WO2018019655A1

WO2018019655A1 - A light emitting device

Info

Publication number: WO2018019655A1
Application number: PCT/EP2017/068110
Authority: WO
Inventors: Marcus Cornelis VAN MEEL; Johannes Gerrit Jan BEIJER; Johannes Petrus Maria Ansems
Original assignee: Philips Lighting Holding B.V.
Priority date: 2016-07-26
Filing date: 2017-07-18
Publication date: 2018-02-01

Abstract

A light emitting device (10) comprising a central core element (11) and a plurality of n LED light sources (12), the central core element (11) being a cylindrical element comprising a circumferential surface (17), a longitudinal direction (L), a longitudinal axis (A) extending in the longitudinal direction and a cross-section in a direction perpendicular to the longitudinal direction, the cross section being shaped like a polygon with N sides (1, 2, 3, 4, 5, 6, 7, 8) of equal length, where n is different from N, the plurality of LED light sources (12) are arranged on the sides of the central core element in n intersection points between the circumferential surface of the central core element and n radial lines extending perpendicular to the longitudinal direction from the longitudinal axis to the circumferential surface in such a way that each of the n lines has the same angle β = 360°/n with the two adjacent lines of the n lines, and at least one LED light source of the plurality of LED light sources (12) are tilted in such a way that its central axis (16) is oriented in the direction of that of said n radial lines extending through that of the n points in which the at least one LED light source of the plurality of LED light sources is arranged.

Description

A light emitting device

FIELD OF THE INVENTION

The invention concerns a light emitting device which comprises a central core element and a plurality of LED light sources where the central core element is a cylindrical element comprising a circumferential surface, a longitudinal direction, a longitudinal axis extending in the longitudinal direction and a cross-section in a direction perpendicular to the longitudinal direction, the cross section being shaped like a polygon with N sides of equal length. Such light emitting devices are typically made in the form of light bulbs, and in particular incandescent light bulbs.

BACKGROUND OF THE INVENTION

Current incandescent light bulbs have LED light sources placed upon a central core element in the form of a regular octagon (i.e. a polygon having 8 sides) extended like a cylinder. The octagon was chosen for the first light bulbs with this architecture and needed 8 LED light sources to have a satisfactory lumen output. Also the diameter of the octagon (diameter of the smallest circle that can fully encircle the octagon) needed to be below 26 mm to assure that it did not touch the glass of the outer bulb while inserted vertically into the bulb. On one hand, to ensure good cooling the octagon needs to have as large a surface as possible, i.e. as large a radius as possible. On the other hand, to ensure good optical performance, i.e. the smallest possible illuminance variation of the glass bulb, the octagon should preferably be small.

To obtain a homogeneous illuminance of the bulb, the LED light sources are preferably equally distributed over the surfaces of the octagon. CN 202001900 U describes an example of such a light bulb, and furthermore teaches that to ensure a high brightness and a homogeneous illuminance of such a light bulb the LED light sources are preferably to be equally distributed over the surfaces of the octagon with the same number of LED light sources present on all surfaces.

However, as the quality of the LED light sources available improves, less LED light sources are needed to achieve a satisfactory high output intensity. Likewise, when smaller and cheaper LED light sources become available, more LED light sources are needed to achieve a satisfactory high output intensity. Also, lamps with different light levels or different white colors (different efficiencies of the LED light sources) will need different numbers of LED light sources. Changing the octagon to a polygon with a different number of sides is costly, and also light emitting devices with different light levels or different white colors (i.e. different efficiencies of the LED light sources) will need different LED light source counts, resulting in many different mechanical designs. Many different mechanical designs also require manufacturing and manufacturing machine adjustments.

Still considering a bulb with a central core element in the form of an octagon with 8 LED light sources, it is known that the direct (i.e. from the LED light sources) illuminance variation inside the bulb (in the plane of the LED light sources) is small and that the resulting luminance variation on the outside of the bulb will, for a fairly scattering bulb, be nearly invisible to the human eye. Also part of the direct light on the inside of the bulb will not be transmitted but will scattered back into the bulb. Most of this scattered light will have a second chance to escape the bulb at another position. As a result, the luminance variation on the outside is smaller than the illuminance variation on the inside. The thicker the scattering coating that the bulb may comprise, the smaller the luminance variation on the outer surface of the bulb, but the lower the optical efficiency.

However, if one or more LED light sources are removed from the octagon, then the result is that the direct illuminance variation becomes very large. The direct illumination variation, expressed as (Emax-Emin)/(Emax+Emin), Emax being the maximum illuminance and Emin the minimum illuminance, has been calculated to increase from 0.038 to 0.53. This large variation will result in such a luminance variation on the outside of the bulb that it will be noticed by humans and not be appreciated.

