Dual Plane EL Panel

This invention relates to electroluminescent (EL) lamps and, in particular, to an EL lamp providing illumination in two, parallel planes.

An EL lamp is essentially a capacitor having a dielectric layer between two conductive electrodes, one of which is transparent. The dielectric layer, or a separate layer, includes a phosphor powder which radiates light in the presence of a strong electric field, using very little current. The front electrode is typically a thin, transparent layer of indium tin oxide or indium oxide and the rear electrode is typically a polymer binder, e.g. polyvinylidene fluoride (PVDF), polyester, vinyl, or epoxy, containing conductive particles such as silver or carbon. The front electrode is applied to a polymer substrate, such as polyester or polycarbonate, that provides mechanical integrity and support for the other layers.

Because of the uniformity of the light and the variety of colors of EL lamps, the number of applications for EL lamps grows steadily. EL lamps are planar or sheet devices and there are some applications in which a display is made in two or more stacked planes, as in watches having both an analog display and a digital display. The analog display is a dial and the digital display is a liquid crystal display (LCD) located within the dial. A single EL lamp cannot be used to backlight both displays because an LCD is much thicker than a dial face. Space in a watch is conserved by cutting a hole or window in the dial and positioning the LCD in the window. Even so, the thickness of an LCD precludes the use of a single EL lamp for backlighting both displays. Thus, two lamps and four electrical connections must be included in each analog/digital watch. Each connection adds cost and adds a small but finite chance for failure.

As used herein, an EL "panel" is a single substrate including one or more luminous areas, wherein each luminous area is an EL "lamp."

In view of the foregoing, it is therefore an object of the invention to provide a single EL panel having at least two lamps that can be stacked to provide lamps in at least two planes.

A further object of the invention is to provide a single EL panel having lamps in at least two parallel planes mechanically joined by a common substrate.

Another object of the invention is to provide a single EL panel having at least two lamps in different planes emitting light in substantially the same direction.

A further object of the invention is to provide a single EL panel having lamps in at least two parallel planes electrically interconnected by a single pair of conductors.

The foregoing objects are achieved in this invention in which an EL panel includes a pair of EL lamps on a common substrate, separated by a predetermined distance along a longitudinal axis. A first flexible, electrically conductive trace on the substrate interconnects the front electrodes of the lamps and a second flexible, electrically conductive trace on the substrate interconnects the rear electrodes of the lamps. In a preferred embodiment of the invention, the lamps share a common front electrode and the first trace overlies the front electrode between the lamps. One of the lamps is rotated relative to the other to position the lamps one above the other in separate, parallel planes.

A more complete understanding of the invention can be obtained by considering the following detailed description in conjunction with the accompanying drawings, in which:

FIG. 1 is a plan view of a watch including an analog display and a digital display;

FIG. 2 is a plan view of an EL panel constructed in accordance with a preferred embodiment of the invention;

FIG. 3 is a cross-section of an EL panel constructed in accordance with a preferred embodiment of the invention;

FIG. 4 is a diagram illustrating how an EL panel is rotated about a single axis to provide lamps in two planes emitting light/in substantially the same direction; and

FIG. 5 is a diagram illustrating how an EL panel is rotated about two axes to provide lamps in two planes emitting light in substantially the same direction.

FIG. 1 illustrates a watch having an analog display and a digital display. Watch 10 includes dial 11 and hands 16 and 17 for indicating time of day. Dial 11 can be a transparent plastic sheet with numbers printed on it or numbers representing time of day are printed directly on the front (the transparent substrate) of an EL lamp. Dial 11 has hole 13 in the lower half thereof to provide a window for digital display 15, illustrated as a four digit, liquid crystal display. Button 19 is depressed to turn on a light for illuminating dial 11 and display 15.

Even if the front of display 15 were coplanar with dial 11, an EL lamp backlighting display 15 would be separated from the face of the watch. The enclosed space between the dial and the lamp must be unobstructed to backlight the dial, greatly increasing the thickness of the watch. Thus, a single EL lamp cannot be used for backlighting dial 11 and display 15. In the prior art, two lamps and four connections were required for backlighting two displays.

FIG. 2 illustrates an EL lamp constructed in accordance with the invention for providing backlighting on two parallel planes. In FIG. 2, the luminous areas of panel 20 are indicated by stippling. Panel 20 includes first lamp 21 and second lamp 22 on common substrate 23. Hole 25 in substrate 23 and in lamp 21 provides clearance for a liquid crystal display. A suitable analog dial (not shown) can be printed on the outer surface of substrate 23 (the side facing into the plane of the drawing).

