Patent Grant
9086193
This application claims priority to Italian Patent Application Serial No. TO2013A000190, which was filed Mar. 11, 2013, and is incorporated herein by reference in its entirety.
Various embodiments relate to lighting devices.
Various embodiments may relate to lighting devices using LED sources as light radiation sources.
Lighting modules, such as those for street lighting, using solid state light radiation sources (“Solid State Lighting”, or SSL) can be considered competitive in that they simultaneously meet various requirements in terms of robustness relating to the context of their use “in the field”, namely:
The first aspect mentioned above is related to the phenomena of electric overload: proper electrical insulation is important not only for avoiding the harm caused by electrostatic discharge (ESD) events during the assembly of the lighting module or of the corresponding device, but also in relation to electrical overload events such as those caused by lightning.
The second aspect is related to the thermal dissipation properties of the housing which encloses the module, and may require a considerable part of the lighting device to be made of a metal material (such as aluminum) so that it has a certain degree of weight. If the module has low thermal resistance between the connection points of the light radiation sources (such as LEDs) and the thermal dissipation surface of the module, the corresponding device may also have a rather high thermal resistance between the surface in contact with the module and the external environment.
The third aspect relates to the faults that may arise in the module even without any causation by a specific external event. These events may have a negative effect on the service life, either in the form of “soft” faults (the light flux falls below a certain threshold level, without total loss of light emission), or in the form of “hard” faults (the radiation source ceases to emit radiation and acts as either an open or a closed contact).
The fourth aspect relates to the mechanical strength in the conditions of use in the field, and requires the module to meet certain requirements in terms of mechanical performance, in exterior applications for example (resistance to vibration, impact, and the like).
In various designs of lighting devices, of the solid state type for example, the four aspects mentioned above tend to create opposing constraints.
For example, electrical insulation may be achieved by using mechanically robust substrates, with the risk of adversely affecting the thermal dissipation characteristics and increasing the possibility of hard faults; on the other hand, materials capable of providing electrical insulation together with good thermal dissipation characteristics while also reducing the risks of hard faults may be mechanically fragile.
For example, it is possible to use substrates of the PCB (printed circuit board) type, in other words those resembling printed circuits, with metal cores, using high luminosity LEDs as the light radiation sources. Solutions of this kind have good characteristics in terms of thermal dissipation, electrical insulation and mechanical robustness. However, they may have critical aspects due to the differences in the coefficient of thermal expansion (CTE) that may be encountered, for example, between the ceramic packages of high luminosity LEDs and materials such as aluminum (15-20 ppm/° C.). In all cases, there is a risk of increasing the possibility of hard faults in the soldering points between the package and the LEDs and the PCB if the module is subjected to thermal cycles such as those which may occur to a pronounced degree in exterior applications, and the consequent possibility of observing a marked reduction in the service life of the LEDs: for example, as regards the light emission performance (LED lumen maintenance), the specified values of 100 kilohours may fall to values of 20-30 kilohours when measured in the field.
It has been proposed that these problems should be tackled by replacing aluminum with copper, for which the mismatch with the ceramic materials in terms of CTE is lower, at about 10-15 ppm/° C. However, this solution has the drawback of practically doubling the cost compared with solutions in which aluminum is used for making the PCB, which is unacceptable in applications where the cost of the PCB accounts for a significant part of the overall cost of the device.
A performance substantially comparable to that of copper, in terms of the mismatch of the coefficient of thermal expansion (CTE) with respect to packages of ceramic material, can be achieved by using the material known as FR4, although the latter has a low level of thermal dissipation; attempts may be made to counteract this characteristic by providing thermal bridges (“vias”) through the PCB, but this has negative effects on the electrical insulation characteristics.
It has also been proposed that PCB substrates of ceramic material should be used, as these can provide high performance in terms of thermal characteristics, electrical insulation and the service life of the module, but this would have adverse effects on the mechanical characteristics, particularly where the possibility of using large PCBs is being considered.