Also, if a ninth LED light source is to be added to the octagon, then the result is that the direct illuminance variation will increase considerably. This large variation will result in such a luminance variation on the outside of the bulb that it will be noticed by humans and not be appreciated.

A thicker coating on the bulb can reduce the outside variation. More particularly, by making the coating thicker and thicker more light is reflected/scattered back into the bulb where it will have a new chance to escape the bulb. This backscattered light will be more homogeneously distributed on the bulb. However, this approach will have a cost penalty as the optical efficiency will decrease with the thickness of the coating; i.e. more light will be lost by absorption in the coating or inner parts of the bulb. This drop in optical efficiency will result in the need for creating more light by the LED light sources and hence in higher temperatures and/or higher LED light source counts, both being undesired. Another solution would be to change the central core element to a heptagon shape, but such a change is as mentioned above expensive.

Another way of decreasing the luminance variation without changing the coating (and optical efficiency) and without changing the octagon, that has been attempted, is to alter, particularly increase, the length of the side(s) of the octagon. In case of e.g. 8 LED light sources such an adjusted octagon will exhibit a slightly worse homogeneity. In case of e.g. 9 LED light sources the homogeneity will improve if the side on which the 9^th LED light source is added is increased in length. However, the homogeneity is still too low, and the luminance variation will thus still be noticeable by the human eye. Also, altering the side length of the central core element is a relatively costly solution.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome these problems, and to provide a light emitting device with an arrangement of a plurality of LED light sources that allows for achieving a homogenous illuminance for at least some or even all numbers of LED light sources being different from the number of sides of the central core element, and which is furthermore simpler and less costly to produce and acquire.

According to a first aspect of the invention, this and other objects are achieved by means of a light emitting device comprising a central core element and a plurality of LED light sources, the central core element being a cylindrical element comprising a

circumferential surface, a longitudinal direction, a longitudinal axis extending in the longitudinal direction and a cross-section in a direction perpendicular to the longitudinal direction, the cross section being shaped like a polygon with N sides of equal length, where the plurality of LED light sources comprises a number n of LED light sources, where n is an integer different from N, the plurality of LED light sources are arranged on the sides of the central core element in n points defined as the intersection points between the circumferential surface of the central core element and n radial lines extending perpendicular to the longitudinal direction from the longitudinal axis to the circumferential surface of the central core element in such a way that each of the n lines has the same angle β with the two adjacent lines of the n lines, said angle β being 360°/n, and at least one LED light source of the plurality of LED light sources is tilted in such a way that its central axis, said central axis being defined as the direction in which the at least one LED light source of the plurality of LED light sources exhibits the maximum light intensity, is oriented in the direction of that of said n radial lines extending through that of the n points in which the at least one LED light source of the plurality of LED light sources is arranged.

By providing a light emitting device in which the plurality of LED light sources are arranged on the sides of the central core element in n points defined as the intersection points between the circumferential surface of the central core element and n radial lines extending perpendicular to the longitudinal direction from the longitudinal axis to the circumferential surface of the central core element in such a way that each of the n lines has the same angle β with the two adjacent lines of the n lines, said angle β being 360°/n, and at least one LED light source of the plurality of LED light sources is tilted in such a way that its central axis, said central axis being defined as the direction in which the at least one LED light source of the plurality of LED light sources exhibits the maximum light intensity, is oriented in the direction of that of said n radial lines extending through that of the n points in which the at least one LED light source of the plurality of LED light sources is arranged, the luminance variation is decreased to levels invisible to the human eye.

Thus, such an arrangement of a plurality of LED light sources provides for a light emitting device having a homogenous illuminance for all numbers of LED light sources being different from the number of sides of the central core element, while only necessitating a very thin coating or even no coating at all. Such a light emitting device is therefore simpler in construction and less costly to produce and acquire.

Furthermore, allowing for the plurality of LED light sources to comprise a number n of LED light sources, where n is an integer different from the number N of sides of the central core element provides for a light emitting device which additionally also allows for a much larger degree of freedom in design as regards the position and particularly number of the LED light sources being possible. Also, such a light emitting device is, when n < N, cheaper and simpler in construction as one may use fewer LED light sources.

Finally it is noted that, providing the central core element with sides having an equal length, i.e. providing the central core element with the cross sectional shape of a regular polygon with N sides, has the advantage of the central core element being provided with a particularly simple shape, which in turn provides for a light emitting device being particularly simple and cost effective to produce.

As LED light sources have a certain size, the associated wiring, e.g. copper wiring, on a printed circuit board should advantageously have certain clearance to the edge of the printed circuit board. In case of folded flexible printed circuit board, which is an advantageous embodiment of a central core element according to the invention, it should be avoided that the solder joints joining the respective LED light sources and the wiring are too near to the folding deformation zone - i.e. the edges between adjoining sides of the central core element - to avoid the risk of unreliable solder joints due to deformation thereof.

