EP4706343A1 - A light emitting diode, led, based lighting source comprising two led strings for emitting light, as well as a led based lighting device - Google Patents

Abstract

The invention relates to Light Emitting Diode, LED, based lighting source. The LED based light source comprises a substrate, a first LED string, provided on said substrate and comprising a plurality of in series connected LEDs for emitting light, a second LED string, provided on said substrate and connected in parallel over said first LED string, said second LED string comprising a plurality of LEDs for emitting light, a supply line for providing current, from a power supply, to said first LED string and said second LED string a return line for providing said current back to said power supply after it has passed through said first LED string and said second LED string, wherein a first LED and a last LED in said first LED string, and a first LED and a last LED in said second LED string are all positioned close to one another.

Description

A Light Emitting Diode, LED, based lighting source comprising two LED strings for emitting light, as well as a LED based lighting device

TECHNICAL FIELD

The present disclosure generally related to the field of lighting and, more specifically, to a LED based lighting source comprising at least two in parallel cascaded LED strings.

BACKGROUND

A Light Emitting Diode, LED, based lighting source may comprise in parallel cascaded LED strings provided on top of a substate. The substrate is a Printed Circuit Board, PCB, and may contain a core layer as well as a patterned conductive metal outer layer to connected and supply power to the LEDs of the LED strings.

The metal outer layer is usually made of copper and may be obtained by electro deposition or by Rolling and Annealing. The copper may, for example, be 18, 35 or 70 pm thick. Copper has a relatively high conductivity making it very suitable for this particular purpose. The patterning of the copper layer is typically done by etching.

In Printed Electronics, PE, the conductive layers are typically obtained by curing and/or sintering inks with silver or copper particles. The metal particles create conductive structures with binders in between. These metal PE layers do conduct but typically not as good as conventional copper. The typical thickness of a cured printed layer is between 5 and 20um and the electrical sheet resistance is typically between 2 and 30 mOhm/sq @25um.

The LED based lighting source may be considered a LED PCB. The LED PCB is a circuit board designed specifically for use with LED lighting components. LED PCBs can come in different shapes and sizes, depending on the specific application and design requirements. They can be used in a wide range of lighting products, including automotive lighting, street lighting, commercial and residential lighting, and more. The use of LED PCBs can help to improve the efficiency, performance, and reliability of LED lighting systems. SUMMARY

It would be advantageous to achieve a Light Emitting Diode, LED, based lighting source comprising at least two in parallel connected LED strings, wherein the same amount of light output per string may be obtained.

It would further be advantageous to achieve an LED based lighting device for emitting light, wherein said LED based lighting device comprises an LED based lighting source in accordance with the present disclosure.

In a first aspect of the present disclosure, there is provided a Light Emitting Diode, LED, based lighting source, comprising: a substrate; a first LED string, provided on said substrate and comprising a plurality of in series connected LEDs for emitting light, wherein said first LED string comprises a first set of printed, electrically conductive, tracks for connecting said plurality of in series cascaded LEDs of said first string to one another; a second LED string provided on said substrate and connected in parallel over said first LED string, said second LED string comprising a plurality of LEDs for emitting light, wherein said second LED string comprises a second set of printed, electrically conductive, tracks for connecting said plurality of in series connected LEDs of said second string to one another; wherein a length of said first LED string is longer than a length of said second LED string thereby defining a length difference, and wherein said second set of printed tracks are arranged such that a resistance of said second set of printed tracks compensates for said length difference.

The inventors have found that the resistance of the printed tracks to connect the different LEDs to one another may not be negligibly small. Printed tracks have the inherent property that their conductivity is typically less compared to the more traditional copper based tracks.

Such resistance may play a role in an LED based lighting source as this may cause unequal power loss in the different LED strings of the LED based lighting source. On top of that, the current provided by a power source may then not get equally distributed over the LED strings, such that the light output of the different LED strings may differ. This is undesired. The above is especially the case for LED strings of unequal length, for example the length of the first LED string is longer than a length of the second LED string which defines a length difference.

It was found that it may be beneficial to arrange, or design, the second set of printed tracks such that the resistance of the second set of printed tracks compensates for this particular length difference.

