FIELD OF THE INVENTION

The present invention generally relates to a LED light source comprising a substrate arranged to support one or more light emitting diodes. BACKGROUND OF THE INVENTION

A global need and desire for a reduced use of energy and in particular electricity has rapidly advanced the development of more energy efficient light sources. To this end light emitting diodes, LEDs, are employed in a wide range of lighting applications, such as domestic and automotive applications. As LEDs have the advantage of providing a bright light, being reasonably inexpensive and energy efficient, it is becoming increasingly attractive to use LEDs as an alternative to traditional lighting such as incandescent light bulbs or similar. Furthermore, LEDs have a long operational lifetime bringing about reduced service and maintenance costs.

To this end numerous of retrofit LED light sources are provided in order to exchange traditional lighting with an alternative consuming less energy and having a longer service life.

In general LED retrofit light sources or lamps rely on prior knowledge of the application where the light source in question is to be used. This means that retrofit LED light sources are designed taking the secondary optics of the application in question into consideration, such that a sufficient light level is achieved in the direction/position that is needed for the specific application. This does in turn mean that numerous retrofit LED light sources are designed for a particular application or applications, rendering the retrofit LED light sources less useful or not at all useful for other applications than the intended one or intended ones.

Generally LED light sources have an undesired light distribution due to the directionality of packaged LEDs making up the light source itself. Commonly the light emitting element of the LED is mounted in a package with a mirror on the bottom. This means that the light emission is restricted to a hemispherical emission. This brings about that if an omni-directional light distribution is needed, additional optics or multiple light sources are needed. This does in turn mean that the complexity and cost generally increases when producing a LED light source.

In conclusion, retrofit LED light sources tend to be too specific to be used in a wide range of applications. Further, the costs for producing retrofit LED light sources tend to be unnecessarily high.

EP 2 597 354 Al discloses a LED light source in form of a light bulb shaped lamp. The disclosed lamp resembles the shape and appearance of a traditional incandescent light bulb. The disclosed LED light source has a limited light flux meaning that the light source is suitable for some applications but not for others.

US 2011/163683 Al discloses LED light sources wherein a substrate or plurality of substrates is/are used to support a number of LEDs. The LED light sources disclosed have various shapes and constructions, some including a bulb.

US 2013/271989 Al discloses a LED light source where a LED array is provided on a stem within a transparent enclosure. The enclosure is provided with a gas contained in the enclosure to provide thermal coupling to the LED array.

DE 10 2012 218181 Al discloses a solid state light source, wherein a plurality of solid state light sources are provided on a plurality of light carries within a transparent bulb.

US 2012/320581 Al discloses electronic devices including arrays of printable LEDs having various device geometries. Large area, transparent, and flexible LED arrays useful for e.g. display and lightning technology are disclosed.

Hence, there is a need for improved LED light sources which may be cost- effectively used in a wide range of applications. SUMMARY OF THE INVENTION

According to an aspect of the invention, the above is at least partly alleviated by a LED light source comprising: a substrate arranged to support one or more light emitting diodes, a socket, and a thermal conducting clamp, the substrate having an envelope area, the one or more light emitting diodes covering less than 1% of the envelope area, the clamp being arranged to connect the substrate to the socket and comprising a groove adapted to receive the substrate.

The present invention is based on the realization that by providing one or more light emitting diodes on a substrate having a relatively speaking large overall envelope area as compared to the part of the envelope area covered by the light emitting diode or diodes, the efficiency of the LED light source may be increased such that the light flux of the LED light source is improved and at the same time the heat spreading or heat dissipation form the LED light source is improved. In other words, the relatively speaking large substrate brings about that the light emitting diode or diodes of the LED light source may be operated in a more intense manner bringing about a higher light flux without being overheated or suffering from a decreased service life.

