Integral lamp for tricolor picture element

Abstract: A tri-color lamp for use as an element in the optical presentation of information. The lamp includes a sealed envelope having a common envelope member and a plurality (e.g., three) of longitudinally extending leg members. A common electrode is located within the common envelope member and is spacedly located from opposing electrodes located within each of the leg members. A phosphor layer within the sealed envelope subtends at least the major body portion of each of the leg members such that the surface brightness of the phosphor layer as viewed through the end portions of the lamp is greater than the intensity of the external surface brightness of the phosphor layer on the major body portion. In the presentation of color information, each of the leg members is coated with respective phosphors emitting the primary colors red, green and blue.

Description: This invention relates to an arc discharge lamp according to the first part of claim 1, and more particularly, but not exclusively, to low pressure discharge lamps adaptable for use both as an element in a picture display and in certain general illuminating applications wherein a considerable portion of the light emitted from the lamp is directed in a particular direction. Such a lamp is known from US-A-4625152. Low-pressure arc discharge lamps have been used for optical presentation of information, i.e., presentation of alpha numeric signs, graphics and pictures displayed on a screen or display, respectively. Such a display consists of a matrix of picture elements, each picture element consisting of a monochrome light signal source in the case of a monochrome display. In the case of a colour presentation of information, one picture element is composed on three single lamps of the primary colours red, green and blue. The desired colour impression is then created physiologically by additive mixture of the three primary colours within the human eye/brain system. There have been proposed a wide variety of fluorescent lamps of such special configuration as to be applicable to such displays. For example, FIG. 1 of GB-A-2145873 (= US-A-4625152) shows one typical lamp which comprises a phosphor-coated tubular envelope of convoluted three way configuration that contains a pair of electrodes and an ionizable medium. For construction of the colour display, a multiplicity of the above fluorescent lamps are arranged in a matrix (FIG. 2) so as to form one picture element by the combination of three lamps having the envelope coated with respective phosphors emitting the different primary colours, i.e., red, green and blue. GB-A-2145873 also shows a fluorescent lamp comprising a gas-filled envelope enclosing a plurality of discharge paths defined by U-shaped phosphor-coated tubes. GB-A-2167895 shows in FIG. 18 a fluorescent lamp comprising a central lamp base 201 with a cell 205 having a common electrode 208 therein and U-shaped lamp tubes 209a, 290b and 209c joined to communicate their interior with cell 205. Although the known lamps operate satisfactorily when used in some of such displays, drawbacks still exist. Presenting information to a large audience in the open air means looking for a correspondingly large area display which is distinctly visible not only at night but also during daylight and with sufficient optical resolution from a greater viewing distance. In the above known lamps, only the curved portion of the U-shaped envelope is presented towards the audience so that no more than approximately 20 percent of the radiation is effective. The rest is dissipated, especially through the parallel legs of the U-shaped envelope which are arranged parallel to the longitudinal axis of the lamp and substantially normal or perpendicular, respectively, to the plane of fixation of a unit, said plane being also substantially normal to the viewing direction of the spectators. The surface brightness along the envelope is substantially constant, i.e., one area along the envelope does not appear brighter than another area. Other low-pressure arc discharge fluorescent lamps primarily used for general illumination are known in which the envelope includes at least two longitudinally extending leg members joined together by a transversely extending envelope portion. Examples of such lamps which are commercially available are the "Twin Tube" and "Double Twin Tube" fluorescent lamps manufactured by Osram Sylvania, Danvers, Massachusetts. Other examples are disclosed in US-A-4374340, US-A-4426602 and US-A-4481442. Lamps described in the above-mentioned US patents allow most of the radiation to be dissipated through the longitudinally extending leg members. The surface brightness along the envelope is also substantially constant. In co-pending EP-A-0296535 there is disclosed an arrangement for improving performance, in which a window is provided at the end of tubular portion of an arc discharge lamp. The phosphor layer and/or a reflective layer are absent in the region of the window. The brightness of the lamp viewed through the window is of greater intensity than the external surface brightness of the tubular portion. In JP-A-6091546 there is disclosed an arc discharge