The underlying concept of the present disclosure is that the total resistance encountered by current flowing through the first set of printed tracks may be substantially equal to the total resistance encountered by current flowing through the second set of printed tracks.

As mentioned above, this may have multiple benefits. The light output, i.e. Lumen output, may then be substantially the same. The life expectancy of the LED based lighting source may also be increased given that the LED strings are substantially equally stressed.

Several pragmatic options exist to design the second set of printed tracks to compensate for the length difference. These options are discussed further below.

In an example, a resistance of said first set of printed tracks is substantially equal to a resistance of said second set of printed tracks.

In another example, the first set of printed tracks are, on average, wider than said second set of printed tracks.

In fact, the average reciproke area over length may be wider for the first set of printed tracks compared to reciproke area over length for the second set of printed tracks.

By making the printed tracks wider, the resistance encountered by current flowing there trough is reduced. The total length of the first set of printed tracks is larger compared to the total length of the second set of printed tracks. By making the second set of printed tracks thinner, or the first set of printed track wider, the total resistance of the first LED string may be matched to the total resistance of the second LED string.

The first set of printed tracks may, for example, have local width variations. These local width variations may be an effective way to balance the resistance in both strings.

The resistance of a track may be equal to the material resistivity p multiplied by the integral over the length over 1/A, wherein A is the cross section of the track:

R= p] O lengthl (1/A)] dx The integral is thus made over the length of all the tracks - the resistance is thus accumulated over the length of the tracks. The first set of printed tracks may have a resistance R1 that is equal to the resistance of the second set of printed tracks R2 in accordance with the above provided equation.

In a further example, the first set of printed tracks have a first uniform width and wherein said second set of printed tracks have a second uniform width.

The above entails that all printed tracks within a particular LED string have a uniform width. The widths of the printed tracks between the LED strings may differ to compensate for the length difference. The advantage of having a uniform width is that the life expectancy may be improved. There may be no weak link between the printed tracks, such that all printed tracks are stressed, more or less, equally and thus have the same life expectancy.

In a further example, the second string comprises the same number of LEDs as the number of LEDs comprised by the first string.

The LEDs of the second LED string may be of the same type as the LEDs of the first LED string.

There are many different types of LEDs that can be used with the present disclosure, each with their own unique characteristics and intended applications. For example, standard LEDs are the most common type of LED, typically used for indicator lights or small displays. They come in a range of colors, including red, green, blue, yellow, and white. High-power LEDs are designed to emit much more light compared to standard LEDs, and are used in applications such as automotive lighting, streetlights, and commercial lighting. RGB LEDs may comprise three separate LED chips, i.e. red, green, and blue, which can be combined to create any colour of light, preferably for general illumination. Any of these types of LEDs may be used in a particular LED string.

In a further example, a sum of forward voltages of said plurality of LEDs of said first string is substantially equal to a sum of forward voltages of said plurality of LEDs of said second string.

In a further example, the first and second set of printed, electrically conductive, tracks comprise cured or sintered ink and may comprise any of silver and copper particles.

In a further example, the first set of printed tracks are thicker than said second set of printed tracks. The inventors have found that the width of the printed tracks may be adjusted to compensate for the length difference. Another option is to adjust the height of a printed track. For example, a particular track may be printed twice, three times, or even more to create multiple tracks on top of each other thereby improving the conductivity.

In yet another example, the first set of printed tracks have a first uniform thickness and wherein said second set of printed tracks have a second uniform thickness.

In a second aspect of the present disclosure, there is provided a Light Emitting Diode, LED, based lighting device arranged for emitting light, wherein said LED based lighting device comprises an LED based lighting source in accordance with any of the previous examples.

In another example, the LED based lighting device comprises a driver for powering the LED based lighting source.

It is noted that the advantages as explained with reference to the first aspect of the present disclosure, being the LED based lighting source are also applicable to the second aspect of the present disclosure, being the LED based lighting device.

The inventors have further found that it would be advantageous to achieve a Light Emitting Diode, LED, based lighting source comprising at least two in parallel connected LED strings, wherein the LED strings are oriented in such a way on the substrate that it is made possible to reduce supply lines and return lines. This is advantageous as this reduces the total resistance encountered by the current flowing from the power supply through the LED strings.

It would further be advantageous to achieve a corresponding LED based lighting device for emitting light.