It should be noted that within the context of this application the term

"substrate" may be any material body being suitable to support one or more light emitting diodes. Further, the substrate may have any suitable shape and may be made of any suitable material. The light emitting diode or diodes used may be provided directly or indirectly on the substrate. The light emitting diodes may be bare or may be encased. In the latter case, the substrate may thus support the light emitting diode or diodes used indirectly by supporting the casing encasing the light emitting diode or diodes used.

Further, "envelope area" is to be construed as the combination of any outer surface area surrounding and thus enveloping the substrate. For instance, in case of a substrate in form of a cuboid the envelope area will be the combination of the six outer surfaces of the cuboid.

By the LED light source comprising a socket, and a thermal conducting clamp, wherein the clamp being arranged to connect the substrate to the socket, heat generated by the one or more light emitting diodes may be transferred away from the one or more light emitting diodes in a more efficient manner, meaning that the heat transfer may be further enhanced.

It should be noted that within the context of this application the term "socket" may be any element or body used to connect the LED light source to the ambient. The socket may thus be used to connect the LED light source to one or more power sources and/or may be used to mechanically connect and secure the LED light source to an external element or body. The socket may be threaded, comprise pin or flanges. Further, the socket may comprise pins or wires.

Further, a "thermal conducting clamp" is to be construed as a clamp or other suitable element being thermally conductive and used to hold and connect the substrate to the socket. The clamp may thus be so constructed that it efficiently transfers heat, generated by the one or more light emitting diodes, from the substrate to the socket by conducting the heat through the clamp itself. By the clamp comprising a groove adapted to receive the substrate, the substrate being supported by the clamp in a simple and efficient manner and at the same time a reliable thermal connection between the substrate and the clamp is established.

In an embodiment, the groove may have an extension being equal to or smaller than a width of a side of the substrate facing the groove, which is advantageous in that the thermal connection between the substrate and the clamp may be tuned in a simple manner without using superfluous material in the clamp.

In an embodiment, the contact surfaces between the clamp and the substrate may be complementary, which is advantageous in that an efficient thermal connection between the substrate and the clamp may be achieved.

By "complementary" is meant that the surfaces are so shaped that they will complement each other meaning that they will come into contact with each other when brought together.

In an embodiment, a thermal conducting material may be arranged between the clamp and the substrate, which is advantageous in that the thermal connection between the substrate and the clamp may be further improved.

In an embodiment, an angle between a light emitting diode supporting surface of the substrate and an outer surface of the clamp may be between 110 and 160 degrees. This is advantageous in that an airflow present by the outer surface of the clamp may be optimized such that heat is dissipated from the clamp to the ambient in a more efficient manner.

In an embodiment, the substrate may be provided with a through cut between the one or more light emitting diodes and a side of the substrate facing the socket. This is advantageous in that less heat generated by the light emitting diode or diodes used may be transferred internally in the substrate towards a location where the substrate is connected to the socket. This means that the portion of the substrate used to connect the substrate to the socket will be heated less by the heat generated by the light emitting diode or diodes used. It is thus possible to counteract unwanted heating of e.g. driver electronics present in proximity to the portion of the substrate used to support the substrate.

In an embodiment, the LED light source may further comprise a bulb, the bulb encasing the substrate. The presence of a bulb brings about that the elements of the LED light source are protected from outside conditions. This means that the LED light source becomes less sensitive to dirt, particles, moisture or similar.

According to an embodiment, the substrate may be translucent. The use of a translucent substrate brings about that light emitted from the light emitting diode or diodes used may pass through the substrate such that light from a light emitting diode present on one side of the substrate may leave the substrate on a different side of the substrate.

The wording "translucent" is to be understood as permitting the passage of light. Hence, translucent is to be understood as "permitting the passage of light" and a translucent material may either be clear, i.e. transparent, or transmitting and diffusing light so that objects beyond the translucent material cannot be seen clearly. Transparent on the other hand is to be understood as "able to be seen through".