lamp in which a slit is provided in which there is no phosphor, to prevent damage to a curved tubular portion. According to the present invention there is provided an arc discharge lamp comprising a sealed envelope having a base end and a top end, the envelope including a plurality of elongate tubular portions each containing an electrode at the base end thereof, the elongate tubular portions each being in communication with a common portion of the envelope in which is provided a common electrode, and each tubular portion having extending therealong a coating comprising phosphor as a component, characterised in that the tubular portions form the envelope and have sealed top ends, the communication with the common portion being in the region of the top ends, in that the top end of each tubular portion is provided with a window over which at least part of the coating is absent across the area of the window, and in that the brightness of the lamp viewed through the windows is of greater intensity than the external surface brightness of the elongate tubular portions. In one arrangement the coating consists of phosphor and the phosphor is absent across the windows. In another arrangement, the coating consists of a reflective layer and phosphor, and the reflective layer is absent across the windows. In a preferred arrangement the interconnection between each tubular portion and the common portion is spaced by a distance towards the base of the tubular portion from the top end thereof. Preferably, the top ends of the tubular portions are flat and perpendicular to the axes of the tubular portions. The tubular portions preferably communicate with the common portion by means of respective transverse portions. The common portion is preferably positioned centrally between the tubular portions. In the preferred arrangement, each of the tubular portions contains a phosphor layer of a different spectral power distribution, and there are three tubular portions respectively emitting red, green and blue light. The three tubular portions are preferably positioned triangularly around the common portion. In a preferred arrangement the common portion is in the form of an elongate tube and the common electrode is positioned at the base end of the tube. Some embodiments of the invention will now be disclosed by way of example and with reference to the accompanying drawings, in which:- Fig. 1 is a front elevational view of an embodiment of an arc discharge lamp in accordance with the invention; Fig. 2 is a plan view of the lamp of Figure 1; Fig. 3 is a vertical section of part of the lamp of Figure 1 showing its construction; Fig. 4 is a section through Figure 3; Fig. 5 is a vertical section of part of the lamp of Figure 1 showing another form of construction; Fig. 6 is a section through Figure 5; Fig. 7 shows part of an alternative arrangement; and Fig. 8 shows part of a further alternative arrangement. Figs. 1 and 2 show an arc discharge lamp which can be used in a colour picture display. An arc discharge lamp 100 is shown including a sealed envelope 102. Sealed envelope 102 includes a common envelope member 104 and a plurality of longitudinally extending leg portions 106,108,110 joining common envelope member 104. Each of the elongate, tubular longitudinally extending leg portions 106,108,110 is joined to common elongate envelope portion 104, also tubular, through a transversely extending envelope portion 118,120,122, respectively, spaced downwardly from the respective ends 130,132,134. These end portions 130,132,134 are located at a top end 126 of lamp 100. A compactly configured lamp can be obtained, for example, by triangularly disposing longitudinally extending tubular leg members 106,108,110 around the common portion 104 which is centrally disposed therebetween, as shown in Figure 2. A common electrode 124 is located within common portion 104 at a second, or base, end 128 of lamp 100. An opposing electrode 136,138,140 is located respectively within each of the longitudinally extending leg portions 106,108,110 at this base end 128 of lamp 100. Opposing electrodes 136,138,140 are thus spaced from common electrode 124. Accordingly an arc discharge can be selectively generated between common electrode 124 and one or more of the opposing electrodes 136,138,140. For example, by electrically selecting common electrode 124 and first opposing electrode 136, an arc discharge can be established from common electrode 124 (cathode) through common envelope portion 104, first transversely extending envelope portion 118, first longitudinally extending tubular portion 106, to first opposing electrode 136 (the anode). Simultaneously, an arc discharge can be established, for example, from common electrode 124 through common envelope portion 104, second transversely extending portion 120, second longitudinally extending leg portion 108, to second opposing electrode 138. It is understood that electrodes 124,136,138,140 may be configured or be made to operate as either an anode or cathode. Sealed envelope 102 contains an ionizable medium having a quantity of mercury and an inert starting gas at a low pressure, for example, in the order of 1.3 x 10⁻³ to 6.5 x 10⁻³ bar (1-5 mm