The use of what are known as “Chip On Board” (CoB) products appears more promising, although these products are uncompetitive, at the present time at least, in terms of the lighting density (known as the cost per lumen), while they do not allow a high chip density in the CoB.
It is also possible to consider the use of medium- to low-power LED sources as light radiation sources, thus enabling non-ceramic packages to be used and increasing the reliability of the soldered connections. However, this solution also has the drawback of a high cost per lumen and rather low resistance to possible corrosion by environmental factors (such as sulfuric components).
Various embodiments overcome the aforementioned drawbacks.
Various embodiments may be based on the provision of at least one element (made in the form of a reflector, for example) which can act simultaneously to provide not only optical functions, but also mechanical and electrical functions, allowing in all cases the use of solid state light radiation sources, such as high luminosity LEDs, as light radiation sources. These sources may be, for example, LEDs which are not mounted in a package but are simply placed on a substrate, for example one resembling a printed circuit board (PCB), fitted in a housing of plastic or metal material.
Various embodiments may be applied to solutions in which the light radiation sources are installed in an area which is sufficiently small to provide adequate properties of mechanical robustness for the support, of the PCB type for example.
In various embodiments, the aforesaid element may have:
In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being replaced upon illustrating the principles of the disclosure. In the following description, various embodiments of the disclosure are described with reference to the following drawings, in which:
The following description illustrates various specific details intended to provide a deeper understanding of various exemplary embodiments. The embodiments may be produced without one or more of the specific details, or with other methods, components, materials, etc. In other cases, known structures, materials or operations are not shown or described in detail, in order to avoid obscuring various aspects of the embodiments.
The reference to “an embodiment” in this description is intended to indicate that a particular configuration, structure or characteristic described in relation to the embodiment is included in at least one embodiment. Therefore, phrases such as “in an embodiment”, which may be present in various parts of this description, do not necessarily refer to the same embodiment. Furthermore, specific formations, structures or characteristics may be combined in any suitable way in one or more embodiments.
The references used herein are provided purely for convenience and therefore do not define the scope of protection or the extent of the embodiments.
Various embodiments may relate to a lighting device 10 which can be used, for example, for street lighting applications.
The device 10 can be mounted on a support P such as a pole, a bracket, an overhead line, or the like, according to the procedures currently used in the lighting field.
In various embodiments, the device 10 may be intended for fitting into a containment structure S which in turn is intended to be fastened to the support P and serves to protect the device 10, while also allowing the light radiation emitted by the latter to be projected into the environment. This containment structure S, shown schematically in broken lines in
In various embodiments, a lighting device 10 as illustrated may include a tray-like containment housing 12 (of rectangular shape, for example), having a base wall 12a.
In various embodiments, one or more light radiation sources 14, of the LED type for example, may be applied to the base wall 12a of the housing 12.
In various embodiments, the light radiation sources 14 may be electrically powered through electrical contact pads 14a provided, for example, on a plate-like substrate 140 so as to be placed in an opposite position from the base wall 12a of the housing 12.
In various embodiments, a circuit board 16, which can be made, for example, by procedures substantially similar to those used for a printed circuit board (PCB), may have electrically conductive tracks (or lines) 160.
In various embodiments, the conductive lines 160 may extend on the opposite face of the board 16 from the base wall 12a of the housing 12 between respective electrical connection pads 16a.
In various embodiments, as shown more clearly in the views of
In various embodiments, one or more optical elements 18 operating by reflection and/or refraction may be mounted in the housing 12, each element having at least one input 18a and at least one output 18b for the light radiation. The input 18a can be placed at the light radiation source or at one of the light radiation sources 14 so as to capture the radiation emitted by this source and then guide it toward the output or outputs 18b, thus projecting it toward the outside of the lighting device 10.
In various embodiments, the optical element or elements 18 may take the form of one or more reflectors which can be mounted in the housing 12 with the base part 18 of the reflector, or of each reflector, (the part indicated by 18′, shown more clearly in the views from below in
Thus the base wall 180 (which can be made of an electrically insulating material such as plastic material, as can the whole body of the reflector 18 if required) may rest on the light radiation source or sources 14 and on the circuit board 16 (which extends adjacent to the light source or sources 14), and may press these elements against the base wall 12a.