According to an embodiment, the one or more light emitting diodes may be provided with a phosphor comprising material. This is advantageous since the phosphor comprising material may be used to convert the wavelength of the light being emitted by the light emitting diode or diodes used in to a desired wavelength. Further, the phosphor comprising material may reduce the thermal resistance between the light emitting diode or diodes used and the substrate, meaning that a more efficient heat transfer may be achieved.

According to an embodiment, the LED light source may further comprise primary optics, the primary optics being arranged directly or indirectly on the substrate. This is advantageous since it makes it possible to shape the light field of the light being emitted by the light emitting diode or diodes used. By shaping the light field or near field light, the light emitted by LED light source may be altered such that the emitted light simulates a filament of a traditional incandescent light bulb. This may be achieved by for instance by altering a directed light field to an omni-directional light field. By simulating a filament, a true retrofit LED light source may be accomplished, meaning that no prior knowledge of the secondary optics of a specific application is needed.

The wording "primary optics" is to be understood as any optics or optical element used to shape the light field of the light being emitted by the light emitting diodes of the LED light source.

In an embodiment, the primary optics may comprise an element chosen from the group consisting of: a scattering element, a refractive element, a reflective element and a diffractive element, which is advantageous in that standard optical components may be used to shape the light field of the LED light source.

BRIEF DESCRIPTION OF THE DRAWINGS

The aspects of the invention, including its particular features and advantages, will be readily understood from the following detailed description and the accompanying drawings, in which: Fig. 1 conceptually illustrates a LED light source having a substrate employed with a number of light emitting diodes:

Fig. 2 conceptually illustrates a LED light source having a substrate employed with a number of light emitting diodes arranged in two parallel rows;

Fig. 3 conceptually illustrates a LED light source employed with a bulb encasing the substrate of the LED light source; and

Fig. 4 conceptually illustrates a LED light source where the substrate comprises a through cut. DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person. Like reference characters refer to like elements throughout.

Referring now to the drawings and to Fig. 1 in particular, there is conceptually depicted a LED light source 100. The LED light source 100 comprises a substrate 102 used to support a number of light emitting diodes 104. The substrate 102 is supported by a thermal conducting clamp 106 which in turn is supported by a socket 108. This means that the substrate 102 is connected to the socket 108 by means of the clamp 106. Further, the LED light source 100 is provided with a space 109 within the socket. The space 109 is used to house driver electronics, not shown, or similar of the LED light source 100.

It is to be noted that the various elements of the LED light source 100 are not drawn to scale, but are drawn in an exemplifying manner to clearly indicate the basic construction of the LED light source 100. For instance, the size of the light emitting diodes 104 are exaggerated in order to more clearly show the light emitting diodes 104.

The light emitting diodes are preferably made up of bare epi material and are provided directly or indirectly on the substrate 102. By epi material is meant the epitaxially grown material of the light emitting diodes 104 which forms the light emitting portions of the light emitting diodes 104. In other words, the epi material of the light emitting diodes 104 is preferably not packaged in any type of package used to protect the light emitting diodes 104 from ambient conditions. The use of bare or unpackaged light emitting diodes 104 brings about several advantages. Bare light emitting diodes 104 are inherently more efficient than packaged ones, since the light losses in unpackaged light emitting diodes 104 are significantly lower than for packaged light emitting diodes using for instance a bottom reflector to direct the light being emitted. This means that the efficiency of the light emitting diodes 104 are increased. The efficiency or gain may for instance be expressed using the so-called extraction efficiency. The extraction efficiency for packaged light emitting diodes is typically 80% whereas the extraction efficiency for bare light emitting diodes is typically roughly 85%. Moreover, bare light emitting diodes 104 tend to emit light in a more omni-directional manner as compared to packaged light emitting diodes.

Another advantage of using bare light emitting diodes is that the thermal performance of the LED light source 100 may be increased as the number of thermal interfaces may be reduced by using bare light emitting diodes 104.