of mercury). The starting gas may be, for example, argon, krypton, neon or helium or a mixture of these and/or other gases. Sealed envelope 102 can be made entirely of soda-lime or lead glass. Alternatively, transverse end portions 130,132,134 at the top end 126 can be made of a light-transmitting material and the remainder of the envelope made of a non-light-transmitting material. A phosphor layer within sealed envelope 102 extends along at least the major part 112,114,116 of each of the longitudinally extending leg portions 106,108,110. The phosphor layer is either disposed on the internal surface of the portions thereof or on an underlying reflective layer. The surface brightness of the phosphor layer as viewed through each of the transverse end portions 130,132,134 is of greater intensity than the external surface brightness of the phosphor layer along the major body portions 112,14,116 of the respective longitudinally extending leg portions 106, 108,110 during operation of lamp 100. In a first embodiment, the phosphor layer is absent across at least a part of the transverse end portions associated with the longitudinally extending leg portions. In a second embodiment, the phosphor layer may also extend over the internal surface of a transverse end portion, but a reflective layer is omitted therefrom. For use in a colour picture display, the longitudinally extending leg portions 106,108,110 can be provided with respective fluorescent phosphor layers of different spectral power distributions emitting the different primary colours, i.e., red, green and blue such as YOX(Y₂O₃:Eu), CAT(MgAl₁₁O₁₉: Ce, Tb) and BAM(BaMg₂Al₁₆O₂₂:Eu), respectively. Turning the differently coloured leg portions on and off at a rate faster than the eye can react (e.g., faster than 30 times per second), a single pixel is seen by the unaided eye as a spot of light at normal viewing distances. The colour and intensity thereof is determined by the length of time each colour portion of the lamp is turned on. The colour can be varied from pure red to pure green to pure blue along with colour combinations therebetween. Preferably, the sealed envelope is configured and coated according to the present teachings to produce one pixel per lamp. If the sealed envelope 102 is configured and coated according to the present teachings, three colour elements or dots per envelope will be produced. At normal viewing distances, the coloured dots will appear to form a single pixel to the unaided eye. A filter coating or externally mounted filter can also be used to vary the colour of the lamps. Common envelope portion 104, including the transverse top portion thereof, is left uncoated with phosphor or coated with a non-light emitting coating so as not to produce light. In this embodiment, arc discharge lamp 100 includes a base member 144 supporting sealed envelope 102. Electrical contact means, such as pins 146, project from a surface 150 on base member 144 in order to provide connection from an electrical socket to the lamp electrodes. Referring now to Figures 3 and 4, there is illustrated part of a lamp 10 in accordance with the invention, showing one elongate tubular portion joined to a common portion. Thus, there is shown a sealed envelope 12 containing an ionizable medium including a quantity of mercury and an inert starting gas at low pressure, for example, of the order of 1-5 mm of mercury. The starting gas can be, for example, argon, krypton, neon, or helium, or a mixture of these and other gases. An electrode 16 supported by lead-in wires 22,24, is spacedly located within envelope 12 for generating an arc discharge during operation of lamp 10. Electrode 16 can be, for example, a double or triple-coiled tungsten filament of the usual type and carry a coating thereon which is usually in the form of carbonates which upon processing, are converted to oxide. Alternatively, the electrode may be in the form of an anode suitable for D.C. operation and requires only support from a single lead-in wire. A phosphor layer within sealed envelope 12 converts the ultraviolet radiation generated in the mercury discharge into visible radiation. Envelope 12 of arc discharge lamp 10 in FIGS. 1 and 2 includes a longitudinally extending leg member 30. Also included with envelope 12 is a transversely extending portion 32 joining the longitudinally extending leg member 28 to a common portion 38 to form a continuous passage therethrough for the arc discharge. Transversely extending envelope portion 32 is longitudinally spaced a predetermined distance D (e.g., 0.375 inch) from an end portion of envelope 12. The transversely extending envelope portion may have various other shapes, for example, a squared U-shape configuration as illustrated by 42 in the partial front elevational view of the arc discharge lamp 10A of FIG. 5 or a rounded U-shape configuration as illustrated by 43 in the partial front elevational view of the arc discharge lamp 10B of FIG. 6. In the embodiment shown in FIGS. 1 and 2, envelope 12 includes a major body portion 36 and first and second end portions 38 and 40, respectively associated with the longitudinally extending leg member 28 and the common portion. A phosphor layer 26 is disposed