To reduce or altogether avoid this risk, one or more of the LED light sources of the plurality of LED light sources are in an embodiment shifted in position such that each LED light source of the plurality of LED light sources is arranged in a predefined minimum distance from a point of intersection between two sides of the central core element.

When one or several LED light sources of the plurality of LED light sources are also tilted in such a way that for each of the several LED light sources of the plurality of LED light sources its central axis is oriented in the direction of that of said n radial lines extending through that of the n points in which the respective LED light source is arranged, a particularly homogeneous illuminance may be obtained.

The predefined minimum distance between the position of a LED and a point of intersection between two sides of the central core element may be any one of at least half the diameter or width of the solder point connecting the LED light source to the central core element, at least equal to the diameter or width of the solder point connecting the LED light source to the central core element, at least 1 mm or at least 2 mm.

In an embodiment the at least one LED light source of the plurality of LED light sources is furthermore tilted to a point at which its central axis is pointing at a point of intersection between that of said n radial lines extending through that of the n points in which the at least one LED light source of the plurality of LED light sources is arranged and a circle, said circle enveloping the central core element, having its center on the longitudinal axis of the central core element and lying in the same plane as the n radial lines.

Thereby a light emitting device having an even more homogenous illuminance for all numbers of LED light sources being different from the number of sides of the central core element, while only necessitating an even thinner coating or even no coating at all is provided for.

In an embodiment several LED light sources of the plurality of LED light sources are tilted in such a way that for each of the several LED light sources of the plurality of LED light sources its central axis is oriented in the direction of that of said n radial lines extending through that of the n points in which the respective LED light source is arranged.

In an embodiment several LED light sources of the plurality of LED light sources are furthermore tilted to a point at which for each of the several LED light sources of the plurality of LED light sources its central axis is pointing at a point of intersection between that of said n radial lines extending through that of the n respective points in which the respective LED light source is arranged and a circle, said circle enveloping the central core element, having its center on the longitudinal axis of the central core element and lying in the same plane as the n radial lines.

Either of these two embodiments provides for a light emitting device having a particularly homogenous illuminance for all numbers of LED light sources being different from the number of sides of the central core element, while making it possible to omit the provision of a coating altogether.

In a further embodiment one or several LED light sources of the plurality of LED light sources are tilted beyond the point where for each of the several LED light sources of the plurality of LED light sources its central axis is pointing at a point of intersection between that of said n radial lines extending through that of the n respective points in which the respective LED light source is arranged and a circle, said circle enveloping the central core element, having its center on the central axis of the central core element and lying in the same plane as the n radial lines. Thereby a light emitting device having an even more homogenous illuminance may be obtained.

In an embodiment the number n of LED light sources is any one of 5, 6, 7, 9 and an integer larger than 9.

In an embodiment the number N of sides of the central core element is any one of 6, 7 and 8.

In an embodiment the central core element is a prismatic element. Thereby a further optimization of the homogenous illuminance as well as the direct illumination variance is obtained.

In an embodiment at least one LED light source of the plurality of LED light sources are tilted in such a way that its central axis extends in an angle different from 90 degrees with the longitudinal axis of the central core element. Thereby, the pattern of the far field light distribution can be influenced, particularly to conform to Energy star requirements for the far field light distribution.

In an embodiment the light emitting device further comprises any one or more of a homogenous outer bulb, a scattering coating and a socket element.

The light emitting device according to the invention may be a light bulb, such as an incandescent light bulb or any other type of light bulb.

The invention thus furthermore concerns a light bulb comprising a light emitting device according to the invention. According to a second aspect of the invention the above and other objects are likewise achieved by means of a method for arranging a plurality of LED light sources on a central core element of a light emitting device, the method comprising the steps of:

providing a plurality of LED light sources,

providing a central core element being a cylindrical element comprising a circumferential surface, a longitudinal direction, a longitudinal axis extending in the longitudinal direction and a cross-section in a direction perpendicular to the longitudinal direction, the cross section being shaped like a polygon with N sides of equal length,

providing the plurality of LED light sources in a number n of LED light sources, where n is an integer different from N,

arranging the plurality of LED light sources on the sides of the central core element in n points defined as the intersection points between the circumferential surface of the central core element and n radial lines extending perpendicular to the longitudinal direction from the longitudinal axis to the circumferential surface of the central core element in such a way that each of the n lines has the same angle β with the two adjacent lines of the n lines, said angle β being 360°/n, and tilting at least one LED light source of the plurality of LED light sources in such a way that its central axis, said central axis being defined as the direction in which the at least one LED light source of the plurality of LED light sources exhibits the maximum light intensity, is oriented in the direction of that of said n radial lines extending through that of the n points in which the at least one LED light source of the plurality of LED light sources is arranged.

Further embodiments of a method according to the invention appear from the detailed description and the dependent method claims.