In a third aspect of the present disclosure, there is provided a Light Emitting Diode, LED, based lighting source, comprising: a substrate; a first LED string, provided on said substrate and comprising a plurality of in series connected LEDs for emitting light; a second LED string, provided on said substrate and connected in parallel over said first LED string, said second LED string comprising a plurality of LEDs for emitting light; a supply line for providing current, from a power supply, to said first LED string and said second LED string; a return line for providing said current back to said power supply after it has passed through said first LED string and said second LED string; wherein a first LED and a last LED in said first LED string, and a first LED and a last LED in said second LED string are all positioned close to one another.

The inventors have found that it is beneficial when the first LED and the last LED in said first LED string, and the first LED and the last LED in said second LED string are all positioned close to one another. This reduces the length of the supply line and/or the return line, and thus reduces undesired resistance(s). The track resistance is thus reduced.

In other words, the first LED string and the second LED string may be provided on the substrate in such a way that the end of the corresponding LED string is close to the beginning of that LED string.

The first and/or the second LED string may thus, for example, be provided in a U-shape, a circular shape, an ellipse shape, or anything alike.

In an example, the distance between the first and the last LED in the string is not larger than twice the distance between any two sequential LEDs in the string.

In an example, the distance between any of the first LED in the first LED string, the last LED in the first LED string and/or the distance between the first LED in the second LED string and the last LED in the second LED string is at most 30%, for example between 10%-20%, but more preferably less than 10%, of a length of the first LED string or the length of the second LED string.

The above entails that the distance between these reference points is small, thereby reducing any track resistance(s).

In a further example, any of the first LED string and the second LED string have a substantially closed shape.

Examples of closed shapes include circles, rectangles, triangles, and many others. A closed shape is a shape whose boundary forms a complete, continuous loop, with just a small gap or opening - as otherwise a short circuit may arise. This means that all points on the boundary are considered part of the shape, and the shape encloses a region of space.

In a further example, the supply line crosses said return line thereby providing a crossing having a first supply line terminal, a second supply line terminal, a first return line terminal and a second return line terminal, and wherein: a first end of said first LED string is connected to said first supply line terminal, a first end of said second LED string is connected to said second supply line terminal, a second end of said first LED string is connected to said first return line terminal; a second end of said second LED string is connected to said second return line terminal.

It was found that it may be beneficial that the supply line and the return line cross each other. The result is that a crossing is achieved.

From a visual perspective, this may resemble an “X”, wherein the crossing has four different terminals. These four different terminals correspond to the ends of the legs of the “X”.

The first end of the first LED string is connected to the first supply line terminal. This is, for example, the left-bottom side leg of the “X”.

The first end of the second LED string is connected to the second supply line terminal. This is, for example, the right-top side leg of the “X”.

The second end of the first LED string is connected to the first return line terminal. This is, for example, the right-bottom side leg of the “X”.

The second end of the second LED string is connected to the second return line terminal. This is, for example, the left-top side leg of the “X”.

Of course, at the crossing, the supply line does not electrically connect with the return line as this would result in an electrical short. The supply line, or the return line, may cross the other of the two at a different layer of the PCB. This may be accomplished using a VIAs or using a jumper e.g., a 0 Ohm resistor that can be placed over a track to function as a bridge with lowest possible resistance.

The crossing can be made on the substrate, in the connector on the substrate, using the connector cables towards the power supply, or provide two return connections on the driver, as examples.

The advantage of the above is that long return lines, or long supply lines, may become superfluous given that the ends of the LED strings are located close to one another.

The above entails, implicitly, that the ends of the first LED string are located close to one another, such that the first LED string may resemble the shape of a circle, a square, a rectangle, or anything alike. The shape may resemble an almost closed loop. The same is valid for the second LED string. In an example, the substrate is elongated in shape, said substrate having a length and a width, wherein said crossing is provided on said substrate at substantially halfway said length of said substrate.

In a detailed example, the substrate is elongated in shape, said substrate having a length and a width, wherein said crossing is provided on said substrate at substantially halfway said width of said substrate.

For example, the crossing may be provided at substantially a center of gravity location of said substrate.

In a further example, a length of said first LED string is substantially equal to a length of said second LED string.