on the internal surface 34 of major body portion 36 of envelope 12. Preferably substantially the entire internal circumference of leg member 28 and the common portion is coated with phosphor layer 26. The phosphor layer is not disposed on the internal surface of the transverse end portions. As illustrated flat surfaces 41 on the transverse end portions 38 and 40, which lie in a plane substantially perpendicular to the longitudinal axis of lamp 12, are devoid of phosphor. The transverse end portions may have a more curvilinear shape (see FIG. 5). The internal surface brightness of the phosphor layer as viewed through the transverse end portions devoid of phosphor can be five or six times greater than the intensity of the external surface brightness of the phosphor layer over the major body portion of the envelope during operation of the lamp. An envelope with a T6 (0. 75 inch) outside diameter will result in total area of increased surface brightness of approximately one square inch. The area of increased surface brightness can be varied by simply changing the diameter of the envelope. In the embodiments of FIGS. 5 and 6, the minor transverse end portion is located on the transversely extending envelope portion. In FIG. 5, transverse end portion 44 is located on a squared U-shaped transversely extending envelope portion 42. As illustrated, a flat surface 41 on end portion 44 is devoid of a phosphor layer. When viewed through the uncoated part of transverse end portion 44, the internal surface brightness of phosphor layer 26 is of greater intensity than the external surface brightness of phosphor layer 26 during lamp operation. In FIG. 6 a transverse end portion 46 is located on a rounded U-shaped transversely extending envelope portion 43. As shown, a curvilinear U-shaped surface 48 on end portion 46 is devoid of a phosphor layer. Similarly during lamp operation, the internal surface brightness of phosphor layer 26 is of greater intensity than the external surface brightness of phosphor layer 26 when viewed through the uncoated part of transverse end portion 46. Reference is now made to FIGS. 7 and 8 which show another embodiment of an arc discharge lamp according to the present invention. An arc discharge lamp 50, such as a fluorescent lamp, is shown including a sealed envelope 52 containing an ionizable medium including a quantity of mercury and an inert starting gas. An electrode 56 supported by lead-in wires 62,64, is spacedly located within envelope 52 for generating an arc discharge during operation of lamp 50. Envelope 52 includes longitudinally extending leg member 70. Also included with envelope 52 is a transversely extending envelope portion 72 joining the longitudinally extending leg member 70 and a common portion to form continuous passage therethrough for the arc discharge. Transversely extending envelope portion 72 is longitudinally spaced a predetermined distance D from an end portion of envelope 52. Envelope 52 includes a major body portion 76 and first and second transverse end portions 78 and 80, respectively associated with the longitudinally extending leg member 70 and the common portion. To increase the surface brightness of lamp 50, a reflector layer 65 is disposed on the internal surface 74 of major body portion 76 of envelope 52. According to the teachings of the present invention, the reflector layer is not disposed on the internal surface of the transverse end portions. In the embodiment illustrated in FIGS. 7 and 8, a part of each of the transverse end portions 78 and 80 is devoid of the internal reflector layer. Reflector layer 65 can be a non-absorbing material, such as, titanium dioxide or alumina. Thus the light which would normally be emitted out of the leg members would be reflected back into the lamp to further increase surface brightness. A phosphor layer 66 is disposed on reflector layer 65 and, if desired, on a part of the internal surfaces of one or both of the transverse end portions. As shown in FIGS. 7 and 8, phosphor layer 66 is extended over the internal surfaces 81 of both transverse end portions 78 and 80. During lamp operation, the surface brightness of phosphor layer 66 as viewed through minor transverse end portions 78 and 80 of envelope 52 is of greater intensity than the external surface brightness of phosphor layer 66 on major body portion 76 of envelope 52. Preferably, as shown in FIGS. 7 and 8, substantially the entire internal circumference of leg member 68 is coated with reflector layer 65 and overcoated with phosphor layer 66. In the embodiments shown at least the transverse end portions are of light-transmitting vitreous material such as soda-lime or lead glass. Major body portions 36 and 76 can be made of a non-light transmitting material, if desired. While there have been shown and described certain embodiments of the invention, it will be apparent to those skilled in the art that various changes and modifications can be made herein without departing from the scope of the claims. For example, instead of an internal reflector layer or in addition thereto, an external non-absorbing reflector layer having a higher reflectivity than that of the internal reflector layer may be employed.

