Patent Description:
A trend in lighting is LED filament lamps. An LED filament lamp is an LED lamp which is designed to resemble a traditional incandescent light bulb with a visible filament for aesthetic and light distribution purposes, but with the high efficiency of light-emitting diodes. The LED filament may be arranged in a straight configuration or in a coil configuration. An example of the latter is disclosed in <CIT>.

It is an object of the present invention to improve the performance and/or appearance of LED filament lamps.

According to a first aspect of the invention, this and other objects are achieved by an LED filament for providing LED filament light, comprising: an elongated carrier; and a plurality of light emitting diodes arranged on the elongated carrier, wherein the LED filament is arranged in a coiled-coil configuration, and wherein the coiled-coiled configuration comprises a primary coil having a primary diameter D1, which primary coil is coiled into a secondary coil having a secondary diameter D2. Especially, the coiled-coil configuration comprises a primary coil having a primary diameter D<NUM>, which primary coil is coiled into a secondary coil having a secondary diameter D<NUM>, wherein the primary coil comprises a plurality of primary loops and the secondary coil comprises a plurality of secondary loops.

The present LED filament may be referred to as a coiled-coil (or coiled coil) LED filament or coil-in-coil LED filament. A coil is defined as a structure consisting of something wound in a continuous series of loops i.e. comprising a plurality of loops. Hence, a coiled-coil comprises a continuous series of coiled loops.

The coiled-coil configuration of the present LED filament has several advantages. For example, it creates a thicker LED filament while using a thin LED filament. Thicker LED filaments are desired because more light is emitted from the LED filament having a certain length or larger dimensions allow to reduce the intensity/brightness (measured at the surface of the LED filament) preventing/reducing glare. Furthermore, the coiled-coil configuration of the LED filament improved thermal management compared to a thick LED filament providing the same amount of light, because better fluid (such as a gas, e.g. air) flow around the LED filament. Furthermore, the coiled-coil configuration of the LED filament results in an improved decorative appearance.

It can be noted that coiled coil filaments for incandescent light bulb are known, but not coiled-coil LED filaments.

The primary diameter D<NUM> may be in the range from <NUM> to <NUM>. If D<NUM> is < <NUM>, the packing of the LED filament becomes too dense to adequately handle heat dissipation. If D<NUM> > <NUM>, the compactness of the coiled-coil configuration, having the benefit of a high light output in a relatively small space, becomes too small.

The secondary diameter D<NUM> may be in the range from 4D<NUM> to 12D<NUM>. The secondary diameter D<NUM> may be uniform over the length of the LED filament. Alternatively, the secondary diameter D<NUM> may vary over the length of the LED filament. The secondary diameter D<NUM> may for example be small(er) at the ends of the LED filament and be large(r) at the longitudinal centre of the LED filament.

The primary coil may comprise N<NUM> primary loops (or smaller loops, i.e. smaller than the secondary loops) and the secondary coil may comprise N<NUM> secondary loops (or larger loops, i.e. larger than the primary loops), wherein N<NUM>≥5N<NUM>, preferably N<NUM>≥8N<NUM>, more preferably N<NUM>≥10N<NUM>, and most preferably N<NUM>≥12N<NUM>. N<NUM> is preferably ≥<NUM>, more preferably N<NUM>≥<NUM>, and most preferably N<NUM>≥<NUM>. Furthermore, N<NUM> is preferably ≤<NUM>, more preferably N<NUM>≤<NUM>, and most preferably N<NUM>≤<NUM>. The secondary coil may have a secondary pitch P<NUM> in the range from 2D<NUM> to 10D<NUM>.

The plurality of light emitting diodes may comprises blue and/or UV light emitting diodes. The plurality of light emitting diodes may be covered by an elongated encapsulant. The elongated encapsulant may comprise luminescent material configured to at least partly convert LED light emitted by the blue and/or UV light emitting diodes into converted light. The elongated encapsulant may be flexible. The elongated encapsulant may be a polymer material, such as for example a silicone. The luminescent material may for example be a (yellow and/or red) phosphor.

