Segmented electroluminescent device with distributed load elements
The invention relates to an electroluminescent lighting device, which is based on an array of standard electroluminescent tiles (D 1 -D n ) combined with an array of ballast components (R 1 -R n ) mounted on a carrier board ( 30 ) in such a way that the power loss is evenly spread across the whole board area to minimize local electric power in the ballast components. The unavoidable remaining hot spots and electroluminescent tiles are thermally coupled in such a way that the additional thermal load on the electroluminescent emission layer is as symmetric as possible with respect to the self heating of the electroluminescent device. This can be achieved by a combination of properly designed heat spreading and thermal isolation of the electroluminescent and ballast components. Heat spreading is achieved by a properly designed interconnection structure ( 40 ) on the carrier board. Different options are proposed to thermally isolate the electroluminescent tiles from the hot spots.
1. An electroluminescent device comprising:
a) a plurality of standard electroluminescent segments;
b) a plurality of standard load elements;
c) a common carrier substrate on which said electroluminescent segments and said elements are mounted;
d) an interconnecting structure that is distinct from said load elements for connecting said electroluminescent segments and said load elements and for providing a predetermined heat spreading; and
e) an isolation structure for thermally isolating said electroluminescent segments from hot spots created by said load elements;
f) wherein said interconnecting structure and said isolation structure are arranged to combine said predetermined heat spreading and thermal isolation in such a way that local power loss is minimized at hot spots on said common carrier structure and that additional thermal load on an emission layer of said electroluminescent segments is symmetrized with respect to self heating of said light emitting device.
2. The device according to claim 1 , wherein the load elements are resistor elements and wherein at least one resistor element and one electroluminescent segment are electrically connected in series to form a pair, wherein said electroluminescent device comprises a plurality of said pairs, and wherein said pairs are adapted to be directly operable from a power supply to which said electroluminescent device is connected.
3. The device according to claim 2 , wherein said interconnecting structure is adapted to provide thermal coupling between said pairs by connecting all pairs in series and to serve as a heat spreader for heat generated by said resistor elements (R1-Rn).
4. The device according to claim 1 , wherein said isolation structure comprises an isolation pad arranged between said electroluminescent segments and said common carrier substrate and wherein electrode wires of said electroluminescent segments are connected to said interconnecting structure.
5. The device according to claim 4 , wherein said load elements are provided on the opposite surface of said common carrier substrate as compared to said luminescent segments.
6. The device according to claim 1 , wherein said isolation structure comprises a plurality of holes of the common carrier structure, by which said electroluminescent segments are thermally isolated.
7. The device according to claim 1 , wherein said isolation structure comprises a plurality of glass lids sandwiched between said electroluminescent segments and said common carrier structure.
8. The device according to claim 7 , wherein a respective cavity is provided between said glass lids, and said electroluminescent segments.
9. The device according to claim 1 , wherein said load elements comprise a combination of capacitors and resistors.
10. The device according to claim 1 , wherein said load elements comprise a combination of capacitors and current sources, and wherein said current sources are formed by a circuit of resistors, transistors and diodes.
11. The device according to claim 1 , wherein said interconnecting structure is arranged in a plane of said device and wherein, for at least one of said segments, said interconnecting structure is arranged symmetrically, in said plane, about a corresponding load element of said at least one of said segments.
12. The device according to claim 1 , wherein said plane is parallel to a surface of said substrate on which said electroluminescent segments are mounted.
13. The device according to claim 11 , wherein said interconnecting structure covers said at least one of said segments over a majority of an area delineated by said at least one of said segments.
14. The device according to claim 11 , wherein said interconnecting structure surrounds a majority of said at least one of said segments.