United States Patent [19J
`Lengyel et al.
`
`111111
`
`1111111111111111111111111111111111111111111111111111111111111
`US005907222A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,907,222
`May 25,1999
`
`[54] HIGH EFFICIENCY BACKLIGHTING
`SYSTEM FOR REAR ILLUMINATION OF
`ELECTRONIC DISPLAY DEVICES
`
`[75]
`
`Inventors: J. Michael Lengyel, Ramona; Loy L.
`Spears, Placentia, both of Calif.
`
`[73] Assignee: Litton Systems, Inc., Woodland Hills
`
`[21] Appl. No.: 08/967,442
`
`[22] Filed:
`
`Nov. 11, 1997
`
`Related U.S. Application Data
`
`[ 63] Continuation of application No. 08/632,752, Apr. 16, 1996,
`abandoned, which is a continuation of application No.
`08/150,355, Nov. 3, 1993, abandoned.
`Int. Cl.6
`..................................................... H05B 41/16
`[51]
`[52] U.S. Cl. ............................ 315/158; 315/309; 315/97;
`345/102; 313/493; 313/573; 313/576
`[58] Field of Search ..................................... 315/105, 309,
`315/158, 49, 57, 94, 97, 115, 151; 362/84;
`313/493, 549, 573, 576; 345/102
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`0477922
`0489477
`0 650 313 A2
`43 13 195 A1
`3285296
`
`4/1992 European Pat. Off ..
`6/1992 European Pat. Off ..
`4/1995 European Pat. Off ..
`4/1992 Germany .
`12/1991
`Japan .
`
`OTHER PUBLICATIONS
`
`Aldo, et al., "Discharge Lamp Lightup Device", Matsushita
`Electric Works, Ltd., Apr. 6, 1990, pp. 1-9.
`Imamura, Hiroshi, "Rapid Start Type Flourescent Lamp",
`Matsushita Electric Works, Ltd., Jul. 16, 1980, pp. 1-4.
`Hiroyasu, Eriguchi, "Luminous Radiation Electron Tube
`Lighting Device", Matsushita Electric Works, Ltd., Dec. 8,
`1992, pp. 1-7.
`Osamu, Miyata, et al., "Heater Control Devise", Stanley
`Electric Co., Ltd., Feb. 17, 1989, pp. 1-6.
`Satohiko, Kitahara, "Power Unit", Canon, Inc., Jan. 14,
`1994, pp. 1-9.
`"Simple Dimming Circuit for Fluorescent Lamp", IBM
`Technical Disclosure Bulletin, Sep., 1991, p. 2.
`J. Michael Lengyel, "Woe is the Backlight", presented at
`Aerospace Lighting Institute, Feb. 1992.
`
`Primary Examiner-Robert Pascal
`Assistant Examiner-Justin P. Bettendorf
`Attorney, Agent, or Firm-Price Gess & Ubell
`
`[57]
`
`ABSTRACT
`
`2,213,868
`2,259,416
`2,687,486
`2,702,862
`3,012,165
`3,531,687
`3,546,521
`3,912,967
`4,374,340
`
`9/1940 Lucian ...................................... 40/134
`10/1941 Gardner ... ... ... .... ... ... ... ... ... ..... 240/2.25
`8/1954 Heine et a!. ............................ 313/109
`2/1955 Finney ...................................... 250/43
`12/1961 Schmidt .................................. 313/185
`9/1970 Greber .. ... ... ... .... ... ... ... ... ... .... .. 315/309
`12/1970 Gelder ..................................... 313/192
`10/1975 Longnecker ............................ 315/309
`2/1983 Bouwknegt eta!. ................... 313/220
`
`(List continued on next page.)
`
`FOREIGN PATENT DOCUMENTS
`
`A fluorescent cavity backlight system that provides a high
`efficiency light source suitable for rear illumination of
`transmissive electronic display devices. The inventive fluo(cid:173)
`rescent cavity backlight system can be adapted to a wide
`variety of fiat panel display applications. The invention takes
`a complete system approach towards designing a high
`efficiency backlight source. The backlight system comprises
`three major subassemblies: a phosphor illuminator, a fluo(cid:173)
`rescent cavity, and improved control/driver electronics.
`Each of the subassemblies has been optimized internally,
`and with respect to each of the other subassemblies.
`
`0 422 594 A1
`
`4/1991 European Pat. Off ..
`
`17 Claims, 5 Drawing Sheets
`
`ARC
`CURRENT
`REGULATOR
`
`.-----------------,
`
`PHOSPHOR ;m
`
`0
`52
`
`ILLUMINATION
`LAMP
`
`50
`
`I
`I
`
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`14
`
`_r-30
`
`FILLIMENT
`CURRENT
`REGULATOR
`
`Vizio EX1029 Page 0001
`
`