It is noted that the invention relates to all possible combinations of features recited in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiment(s) of the invention. Fig. 1 shows a schematic illustration of a first embodiment of a light emitting device according to the invention and comprising a central core element with a cross sectional shape of a polygon with N = 8 sides, i.e. an octagon, and a plurality of LED light sources. Fig. 2 shows a cross sectional view of a first embodiment of a central core element of a light emitting device according to Fig. 1 seen along the line X-X and illustrating the arrangement of seven LED light sources on the eight sides of the central core element.

Fig. 3 shows a graph illustrating the direct illumination variation on an outer bulb of a light emitting device according to the invention with a central core element as shown in Fig. 2.

Fig. 4 shows a cross sectional view of the central core element according to Fig. 2 seen along the line X-X in Fig. 1 where the seven LED light sources are furthermore shifted away from the corner points of the central core element.

Fig. 5 shows a graph illustrating the direct illumination variation on an outer bulb of a light emitting device according to the invention with a central core element as shown in Fig. 4.

Fig. 6 shows a cross sectional view of a first embodiment of a central core element of a light emitting device according to Fig. 4 seen along the line X-X in Fig. 1 where the LED light sources are tilted further.

Fig. 7 shows a graph illustrating the direct illumination variation on an outer bulb of a light emitting device according to the invention with a central core element as shown in Fig. 6.

Fig. 8 shows a cross sectional view of a first embodiment of a central core element of a light emitting device according to Fig. 6 seen along the line X-X in Fig. 1 where the LED light sources are tilted further still.

Fig. 9 shows a graph illustrating the direct illumination variation on an outer bulb of a light emitting device according to the invention with a central core element as shown in Fig. 8.

Fig. 10 shows a cross sectional view of a first embodiment of a central core element of a light emitting device according to Fig. 1 seen along the line X-X and illustrating the arrangement of six LED light sources on the eight sides of the central core element.

Fig. 11 shows a graph illustrating the direct illumination variation on an outer bulb of a light emitting device according to the invention with a central core element as shown in Fig. 10.

Fig. 12 shows a cross sectional view of a first embodiment of a central core element of a light emitting device according to Fig. 1 seen along the line X-X and illustrating the arrangement of five LED light sources on the eight sides of the central core element. Fig. 13 shows a graph illustrating the direct illumination variation on an outer bulb of a light emitting device according to the invention with a central core element as shown in Fig. 12.

Fig. 14 shows a cross sectional view of a first embodiment of a central core element of a light emitting device according to Fig. 1 seen along the line X-X and illustrating the arrangement of nine LED light sources on the eight sides of the central core element.

Fig. 15 shows a graph illustrating the direct illumination variation on an outer bulb of a light emitting device according to the invention with a central core element as shown in Fig. 14.

As illustrated in the figures, the sizes of layers and regions are exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures of

embodiments of the present invention. Like reference numerals refer to like elements throughout.

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.

Fig. 1 shows a light emitting device 10 according to the invention. The light emitting device 10 comprises a central core element 11 and a plurality of LED light sources 12. The central core element 11 is a cylindrical element comprising a circumferential surface 17, a longitudinal direction L, a longitudinal axis A extending in the longitudinal direction L and a cross-section in a direction perpendicular to the longitudinal direction.

Generally, the cross section is shaped like a regular polygon with N sides. In other words all N sides have the same length. In the embodiment shown, the cross section is shaped like a polygon with N = 8 sides, i.e. an octagon. In other embodiments the cross section may be shaped like a polygon with N = 6 or 7 sides, i.e. a hexagon or a heptagon. In yet other embodiments the cross section may be shaped like a polygon with N > 8 sides

The plurality of LED light sources 12 generally comprises a number n of LED light sources different from the number of sides N. The plurality of LED light sources 12 are arranged on the eight sides of the central core element in a way that will be described further below. It is noted that although all examples given herein is based on a central core element with N = 8 sides, the same principles for arranging the LED light sources on the central core element applies also for central core elements with another number of sides than 8, and in particular to central core elements with N = 6 or 7 sides.

In the embodiment shown, the light emitting device 10 further comprises a homogenous outer bulb 13 as well as a socket element 14 with electrical connectors 15, which are all optional. The homogenous outer bulb 13 may be a clear bulb or it may comprise a scattering coating which is also optional.

Hence, the light emitting device 10 is in the embodiment shown a light bulb, such as an incandescent light bulb. Other types of light bulbs are, however, also feasible.

Fig. 2 shows a cross sectional view of a first embodiment of a central core element 11 of the light emitting device according to Fig. 1. In this embodiment the central core element is provided with the cross sectional shape of a regular octagon. In other words all N = 8 sides 1, 2, 3, 4, 5, 6, 7, 8 have the same length. Furthermore a number n = 7 of LED light sources 12 are provided.