Further, the reliability of the light emitting diodes 104 and hence the LED light source 100 may be increased by using bare light emitting diodes 104. This is mainly due to the fact that no solder joints are needed in order to connect the light emitting diodes 104 to the substrate 102. Solder joint failure is often limiting the lifetime of packaged light emitting diodes used in LED light sources due to mismatches in the coefficient of thermal expansion, CTE, between package and substrate onto which the light emitting diode is attached.

Furthermore, the use of bare light emitting diodes 104 brings about that the light emitting diodes 104 may be run at higher temperatures because of the absence of any limiting package. Also the price of the price of the light emitting diodes 104 may be reduced because of the absence of any package.

Light emitting diodes 104 may be employed on a single side of the substrate 102 or may be employed on multiple sides of the substrate 102. The light emitting diodes 104 may be positioned in any position and in any pattern on the substrate 102.

Further, various types of light emitting diodes 104 emitting light at various wavelengths may be used in accordance with the present invention. Moreover, packaged light emitting diodes 104 may alternatively very well be used according to the present invention.

The substrate 102 is preferably made of a translucent material implying that light emitted by the light emitting diodes 104 may be shined through the substrate 102. This means that light emitted by light emitting diodes 104 present on one side of the substrate 102 may leave the substrate on a different side thereof. In other words, light emitting diodes 104 present on a single side of the substrate 102 may result in a substantially omni-directional light distribution pattern. Further, the substrate 102 may be transparent, such that light passing the substrate 102 is in principle not scattered by the substrate 102.

The fact that the substrate 102 has a large envelope area as compared to the area covered by the light emitting diodes 104 brings about that the substrate will work as an efficient heat sink transferring heat produced by the light emitting diodes 104 to the ambient. Further, the thermal resistance between bare light emitting diodes 104 and the substrate 102 is very low in comparison to when packaged light emitting diodes are used. This does in turn mean that the substrate can reach higher temperatures as compared to when packaged light emitting diodes are used. The use of higher temperatures brings about thermal radiation will play a significant or dominant role in when transferring heat produced by the light emitting diodes 104 of the LED light source 100 to the ambient. In other words, a LED light source 100 using bare light emitting diodes 104 will a lower absolute thermal resistance, R _th , than similar solutions using packaged light emitting diodes. As a result of the lower R _th the LED light source 100 becomes less sensitive of its surroundings such that an efficient thermal management of the LED light source 100 is still possible in situations where convection is limited, due to e.g. a bulb or similar enclosing the LED light source 100.

The thermal performance resulting from the use of a relatively speaking large substrate 102 brings about a beneficial "lumen per lamp volume" ratio. This means that the LED light source 100 of the described type is capable of generating a larger light flux given its outer dimensions as compared to LED light sources using relatively speaking smaller substrates.

The substrate 102 used may be made of several materials and still function as a heat sink. However, it is preferred that the substrate 102 is translucent or transparent as described above. Further, it is preferred that the substrate has a high thermal conductivity such that heat may be efficiently conducted by the substrate 102 and thus removed from the light emitting diodes 104 producing the heat. Examples of materials which may be used for a translucent substrate are sapphire and ceramics. Examples of suitable ceramics are various forms of A10 _x .

However, the substrate 102 may be made of a diffuse or reflective material like aluminum, FR4, CEM3, or other suitable materials having a desired emissivity. In this case, the light emitting diodes 104 are preferably provided with a reflective material or mirror material on a side facing the substrate 102. This may be realized by using packaged light emitting diodes. According to one embodiment, a substrate 102 having a substrate area of 2000 mm ² is used. By substrate area is meant the side of the substrate 102 onto which the light emitting diodes 104 are provided, i.e. the front side or the backside of the substrate 102.