`

`5,907,222
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`4,492,899
`4,583,026
`4,744,012
`4,881,007
`4,974,122
`4,978,890
`5,019,749
`5,021,931
`5,043,634
`5,072,155
`
`1!1985 Martin ... ... ... ... .... ... ... ... ... ... .... .. 315/309
`4/1986 Kajiwara et a!. ....................... 315/226
`5/1988 Bergkvist .................................. 362/84
`11/1989 Egelstam ................................. 313/493
`11/1990 Shaw ......................................... 362/31
`12/1990 Sekiguchi et a!. ...................... 315/117
`5/1991 Ito ........................................... 315/309
`6/1991 Matsui et a!. ............................. 362/84
`8/1991 Rothwell, Jr. et a!. ................. 315/246
`12/1991 Sakurai ................................... 315/219
`
`3/1992
`5,101,142
`5,161,041 11/1992
`5,193,899
`3/1993
`5,207,504
`5/1993
`5,211,467
`5/1993
`5,229,842
`7/1993
`5,404,277
`4/1995
`5,406,172
`4/1995
`5,489,819
`2/1996
`5,523,655
`6/1996
`
`Chatfield ................................. 315/309
`Abileah et a!. ........................... 359/40
`Oe eta!. ................................. 362/224
`Swift eta!. ............................. 362/260
`Seder ........................................ 362/84
`Dolan eta!..
`Lindblad ................................... 362/31
`Be nett ....................................... 315/49
`Sakai eta!. ............................... 315/49
`J ennato et a!. .......................... 315/246
`
`Vizio EX1029 Page 0002
`
`

`

`U.S. Patent
`
`May 25, 1999
`
`Sheet 1 of 5
`
`5,907,222
`
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`
`Vizio EX1029 Page 0003
`
`

`

`U.S. Patent
`
`May 25, 1999
`
`Sheet 2 of 5
`
`5,907,222
`
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`Vizio EX1029 Page 0004
`
`

`

`U.S. Patent
`
`May 25, 1999
`
`Sheet 3 of 5
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`5,907,222
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`Vizio EX1029 Page 0005
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`Vizio EX1029 Page 0006
`
`

`

`U.S. Patent
`
`May 25, 1999
`
`Sheet 5 of 5
`
`5,907,222
`
`4ms
`
`FIG.6
`
`ARC
`CURRENT
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`
`Vizio EX1029 Page 0007
`
`

