Patent Description:
Incandescent lamps are rapidly being replaced by solid state light sources e.g. light emitting diodes (LED) based lighting solutions. It is nevertheless appreciated and desired by users to have retrofit lamps which have the look of an incandescent bulb. For this purpose, one can simply make use of the infrastructure for producing incandescent lamps based on glass and replace the conventional filament with a "LED filament", i.e. a linear array of LEDs arranged on a carrier. One or several such LED filaments may be arranged in a retrofit lamp, i.e. in a light bulb which has the appearance and interface of a conventional incandescent light bulb. Such a retrofit LED bulb will thus include a standard socket (e.g. E27), a light transmissive (e.g. glass) envelope, and one or several LED filaments arranged in the envelope. Such retrofit light bulbs have become increasingly popular for their practical and decorative lighting capacity.

Most commercially available LED retrofit lamps include LED filaments that provide white light with a single color temperature. Such LED filaments typically include one type of LEDs (e.g. blue or UV LEDs) covered by a luminescent coating (e.g. a polymer layer comprising a phosphor). Recently, however, LED filaments have been proposed which are controllable between a warm white (WW) and a cool white (CW) light. Such temperature control may be accomplished with using a first LED filament emitting WW light and a second LED filament emitting CW light and individually controlling the intensity of the individual LED filament. Alternatively, an array of alternating blue and red LEDs (R-B-R-B-R-B) covered by a luminescent coating. By varying the relative intensity of the red and blue LEDs, the resulting white light will have a different color temperature. Alternatively, as shown in <CIT>, two arrays of identical LEDs may be provided with different types of phosphors. Again, the color temperature may be controlled by controlling the relative intensity of the LEDs in the two arrays.

However, current color tunable LED filaments have several drawbacks and/or limitations. They are limited in color and/or color temperature control performance such as a limited color gamut space and/or color temperature range; and/or they provide an unpleasant appearance in the on-state of the lighting device such as a spottiness/dark appearance e.g. when one LED array is dimmed or off (which may have the appearance of a mall functioning filament); and/or they provide an insufficient spatial light distribution e.g. no omnidirectional (white) light; and/or they provide a poor light quality e.g. do not emit flame / extreme warm white light and/or they do not emit white light having a high color rendering index; and/or they do not have the possibility to switch to saturated colored light (e.g. color controllable).

<CIT> discloses a filament type light emitting diode (LED) light source which includes a plurality of LED modules, a coupler, and a common connection portion. The LED modules are in a polygonal prism structure and emit white light having different color temperatures or light of different wavelengths. Each LED module having a bar shape at a respective side surface of the polygonal prism structure and includes a first connection electrode and a second connection electrode. The coupler couples the LED modules to maintain the polygonal prism structure. The common connection portion is at one end of the polygonal prism structure and is commonly connected to the second connection electrode of each of the LED modules.

<CIT> discloses a lamp which includes an optically transmissive enclosure for emitting an emitted light and a base connected to the enclosure. At least one first LED filament and at least one second LED filament are located in the enclosure and are operable to emit light when energized through an electrical path from the base. The first LED filament emits light having a first correlated color temperature (CCT) and the second LED filament emits light having a second CCT that are combined to generate the emitted light. A controller operates to change the CCT of the emitted light when the lamp is dimmed.

It is therefore an object of the present invention to provide an improved or alternative LED filament or LED filament which overcomes or at least alleviate at least one of the above-discussed problems of the prior art.

This and other objects are achieved by providing a LED filament having the features in the independent claim.

Hence, according to the present invention, there is provided a LED filament. The LED filament provides LED filament light. The LED filament comprises a first linear array of LEDs, a second linear array of LEDs, and a carrier. The first linear array of LEDs is arranged on a first surface of the carrier including only first LEDs configured to emit first white light. The second linear array of LEDs is arranged on a second surface of the carrier, opposite to said first surface, including only second LEDs configured to emit color controllable light. The LED filament light comprises the first white light and the color controllable light.

The present invention is advantageous in that the LED filament is able to provide (extreme) (warm) white light and/or the colored light e.g. saturated colors, off-blackbody-line (BBL) light and/or a high light quality (high color rendering index CRI). The LED filament may provide sequentially (extreme) (warm) white light and the colored light.

The present invention is further advantageous in that the LED filament provides a pleasant appearance in the on-state.