Seven light emitting diodes 104, each having a surface area of 1mm ² , are attached to the substrate in a row with a 1 mm pitch. The total area covered by the light emitting diodes is thus 7 mm ² . This means that the ratio between the surface area and the area covered by the light emitting diodes 104 is 286. In other words, light emitting diodes 104 covers about 0,35% of the surface area of the substrate 102. This means that the light emitting diodes 104 covers less than 0.17% of the envelope area of the substrate 102. The substrate has a thickness of 1 mm and has a thermal conductivity of 30 W/(mK). Further, the substrate has a heat transfer coefficient of 15 W/(m ² K). In the current example, the light emitting diodes are run at a temperature close to 150 degrees Celsius. The fin length for the particular substrate being described may be calculated using standard calculations. In this particular example, the fin length is determined to be 32 mm. This means that a substrate of the above type will benefit from a length of 32 mm in a tangential direction from the row of light emitting diodes 104. In other words, the substrate can spread heat up to 32 mm away from the row of light emitting diodes 104. This means in practice that the heat spreading properties of the substrate will not benefit from a length being above 32 mm. In other words, there is no point in making the substrate in the above example any larger.

The light emitting diodes 104 of Fig. 1 are arranged in a row. The arrangement of the light emitting diodes 104 in a row brings about that the light emitting diodes 104 simulates a filament of a traditional incandescent light source. In other words, the row of light emitting diodes 104 is orientated and positioned in a position with respect to the socket 108, where a filament of a traditional incandescent light source would be positioned. This means that the LED light source 100 will work as a retrofit light source, as it will behave as it was employed with a filament.

In order to shape the light field emitted by the light emitting diodes 104, the substrate may be employed with primary optics, not shown. The primary optics may be used to shape the light emitted to more accurately mimic the light emitted by a filament of a traditional incandescent light source. The choice of primary optics will for instance depend on the light emitting diodes used, the substrate used and the size and shape of the filament being simulated. Various elements may be used to shape the light field to simulate a filament, such as scattering elements, refractive elements, reflective elements and diffractive elements. By simulating a filament, the LED light source 100 will when replacing a traditional incandescent light behave like the traditional incandescent light it replaces, meaning that no prior knowledge of any secondary optics is required. By secondary optics is meant optics present in the application or system where the LED light source 100 is used.

The light emitting diodes 104 may be employed with a phosphor comprising material, not shown. The phosphor comprising material is used to alter the wavelength of the light being emitted from the light emitting diodes 104. In practice phosphor comprising materials are for instance used to alter blue light emitted by the light emitting diodes 104 into a desired wavelength.

The phosphor comprising material may be added to the light emitting diodes 104 using various techniques. For instance, the phosphor comprising particles may be introduced in glue used to attach the light emitting diodes 104 to the substrate 102. This means that the phosphor particles of the glue will be present between the light emitting diodes 104 and the substrate 102. The glue may also cover the light emitting diodes 104 such that the phosphor particles will be present on any outer surface of the light emitting diodes 104. When phosphor particles are present between the light emitting diodes 104 and the substrate 102, the grain size of the particles will determine the distance between the light emitting diodes 104 and the substrate 102.

It is to be noted that phosphor particles in for instance a transparent silicone based glue can help in reducing the thermal resistance because of the high thermal conductivity of the phosphor particles as compared to the glue itself.

Further, phosphor may be deposited on the light emitting diodes 104 using other suitable techniques. When it is desirable to use larger phosphor particles the phosphor particles are preferably positioned in other locations than between the light emitting diodes 104 and the substrate 102, as the use of larger phosphor particles may result in an undesired large distance between the light emitting diodes 104 and the substrate 102, reducing the thermal conductivity.

Another beneficial method is to use a ceramic substrate 102, which is highly, fully or locally doped with Ce or YaG:Ce. A commercially available example of such a substrate is Lumiramic from Philips. The doped substrate 102 can then convert blue light emitted from the bottom side, i.e. the side facing the substrate 102, of light emitted diodes 104 into a desired wavelength. When using a doped substrate a phosphor comprising layer is preferably applied on the top side of the light emitting diodes 104.