Lamp 21 and lamp 22 are physically separated along longitudinal axis 26 and are mechanically connected by common substrate 23. In a preferred embodiment of the invention, the width of substrate 23 between the lamps is less than the width of either lamp, forming isthmus 27. Substrate 23 is preferably a sheet of polyester or polycarbonate and the lamps formed thereon are coplanar. Isthmus 27 permits lamp 22 to be reoriented relative to lamp 21 to provide stacked lamps in separate planes.

FIG. 3 is a cross-section of panel 20. Lamp 21 includes substrate 23, transparent front electrode 31, electroluminescent layer 33 and rear electrode 35. Lamp 22 includes substrate 23, transparent front electrode 31, electroluminescent layer 37, and rear electrode 39. Transparent front electrode 31 is preferably a thin layer of indium oxide or indium tin oxide. Such a layer is relatively frail and vigorous flexing of substrate 23 would likely result in a plurality of fractures in electrode 31. Conductive trace 41 is deposited on electrode 31 to strengthen the electrode. In a preferred embodiment of the invention, a conductive ink is screen printed on front electrode 31 to provide a rugged, flexible, conductive trace mechanically and electrically connected to the electrode.

As illustrated in FIG. 2, conductive trace 41 extends the length of isthmus 27, electrically connecting lamp 21 to lamp 22. Conductive trace 42 extends parallel to trace 41 and interconnects the rear electrodes of lamp 21 and lamp 22. Trace 42 is deposited on a substrate 23 in the isthmus. The ends of trace 42 overlap the rear electrodes (not shown) of lamp 21 and lamp 22, electrically connecting the lamps. Contact to panel 20 is made anywhere along the length of conductive traces 41 and 42, e.g. by pins or by an adherent conductor.

FIG. 4 illustrates the orientation of panel 20 for providing two planes of backlighting. Dial 11 is back lit by lamp 21 and liquid crystal display 15 is back lit by lamp 22. Lamp 21 is connected to lamp 22 by isthmus 27. Both lamp 21 and lamp 22 emit light in a direction to the left of the diagram as illustrated in FIG. 4. In order to do this, lamp 22 is rotated 360.degree. about axis 29 (FIG. 2). This rotation brings lamp 22 behind lamp 21 and facing in the same direction as lamp 21. In FIG. 2, the corresponding rotation would be for lamp 22 to be pushed into the plane of the drawing and rotated about axis 29 until lamp 22 is aligned with hole 25.

Rotational axis 29 is perpendicular to longitudinal axis 26 and can be located anywhere along the lower half of isthmus 27, as oriented in FIG. 2, or can be located anywhere along the length of lamp 22. Isthmus 27 is preferably more than twice the length of lamp 22, as measured along axis 26. The preferred length of isthmus 27 assures that lamp 22 can rotate 360.degree..

FIG. 5 illustrates an alternative embodiment of the invention wherein lamp 52 is rotated 180.degree. about axis 29 and is rotated 180.degree. about axis 26 to align lamp 52 to face in the same direction as lamp 51. Lamp 51 is connected to lamp 52 by conductive strip 54, all of which are constructed on a common substrate as described above. Strip 54 is shorter than isthmus 27 (FIG. 2) because strip 54 does not have to overlap the lamp, as shown in FIG. 4. Either technique for producing parallel, stacked lamps can be used to suit a particular application.

The invention thus provides a single EL panel having at least two lamps that can be stacked to provide lamps in two planes, wherein the lamps are on a single substrate. Further, power to the lamps is applied through a single pair of connections, rather than through two pairs of connections as in the prior art.

Having thus described the invention, it will be apparent to those of skill in the art that various modifications can be made within the scope of the invention. For example, the number of planes is determined by the particular application. A second isthmus and a third lamp could be connected to the top of panel 20 (FIG. 2). Still more lamps could also be provided. Because the lamps are physically separated, the lamps can be different colors. Each color requires a separate printing step but is easily accomplished. Although described in a preferred embodiment as a lamp panel for watch applications, the invention can be used in any application requiring lamps in different planes, e.g. instrumentation or portable electronic devices such as pagers or transceivers.