The seven LED light sources 12 are arranged on the sides of the circumferential surface 17 (cf. Fig. 1) of the central core element in n = 7 points being the respective intersection points 30, 31, 32, 33, 34, 35, 36 between the sides of the

circumferential surface 17 (cf. Fig. 1) of the central core element 11 and n = 7 radial lines 20, 21, 22, 23, 24, 25, 26 extending perpendicular to the longitudinal direction L from the longitudinal axis A to the circumferential surface 17 (cf. Fig. 1) of the central core element 11. The seven radial lines 20, 21, 22, 23, 24, 25, 26 are arranged in such a way that each of the seven radial lines (cf. by way of example the radial line 21) has the same angle β with the two adjacent lines (cf. by way of example the radial lines 20 and 22) of the seven radial lines, where the angle β is defined as 360°/n with n = 7.

Furthermore, the seven LED light sources 12 are tilted in such a way that each of the seven LED light sources has its central axis 16 oriented in the direction of that of the seven radial lines 20, 21, 22, 23, 24, 25, 26 extending through that of the seven intersection points 30, 31, 32, 33, 34, 35, 36 in which the respective LED light source is arranged. In this connection the central axis 16 of a LED light source is defined as the axis in the direction in which the LED light source exhibits the maximum light intensity when emitting light.

In practice, the tilting of the LED light sources according to all embodiments described herein may be obtained by using variable solder quantities on the LED solder pads attaching the respective LED light sources 12 to the central core element 11. Other ways of obtaining the tilting of the LED light sources may also be feasible.

The resulting variation in direct illumination is illustrated in Fig. 3 showing the relative illuminance as a function of the angle from which the light emitting device is observed by a viewer. As a result of the above described arrangement of the LED light sources, the variation in direct illumination has decreased to levels invisible to the human eye. In practice the resulting direct illumination variation may in this case be lowered to as little as about 0.057.

By way of comparison, in case the n = 7 LED light sources were rather arranged centrally on each side of the central core element, thus leaving one of the N = 8 sides without any LED light source, the resulting direct illumination variation would be as high as about 0.53. Thus a considerable reduction of the illumination variation is obtained.

Fig. 4 shows a cross sectional view of the same central core element 11 as shown in Fig. 2 but where at least some of the LED light sources 12, in the embodiment shown more particularly the two LED light sources 12 and 12' have been shifted away from the corner points where two sides of the central core element 11 meet such that they are in a predetermined minimum distance from the corner points.

The predetermined minimum distance from the corner points corresponds in one embodiment to at least half the diameter or width of the solder point connecting the LED light source to the central core element. The predetermined minimum distance from the corner points coresponds in another embodiment to at least the diameter or width of the solder point connecting the LED light source to the central core element. In specific embodiments the predetermined minimum distance from the corner points may be e.g. 1 mm or 2 mm.

It is noted that the number of LED light sources for which such a shift is necessary to ensure that all LED light sources 12 are in a predetermined minimum distance from the corner points may vary both with the length of the sides of the central corner element and with the number n of LED light sources.

The resulting variation in direct illumination is illustrated in Fig. 5 showing the relative illuminance as a function of the angle from which the light emitting device is observed by a viewer. Shifting the LED light sources as described above comes with a cost of the illumination homogeneity, as can be observed in the graphs shown in both of Fig. 5 and Fig. 7. Namely, in the present case, at viewing angles of about 340° an under-illumination may be observed due to the shift of the two LED light sources 12 and 12' that were otherwise too close to a corner point. In practice the resulting direct illumination variation may thereby be raised slightly as compared to that illustrated in Fig. 3 namely to about 0.11, which is, however, still way below the above-mentioned example of comparison.

Fig. 6 shows a cross sectional view of the same central core element 11 as shown in Figs. 2 and 4 but where the LED light sources have been tilted further as compared to those of Figs. 2 and 4. More particularly, the LED light sources 12 and 12' are tilted in such a way that their respective central axis 16 and 16' is pointing at a point of intersection 35 and 36, respectively, between that of the radial lines 25 and 26, respectively, extending through that of the respective points in which the respective LED light source 12 and 12' is arranged and a circle 40, where the circle 40 is enveloping the central core element, having its center on the longitudinal axis A of the central core element and lying in the same plane as the radial lines 25 and 26.

The resulting variation in direct illumination is illustrated in Fig. 7 showing the relative illuminance as a function of the angle from which the light emitting device is observed by a viewer. As can be seen, the dip in the illumination homogeneity at viewing angles of about 340° described above with reference to Fig. 4 is reduced by giving the shifted LED light sources an extra tilt as described above. In practice the resulting direct illumination variation may thereby be lowered to as little as about 0.080.

Fig. 8 shows a cross sectional view of the same central core element 11 as shown in Fig. 6 but where the LED light sources 12 and 12' have been tilted even further as compared to those of Fig. 6 in the same direction of tilt as for those of Fig. 6.