The plurality of light emitting diodes may comprise a first set of first light emitting diodes and a second set of second light emitting diodes, wherein the first set is individually controllable (by a controller) in relation to the second set. The sets may be arranged for emitting LED light e.g. of different colors or spectrums. In this way, the coil-coiled LED filament may be tunable, for example with respect to color and/or color temperature.

The LED filament may further comprise a ductile element arranged along at least a major (><NUM>%, e.g. ><NUM>%) portion of the length of the elongated carrier for allowing the LED filament to be shaped. "Ductile" means capable of being shaped and is dimensionally stable i.e. when deformed from a first shape into a second shape it remains in the second shape. The ductile element may for example be a (thin) metal wire or strip e.g. made of aluminium or copper. The thickness of the ductile element is preferably in the range of <NUM>-<NUM>. The ductile element can be arranged at a non-light blocking location; the ductile element can for example be arranged on a second major surface of the elongated carrier, whereas the plurality of light emitting diodes are arranged on an opposite first major surface of the elongated carrier. The ductile element can be light reflecting, so that at least part of the LED filament light may be reflected by the ductile element. The ductile element can be substantially non-light-absorbing (e.g. made of metal or having a reflective coating), so that it does not deteriorate the light output performance of the LED filament. The ductile element can be non-visible; the ductile element may for example be integrated in the elongated carrier or be covered by the aforementioned elongated encapsulant.

The ductile element may be configured to allow the LED filament to be shaped from a basic shape into a first coiled shape (corresponding to said primary coil) and/or a second coiled shape (corresponding to said secondary coil), wherein the first coiled shape and the second coiled shape are dimensionally stable. The basic shape will typically be flat/straight. "Dimensionally stable" may here mean here that the shapes will be maintained after the force(s) used to form them have been removed.

Instead of, or in addition to, using the ductile element, at least the shape of the primary coil may be fixed by using a glue or a thermoplastic polymer which can be deformed by heating the LED filament above the glass-transition temperature (Tg) and/or melting point (Tm) of said thermoplastic material and cooling it down to room temperature. For the latter technology, a polymer with a high Tg and/or Tm should be chosen, because when the LED filament is lit the temperature of the lit LED filament should be below the Tg and/or Tm, preferably at least a difference of <NUM>.

The primary coil may be formed around and mounted to a rod, wherein the rod has one or more of the following properties: (i) (highly) reflective to reflect at least part of the LED filament light; (ii) light diffusive to diffuse at least part of the LED filament light; (iii) light converting to convert at least part of the LED filament light; (iv) transmissive to act as a lightguide guiding at least part of the LED filament light; and (v) thermal conductive to act as a heatsink. In this way, the rod can facilitate manufacturing of the LED filament as well as beneficially affect the optical and/or thermal performance of the LED filament. The rod is preferably shapable.

The present coiled-coil LED filament will typically be arranged in a (substantially) straight configuration. Alternatively, the LED filament may be arranged in a triple coiled coil configuration, for even higher compact light output and/or to simulate an appearance of a glowing 3D filled sphere light emitting body (alike the sun).

According to a second aspect of the invention, there is provided a(n LED) lamp or a luminaire comprising at least one (coiled-coil) LED filament according to the first aspect arranged behind a light exit window. The lamp may further comprise: an envelope at least partly forming said light exit window and at least partly enclosing the at least one coiled-coil LED filament; and a cap for electrically and mechanically connecting the lamp to a socket. The lamp may for example be a 'giant' bulb (dimension ≥<NUM>). The luminaire may be mountable in, on, or from a ceiling, for example.

The at least one coiled-coil LED filament may be a plurality of coiled-coil LED filaments. The plurality of coiled-coil LED filaments may for example comprises at least two coiled-coil LED filaments entangled.