`

`1
`HIGH EFFICIENCY BACKLIGHTING
`SYSTEM FOR REAR ILLUMINATION OF
`ELECTRONIC DISPLAY DEVICES
`
`This is a continuation of application Ser. No. 08/632,752,
`now abandoned filed on Apr. 16, 1996, which application is
`a continuation of U.S. application Ser. No. 08/150,355, filed
`on Nov. 3, 1993, and now abandoned.
`
`BACKGROUND OF THE INVENTION
`
`5,907,222
`
`2
`
`High heat generation
`High ignition voltages
`External heating required for cold starts
`Accordingly, there is a need to provide a high efficiency
`5 backlighting system that is suitable for back-illuminating
`transmissive electronic display devices and which over(cid:173)
`comes these problems. The present invention provides such
`a system.
`
`1. Field of the Invention
`This invention relates to a method and apparatus for
`illumination of electronic display devices, and more particu(cid:173)
`larly to a high efficiency backlighting system suitable for
`back-illuminating transmissive electronic display devices.
`2. Description of Related Art
`Transmissive electronic display devices, such as active
`matrix liquid crystal displays (AMLCDs) or passive matrix 20
`liquid crystal displays (PMLCDs), are not emissive displays.
`That is, such transmissive displays are not themselves a
`source of light, as is, for example, a cathode ray tube (CR1).
`Accordingly, transmissive displays require a source of rear
`or back illumination to be usable in most applications and 25
`under widely varying ambient lighting conditions.
`FIG. 1 shows a typical use of a fiat panel transmissive
`display 1 as an output device (i.e., a visual display). (In the
`example shown, a graphical map 2 of a street intersection is
`displayed.) Typical uses of transmissive displays include
`sensor indicators and information outputs for automobiles,
`aircraft, scientific instruments, computers, airport inform a(cid:173)
`tion terminals, etc.
`In the prior art, transmissive displays of the type shown in
`FIG. 1 have typically been backlit by bent or serpentine(cid:173)
`shaped fluorescent lamp mounted behind the rear surface of
`the transmissive display. FIG. 2 diagrammatically shows a
`typical shape for such a fluorescent lamp 3. An essentially
`conventional straight fluorescent tube is heated and bent to
`the shape shown. Such a lamp 3 may be used in a reflective
`cavity and with a diffuser to provide a rudimentary backlight
`"system" behind a transmissive display. A fluorescent lamp
`backlight system is proven technology with moderately low
`development risk for most applications. Because of the low
`risk factor, moderate cost, efficiency, and limited alternative
`approaches, serpentine fluorescent backlighting systems are
`the primary backlighting approach for many military and
`commercial fiat panel transmissive displays.
`However, performance parameters and operating condi(cid:173)
`tions of transmissive displays can vary greatly. For example,
`commercial transmissive displays do not require the same
`level of performance and operational ruggedness as military
`or automotive display devices. Consequently, backlight sys(cid:173)
`tems can vary in complexity, effectiveness, efficiency, and
`reliability, depending on the performance and operational
`requirements of their associated transmissive display. In
`general, prior art backlight systems do not have the charac(cid:173)
`teristics necessary to be used in a wide range of applications.
`In particular, it has been found that conventional prior art
`fluorescent backlight systems have a number of problems,
`most notably:
`Poor luminous efficiency
`Poor uniformity of lighting
`Short useful life
`Narrow dimming range
`
`10
`
`SUMMARY OF THE INVENTION
`This invention comprises a fluorescent cavity backlight
`system that provides a high efficiency light source suitable
`for rear illumination of transmissive electronic display
`devices. The inventive fluorescent cavity backlight system
`15 can be adapted to a wide variety of fiat panel display
`applications. The preferred embodiment of the present
`invention has more than 5 times the efficiency of conven(cid:173)
`tional prior art backlight systems.
`The invention takes a complete system approach towards
`designing a high efficiency backlight source. The inventive
`system comprises three major subassemblies: a phosphor
`illuminator, a fluorescent cavity, and improved control/
`driver electronics. Each of the subassemblies has been
`optimized internally, and with respect to each of the other
`subassemblies. More particularly, the preferred embodiment
`of the invention includes the following characteristics:
`(1) Phosphor illuminator-this comprises an ultraviolet
`(UV) gas discharge light tube having no coating phosphor,
`30 internally or externally, in or on the tube. The light tube is
`fabricated to provide the highest UV flux density per unit
`volume of the phosphor illuminator. The tube is preferably
`miter-cut and joined together to provide better illumination
`at the corners of the joints and to provide a better fit to the
`35 shape of the fluorescent cavity. The typical fabrication
`process with this configuration allows spacing between the
`legs of the lamp down to about 2 mm. However, several
`alternative fabrication processes may be used.
`The preferred fill gas for the phosphor illuminator lamp is
`40 a mixture of about 95% argon and 5% neon, with typical gas
`pressure in the range of about 0.5 to about 3.0 torr. This
`mixture and pressure range provides for significantly lower
`ignition voltage than the prior art, particularly at low tem(cid:173)
`perature (about -55° C.) operation. The fill gas and pressure
`45 range permits use of variable duty cycle driving currents to
`provide a dimming function for the lamp. The lower ignition
`voltage provided by the inventive lamp reduces the com(cid:173)
`plexity of the drive circuitry.
`(2) Fluorescent cavity-The phosphor illuminator lamp is
`50 placed in a box-like fluorescent cavity. The rear and side
`surfaces of the cavity are coated with a photoluminescent
`phosphor, which converts UV from the phosphor illuminator
`lamp into visible light. A diffusing cover is provided for the
`cavity which is phosphor coated on the side facing the inside
`55 of the cavity. The external side of the cover may be ground
`or textured in order to provide better light diffusion. A
`typical fluorescent cavity would be approximately 6x8
`inches by 1 inch deep using a 12 mm diameter phosphor
`illuminator lamp. A focusing element (a directional
`60 intensifier) can be overlaid onto the face of the cover to
`redirect scattered or diffused light, resulting in an increase of
`luminescence on the face of the display from selected
`viewing angles. One way to do this is by using microrepli(cid:173)
`cated optics. In practice, this could be an array of achromatic
`65 refracting prisms or similar structures.
`(3) Control/driver-The control/driver of the present
`invention provides for dimming ratios in excess of the
`
`Vizio EX1029 Page 0008
`
`