The resulting variation in direct illumination is illustrated in Fig. 9 showing the relative illuminance as a function of the angle from which the light emitting device is observed by a viewer. As can be seen, the dip in the illumination homogeneity at viewing angles of about 340° described above with reference to Fig. 4 is reduced even further by giving the shifted LED light sources the further tilt as described above. In practice the resulting direct illumination variation may thereby be lowered to as little as about 0.057.

As mentioned above, the same procedure used for arranging the n = 7 LED light sources on a central core element 11 with N = 8 sides may also be applied for the case of n = 6 LED light sources on a central core element 11 with N = 8 sides as well as for the case of n = 5 LED light sources on a central core element 11 with N = 8.

Fig. 10 thus illustrates a central core element 11 with N = 8 sides on which n = 6 LED light sources 12 are arranged in the same way as described above in connection with Fig. 2. That is, in this case there is n = 6 radial lines 20-25, n = 6 intersection points 30-35 and the angle β is 360°/n with n = 6. Furthermore, the n = 6 LED light sources 12 have been shifted as described above in connection with Fig. 4 as well as tilted further as described above in connection with Fig. 6, as the case and need may be.

The resulting variation in direct illumination is illustrated in Fig. 11 showing the relative illuminance as a function of the angle from which the light emitting device is observed by a viewer. In practice the resulting direct illumination variation may in this case be lowered to as little as about 0.063.

Fig. 12 illustrates a central core element 11 with N = 8 sides on which n = 5 LED light sources 12 are arranged in the same way as described above in connection with Fig. 2. That is, in this case there is n = 5 radial lines 20-24, n = 5 intersection points 30-34 and the angle β is 360°/n with n = 5. Furthermore, the n = 5 LED light sources 12 have been shifted as described above in connection with Fig. 4 as well as tilted further as described above in connection with Fig. 6, as the case and need may be.

The resulting variation in direct illumination is illustrated in Fig. 13 showing the relative illuminance as a function of the angle from which the light emitting device is observed by a viewer. In practice the resulting direct illumination variation is in this case somewhat higher than for the above described cases, but may nevertheless be lowered to as little as about 0.16.

As also mentioned above, the same procedure used for arranging the n = 7 LED light sources on a central core element 11 with N = 8 sides may even also be applied for the case of n = 9 LED light sources on a central core element 11 with N = 8 sides.

Fig. 14 thus illustrates a central core element 11 with N = 8 sides on which n = 9 LED light sources 12 are arranged in the same way as described above in connection with Fig. 2. That is, in this case there is n = 6 radial lines 20-28, n = 9 intersection points 30-38 and the angle β is 360°/n with n = 9. Furthermore, the n = 9 LED light sources 12 have been shifted as described above in connection with Fig. 4 as well as tilted further as described above in connection with Fig. 6, as the case and need may be.

The resulting variation in direct illumination is illustrated in Fig. 15 showing the relative illuminance as a function of the angle from which the light emitting device is observed by a viewer. In practice the resulting direct illumination variation may in this case be lowered to as little as about 0.053 and thus even smaller than for the case with n = 7 LED light sources.

Furthermore, and as also mentioned above, the same procedure for arranging the n = 7 LED light sources on a central core element 11 with N = 8 sides may even also be applied for the case of a central core element 11 with a number N of sides being different than 8, and in particular for N = 6 or 7, so long as the number n of light sources is different from the number N of sides of the central core element.

The arrangement of the n LED light sources 12 as described above, particularly in relation to Figs. 2 to 9, respectively, may also be described in terms of steps of a method according to the second aspect of the invention.

In this case, a method of arranging n = 7 LED light sources 12 on a central core element 11 of a light emitting device 10 as shown on Fig. 2 comprises, in addition to the steps recited in the introductory description, the following step:

Tilting each of the n = 7 LED light sources of the plurality of LED light sources 12 in such a way that for each of the n = 7 LED light sources of the plurality of LED light sources its central axis 16 is oriented in the direction of that of said n = 7 radial lines 20,

21, 22, 23, 24, 25, 26 extending through that of the n = 7 points 30, 31, 32, 33, 34, 35, 36 in which the respective LED light source is arranged.

A method of arranging n = 7 LED light sources 12 on a central core element

11 of a light emitting device 10 as shown on Fig. 4 further to the above comprises the following step:

Arranging each of the n = 7 LED light sources of the plurality of LED light sources in a predefined minimum distance from a corner point of the central core element, or in other words a point of intersection between two sides of the central core element.

This step may be carried out by shifting or sliding at least one of the LED light sources, particularly the LED light source(s) initially not satisfying the predefined minimum distance requirement, along the side of the central core element 11, or by otherwise moving at least one of the LED light sources to a position satisfying the predefined minimum distance requirement.

