ELECTROLUMINESCENT LIGHT SOURCES

Description

RC / PETR / giE1248 prow. - 2 - DR. ENG. A. RACHELI & C. srl Description of the invention entitled: ELECTROLUMINESCENT LIGHT SOURCES Of the Company: JERUSALEM COLLEGE OF TECHNOLOGY of Israeli nationality, with headquarters in Jerusalem (Israel) which appoints as agents and domiciliaries, also severally between them, Dr. Diana Domenighetti, Dr. Ing. Aldo Petruzziello, Dr. Maria Teresa Marinello, Dr. Maria Chiara Zavattoni of the Office DR. ING. A. RACHELI & C. srl - Milan - Viale San Michele del Karst, 4. Inventors: Voskoboinik Moses, Baumberg Israel, Bodenheimer Joseph S. Filed on: «Λ_ . 'ODJC. 1993 “Jì sle «fi Φ Φ DESCRIPTION N.: M193A / 02600 The present invention relates to electroluminescent light sources, in particular to linear, flexible, monochrome or polychrome electroluminescent light sources. Point-shaped electroluminescent (EL) light sources—light-emitting diodes (LEDs) and area EL displays (EL)—are well known. The disadvantages of LEDs are their small emitting area and the directionality of the emitted light. Currently, flexible polymer-based EL displays are also known. These displays are essentially constructed as follows: the first electrode consists of a transparent, flexible substrate material, on which a transparent conductive layer is deposited. A layer of electroluminescent powder, within a dielectric acting as a binder, is applied over the conductive layer, and a further conductive layer, the second electrode, is applied over the conductive layer. - 3 - DR. ENG. A. RACHELI & C. srl the first. By applying a DC voltage, such a screen emits light, which F color depends on the type of electroluminophore. An EL screen can also be driven by an AC voltage source, if an additional transparent dielectric layer is introduced, applied between the transparent electrode and the electroluminescent powder layer inside the dielectric binder. The disadvantages of these structures are their poor flexibility and the anisotropy of their light output. None of these sources provides a solution to the need for an essentially linear light source that can flexibly and freely adapt to various shapes and radiate light uniformly in all directions. One of the objects of the present invention is to overcome the drawbacks and disadvantages of prior art EL light sources, and to provide a linear EL light source which is flexible, adaptable, monochromatic, and which radiates light uniformly in all directions. Another objective of the present invention is to provide a linear, flexible, adaptable, polychromatic EL light source with similar isotropic light emission characteristics. A further object of the invention is to provide such a linear, polychromatic EL light source, which emits light of variable color. In accordance with the invention, this is achieved by providing: a cable-shaped EL light source, comprising at least two electrodes, mutually arranged in such a way as to create an electric field between them, when a voltage is applied to them; at least one type of electroluminophore powder dispersed in a dielectric binder and arranged in such proximity to said electrodes, as to be - 4 - DR. ENG. A. RACHELI & C. srl actually excited by said electric field when created and to emit light of a specific color; and a transparent polymer sheath, enclosing said electrodes and said electroluminophore. The invention will now be described in connection with some preferred embodiments, with reference to the accompanying illustrative figures, so that it may be more fully understood. With specific reference to the detailed figures, it is emphasized that the details are shown by way of example and for the sole purpose of an illustrative discussion of preferred embodiments of the present invention. Such details are presented for the purpose of providing what is believed to be the most useful and easily understandable description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to present the structural details of the invention more precisely than is necessary for a fundamental understanding of the invention, while the description, along with the drawings, provides sufficient clarity to those skilled in the art as to how the various forms of the invention may be practiced. In the drawings: Fig. 1 is a longitudinal sectional view of an embodiment of the EL light source according to the invention, having a pair of twisted electrodes; Fig. 2 - is a cross-sectional view, along the II-II plane, of the EL source of Fig.1; Fig. 3 represents a longitudinal section of another embodiment of the EL source, having a central electrode; Fig. 4 is a cross-sectional view, along the IV-IV plane, of the EL source of Fig. 3; - 5 - DR. ENG. A. RACHELI & C. srl Fig. 5 is a sectional view of a further embodiment of the EL source, having coaxial electrodes; Fig. 6 is a cross-sectional view of an embodiment of the EL source, having a flexible dielectric core; Fig. 7 represents a polychrome EL light source with a common central electrode; Fig. 8 illustrates a similar polychromatic source with a flexible dielectric core. Referring to the drawings, Figures 1 and 2 show an EL light source in the form of a longitudinally extending cable incorporating a pair of twisted electrodes 2 and 4, made of copper wire with a diameter of 0.1-0.3 mm, coated with a layer of insulating varnish 6, and wound around each other with a winding pitch of 8-10 turns per cm. The helical cavities between the twisted cables are filled with an EL material 8 containing an electroluminescent powder dispersed in an epoxy resin. Electroluminescent powders are commercially available, e.g. from Sylvania GTE (USA). The concentration of the powder in the resin is 1.5:1 to 2:1 by weight. The twisted electrodes 2 and 4 are completely enclosed by a flexible, transparent layer 10 of polyvinyl chloride, 0.5-0.6 mm thick. To make this structure operational as a light source, an AC voltage with a frequency preferably in the range 50-20,000 Hz and an amplitude preferably in the range 100-300 V, drawn from a power source (not shown), is applied between electrodes 2 and 4. In this way, the particles of the electroluminescent powder are subjected to an alternating electric field and emit light. The color of the emitted light depends essentially on the type of electroluminescent powder. - 6 - DR. ENG. A. RACHELI & C. srl used. The light emission in this and the other embodiments described below is essentially isotropic all around the cable-shaped light source, as indicated by the arrows in Figures 2 and 4. The embodiment illustrated in Figures 3 and 4 comprises a central electrode 2 consisting of a copper wire with a diameter of 0.5–3.0 mm, coated with a layer of EL 8 material, consisting of an electroluminescent powder dispersed in an epoxy resin in a ratio of 1.5:1 to 2:1 by weight. This layer is 0.10.2 mm thick. A second electrode 4, consisting of a copper wire with a diameter of 0.1-0.3 mm, coated with a layer of insulating varnish 6, is wound around this layer. A gap of 0.1-0.2 mm is left between the turns of the wire acting as electrode 4. The structure is completely enclosed within a flexible and transparent polymer sheath 10. To make this structure operational as a light source, an AC voltage is applied between the electrodes 2 and 4, having a frequency preferably in the range 50-20,000 Hz and an amplitude preferably in the range 