`

`5,907,222
`
`4
`phors to make visible light. Key differences over prior art lie
`in the construction of the system and its high degree of
`optimization for specific performance parameters.
`
`OVERVIEW
`
`3
`2,000:1, a requirement typically found in military and com(cid:173)
`mercial applications. This expanded dimming ratio is
`achieved through the use of a unique digitally controlled
`circuit to control the phosphor illuminator lamp excitation
`voltage. The control/driver provides excitation to heat the 5
`cathodes of, and supply a controlled arc current to, a
`hot-cathode phosphor illuminator lamp. Energy is delivered
`to the lamp in the form of voltage and current in time.
`Voltage or current are highly controlled under all operating
`states of the lamp through a variable duty cycle regulated by 10
`the control/driver. The control/driver are designed to provide
`this excitation at a very high efficiency.
`Advantages of the present invention in comparison to the
`prior art include:
`Improved luminous efficiency
`Improved uniformity of lighting
`Longer useful life
`A large dimming range (bright to dim ratio)
`Reduced heat generation
`Low ignition voltages
`No required external heating for cold starts
`The details of the preferred embodiment of the present
`invention are set forth in the accompanying drawings and 25
`the description below. Once the details of the invention are
`known, numerous additional innovations and changes will
`become obvious to one skilled in the art.
`
`15
`
`The inventive system comprises three major subassem(cid:173)
`blies: a phosphor illuminator, a fluorescent cavity, and
`improved control/driver electronics. Each of the subassem(cid:173)
`blies has been optimized internally, and with respect to each
`of the other subassemblies. Each of these elements and
`details of their manufacture are described below in separate
`sections. General factors taken into account in the design of
`the preferred embodiment of the invention include perfor(cid:173)
`mance requirements, efficiency, heat, and dimming.
`Performance Requirements
`Mention of display performance requirements is made
`only to emphasize the importance of an integrated design
`and to show the dependency of a transmissive display on the
`20 backlight. The overall complexity of the integrated display
`assembly and the backlight are very strongly influenced by
`performance requirements. Typical performance require(cid:173)
`ments for such displays are listed below:
`Daylight readable
`High luminance
`High contrast
`Broad viewing angles
`Large color palette
`High luminance uniformity
`High bright to dim ratios
`Night Vision Imaging System (NVIS) Compatible
`Display performance is influenced heavily by the quality
`and efficiency of the components (such as polarizers, color
`35 filters, and liquid crystal materials) that comprise a liquid
`crystal display (LCD) assembly. For example, color active
`matrix liquid crystal display (AMLCD) assemblies pass only
`about 2 to 4% of the available backlight luminance. A fiat
`panel display does not enjoy the benefit of generating
`40 localized luminance at the face of the display, as does a CRT.
`Accordingly, the entire display area is backlit at a constant
`(but selectable) intensity at all times. The illumination
`characteristics of the backlight are modified by each and
`every component in the optical stack. Thus, the burden of
`45 providing adequate performance of the fiat panel display is
`in large part borne by the backlight. A design criteria of the
`present invention was to provide a high performance back(cid:173)
`light system with high luminance, low power, and a wide
`dimming ratio.
`Efficiency
`The invention employs fluorescence as the lighting agent
`of choice for the generation of visible light for two reasons.
`First, high quantum efficiency fluorescent phosphors offer
`the highest lumen-per-watt conversion efficiency of any
`55 lighting technology presently in common use. Published
`data suggests efficiencies of 40 lumens per watt are achieved
`with conventional fluorescent lamp technology. (This data
`presumes the power dissipated by the lamp is delivered to
`the positive column, or mercury arc stream, and does not
`60 account for losses attributed to lamp drivers, heater circuits,
`or filaments.) Second, the narrow band emissions of the
`selected phosphors are well suited to fiat panel display
`applications where high purity primary colors are desired.
`Heat
`In general, all but a very small amount of the power
`consumed by any lighting technology is converted to heat.
`High heat often establishes the limit of visual performance
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a front view of a typical prior art transmissive
`display used as an output device.
`FIG. 2 is a diagram of a typical prior art fluorescent lamp
`shape used to backlight transmissive displays.
`FIG. 3A is a front perspective view of the fluorescent
`cavity and phosphor illuminator of the preferred embodi(cid:173)
`ment of the present invention, showing a single "high fill
`factor" lamp.
`FIG. 3B is a front perspective view of the fluorescent
`cavity and phosphor illuminator of an alternative embodi(cid:173)
`ment of the present invention, showing multiple lamps.
`FIG. 4 is a front perspective partially exploded view of the
`fluorescent cavity and phosphor illuminator and cover of the
`preferred embodiment of the present invention.
`FIG. 5 is a block diagram of the drive/controller electron(cid:173)
`ics of the preferred embodiment of the present invention.
`FIG. 6 is a timing diagram for the drive/controller elec(cid:173)
`tronics of the preferred embodiment of the present inven(cid:173)
`tion.
`FIG. 7 is a schematic diagram of part of the drive/
`controller electronics shown in FIG. 5.
`Like reference numbers and designations in the various
`drawings refer to like elements.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`30
`
`50
`
`Throughout this description, the preferred embodiment
`and examples shown should be considered as exemplars,
`rather than as limitations on the present invention.
`The invention takes a complete system approach towards
`designing a high efficiency backlight source. The invention
`provides a high intensity, very uniform, controllable light
`source for the back illumination of liquid crystal and other 65
`types of transmissive displays. The invention uses ultravio-
`let (UV) photon bombardment of photoluminescent phos-
`
`Vizio EX1029 Page 0009
`
`