Claims: An arc discharge lamp (100) comprising a sealed envelope (102) having a base end (128) and a top end (126), the envelope including a plurality of elongate tubular portions (106,108,110) each containing an electrode (136,138,140) at the base end thereof, the elongate tubular portions each being in communication with a common portion (104) of the envelope in which is provided a common electrode (124), and each tubular portion having extending therealong a coating comprising phosphor as a component, characterised in that the tubular portions form the envelope (102) and have sealed top ends (130,132,134), the communication (118,120,122) with the common portion (104) being in the region of the top ends, in that the top end of each tubular portion is provided with a window over which at least part of the coating is absent across the area of the window, and in that the brightness of the lamp viewed through the windows is of greater intensity than the external surface brightness of the elongate tubular portions. A lamp (100) as claimed in claim 1, characterised in that the coating consists of phosphor (26) and the phosphor is absent across the windows. A lamp (100) as claimed in claim 1, characterised in that the coating consists of a reflective layer (65) and phosphor (66), and the reflective layer (65) is absent across the windows. A lamp (100) as claimed in claim 3, characterised in that there is a reflective layer on the exterior of each tubular portion (106,108,110). A lamp (100) as claimed in any preceding claim, characterised in that each window extends across the entire top end (130,132,134) of the respective tubular portion (106,108,110). A lamp (100) as claimed in any preceding claim, characterised in that the interconnection (118,120,122) between each tubular portion (106,108,110) and the common portion (104) is spaced by a distance (D) towards the base of the tubular portion from the top end thereof. A lamp (100) as claimed in claim any preceding claim, characterised in that the top ends (130,132,134) of the tubular portions are flat and perpendicular to the axes of the tubular portions. A lamp (100) as claimed in any preceding claim, characterised in that the tubular portions (106,108,110) communicate with the common portion (104) by means of respective transverse portions (118,120,122). A lamp (100) as claimed in any preceding claim, characterised in that the common portion (104) is positioned centrally between the tubular portions (106, 108,110). A lamp (100) as claimed in any preceding claim, characterised in that there are more than two elongate tubular portions (106,108,110) and more than two transverse portions (118,120,122). A lamp (100) as claimed in claim 10, characterised in that each of the tubular portions (106,108,110) contains a phosphor layer of a different spectral power distribution. A lamp (100) as claimed in claim 11, characterised in that there are three tubular portions (106,108,110) respectively emitting red, green and blue light. A lamp (100) as claimed in any preceding claim, characterised in that the common portion (104) is in the form of an elongate tube and the common electrode (124) is positioned at the base end (128) of the tube.

Inventors: FOHL TIMOTHY, GUNGLE WARREN C, PAI ROBERT Y, FOHL, TIMOTHY, GUNGLE, WARREN C., PAI, ROBERT Y.
Applicants: GTE PROD CORP, GTE PRODUCTS CORPORATION
Application year: 1988
Main classification: H01J61
IPC codes: H01J61