According to a third aspect of the invention, there is provided method of manufacturing an LED filament, comprising: providing a flexible carrier, wherein a plurality of light emitting diodes are arranged on the flexible carrier; coiling the provided flexible carrier around a rod to provide an LED filament having a primary coil with a primary diameter D<NUM>; and coiling the LED filament having the primary coil into a secondary coil having a secondary diameter D<NUM> to provide an LED filament having a coiled-coil configuration. This aspect may exhibit the same or similar features and technical effects as the first aspect, and vice versa.

These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiments of the invention.

As illustrated in the figures, the sizes of layers and regions may be exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures of embodiments of the present invention.

<FIG> illustrates an LED filament <NUM> for providing LED filament light <NUM> according to an embodiment of the present invention.

The LED filament <NUM> comprises an elongated flexile carrier <NUM>, and plurality of LEDs (light emitting diodes) <NUM> arranged on the elongated carrier, see also <FIG>. In <FIG>, only some of the LEDs <NUM> are illustrated for brevity.

According to the present invention, the LED filament <NUM> is arranged in a coiled-coil configuration, as shown for example in <FIG>. Specifically, the coiled-coil configuration comprises a primary coil <NUM> having a primary (outer) diameter D<NUM>, see also <FIG>. Furthermore, the primary coil <NUM> is coiled into a secondary coil <NUM> having a secondary diameter D<NUM>. The secondary coil <NUM> comprises N<NUM> secondary loops. In <FIG>, N<NUM> is <NUM>. The coiled-coil LED filament <NUM> will typically be arranged in a straight configuration, as also shown in <FIG>.

Turning to <FIG>, the LED filament <NUM> may be manufactured as follows. At S1, the elongated flexile carrier <NUM> is provided, wherein the plurality of LEDs <NUM> are arranged on the flexible carrier <NUM>, see also <FIG>. The LEDs <NUM> may be arranged in at least one linear array. Preferably, the elongated flexile carrier <NUM> has a length L' and a width W, wherein L'>20W, preferably L'>40W, more preferably L'>60W, and most preferably L'>80W. The width W of the carrier <NUM> of the LED filament <NUM> may be in a range from <NUM> to <NUM>. The LEDs <NUM> may be (evenly) distributed throughout the complete length' L of the carrier <NUM>. The carrier <NUM> may comprises a first major surface 22a and an opposite second major surface 22b, and the LEDs <NUM> may be arranged on at least one of these surfaces. In <FIG>, the LEDs <NUM> are arranged on the first major surface 22a. The flexible carrier <NUM> may for example be made of a polymer or metal, e.g. a film or foil. The carrier <NUM> may be a flexible PCB (printed circuit board).

The LEDs <NUM> may for example be blue and/or UV LEDs, although other LEDs could be used instead, such as RGB LEDs. Furthermore, the LEDs <NUM> and the first major surface 22a may be covered by an elongated flexible encapsulant <NUM>. The encapsulant <NUM> may for example be a silicone material. The encapsulant <NUM> may comprise luminescent material configured to at least partly convert LED light <NUM> emitted by the blue and/or UV LEDs <NUM> into converted light <NUM>. The LED light <NUM> and the converted light <NUM> may form the LED filament light <NUM>. The luminescent material may for example be a phosphor, such as an inorganic phosphor and/or quantum dots or rods.

Furthermore, the LEDs <NUM> may comprise a first set of first LEDs and a second set of second LEDs, wherein the first set is individually controllable by a controller (not shown) in relation to the second set. In this way, the LED filament <NUM> may be tunable, for example with respect to color and/or color temperature.