When using a highly, fully or locally doped ceramic substrate 102, a light emitting diode 104 or a plurality of light emitting diodes 104 in form of bare epi material may be connected to the ceramic substrate 102. The connection of the light emitting diodes 104 to the substrate 102 is preferably done by means of Au contact pads provided on the substrate 102 and on the light emitting diodes 104, i.e. an Au-Au interconnect is thus achieved. If a locally doped substrate 102 is used, the bare LED light sources are preferably provided in positions corresponding to the locally doped regions of the substrate 102. This brings about that the substrate 102 can convert blue light emitted from the bottom side, i.e. the side facing the substrate 102, of light emitted diodes 104 into a desired wavelength.

The light emitting diodes 104 may further be covered with a small piece or platelet, not shown, of a doped material. A single platelet may be used for plurality of light emitting diodes 104 or for a single light emitting diode 104. The platelet can thus convert blue light emitted from the top side, i.e. the side not facing the substrate 102, of light emitted diodes 104 into a desired wavelength. The platelet is advantageously attached to the light emitting diodes 104 and the substrate 102 using a silicone based glue or similar.

The platelet or platelets used may alternatively be supported on supporting structures around the light emitting diodes 104 meaning that no glue or less glue has to be used. The supporting structures are preferably designed such that good thermal properties are achieved, i.e. the supporting structures are designed so as to conduct and dissipate heat from the platelets and the light emitting diodes 104. Also when using supporting structures for the platelet or platelets used, phosphor particles may be used to convert the wavelength of the light being emitted by the light emitting diodes 104 as discussed above. When using supporting structures, red phosphor which is more temperature sensitive than yellow phosphor may advantageously be used.

An encapsulant, not shown, encasing the light emitting diodes 104 may be applied onto the light emitting diodes 104 to protect the light emitting diodes 104 and the connections used to contact the light emitting diodes 104 from outside action. It is thus possible to realize a more reliable LED light source 100 being less sensitive by employing an encapsulant. Examples of suitable encapsulants are silicones.

The thermal conducting clamp 106 in the depicted embodiment of Fig.1 is made of copper. However, the clamp 106 may be made of other suitable materials such as aluminum, iron, silver, steel, ceramics and the like. The clamp 106 comprises a groove 110 into which the substrate 102 is inserted, i.e. the substrate 102 is received by the groove 110 of the clamp 106.

An upper surface 112 of the depicted clamp 106 is inclined such that air more easily may flow along the upper surface 112 of the clamp 106 and the substrate 102. Preferably the angle between a light emitting diode supporting surface of the substrate 102 and the upper surface 112 of the clamp 106 is between 110 and 160 degrees, so as to optimize the flow of air along the upper surface 112 of the clamp 106 and the substrate 102. For instance in automotive applications, the ambient of the LED light source 100 are usually well defined and a certain airflow can be expected. Depending on the direction of this air flow and the position of the LED light source 100 in vehicle, the shape of the clamp 106 may be optimized.

As can be seen in Fig. 1, the groove 110 has an extension being smaller than the width of the side of the substrate 102 facing the groove 110 in the depicted embodiment, i.e. the substrate 102 is wider than the clamp 106 comprising the groove 110. The width of the substrate 102 with respect to the extension of the groove 110 may vary between different embodiments of the invention. This means that the groove 110 may have an extension being smaller than, equal to or larger than the width of the side of the substrate 102 facing the groove 110.

The interior surfaces of the groove 110 contacts the substrate 102 such that heat may be transferred from the substrate to the clamp 106. In order to achieve an efficient thermal connection between the clamp 106 and the substrate 102, the contact surfaces between the clamp 106 and the substrate 102 are complementary. This means that the respective contact surfaces are shaped such that they fit each other in the sense that contact between the surfaces is established when the substrate 102 is inserted into the groove 110 of the clamp 106. In the depicted embodiment of Fig. 1, the groove 110 is straight and the substrate 102 is straight, i.e. not curved. However, according to other embodiments, the groove 110 and the substrate 102 may for instance be curved with the same radius of curvature such that that contact between the surfaces of the groove 110 and the substrate 102 is established when the substrate 102 is inserted into the groove 110 of the clamp 106.