`

`5,907,222
`
`5
`m fiat panel transmissive display technology, where pro(cid:173)
`longed exposure to high heat would cause catastrophic
`failure of the liquid crystal display assembly. For this reason,
`it is necessary to keep the heat generated in the backlight
`assembly to a minimum. For example, backlight systems 5
`that provide 5,000 to 6,000 foot-Lamberts (fL) of uniform
`diffuse luminance are considered exceptional by today's
`standards. Using a serpentine fluorescent lamp with a heavy
`diffuser to achieve this level of performance requires sig(cid:173)
`nificant power, and hence heat. A design criteria of the 10
`present invention was to reduce heat while providing high
`levels of luminance by providing high luminous efficiency.
`Dimming
`The luminous intensity of a display is adjusted for view(cid:173)
`ability above the surrounding ambient light. Viewability will 15
`vary for different types of displays and for the environment
`in which it is used. Where large dimming ratios are required
`(2,000: 1 or greater, as might be found in a military aircraft
`or automotive applications), it is necessary to dim the
`illuminator in the inventive backlight system to a very low 20
`level. This invention accomplishes flicker free dimming at a
`low light level operating mode via digital control/driver. The
`ability of the present invention to operate the ultraviolet
`phosphor illuminator in an unstable but highly controlled
`manner is important for this high range of dimming.
`
`(1) PHOSPHOR ILLUMINATOR
`Conventional Fluorescent Lamps
`The body of a conventional fluorescent lamp is a tubular
`(usually round) glass or quartz envelope which is transparent
`to visible light but not to UV. The envelope houses (1) a
`blend of photoluminescent phosphors (that is, phosphors
`that release visible light when exposed to UV photons; these
`phosphors differ from CRT phosphors that require electron
`stimulation to release visible light), (2) inert fill gases such 35
`as argon or krypton, (3) a small amount of mercury to
`provide ultraviolet (UV) emission lines at 186 nm and 254
`nm when ionized, (4) a cathode to provide a source of
`electrons for ionizing the mercury and sustaining the result(cid:173)
`ing plasma (arc stream), and (5) an anode to provide a return 40
`path for current flow out of the lamp. The electrical energy
`for the lamp is provided by an ordinary electrical ballast,
`which is generally inefficient and not dimmable over wide
`ranges of visual light output.
`Light manufactured in a fluorescent lamp is the result of 45
`a fairly complex energy conversion process (electron energy
`to UV light energy to visible light energy) that is influenced
`by many factors. These factors include: lamp length, lamp
`diameter, fill gas type, fill gas pressure, amount of mercury
`present in the lamp (mercury pressure), filament type, fila- 50
`ment materials, filament temperature, and filament location.
`The power-to-light conversion process that occurs in a
`conventional fluorescent lamp is a result of current flow
`propagated by the motion of electrons and ions inside the
`lamp. Electron mobility is much greater than ion mobility, 55
`and thus electrons carry essentially all the current and
`receive essentially all of the electrical power input. Lamp
`behavior is determined to a large degree by how the elec(cid:173)
`trons dissipate that power. Electrons can collide with each
`other, sharing energy with each other. This establishes an 60
`electron energy distribution inside the lamp envelope. Elec(cid:173)
`trons also can collide "elastically" with inert gas atoms,
`transferring a very small amount of kinetic energy to the gas
`atoms per collision. However, there are many such
`collisions, and this is an energy conversion loss.
