
`arranged in accordance with the invention is shown in
`FIG. 1. A light emitting source 10 is inserted into a
`recess 12 formed in a photoconductor or light passage
`member 14 which is covered on one or more sides by a
`light scattering and reflecting element 16 facing an
`upper surface (light output surface) 18 ofphotoconduc(cid:173)
`tor 14 being uncovered for illuminating a liquid crystal
`panel20.
`If photoconductor 14 had a uniform thickness, the
`intensity of light would be decreased in inverse propor(cid:173)
`tion to the square of the distance from light source 10 to
`panel 20 for the various light paths. In other words, if
`photoconductor 14 is uniform in thickness, the intensity
`of the backlight is higher at positions closer to light
`source 10 and is lower at positions further from light
`source 10. Accordingly, parts closer to light source 10
`would be viewed with a higher contrast and parts fur(cid:173)
`ther from light source 10 would have a lower contrast.
`In view of this fact, the thickness of photoconductor 14
`is decreased as the distance from light source 10 in(cid:173)
`creases.
`Thus, the illumination intensity of backlight beam 22
`corresponds distance travelling by light emitted by
`source 10 and scatter and reflected by reflector 16. For
`this reason, photoconductor 14 is made thinner at light
`scattering and reflecting element region 26 distal from
`light source 10 so that the intensity of backlight beam 22
`
`LGD_001797
`
`

`

`3
`farther from light source 10 approaches that of back(cid:173)
`light beam 22 closer to light source 10.
`In order to accomplish this, the bottom 28 of photo(cid:173)
`conductor 14 slopes in a straight line from one side of
`the photoconductor 14 towards the distal end. As a 5
`result, the intensity of backlight beam 22 farther from
`light source 10 is substantially equal to that of backlight
`beam 22 closer to light source 10. Accordingly, when
`liquid crystal panel 20 is illuminated by backlight beams
`22, the brightness and contrast produced are substan- 10
`tially uniform throughout the area of the panel illumi(cid:173)
`nated by photoconductor 14. For best results the panel
`20 should abuttingly engage upper surface 18.
`Conservation of power supply power is of substantial 15
`importance for portable battery powered devices. In
`this regard, the present invention includes two features.
`The first feature is the dual wedge portions 14 as shown
`in FIG. 1. For a large display 20, rather than have only
`one wedge with a single light source 10, a dual light 20
`source 10 is used with dual wedge sections. This ar(cid:173)
`rangement permits increased intensity of illumination
`while still accommodating a larger display area. Addi(cid:173)
`tionally, it is more economical from a power drain
`standpoint to use two light sources 10 for a pair of 25
`wedges 14 instead of one larger wedge 14 with one
`brighter light source 10.
`Secondly, the pair of light sources 10 and the circuit
`connecting said light sources substantially reduces
`power usage for the light intensity provided. Incandes- 30
`cent bulbs provide adequate lighting but require sub(cid:173)
`stantial power for operation. Typically, hand-held por(cid:173)
`table equipment often operate at voltages greater than
`or equal to five volts. High efficiency light emitting
`diodes (LED) provide new high efficiency and low 35
`power devices which provide good illumination at cur(cid:173)
`rent levels of 2 milliamperes (rna) instead of the 20 rna
`required for incandescent lamps.
`In the exemplary embodiment the LED's can be any
`appropriate color, e.g., red, yellow and green. How(cid:173)
`ever, for military purposes, where night vision infrared
`spotting is an important consideration a green colored
`LED would emit minimal infrared radiation for detec-
`tion by an enemy.
`Referring now to FIG. 2, there is shown the electrical
`schematic for the light sources 10. LED's 30 which
`correspond to the respective light sources 10 are con(cid:173)
`nected in series for a forward voltage drop across each
`LED of 1.9 volts. A two lead constant current regulator 50
`32 assures that the LED current is limited to 2 rna
`which is sufficient for securing light emittance from the
`
`45
`
`4
`LED's 30 with the minimum of current drain for the
`given light output.
`The photoconductor 14 can be made of any appropri(cid:173)
`ate transparent material such as glass or aery! material
`and in the present embodiment is made of plexiglass in
`which the LED's are mounted and forms an optical
`coupling to the LCD device. In the present embodi(cid:173)
`ment, reflector 16 is a matted but highly reflecting mate(cid:173)
`rial such as non-shiny white paper or green paper to
`match a green LED, and is secured by glue or the like
`to the angled faces of the plexiglass which add to the
`uniformity in the backlight diffusion. In the exemplary
`embodiment, reflector 16 is disposed on all surfaces
`except for light output surface 18. In a like manner,
`appropriately colored plastic or paint can be used for
`reflector 16.
`While there has been illustrated and described what is
`at present considered to be a preferred embodiment of
`the present invention, it will be appreciated that numer(cid:173)
`ous changes and modifications are likely to occur to
`those skilled in the art and it is intended in the appended
`claims to cover all those changes and modifications
`which fall within the true spirit and scope of the present
`invention.
`What is claimed is:
`1. A liquid crystal display of the backlighting type
`comprising: a panel having a front view surface and a
`rear surface, a light passage member gradually reducing
`in thickness from spaced light input portions at opposite
`ends thereof and bounded by a light output surface and
`a light reflecting surface, a semiconductor light source
`comprising a battery source of voltage above a mini(cid:173)
`mum level and two light emitting diodes disposed at the
`light input portions from which light enters into the
`light passage member, at an effective illumination level
`and light reflective means disposed at and attached to
`the light reflecting surface for diffusing and reflecting
`the light at said effective illumination level toward the
`light output surface with generally uniform distribution
`of illuminating intensity, said light reflecting surface
`being angled with respect to and facing the light output
`surface, said diffused and reflected light at the effective
`, illumination level exiting the light output surface on the
`rear surface of the panel, the improvement residing in
`current regulator means electrically interconnecting the
`light emitting diodes in series with the battery source
`for generation of said light at the effective illumination
`level by constant current conducted through the light
`emitting diodes with minimum drain of the battery
`source while maintained thereby above the minimum
`voltage level.
`• * * * *
`
`4,915,478
`
`40
`
`55
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`60
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`65
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`LGD_001798
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`