One or more of the above-mentioned effects are achieved because first LEDs (white LEDs) which emit first white light are arranged on the first surface of the carrier and the second LEDs (colored LEDs) which emit color controllable light are arranged on the second surface of the carrier. The spottiness appearance e.g. when one LED array is dimmed or off (which may have the appearance of a mall functioning filament) is not present as both arrays are arranged on a different surface/side (vs. e.g. an -R-G-B-WW- or -R-G-B-WW-CW- architecture on the same side).

A LED filament (lamp), for example, disclosed in <CIT> is unable to provide white light and/or the colored light. The reason is that no colored LEDs are used. Furthermore, (in case of adding colored LEDs) the light emitted from such a LED filament provides a spottiness appearance. For example, in case the LED filament disclosed in <CIT> is providing (extreme) warm white light, certain (white) LEDs are not lit and thus provides a spottiness appearance. In case of using a first LED filament providing WW light and a second LED filament providing CW light, in a WW light setting the second LED filament is off (i.e. no light) and having the appearance of a malfunctioning LED filament.

According to an embodiment of the present invention, the first LEDs comprise UV LEDs which emit UV light and/or blue LEDs which emit blue light. The UV LEDs and/or blue LEDs are covered by a first encapsulant which comprises a luminescent material which is configured to at least partly (or fully) convert the UV light and/or the blue light into converted light. The white light comprises (i) the converted light and optionally (ii) the (non-converted) UV light and/or the (non-converted) blue light. Such an architecture is low cost in terms of materials and/or assembly, and provides high quality light (e.g. with respect colored LEDs (RGB LEDs). The reason is that such LEDs are low cost, only a single type (or two types) of LEDs are needed, a light of a phosphor is broader than light of a direct emitting (colored) LED.

According to an embodiment of the present invention, the first encapsulant is provided as a continuous layer over the first LEDs and at least part of the first surface of the carrier. The obtained effect is a more homogenous light emission. The reason is that light is also generated at regions between LEDs.

According to an embodiment of the present invention, the second linear array of LEDs comprises a plurality of M groups, each group comprises a red LED, a green LED and a blue LED. Optionally, LEDs of another color may be added e.g. an amber LED.

The first LEDs comprise UV LEDs emitting UV light and/or blue LEDs emitting blue light, the UV LEDs and/or blue LEDs being covered by a first encapsulant comprising a luminescent material configured to at least partly convert the UV light and/or the blue light into converted light, wherein the white light comprises (i) the converted light and optionally (ii) the non-converted UV light and/or the non-converted blue light; and the second linear array of LEDs comprises a plurality of M groups, each group comprising a red LED, a green LED and a blue LED. The obtained effect that the LED filament is able to provide (extreme) (warm) white light and/or the colored light e.g. saturated colors, off-blackbody-line (BBL) light and/or a high light quality (high color rendering index CRI). The LED filament may provide sequentially (extreme) (warm) white light and the colored light.

According to an embodiment of the present invention, the plurality of M groups is at least <NUM> and the first linear array of LEDs comprises at least <NUM> first LEDs. More preferably M is at least <NUM>, and most preferably M is at least <NUM>.

According to an embodiment of the present invention, the second LEDs are covered by a second encapsulant which comprises a light scattering material which is configured to scatter the color controllable light. The second encapsulant may be provided as a continuous layer over the second LEDs and at least part of the second surface of the carrier. The second encapsulant is free from a luminescent material. The obtained effect is an improved spatial and spectral light distribution. The reason is that the color controllable light is mixed by the light scattering material.

According to an embodiment of the present invention, the carrier is translucent. The carrier may be diffuse, but is preferably transparent. The obtained effect is improved spatial and spectral light distribution. The reason is that first white light and the color controllable light is emitted to both directions, namely the white light emitted by the first LEDs is also transmitted through the carrier and the color controllable light is also transmitted through the carrier.

According to an embodiment of the present invention, the first LEDs are arranged at equidistance in the first linear array and have a first pitch. The second LEDs are arranged at equidistance in the second linear array and have a second pitch. The first pitch is different from the second pitch. The obtained is better thermal management. The reason is that less first LEDs and second LEDs are aligned with respect to each other.

According to an embodiment of the present invention, the first LEDs and the second LEDs are interleaved. The obtained is better thermal management. The reason is that no first LEDs are aligned with respect to the second LEDs.

According to an embodiment of the present invention, the first LEDs and the second LEDs are aligned. The obtained effect is improved spatial and spectral light distribution. The reason is that a larger area of a transparent carrier may allow light transmission from the first side of the carrier to the second side of the carrier.