In yet another example, a length of said first LED string is longer than a length of said second LED string thereby defining a length difference, and wherein said first LED string comprises a first set of printed, electrically conductive, tracks for connecting said plurality of in series cascaded LEDs of said first string to one another; wherein said second LED string comprises a second set of printed, electrically conductive, tracks for connecting said plurality of in series connected LEDs of said second string to one another; wherein said second set of printed tracks are arranged such that a resistance of said second set of printed tracks compensates for said length difference.

In an example, the first set of printed tracks are wider than said second set of printed tracks.

In a further example, the first set of printed tracks have a first uniform width and wherein said second set of printed tracks have a second uniform width.

In an example, the first and second set of printed, electrically conductive, tracks comprise cured or sintered ink.

The ink may, for example, comprise any of silver and copper particles.

In an example, the first set of printed tracks are thicker than said second set of printed tracks.

In yet another example, the first set of printed tracks have a first uniform thickness and wherein said second set of printed tracks have a second uniform thickness.

In another example, the second string comprises the same number of LEDs as the comprised by the first string. In an example, the LEDs of said second string are of a same type as said LEDs of said first string.

In another example, the LEDs of said second string are wherein a sum of forward voltages of said plurality of LEDs of said first string is substantially equal to a sum of forward voltage of said plurality of LEDs of said second string.

In a fourth aspect, there is provided a Light Emitting Diode, LED, based lighting device arranged for emitting light, wherein said LED based lighting device comprises an LED based lighting source in accordance with any of the examples provided above.

The present disclosure is described in conjunction with the appended figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

In the appended figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.

The above and other aspects of the disclosure will be apparent from and elucidated with reference to the examples described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 discloses an example of a Light Emitting Diode, LED, based lighting source in accordance with the prior art;

Fig. 2 discloses an example of an LED based lighting source in accordance with the present disclosure;

Fig. 3 discloses an example of an LED based lighting source in accordance with the present disclosure;

Fig. 4 discloses an example of an LED based lighting source in accordance with the present disclosure;

Fig. 5 discloses a further example of an LED based lighting source in accordance with the present disclosure; DETAILED DESCRIPTION

It is noted that in the description of the figures, same reference numerals refer to the same or similar components performing a same or essentially similar function.

A more detailed description is made with reference to particular examples, some of which are illustrated in the appended drawings, such that the manner in which the features of the present disclosure may be understood in more detail. It is noted that the drawings only illustrate typical examples and are therefore not to be considered to limit the scope of the subject matter of the claims. The drawings are incorporated for facilitating an understanding of the disclosure and are thus not necessarily drawn to scale. Advantages of the subject matter as claimed will become apparent to those skilled in the art upon reading the description in conjunction with the accompanying drawings.

The ensuing description above provides preferred exemplary embodiment s) only, and is not intended to limit the scope, applicability or configuration of the disclosure. Rather, the ensuing description of the preferred exemplary embodiment(s) will provide those skilled in the art with an enabling description for implementing a preferred exemplary embodiment of the disclosure, it being understood that various changes may be made in the function and arrangement of elements, including combinations of features from different embodiments, without departing from the scope of the disclosure.

Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise," "comprising," and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to." As used herein, the terms "connected," "coupled," or any variant thereof means any connection or coupling, either direct or indirect, between two or more elements; the coupling or connection between the elements can be physical, logical, electromagnetic, or a combination thereof. Additionally, the words "herein," "above," "below," and words of similar import, when used in this application, refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the Detailed Description using the singular or plural number may also include the plural or singular number respectively. The word "or," in reference to a list of two or more items, covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list.

These and other changes can be made to the technology in light of the following detailed description. While the description describes certain examples of the technology, and describes the best mode contemplated, no matter how detailed the description appears, the technology can be practiced in many ways. Details of the system may vary considerably in its specific implementation, while still being encompassed by the technology disclosed herein. As noted above, particular terminology used when describing certain features or aspects of the technology should not be taken to imply that the terminology is being redefined herein to be restricted to any specific characteristics, features, or aspects of the technology with which that terminology is associated. In general, the terms used in the following claims should not be construed to limit the technology to the specific examples disclosed in the specification, unless the Detailed Description section explicitly defines such terms. Accordingly, the actual scope of the technology encompasses not only the disclosed examples, but also all equivalent ways of practicing or implementing the technology under the claims.