Further, the respective contact surfaces of the groove 110 and the substrate 102 may be subjected to various processes aiming at achieving a desired surface roughness or overall surface flatness in order to enhance the thermal connection between the substrate 102 and the clamp 106. This means that the respective contact surfaces, for instance may be polished or milled in order to fulfil desired roughness and flatness criteria.

Moreover, a thermal conducting material, not shown, may be arranged between the clamp 106 and the substrate 102. By arranging a thermal conducting material between the clamp 106 and the substrate 102, the thermal conduction between the clamp 106 and the substrate 102 may be enhanced. The thermal conducting material is preferably in the form of a paste or a non-rigid material. By using a paste or a non-rigid material, the paste or non-rigid material will help in filling or even surface roughness or non flatness between the contact surfaces. In other words, the use of a paste or a non-rigid material may increase the contact area between the clamp 106 and the substrate 102. Zink, silver, copper and aluminum comprising pastes or materials or similar may preferably be used due to the good thermal conductivity.

The clamp 106 is thermally connected to the socket 108 such that heat may be transferred from the clamp 106 to the socket 108. This means in turn that heat may be transferred from the socket 108 to the ambient, e.g. to a light fitting used to hold or support the LED light source 100.

Now referring to Fig. 2, here is conceptually depicted a LED light source 100 according to a currently preferred embodiment of the invention. The LED light source 100 of Fig. 2 is similar to the light source 100 of Fig. 1, why only the differences between the respective LED light sources 100 of Fig. 1 and Fig. 2 will be described below.

As can be seen from Fig. 2, the LED light source 100 of Fig. 2 is employed with two rows of light emitting diodes 104a, 104b. The respective rows of light emitting diodes 104a, 104b are positioned at different positions on the substrate 102.

The use of two rows of light emitting diodes 104a, 104b brings about that the LED light source 100 simulates two filaments, i.e. the LED light source 100 mimics a traditional incandescent light bulb having two different filaments. The light emitting diodes 104a are simulating a first filament whereas the light emitting diodes 104b are simulating a second filament. Light bulbs having more than one filament are for instance commonly used in automotive applications such as automotive signalling lights.

The above embodiments and variations of the invention described in relation to Fig. 1 may also be advantageously used in a LED light source simulating two filaments as shown in fig 2. Moreover, a LED light source simulating any number of filaments may be realized without departing from the scope of the present invention.

Now referring to Fig. 3, here is conceptually depicted a LED light source 100 according to a currently preferred embodiment of the invention. The LED light source 100 of Fig. 3 is similar to the light source 100 of Fig. 1, why only the differences between the respective LED light sources 100 of Fig. 1 and Fig. 3 will be described.

As can be seen from Fig. 3, the LED light source 100 of Fig. 3 is employed with a transparent bulb 114 encasing the substrate 102 and the clamp 106. The transparent bulb 114 is consequently protecting the substrate 102, the light emitting diodes 104 and the clamp 106 from the ambient. The bulb also makes the LED light source 100 look more like a traditional incandescent light bulb.

The size, shape and material of the bulb 114 may be altered to suit the needs of the LED light source 100. For instance, the bulb may be shaped to mimic the bulbs of various traditional incandescent light bulbs. Further, the bulb 114 may be formed from a translucent material not being transparent, such that the interior of the bulb may not be seen clearly from an outside of the bulb 114.

The substrate 102 of the LED light source of Fig. 3 has the same with as the length of the groove 110 of the clamp 106, i.e. the clamp 106 and the substrate 102 has the same width. Further, it may be seen that the substrate 102 is inserted deeper into the groove 110 as compared to the LED light source 100 depicted in Fig. 1. The fact that the substrate 102 is inserted deeper into the groove 110 brings about the area of the contact surface is increased.