The carrier <NUM> may be provided with a ductile (shapable) element <NUM>. The ductile element <NUM> allows the LED filament <NUM> to be shaped and also maintain the new shape. The ductile element <NUM> may be arranged along at least a major portion of the length L' of the carrier <NUM>, preferably along (substantially) the complete length L' of the carrier <NUM>. The ductile element <NUM> can for example be arranged on the second major surface 22b of the carrier <NUM>, as shown in <FIG>. In this way, the ductile element <NUM> will not block LED light emitted by the LEDs <NUM> arranged on the opposite first major surface 22a. Alternatively, the ductile element <NUM> could be integrated in the carrier <NUM>, i.e. provided inside the carrier <NUM>. In this way, apart from not blocking LED light emitted by the LEDs <NUM>, the ductile element <NUM> may also be invisible for a user/viewer. In another alternative, the ductile element <NUM> could be covered by the encapsulant <NUM> to become non-visible. The ductile element <NUM> may for example be a thin* metal wire or strip e.g. made of aluminium or copper. As such, the (metal) ductile element <NUM> may be light reflecting and/or substantially non-light-absorbing. *The thickness of the ductile element <NUM> is preferably in the range of <NUM>-<NUM>.

In step S1, the unfinished LED filament <NUM>' has a basic shape, typically flat/straight, as shown in <FIG>.

At S2, the unfinished LED filament <NUM>' including the carrier <NUM> is coiled, preferably around a rod <NUM>, to provide unfinished LED filament <NUM>" having a primary coil <NUM> with primary diameter D<NUM>. In case the LEDs <NUM> are arranged only on the first major surface 22a, the carrier <NUM> may be coiled such that the first major surface 22a with the LEDs <NUM> is on the outside of the primary coil <NUM>. An advantage of this is improved LED filament light <NUM>, because the light is emitted in a direction away from the LED filament <NUM> and is thus less absorbed. Furthermore, such configuration is more reliable because it is less likely that electrical connections are broken. The primary coil <NUM> may also be mounted to the rod <NUM>. In step S2, the ductile element <NUM> allows the LED filament <NUM>' to be shaped from the basic shape (<FIG>) into a first coiled shape corresponding to said primary coil <NUM>, which first coiled shape is dimensionally stable.

The rod <NUM> may be at least one of: (i) reflective, (ii) light diffusive, (iii) light converting, (iv) transmissive, (v) thermally conductive, and (vi) shapable. The rod <NUM> may be (i) highly reflective, wherein preferably the reflectance R is > <NUM>%. Regarding (ii), the rod <NUM> may have a reflectance R > <NUM>%. Regarding (iii), the rod <NUM> may be configured to convert at least <NUM>% of the LED filament light. Regarding (iv), the rod <NUM> is preferably ><NUM>% transmissive, more preferably transparent. Regarding (v), the rod preferably has a thermal conductivity ><NUM> W/mK, more preferably ><NUM> W/mK, and most preferably><NUM> W/mK.

The rod <NUM> may be included in the final/finished LED filament <NUM> and as such be arranged in the LED filament lamp <NUM> or a luminaire, but could alternatively be removed after step S2 and hence not be included in the final/finished LED filament <NUM>.

The primary diameter D<NUM> may be in the range from <NUM> to <NUM>. Furthermore, the primary coil <NUM> may comprise N<NUM> primary loops. N<NUM> may be ≥5N<NUM>, preferably N<NUM>≥8N<NUM>, more preferably N<NUM>≥10N<NUM>, and most preferably N<NUM>≥12N<NUM>. So for N<NUM> = <NUM> as in <FIG>, the primary coil <NUM> could comprise more than <NUM> primary loops.

At S3, the unfinished LED filament <NUM>" (with or without rod <NUM>) is coiled into a secondary coil <NUM> having secondary diameter D<NUM> to provide the (final/finished) LED filament <NUM> having a coiled-coil configuration. In other words, the coil shaped LED filament <NUM>' obtained in step S2 is subsequently coiled e.g. in a spiral/helix shape to obtain the coiled-coil LED filament <NUM>. In step S3, the ductile element <NUM> allows the LED filament <NUM>'' to be shaped into a second coiled shape corresponding to said secondary coil <NUM>, wherein the second coiled shape is dimensionally stable.