As shown more clearly in the representation in
In various embodiments, the housing 12 (or at least the base wall 12a thereof) may be made of a metal material, for example aluminum, that is to say a material having good thermal dissipation characteristics.
In various embodiments, the circuit board 16 can be made by the methods currently used to make printed circuit boards (PCBs).
In various embodiments, the board 16 may be provided with conductive lines or tracks 160 organized so as to form anode and cathode power supply paths, respectively, for the light radiation sources (of the LED type, for example, which is the reason for the reference to the presence of an anode and a cathode), running from two power supply input pads indicated by 16b. The power supply input pads 16b can receive electrical power from a power supply cable 20 which is shown in
In various embodiments, as shown by way of example in
In embodiments such as those shown by way of example in
In various embodiments, a ceramic material may be used for the substrate 140 of the light radiation sources 14. A plate-like substrate of this type, for example one having dimensions such as those described above, is small enough to provide the typical advantages of ceramic materials, at lower cost, while also being capable of resisting mechanical stresses such as vibration.
In various embodiments, the substrate 140 can be made by a method similar to that used for printed circuit boards (PCBs), for example those with metal cores.
A similar method may be chosen for the circuit board 16; in this case, it is possible to use a PCB structure, using materials such as those known as CEM or FR4, or a flexible module structure of the type commonly known as “flex”, which can be applied adhesively to the base wall 12a of the housing 12 or applied in other ways.
In embodiments such as those shown by way of example in
In embodiments such as those shown by way of example in
As regards the optical element 18, embodiments such as those shown in the figures (see for example
As mentioned in the introductory part of the present description, the optical element, or each of the optical elements shown here by way of example as the reflector 18 can provide a plurality of functions.
For example, in the assembled condition of
As will be clear from the views of
In embodiments such as those shown by way of example in
In addition to these mechanical and electrical functions, the element or each of the elements 18 may also provide its own optical function by guiding the light radiation generated by the source 14 associated with the element toward the outside of the device 10 (by reflection and/or refraction).
In various embodiments, the element 18 may be made in the form of a reflector with a body (a hollow body, for example) made of molded plastic material.
In various embodiments, the component 18 may be made with a body having:
In this respect it is possible to adopt the solution described in the industrial patent application TO2012A000836 submitted by the present applicants.
In various embodiments, the body of the element 18 may be made of a material and/or treated with a material having a high level of reflectivity to light radiation (for example, the inner surface of the reflector may be aluminum-coated).
The embodiments described here by way of example may be varied in respect of numerous aspects, such as those shown below (the list given here is provided by way of non-limiting example):
Various embodiments may enable one or more of the following advantages to be obtained:
In various embodiments, it is possible to use optical elements (such as reflectors) 18 of aluminum-coated plastic material with a three-dimensional (3D) electrical configuration created directly on the reflector by the method known as MID (molded interconnect devices) which can be implemented by laser, chemical or plasma structuring techniques. A layout of the MID type can enable strip contacts to be connected to the connectors used to connect the reflector to the power supply cable 20 or to other reflectors. In various embodiments it is possible to use connectors and contacts embedded in the base part 180 of the reflector 18.
While the disclosed embodiments have been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the disclosed embodiments as defined by the appended claims. The scope of the disclosed embodiments is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.
| Number | Date | Country | Kind |
|---|---|---|---|
| TO2013A0190 | Mar 2013 | IT | national |
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| Entry |
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| Search Report issued in the corresponding Italian application No. TO2013A0190, dated Nov. 4, 2013, Nov. 3, 2013. |
| Search Report issued in the corresponding EP application No. 14156877.4, dated May 19, 2014. |
| Number | Date | Country | |
|---|---|---|---|
| 20140254159 A1 | Sep 2014 | US |