`Electrons also can collide "inelastically" with mercury
`atoms, converting the bulk of electron kinetic energy into
`
`6
`excitation energy of the mercury atoms. Such excitation
`causes loosely bound electrons in the mercury atoms to be
`elevated to a higher energy level. The excited mercury atoms
`then relax to the previous unexcited state and the result of
`this relaxation is energy released through radiation. Most of
`this radiation is ultraviolet (mercury 186 nm and 254 nm
`emission lines) that is used at almost 100% efficiency by the
`internal phosphor to make visible light. In general, the
`efficiency of the lamp is determined by the fraction of
`electrical power consumption that is dissipated through this
`channel.
`The burden of establishing a balance among all of the
`physical, electrical, and mechanical factors that influence
`fluorescent lamp efficiency and performance is usually
`shouldered by the lamp manufacturer. Thus, prior art fluo(cid:173)
`rescent lamps as used in backlights are typically not
`designed from a system viewpoint. Accordingly, seldom are
`the performance requirements for backlit transmissive dis-
`plays as a system fully met with a serpentine fluorescent
`backlight.
`A principal problem of prior art fluorescent lamps is the
`use of internal phosphors. Because of the ease with which
`ultraviolet photons are absorbed by most materials, the
`phosphor material is usually in intimate contact with the
`25 gaseous or vapor mixture. Several deficiencies of previous
`designs arise from the fact that the phosphors, gaseous
`mixture, and cathodes are all exposed to each other. Mercury
`vapor from the gaseous mixture and metal ions which boil
`off the cathodes interact with the phosphors, reducing their
`30 life.
`Further, all known materials that are available for use as
`a binder for the phosphor slurry that is applied to the inside
`of a conventional fluorescent lamp absorb UV. In conven(cid:173)
`tional fluorescent lamps, an organic material is used for
`adhesion to the glass envelope and is "baked out" of the
`phosphor in an attempt to eliminate UV absorption. This is
`not a 100% effective solution to the problem. Manufacturing
`processes may not eliminate all the residual binder
`materials, and the arc stream can become contaminated.
`Contamination can result in degraded lamp performance and
`shortened lamp life.
`Phosphor Illuminator Lamp
`Rather than using a conventional fluorescent lamp, the
`present invention uses a phosphor illuminator lamp 14 (see
`FIG. 3A) in conjunction with a fluorescent cavity (described
`below). The phosphor illuminator lamp 14 comprises a UV
`gas discharge lamp, the envelope or tube of which is made
`of quartz, glass, or other material that has high UV trans-
`mittance. (In contrast, prior art fluorescent lamps have an
`envelope made of soda lime or borosilicate glass, which
`absorb the ultraviolet energy necessary for photolumines(cid:173)
`cence of the phosphors within the tube.) Avoiding phosphor
`and residual binder contaminants inside of the lamp enve(cid:173)
`lope contributes to a projected longer lamp life.
`The envelope of the phosphor illuminator lamp 14 pref(cid:173)
`erably has a generally tubular configuration. The lamp tube
`generally has a round cross-section, and has about a 1-2 mm
`wall thickness and an inside diameter of about 7 mm to
`about 13 mm in the preferred embodiment. If desired, the
`envelope may be formed with indentations to provide
`greater surface area and/or effective tube length.
`While the tubing of the phosphor illuminator lamp 14
`preferably has a round cross-section, the tubing may also be
`65 elliptical, oval, square, hexagonal, or any other desired
`shape. Further, other diameters and wall-thicknesses may be
`used.
`
`Vizio EX1029 Page 0010
`
`