100-300 V. In this way, the particles of the electroluminophore powder are subjected to an alternating electric field and emit light, which escapes through the spaces between the turns. The color of the emitted light depends essentially on the type of electroluminophore powder used. Fig. 5 represents a coaxially configured EL light source structure. The central electrode consists of a copper wire, 0.25 mm in diameter, coated with a layer of insulating varnish 6. The EL material layer 8, comprising an electroluminescent powder dispersed in an epoxy resin in a ratio of 1.5:1 to 2:1 by weight, is applied to the central electrode 2, over the varnish 6. The EL layer 8 is 0.1-0.2 mm thick. A second electrode 4 consists of -7 - DR. ENG. A. RACHELI & C. srl by a transparent and conductive layer, such as 1 micron thick tin dioxide, which is applied over the EL material layer 8. The entire structure is completely enclosed within a flexible and transparent polymer sheath 10. To make this structure operational as a light source, an AC voltage having a frequency preferably in the range 50-20,000 Hz and an amplitude preferably in the range 100-300 V is applied between the first central electrode 2 and the second electrode in the form of a conductive layer 4. In this way, the particles of the electroluminophore powder are subjected to an alternating electric field between the electrodes 2 and 4 and emit light, which exits through the second transparent electrode 4 and the transparent sheath 10. The color of the light emitted by the source depends essentially on the type of electroluminophore powder used. Fig. 6 shows an EL light source structure incorporating a flexible dielectric core 12. The electrode 2 consists of a copper wire with a diameter of 0.1–0.3 mm, coated with a layer of insulating varnish 6, and helically wound around a core in the form of a plastic cord with a diameter of 3–10 mm. The winding pitch of the electrode 2 is approximately equal to the diameter of the electrode itself. Over the turns of the electrode 2 is applied a layer of EL material 8, comprising an electroluminescent powder dispersed in an epoxy resin in a ratio of 1.5:1 to 2:1 by weight. The layer of EL material 8 is 0.1–0.2 mm thick. Over this layer is applied a second electrode 4, constituting a transparent and conductive layer. The entire structure is completely enclosed within a flexible polymer sheath 10.To make the structure operational as a light source, a voltage is applied between the first electrode 2 and the second electrode 4 in the form of a conductive layer. - 8 - DR. ENG. A. RACHELI & C. srl AC having a frequency preferably in the range 50-20,000 Hz, and having an amplitude preferably in the range 100-300 V. In this way, the particles of the electroluminophore powder are subjected to an alternating electric field between the electrodes 2 and 4 and emit light, which exits through the transparent layers 4 and 10. The color of the emitted light depends essentially on the type of electroluminophore powder used. EL light sources according to this invention can also be designed to produce polychromatic light. A first embodiment of such an EL source is illustrated in Fig. 7. A central electrode 2, a copper wire with a diameter of 1–3 mm, as well as three copper wire electrodes 4R, 4G, and 4B, where R stands for red, G for green, and B for blue, are provided. These electrodes each have a diameter of 0.1–0.2 mm and are coated with a layer of insulating varnish 6. On top of these varnish layers, electrodes 4R, 4G, and 4B are coated with 0.1–0.2 mm thick layers of EL material, designated 8R, 8G, and 8B (for red, green, and blue emitted light), respectively, and are then wound, preferably in a triple helix, around the central electrode 2, with a gap of 0.1–0.2 mm between adjacent coating layers. The structure is then completely enclosed within a transparent polymer sheath 10. To make this structure operational as a polychromatic source, an AC voltage having a frequency preferably in the range of 5020,000 Hz, and having an amplitude preferably in the range of 100300 V is applied between the central electrode 2 and any one of the electrodes 4R, 4G and 4B. The dust particles in the respective EL materials 8R, 8G and 8B, subjected to an alternating electric field, will emit red, green or blue light. - 9 - DR. ENG. A. RACHELI & C. srl respectively. Light escapes through the spaces between the coils and through the transparent sheath 10, such that the entire structure will appear to emit light of that particular color. If electrodes 4R, 4G, and 4B were electrically connected together, and a voltage was applied between them and electrode 2, then each of the layers 8R, 8G, and 8B would emit light of its own color, and the eye would perceive the combination of colors emitted by the light source as a substantially white whole. If different AC voltages, in the above-mentioned frequency and amplitude ranges, were applied between electrode 2 and each of electrodes 4R, 4G, and 4B, the light source could emit any color, depending on the frequency and amplitude of the voltage applied to each of electrodes 4R, 4G, and 4B. This allows for the continuous control and variation of the color (hue, saturation, and brightness) of the light emitted by the source by adjusting the amplitudes or frequencies of the voltages on the electrodes. The discontinuous transition from one color to another is achieved by applying discrete voltage variations. The embodiment of Fig. 8, although operating on the same principle, is slightly different in structure, since a flexible dielectric core 12 is provided upon which electrodes 4R, 4G, and 4B are wound. Electrode 2, on the other hand, is in the form of a transparent, electrically conductive layer applied over and completely enclosing electrodes 4R, 4G, and 4B and their respective coatings of EL material (a sequence which is, of course, repeated along the entire length of the triple helix). The operation of this implementation is completely analogous to that of the previous implementation in fig. 7. - 10 - DR. ENG. A. RACHELI & C. srl All embodiments of the EL light source according to the invention are advantageously linear, yet flexible and can be made to take on any desired shape. The electrodes behave essentially like a capacitor, and can therefore be used as a reactive impedance element in a resonant electronic circuit, so that a relatively small input voltage is sufficient to generate EL radiation. Furthermore, given an array of EL sources with electroluminophores emitting different colors, each element of the array can be incorporated into resonant electronic circuits, each with a response to a different frequency. Such a series, when connected to a microphone, can act as a sound-to-color transducer. In resonant circuits, instead of inductors, it would be advantageous to use the inductance of EL electrodes wrapped around a magnetic core. It will be apparent to those skilled in the art that the invention is not limited to the details of the embodiments previously disclosed and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects illustrative and not restrictive, the scope of the invention being set forth in the appended claims rather than in the preceding description, and all modifications falling within the meaning and scope of the claims are therefore to be construed as contained therein.