A method of arranging n = 7 LED light sources 12 on a central core element 11 of a light emitting device 10 as shown on Fig. 6 further to the above comprises the following step:

Tilting each of the n = 7 LED light sources of the plurality of LED light sources 12 further to or even beyond a point at which for each of the n = 7 LED light sources of the plurality of LED light sources 12 its central axis 16 is pointing at a point of intersection between that of the n = 7 radial lines 20, 21, 22, 23, 24, 25, 26 extending through that of the n = 7 respective points 30, 31, 32, 33, 34, 35, 36 in which the respective LED light source is arranged and a circle 40, the circle 40 enveloping the central core element, having its center on the longitudinal axis A of the central core element 11 and lying in the same plane as the n = 7 radial lines 20, 21, 22, 23, 24, 25, 26.

A method of arranging n = 7 LED light sources 12 on a central core element 11 of a light emitting device 10 as shown on Fig. 8 further to the above comprises the following step:

Tilting each of the n = 7 LED light sources of the plurality of LED light sources 12 even further in the same direction of tilt as employed to obtain that for each of the n = 7 LED light sources of the plurality of LED light sources 12 its central axis 16 is pointing at a point of intersection between that of the n = 7 radial lines 20, 21, 22, 23, 24, 25, 26 extending through that of the n = 7 respective points 30, 31, 32, 33, 34, 35, 36 in which the respective LED light source is arranged and a circle 40.

It is noted that the above-described method may also be employed for cases in which the number n of LED light sources is any one of 5, 6, 7, 9 and an integer larger than 9, so long as the number n of LED light sources and the number N of sides of the central core element differ from one another.

It is furthermore noted that the above-described method may also be employed for cases in which the number N of sides of the central core element is any one of 6, 7 and 8, so long as the number n of LED light sources and the number N of sides of the central core element differ from one another.

In any of the above described embodiments one or more of the plurality of

LED light sources 12 may also be tilted vertically, i.e. be tilted in such a way that its central axis 16 extends in an angle different from 90 degrees with the longitudinal axis A of the central core element 1 1. This may be obtained by providing the central core element with a so-called pencil design; i.e. with at least a top section of the central core element 11 having a tapering configuration obtained by providing the sides of at least the top section tapering inwards. A vertical tilt may also be obtained by simply tilting the LED light source with respect to the surface of the central core element 11. The effect and advantage of such a vertical tilt is described below.

For instance, for a current 60 W light bulb design no vertical tilting of the LED light sources results in a far field light distribution that is not conforming to the Energy star requirements. This even holds in case of the outer bulb 13 being a diffuse outer bulb. However, when the LED light sources are given a vertical tilt as described above, a current 60 W light bulb design, whether having a clear outer bulb or a diffuse outer bulb, with a far field light distribution satisfying the Energy star requirements is obtained. 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 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. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.

Claims

CLAIMS:

1. A light emitting device (10) comprising a central core element (11) and a plurality of LED light sources (12),

the central core element (11) being a cylindrical element comprising a circumferential surface (17), a longitudinal direction (L), a longitudinal axis (A) extending in the longitudinal direction and a cross-section in a direction perpendicular to the longitudinal direction, the cross section being shaped like a polygon with N sides (1, 2, 3, 4, 5, 6, 7, 8) of equal length, wherein

the plurality of LED light sources (12) comprises a number n of LED light sources, where n is an integer different from N,

the plurality of LED light sources (12) are arranged on the sides of the central core element in n points (30, 31, 32, 33, 34, 35, 36) defined as the intersection points between the circumferential surface of the central core element and n radial lines (20, 21, 22, 23, 24, 25, 26) extending perpendicular to the longitudinal direction from the longitudinal axis to the circumferential surface of the central core element in such a way that each of the n lines has the same angle β with the two adjacent lines of the n radial lines, said angle β being 360°/n, and

at least one LED light source of the plurality of LED light sources (12) is tilted in such a way that its central axis (16), said central axis being defined as the direction in which the at least one LED light source of the plurality of LED light sources exhibits the maximum light intensity, is oriented in the direction of that of said n radial lines extending through that of the n points in which the at least one LED light source of the plurality of LED light sources is arranged.

2. A light emitting device according to any claim 1, wherein one or more of the LED light sources of the plurality of LED light sources are shifted in position away from a point of intersection where two sides of the central core element meet such that each LED light source of the plurality of LED light sources is arranged in a predefined minimum distance from said point of intersection between two sides of the central core element.

3. A light emitting device according to claim 2, wherein said predefined minimum distance is any one of at least half the diameter or width of the solder point connecting the LED light source to the central core element, at least equal to the diameter or width of the solder point connecting the LED light source to the central core element, at least 1 mm and at least 2 mm.