The secondary diameter D<NUM> may be in the range from 4D<NUM> to 12D<NUM>. Hence, for D<NUM> = <NUM>, the secondary diameter D<NUM> may be as small as <NUM>. And for D<NUM> = <NUM>, the secondary diameter D<NUM> may be as large as <NUM>. The secondary diameter D<NUM> will typically be uniform over the length L of the LED filament <NUM>, as shown in <FIG>.

N<NUM> (i.e. the number of secondary loops of the secondary coil <NUM>) is preferably ≥<NUM>, more preferably N<NUM>≥<NUM>, and most preferably N<NUM>≥<NUM>. Furthermore, N<NUM> is preferably ≤<NUM>, more preferably N<NUM>≤<NUM>, and most preferably N<NUM>≤<NUM>.

Furthermore, the secondary pitch P<NUM> of the secondary coil <NUM> may be in the range from 2D<NUM> to 10D<NUM>. Hence, for D<NUM> = <NUM>, the secondary pitch P<NUM> may be as small as <NUM>. And for D<NUM> = <NUM>, the pitch P may be as large as <NUM>.

In embodiments, the primary pitch P<NUM> of the primary coil <NUM> (see <FIG>) may be much smaller than the secondary pitch P<NUM>. Preferably P<NUM> is at least <NUM> times P<NUM>, more preferably P<NUM> is at least <NUM> times P<NUM>, and most preferably P<NUM> is at least <NUM> times P<NUM>.

In embodiments, the primary pitch P<NUM> may be much smaller than the secondary pitch P<NUM> but not too long. Preferably P2 is at the most <NUM> times P<NUM>.

The length L of the LED filament <NUM> may be at least <NUM>, preferably at least <NUM>, more preferably at least <NUM>, most preferably at least <NUM>.

<FIG> illustrates an LED filament <NUM>‴ for providing LED filament light <NUM> according to another embodiment of the invention. The LED filament <NUM>‴ comprises an elongated carrier (<NUM>) and LEDs (<NUM>) arranged on the elongated carrier, wherein the LED filament <NUM>‴ is arranged in a triple coiled coil configuration. That is, the coiled-coil LED filament <NUM> may be coiled once more, into a tertiary coil. The tertiary coil may have a tertiary (outer) diameter D<NUM>. For this embodiment, the method of <FIG> could include an additional step (S4) of coiling to provide a tertiary coil.

<FIG> illustrates an LED lamp <NUM> comprising the coiled-coil LED filament <NUM>. The LED lamp <NUM> further comprises an envelope <NUM> enclosing the coiled-coil LED filament <NUM>, and a cap <NUM> for electrically and mechanically connecting the LED lamp <NUM> to an external socket (not shown). The LED lamp <NUM> may be a retrofit bulb. The LED lamp <NUM> may be a giant bulb, wherein the diameter or height or width of the envelope <NUM> is ≥<NUM>.

The envelope <NUM> forms a light exit window of the LED lamp <NUM>. The envelope <NUM> may for example be transparent. The envelope <NUM> here has a spherical or globe (G) shape, but other shapes are possible as well, such as general (A) or tubular (T).

The coiled-coil LED filament <NUM> is in <FIG> arranged in a straight and vertical configuration, but it could alternatively be arranged in a horizontal configuration (i.e. perpendicular to the longitudinal axis of the lamp <NUM>), for example. Furthermore, a second coiled-coil LED filament 10a could be entangled with the (first) LED filament <NUM>.

For example, the coiled-coil LED filament <NUM> could be included in a luminaire.

Claim 1:
An LED filament (<NUM>) for providing LED filament light (<NUM>), comprising:
an elongated carrier (<NUM>); and
a plurality of light emitting diodes (<NUM>) arranged on the elongated carrier,
wherein the LED filament is arranged in a coiled-coil configuration, and wherein the coiled-coil configuration comprises a primary coil (<NUM>) having a primary diameter D<NUM>, which primary coil is coiled into a secondary coil (<NUM>) having a secondary diameter D<NUM>.