Further, it is to be noted that the LED light source 100 of Fig. 3 does not comprise any space within the socket used to house driver electronics or similar. However, the LED light source 100 of Fig. 3 may very well be employed with a space for housing driver electronics or similar.

The above embodiments and variations of the invention described in relation to Fig. 1 may also be advantageously used in a LED light source 100 as shown in Fig 3.

Now referring to Fig. 4, here is conceptually depicted a LED light source 100 according to a currently preferred embodiment of the invention. The LED light source 100 of Fig. 4 is similar to the light source 100 of Fig. 1, why only the differences of the between the respective LED light sources 100 of Fig. 1 and Fig. 4 will be described.

As can be seen from Fig. 4, the LED light source 100 of Fig. 4 comprises a substrate 102a, 102b of a type being different as compared to the LED light source 100 of Fig. 1. The Substrate 102a, 102b comprises two different portions 102a, 102b making up the substrate 102a, 102b. The first portion 102a is provided with light emitting diodes 104. This means that the light emitting diodes 104 are arranged on the first portion 102a of the substrate 102a, 102b.

The first portion of the substrate 102a is connected and attached to the second portion of the substrate 102b, such that the two portions 102a, 102b together forms the substrate 102a, 102b. The two portions 102a, 102b may be connected and attached to each other using any suitable techniques, such as gluing, bonding or similar. The respective portions 102a, 102b of the substrate 102a, 102b may be made off different materials or may be made of the same material. Further, the first and second portions 102a, 102b may be integrally formed or made of two separate portions being connected to each other.

By utilizing different materials in the respective portions 102a, 102b of the substrate 102a, 102b the properties of the substrate 102a, 102b may be tailored. For instance, the first portion of the substrate 102a may be optimized such that a desired amount of light emitted from the light emitting diodes 104 is transmitted through the first portion 102a, whereas the second portion 102b of the substrate may be optimized in terms of heat dissipation. This means that the first portion 102a may have a higher light transmittance as compared to the second portion 102b, whereas the first portion 102a may have less heat dissipation or heat transfer capabilities as compared to the second portion 102b.

The substrate 102a, 102b is provided with a through cut 116. As can be seen from Fig. 4, the through cut is U shaped and arranged such that is located between the light emitting diodes 104 and a side of the substrate 102a, 102b facing the socket 108. This means that less heat being generated by the light emitting diodes 104 will be conducted from the light emitting diodes 104 to the socket 108. This do in turn mean that less heat will be transferred to e.g. a light fitting used to hold the LED light source 100. Further, the use of the through cut 116 may counteract undesired heating when driver electronics, not shown, or similar is provided within the socket. The through cut 116 results in that the temperature distribution in the substrate 102a, 102b is divided into different zones, why the concept of using a through cut 116 may be referred to as thermal zoning.

By providing the substrate 102a, 102b with the through cut 116, the temperature of the substrate 102a, 102b in proximity to the socket 108 may limited. This brings about that driver electronics or similar may be provided directly on the substrate 102a, 102b in proximity to the socket 108 or in any other location having a favorable temperature distribution.

As can be seen from Fig. 4, the LED light source 100 of Fig. 4 does not comprise any thermal clamp. However, the LED light source 100 of Fig. 4 may very well be employed with a clamp of the type described above in relation to Fig. 1.

The LED light source 100 of Fig. 4 is employed with a bulb 114 of the type described above in relation to Fig. 3. However, the bulb 114 may very well be omitted in the LED light source 100 of Fig. 4.

The above embodiments and variations of the invention described in relation to Fig. 1 may also be advantageously used in a LED light source 100 as shown in Fig 4. The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications, combinations and variations are possible within the scope of the appended claims.

Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person 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.