According to an embodiment of the present invention, the length and width of the LEDs is preferably smaller that the distance between neighboring LEDs. For example, the LEDs may have a length (and a width) of <NUM>, while the distance between neighboring LEDs is <NUM> or <NUM>. The obtained effect is improved spatial and spectral light distribution. The reason is that a larger area of a transparent carrier may allow light transmission from the first side of the carrier to the second side of the carrier.

According to an embodiment of the present invention, the pitch between the RGB LEDs in a cluster is smaller than the pitch between neighboring LEDs of two clusters. The obtained effect is improved color mixing.

According to an embodiment of the present invention, the first white light has a color temperature in the range from <NUM> to <NUM>, more preferably <NUM> to <NUM>, most preferably <NUM> and <NUM>. Such a color temperature seems preferred by the customer for LED filament lamps. The color rendering index (CRI) is preferably at least <NUM>, more preferably at least <NUM>, most preferably at least <NUM>.

According to an embodiment of the present invention, the first linear array of LEDs and the second linear array of LEDs are both arranged on a same single planar surface. The single planar surface is subsequently folded such that the first linear array of LEDs is arranged on the first surface of a carrier and the second linear array of LEDs is arranged on the second surface of a carrier opposite to said first surface. The folding line may be arranged parallel to the length of the LED filament or perpendicular to the length of the LED filament (between the first LEDs and the second LEDs).

According to an embodiment of the present invention, the first linear array of LEDs and the second linear array of LEDs are arranged on a different carrier. The carriers are subsequently attached e.g. glued together typically with the surfaces which does not comprise any LEDs.

The present invention discloses a LED filament lamp in accordance with claim <NUM>.

According to an embodiment of the present invention, the LED filament lamp further comprises a controller for controlling the LEDs in first linear array of LEDs, and for controlling the LEDs in the second linear array of LEDs.

According to an embodiment of the present invention, the LED filament lamp further comprises at least one LED filament and a controller configured to individually control the power supplied to the red LEDs, the green LEDs and the blue LEDs of the second linear array of LEDs.

According to an embodiment of the present invention, the LED filament lamp comprises at least one LED filament and a controller configured to individually control the power supplied to the first linear array of LEDs, and the blue LEDs, the green LEDs and the red LEDs of the second linear array of LEDs.

According to an embodiment of the present invention, the LED filament lamp comprises at least one LED filament, a light transmissive envelope at least partly surrounding said LED filament, and a connector for electrically and mechanically connecting said LED filament lamp to a socket e.g. of a luminaire. The light transmissive envelope is preferably transparent. The LED filament lamp may comprise a driver and/or a controller. The driver may be arranged to convert an AC current to a DC current. The driver may (also) be arranged to adapt the current level. The controller may be arranged to individually control the first linear array of LEDs and the second linear array of LEDs.

According to an embodiment of the present invention, the LED filament lamp comprises a plurality of N LED filaments. N is preferably in the range from <NUM> to <NUM>, more preferably <NUM> to <NUM>, most preferably <NUM> to <NUM>. The plurality of LED filaments may be arranged at a distance different form zero from the longitudinal axis of the LED filament lamp. The plurality of LED filaments may be each a at a similar distance from the longitudinal axis. Each LED filament (the first LEDs and second LEDs) may be oriented in different directions. For example, in case of <NUM> LED filaments the directions are at angles γ <NUM>, <NUM> and <NUM> degrees; in case of <NUM> LED filaments the directions are at angles γ <NUM>, <NUM>, <NUM> and <NUM> degrees; in case of <NUM> LED filaments the directions are at angles γ <NUM>, <NUM>, <NUM>, <NUM> and <NUM> degrees; in case of <NUM> LED filaments the directions are at angles γ <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> degrees. The angle γ is defined with respect to an axis perpendicular to the longitudinal axis.

According to an embodiment of the present invention, the second surfaces of each LED filament are arranged in a direction facing the inner side of the light transmissive envelope. Alternatively the first surfaces of each LED filament are arranged in a direction facing the inner side of the light transmissive envelope. In this way the spatial-spectral light distribution is improved i.e. is more homogeneous.

According to an embodiment, (i) the second surfaces of each LED filament are arranged in a direction facing the inner side of the light transmissive envelope, or (ii) the first surfaces of each LED filament are arranged in a direction facing the inner side of the light transmissive envelope. With inner side is meant to the central portion (e.g. longitudinal axis) of the light transmissive envelope.

In an example, a luminaire comprises a reflector and the LED filament lamp according to the invention, wherein the LED filament lamp is at least partly arranged inside the reflector. The obtained effect is a decorative luminaire which provides an improved attractive and appealing light effect. The reason is that the LED filament are visible but part of the LED filament light is redirected by the reflector to a certain direction e.g. a table or floor.