Figure 1 discloses an example of a Light Emitting Diode, LED, based lighting source in accordance with the prior art.

A DC current source 1 is provided that is able to provide DC current to the LED based lighting source.

A substrate 100 is provided. The substrate 100 is, for example, a printed circuit board, i.e. a flexible or a rigid printed circuit board.

A first LED string is provided as indicated with the wording “String 1” / 101. The first LED string is provided on the substrate 100, and comprises a plurality of in series connected LEDs for emitting light. The first LED string further comprises a first set of printed, electrically conductive, tracks for connecting the plurality of in series cascaded LEDs of the first string to one another. This is indicated with reference numeral 301.

A second LED string is provided as indicated with the wording “String 2” / 102. The second LED string is provided on the substrate 100, and also comprises a plurality of in series connected LEDs 201 for emitting light. The second LED string further comprises a set of printed, electrically conductive, tracks for connecting the plurality of in series cascaded LEDs of the second string to one another. This is indicated with reference numeral 302.

A return line 303 is provided, wherein the return line is also printed on the substrate. The return line provides for a resistance for the return current to flow back to the DC current source 1 via the wiring 402. The wiring 401 is arranged to provide the current to the two LED strings. The inventors have realized that the printed tracks used to connect the LEDs to each other may have a non-negligible amount of resistance. Compared to traditional copperbased tracks, printed tracks are typically less conductive.

This resistance can cause unequal power loss in the different LED strings, leading to uneven light output. This may especially be problematic when dealing with LED strings of unequal length, where the longer string will experience greater power loss.

To address this issue, the present disclosure suggests to adjust the resistance of the second set of printed tracks to compensate for the length difference between the LED strings. Essentially, the goal is to ensure that the total resistance encountered by the current flowing through the first set of printed tracks is equal to the total resistance encountered by the current flowing through the second set of printed tracks.

The printed tracks, as indicated with reference numerals 302 and 301, may thus not be equal to one another. If the strings are of different lengths, then the widths, or heights, of the printed tracks may be adjusted accordingly.

Figure 2 discloses an example of an LED based lighting source in accordance with the present disclosure.

It is noted that the same reference numerals are used throughout the figures for indicating the same, or similar, features. This is done to increase the readability of the present disclosure.

The inventors have found that the return line, as indicated with reference numeral 303, might be relatively long thereby introducing undesired resistance for the current flowing back to the DC source 1. This is undesired.

The layout of the LED strings may play a role to reduce the length of that particular return line.

It was found that it is beneficial when a first LED and a last LED in said first LED string, and a first LED and a last LED in said second LED string are all positioned close to one another. This is, for example, visualized in Figure 2.

More specifically, the supply line crosses said return line thereby providing a crossing having a first supply line terminal, a second supply line terminal, a first return line terminal and a second return line terminal.

In this particular case, the crossing is provided on the substrate. However, the crossing may also be provided with the wiring between the substrate and the DC power supply. This will be explained later with reference to another figure. A first end of said first LED string is connected to said first supply line terminal, a first end of said second LED string is connected to said second supply line terminal, a second end of said first LED string is connected to said first return line terminal and a second end of said second LED string is connected to said second return line terminal.

Figure 3 discloses an example of an LED based lighting source in accordance with the present disclosure.

The LED based lighting source shown in Figure 3 is a further development of the one shown in Figure 2. Here, the multiple LED strings are provided, wherein each of the LED strings are cascaded in parallel. The ends of the LED strings, and the starts of the LED strings, are again positioned closely to one another to prevent an undesired lengthy supply line or return line.

Figure 4 discloses an example of an LED based lighting source in accordance with the present disclosure.

The concept shown in Figure 4 is comparable to the one shown in Figure 3.

The LED strings are, again, all placed in parallel, only the orientation is a bit different.

Figure 5 discloses a further example of an LED based lighting source in accordance with the present disclosure.

The LED based lighting source comprises three terminals as indicated with reference numerals 401, 402a and 402b. These three terminals are located close to one another to reduce the length of the return line. The terminals are used for providing a wiring connection to the DC source.