Claims

-11- DR. ING. A. RACHELI & C. srl CLAIMS 1. An electroluminescent light source, comprising: at least two electrodes mutually arranged so that an electric field is created between them when a voltage is applied to them; at least one type of electroluminescent powder dispersed in a dielectric binder and arranged in such proximity to said electrodes as to be effectively excited by said electric fields when created and to emit light of a specific color; and a transparent polymer sheath enclosing said electrodes and said electroluminescent powder.

2. The light source according to claim 1, wherein at least one of said electrodes is provided with an electrically insulating coating.

3. The light source according to claim 1, wherein said at least two electrodes consist of two metal wires twisted around each other.

4. The light source of claim 1, wherein one of said electrodes is made of a transparent, electrically conductive substance, tubular in shape, surrounding the other of said electrodes in a coaxial relationship.

5. The light source according to claim 1, wherein one of said electrodes is helically wrapped around the other of said electrodes.

6. The light source according to claim 1, wherein one of said electrodes is helically wrapped around a flexible, dielectric core.

7. The light source according to claim 1, comprising a central electrode and three further electrodes wrapped around said central electrode, forming a triple helix.

8. The light source according to claim 7, wherein each of said three electrodes forming said triple helix is ​​coated with a different electroluminophore powder, which emits, when excited, light of a different color.

9. The light source of claim 1, comprising a flexible dielectric core and three electrodes wrapped around said dielectric core and forming a triple helix, a fourth electrode consisting of a transparent, electrically conductive layer surrounding and enclosing said triple helix.