`

`5,907,222
`
`7
`Two types of quartz can be used for envelope material,
`"ozone producing" and "ozone free". Ozone is the byproduct
`of short wave UV (e.g., the mercury 186 nm line) coming
`into contact with oxygen. The difference in the two materials
`is that a dopant (typically titanium) that absorbs the 186 nm 5
`mercury emission line is added to ozone producing quartz to
`make ozone free quartz. The 186 nm line accounts for
`approximately 15% of the total amount of UV that has the
`potential to make light. For this reason, it is desirable to use
`ozone producing quartz in the backlight assembly if the 10
`ozone can be controlled or contained through other means,
`such as a sealed backlight cavity.
`Lamp Design & Manufacture
`The manufacturing process for the phosphor illuminator
`lamp 14 also differs from the prior art. Phosphor deposition
`and curing processes used when manufacturing conven(cid:173)
`tional fluorescent lamps will not accommodate coating a
`pre-bent envelope. Consequently, the glass envelope of a
`straight fluorescent lamp must be heated and bent to acquire
`a serpentine configuration. Using this process, it is difficult
`to maintain uniform bends. Further, bending a straight lamp
`into a serpentine configuration compromises the integrity of
`the phosphor coating on the inside of the lamp for two
`reasons. First, localized high temperature heating of the
`glass envelope required to bend the lamp can damage the
`phosphor in that immediate area. Second, bending the lamp
`literally increases the envelope length over the outside bend
`radius, resulting in a less dense phosphor coating over the
`bend area and weakening of the lamp tube. Accordingly, the
`extreme corners 6 (see FIG. 2) of the serpentine backlight
`assembly are difficult to light. This results in notable light
`loss at such corners.
`For a prior art serpentine configuration, the manufacturing
`limit that determines the number of lamp legs that can be
`placed inside the reflecting cavity is the spacing between 35
`each leg of the lamp. This spacing is generally limited to the
`diameter of the lamp. For example, for 12 mm diameter
`tubing, adjacent legs are spaced no closer than about 12 mm.
`If the bend radius is smaller than the diameter of the lamp,
`the distorted envelope can restrict the arc stream used to 40
`produce fluorescence of the phosphors, resulting in signifi(cid:173)
`cant light loss in the region of the bend. Likewise, a large
`bend radius will result in fewer legs, reducing the potential
`to make light.
`The surface luminance of a fluorescent lamp is often used
`to rate the potential light output of the backlight. In an ideal
`situation, the relationship of surface luminance for a fluo(cid:173)
`rescent lamp to delivered luminance at the back side of an
`LCD is a direct ratio of the respective areas. For this reason
`it is desirable to have as much active area (lamp surface)
`inside the backlight cavity as possible.
`For example, a fiat panel display surface of 6x8 inches has
`48 square inches that must be uniformly illuminated. The
`backlight cavity is generally limited to a 1 inch depth (or
`less). This size cavity could accommodate a 15 mm diameter
`lamp. With this volume, it is feasible to use a lamp with five
`8-inch lateral legs and maintain acceptable bend radii. This
`results in an overall lamp length of about 40 inches. (Lamps
`of this diameter and length are not generally used in display
`applications because they are extremely difficult to bend.
`However, in this example, a 40-inch lamp length is used for
`simplicity of illustration.)
`The total surface area of the lamp is calculated to be;
`Equation 1: surface area of cylinder=2mL
`or, approximately 94 square inches of illuminated surface
`area in this example.
`
`8
`The total potential back-illumination intensity of this
`configuration would be:
`Equation 2: total fL=(94/48)*surface luminance of lamp,
`or approximately 2 times the surface luminance of the lamp
`in this example.
`Surface luminance of fluorescent lamps is dependent on
`many factors, but luminance values of 6,000 to 10,000 fL
`(measured on the lamp envelope) are common for tri-band
`fluorescent lamps that use high-efficiency rare earth phos(cid:173)
`phors. From Equation 2, the unrestricted light output of the
`example integrated backlight assembly could theoretically
`approach 20,000 fL with moderate power. However, in
`practice, the actual luminance is drastically reduced from
`this potential va