The present examples show that it may be beneficial to provide the ends, and the stars, of the corresponding LED strings somewhere in the middle of the substrate, as this enables the LED strings to be routed over the substrate.

In the description above, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of implementations of the disclosed technology. It will be apparent, however, to one skilled in the art that embodiments of the disclosed technology may be practiced without some of these specific details.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Any reference signs in the claims should not be construed as limiting the scope thereof.

Claims

CLAIMS:

1. A Light Emitting Diode, LED, based lighting source, comprising: a substrate; a first LED string, provided on said substrate and comprising a plurality of in series connected LEDs for emitting light; a second LED string, provided on said substrate and connected in parallel over said first LED string, said second LED string comprising a plurality of LEDs for emitting light; a supply line for providing current, from a power supply, to said first LED string and said second LED string; a return line for providing said current back to said power supply after it has passed through said first LED string and said second LED string; wherein a first LED and a last LED in said first LED string, and a first LED and a last LED in said second LED string are all positioned close to one another such that a distance between the first and the last LED in the string is not larger than twice the distance between any two sequential LEDs in the respective first LED string or second LED string, or such that the distance between any of the first LED in the first LED string, the last LED in the first LED string and/or the distance between the first LED in the second LED string and the last LED in the second LED string is at most 30% of a length of the first LED string or a length of the second LED string.

2. An LED based lighting source in accordance with claim 1, wherein a distance between any of said first LED in said first LED string, said last LED in said first LED string, said first LED in said second LED string and said last LED in said second LED string is at most 30% of a length of said first LED string or said second LED string.

3. An LED based lighting source in accordance with any of the claims 1 - 2, wherein any of said first LED string and said second LED string have a substantially closed shape.

4. An LED based lighting source in accordance with any of the claims 1 -3, wherein said supply line crosses said return line thereby providing a crossing having a first supply line terminal, a second supply line terminal, a first return line terminal and a second return line terminal, and wherein: a first end of said first LED string is connected to said first supply line terminal, a first end of said second LED string is connected to said second supply line terminal, a second end of said first LED string is connected to said first return line terminal; a second end of said second LED string is connected to said second return line terminal.

5. An LED based lighting source in accordance with claim 4, wherein said substrate is elongated in shape, said substrate having a length and a width, wherein said crossing is provided on said substrate at substantially halfway said length of said substrate.

6. An LED based lighting source in accordance with any of the claims 4 -5, wherein said substrate is elongated in shape, said substrate having a length and a width, wherein said crossing is provided on said substrate at substantially halfway said width of said substrate.

7. An LED based lighting source in accordance with any of the claims 5 - 6, wherein said crossing is provided at substantially a center of gravity location of said substrate.

8. An LED based lighting source in accordance with any of the claims 4 - 7, wherein a length of said first LED string is substantially equal to a length of said second LED string.

9. An LED based lighting source in accordance with any of the claims 4 - 7, wherein a length of said first LED string is longer than a length of said second LED string thereby defining a length difference, and wherein said first LED string comprises a first set of printed, electrically conductive, tracks for connecting said plurality of in series cascaded LEDs of said first string to one another; wherein said second LED string comprises a second set of printed, electrically conductive, tracks for connecting said plurality of in series connected LEDs of said second string to one another; wherein said second set of printed tracks are arranged such that a resistance of said second set of printed tracks compensates for said length difference.

10. An LED based lighting source in accordance with claim 9, wherein said first set of printed tracks are wider than said second set of printed tracks.

11. An LED based lighting device in accordance with any of the claims 9 - 10, wherein said first set of printed tracks have a first uniform width and wherein said second set of printed tracks have a second uniform width.

12. An LED based lighting source in accordance with any of the claims 9 - 11, wherein said first and second set of printed, electrically conductive, tracks comprise cured or sintered ink.

13. An LED based lighting source in accordance with claim 12, wherein said ink comprises any of silver and copper particles.

14. An LED based lighting source in accordance with any of the claims 9 - 13, wherein said first set of printed tracks are thicker than said second set of printed tracks.

15. A Light Emitting Diode, LED, based lighting device arranged for emitting light, wherein said LED based lighting device comprises an LED based lighting source in accordance with any of the preceding claims and a driver for powering the LED based lighting device.