The present invention discloses a method for controlling a LED filament in accordance with claim <NUM>.

According to an embodiment of the present invention, the method for controlling a LED filament comprises powering the first linear array of LEDs, and simultaneously and independently controlling a color (point) and/or color temperature of the color controllable light emitted by the second linear array of LEDs.

According to an embodiment of the present invention, the second linear array of LEDs are controlled to emit color controllable light which is second white light. The second white light may have a color temperature in the range from <NUM> to <NUM>. The second white light has a spectral distribution different from the spectral distribution of the first white light. The second white light may be generated by combining the light of the red LEDs, green LEDs and blue LEDs.

According to an embodiment of the present invention, the second linear array of LEDs are controlled to emit second white light having a same color temperature as first white light (emitted by the first linear array of LEDs and/or luminescent material). The obtained effect is a LED filament with advantages described above and having a homogeneous appearance. The reason is that the same color temperature is emitted from both (opposite) sides (surfaces) of the carrier. Preferably the color temperature is in the range from <NUM> to <NUM>, more preferably <NUM> to <NUM>, most preferably <NUM> - <NUM>. The difference in color temperature is preferably less than <NUM>, more preferably less than <NUM>, most preferably less than <NUM>. Abovementioned scenario may occur for a certain duration e.g. at least <NUM> minute or at least <NUM> minutes.

According to an embodiment of the present invention, the LED filament may be arranged in a (3D) spiral or helix configuration. The obtained effect is improved spatial and spectral light distribution. The reason is that the first white light and the color controllable light. Even if the first white light and the color controllable light provide the same color temperature, a (3D) spiral or helix configuration has the advantage of improved spatial and spectral light distribution. The reason is that although the first white light and the color controllable light provide the same color temperature, they differ in spectral distribution.

According to an embodiment of the present invention, the first linear array of LEDs are controlled to emit first white light with a relatively warm color temperature, and the second linear array of LEDs (<NUM>) are controlled to emit second white light with a relatively cool color temperature. The obtained effect is improved decorative effect. The reason is that different color temperature is emitted from different sides (surfaces) of the carrier. The first surface emits relatively warm white light (preferably extreme warm white light) (i.e. a color temperature in the range from <NUM> to <NUM>) while the second surface emits relative cool light (preferably light for good visibility i.e. light having a color temperature in the range from <NUM> to <NUM>). The difference in color is preferably at least <NUM>, more preferably at least <NUM>, most preferably at least <NUM>.

According to an embodiment of the present invention, the color controllable light is not with <NUM> SDCM from the black body locus. In this embodiment, the color controllable light is typically used for making saturated colors which may be added to the first white light.

Further objectives of, features of, and advantages with, the present invention will become apparent when studying the following detailed disclosure, the drawings and the appended claims. Those skilled in the art will realize that different features of the present invention can be combined to create embodiments other than those described in the following.

The schematic drawings are not necessarily on scale.

The same features having the same function in different figures are referred to the same references.

<FIG> show schematic drawings of a LED filament <NUM> according to an embodiment of the present invention. As depicted in <FIG>, the LED filament <NUM> provides LED filament light <NUM>'. The LED filament <NUM> comprises a first linear array of LEDs <NUM> and a second linear array of LEDs <NUM>. The first linear array of LEDs <NUM> are arranged on a first surface <NUM> of a carrier <NUM> including only first LEDs <NUM> which are configured to emit first white light <NUM>. The second linear array of LEDs <NUM> arranged on a second surface <NUM> of the carrier <NUM>, opposite to said first surface <NUM>, including only second LEDs <NUM> configured to emit color controllable light <NUM>. The LED filament light <NUM>' comprises the first white light <NUM> and/or the color controllable light <NUM>. In this example, the first surface <NUM> of a carrier <NUM> does not comprise any LEDs which emit color controllable light <NUM> and second surface <NUM> of the carrier <NUM> does not comprise any LEDs which provides white light <NUM>.

As depicted in <FIG>, the first LEDs <NUM> comprise UV LEDs <NUM> which emit UV light <NUM> and/or blue LEDs <NUM> emitting blue light <NUM>. The UV LEDs <NUM> and/or blue LEDs <NUM> being covered by a first encapsulant <NUM> comprising a luminescent material <NUM> configured to at least partly convert the UV light <NUM> and/or the blue light <NUM> into converted light <NUM>. The white light <NUM> comprises (i) the converted light <NUM> and optionally (ii) the non-converted UV light <NUM> and/or the non-converted blue light <NUM>.