4. A light emitting device according to claim 2 or 3, wherein the at least one LED light source of the plurality of LED light sources (12) furthermore is tilted to or beyond a point at which its central axis (16) is pointing at a point of intersection between that of said n radial lines extending through that of the n points in which the at least one LED light source of the plurality of LED light sources is arranged and a circle, said circle enveloping the central core element, having its center on the longitudinal axis of the central core element and lying in the same plane as the n radial lines.

5. A light emitting device according to any one of the above claims, wherein several LED light sources of the plurality of LED light sources (12) are tilted in such a way that for each of the several LED light sources of the plurality of LED light sources its central axis is oriented in the direction of that of said n radial lines extending through that of the n points in which the respective LED light source is arranged, and/or

wherein several LED light sources of the plurality of LED light sources (12) furthermore are tilted or beyond a point at which for each of the several LED light sources of the plurality of LED light sources its central axis is pointing at a point of intersection between that of said n radial lines extending through that of the n respective points in which the respective LED light source is arranged and a circle, said circle enveloping the central core element, having its center on the longitudinal axis of the central core element and lying in the same plane as the n radial lines.

6. A light emitting device according to any one of the above claims, wherein the number n of LED light sources is any one of 5, 6, 7, 9 and an integer larger than 9.

7. A light emitting device according to any one of the above claims, wherein the number N of sides of the central core element is any one of 6, 7 and 8.

8. A light emitting device according to any one of the above claims, wherein at least one LED light source of the plurality of LED light sources (12) are tilted in such a way that its central axis (16) extends in an angle different from 90 degrees with the longitudinal axis (A) of the central core element (11).

9. A light bulb comprising a light emitting device (10) according to any one of the above claims.

10. A method for arranging a plurality of LED light sources (12) on a central core element (11) of a light emitting device (10), the method comprising the steps of:

providing a plurality of LED light sources (12),

providing a central core element (11) being a cylindrical element comprising a circumferential surface (17), a longitudinal direction (L), a longitudinal axis (A) extending in the longitudinal direction and a cross-section in a direction perpendicular to the longitudinal direction, the cross section being shaped like a polygon with N sides (1, 2, 3, 4, 5, 6, 7, 8) of equal length,

providing the plurality of LED light sources (12) in a number n of LED light sources, where n is an integer different from N,

arranging the plurality of LED light sources (12) on the sides of the central core element in n points (30, 31, 32, 33, 34, 35, 36) defined as the intersection points between the circumferential surface of the central core element and n radial lines (20, 21, 22, 23, 24, 25, 26) extending perpendicular to the longitudinal direction from the longitudinal axis to the circumferential surface of the central core element in such a way that each of the n lines has the same angle β with the two adjacent lines of the n lines, said angle β being 360°/n, and tilting at least one LED light source of the plurality of LED light sources (12) in such a way that its central axis (16), said central axis being defined as the direction in which the at least one LED light source of the plurality of LED light sources exhibits the maximum light intensity, is oriented in the direction of that of said n radial lines extending through that of the n points in which the at least one LED light source of the plurality of LED light sources is arranged.

11. A method according to claim 10, and further comprising the step of shifting one or more of the LED light sources of the plurality of LED light sources in position away from a point of intersection where two sides of the central core element meet such as to thereby arrange each LED light source of the plurality of LED light sources in a predefined minimum distance from said point of intersection between two sides of the central core element.

12. A method according to claim 11, and further comprising the step of furthermore tilting the at least one LED light source of the plurality of LED light sources (12) or beyond a point at which its central axis is pointing at a point of intersection between that of said n radial lines extending through that of the n points in which the at least one LED light source of the plurality of LED light sources is arranged and a circle, said circle enveloping the central core element, having its center on the longitudinal axis of the central core element and lying in the same plane as the n radial lines.

13. A method according to any one of claims 10-12, and further comprising the step of tilting several LED light sources of the plurality of LED light sources (12) in such a way that for each of the several LED light sources of the plurality of LED light sources its central axis is oriented in the direction of that of said n radial lines extending through that of the n points in which the respective LED light source is arranged, and/or

the step of furthermore tilting several LED light sources of the plurality of LED light sources (12) or beyond a point at which for each of the several LED light sources of the plurality of LED light sources its central axis is pointing at a point of intersection between that of said n radial lines extending through that of the n respective points in which the respective LED light source is arranged and a circle, said circle enveloping the central core element, having its center on the longitudinal axis of the central core element and lying in the same plane as the n radial lines.

14. A method according to any one of claims 10-13, and further comprising the step of tilting at least one LED light source of the plurality of LED light sources (12) in such a way that its central axis (16) extends in an angle different from 90 degrees with the longitudinal axis (A) of the central core element (11).

15. A method according to any one of claims 10-14, wherein the number n of LED light sources is any one of 5, 6, 7, 9 and an integer larger than 9, and/or

wherein the number N of sides of the central core element is any one of 6, 7 and 8.