As depicted in <FIG>, the first encapsulant <NUM> is provided as a continuous layer <NUM> over the first LEDs <NUM> and at least part of the first surface <NUM> of the carrier <NUM>.

As depicted in <FIG>, the second linear array of LEDs <NUM> comprises a plurality of M groups <NUM>, each group <NUM> comprises a red LED 119a, a green LED 119b and a blue LED 119c.

As depicted in <FIG>, M is at least <NUM> and the first linear array of LEDs <NUM> comprises at least <NUM> first LEDs <NUM>.

As depicted in <FIG>, the second LEDs <NUM> are covered by a second encapsulant <NUM> comprising a light scattering material <NUM> configured to scatter <NUM> the color controllable light <NUM> (see also <FIG>, which is introduced here below). The second encapsulant <NUM> is provided as a continuous layer <NUM> over the second LEDs <NUM> and at least part of the second surface <NUM> of the carrier <NUM>. The second encapsulant <NUM> is free from a luminescent material <NUM>.

As depicted in <FIG>, the carrier <NUM> is translucent <NUM>.

As depicted in <FIG>, the first LEDs <NUM> are arranged at equidistance in the first linear array <NUM> and have a first pitch P1. The second LEDs <NUM> are arranged at equidistance in the second linear array <NUM> and have a second pitch P2. The first pitch P1 is different from the second pitch P2. In this example, P1>P2. The pitch between the RGB LEDs in a cluster may be smaller than the pitch between neighboring LEDs of two different clusters (i.e. between neighboring clusters). The obtained effect is improved color mixing.

As depicted in <FIG>, the first white light <NUM> may have a color temperature in the range from <NUM> to <NUM>.

<FIG> show schematic drawings of a LED filament <NUM> according to an embodiment of the present invention. As depicted in <FIG>, the first linear array of LEDs <NUM> and the second linear array of LEDs <NUM> are both arranged on a same single planar surface <NUM> which is folded (or bended) such that the first linear array of LEDs <NUM> is arranged on the first surface <NUM> of a carrier <NUM>, and the second linear array of LEDs <NUM> is arranged on the second surface <NUM> of a carrier <NUM> opposite to said first surface <NUM>.

<FIG> shows a schematic drawing of a side-view of a LED filament lamp <NUM> according to an embodiment of the present invention. As depicted in <FIG>, The LED filament lamp <NUM> comprises a light transmissive envelope <NUM> and a connector <NUM>. The light transmissive envelope <NUM> at least partly surrounds said LED filament <NUM>. The connector <NUM> is arranged for electrically and mechanically connecting said LED filament lamp <NUM> to a socket <NUM>. The LED filament lamp <NUM> may also comprise a controller <NUM> and/or a driver <NUM>' and/or an antenna <NUM>".

<FIG> shows a schematic drawing of a top view of a LED filament lamp <NUM> according to an embodiment of the present invention. As depicted in <FIG>, the second surfaces <NUM> of each LED filament <NUM> are arranged in a direction facing the inner side of the light transmissive envelope <NUM>. Alternatively the first surfaces <NUM> of each LED filament <NUM> are arranged in a direction facing the inner side of the light transmissive envelope <NUM>. In this way the spatial-spectral light distribution is improved i.e. is more homogeneous.

As depicted in <FIG>, a method for controlling a LED filament <NUM> is shown. The method comprises powering the first linear array of LEDs <NUM>, and simultaneously and independently controlling a color and/or color temperature of the color controllable light <NUM> emitted by the second linear array of LEDs <NUM>. The second linear array of LEDs <NUM> may be controlled to emit color controllable light <NUM> which is second white light <NUM>. In a first example, the second linear array of LEDs <NUM> are controlled to emit second white light <NUM> which has a same color temperature as first white light <NUM>. The difference in color is preferably less than <NUM>, more preferably less than <NUM>, most preferably less than <NUM>. In a second example, the first white light <NUM> has a relatively warm color temperature, and the second linear array of LEDs <NUM> are controlled to emit second white light <NUM> with a relatively cool color temperature. The difference in color temperature is preferably at least <NUM>, more preferably at least <NUM>, most preferably at least <NUM>.

A LED filament is typically providing LED filament light and comprises a plurality of light emitting diodes (LEDs) arranged in a linear array. Preferably, the LED filament has a length L and a width W, wherein L>5W. The LED filament may be arranged in a straight configuration or in a non-straight configuration such as for example a curved configuration, a 2D/3D spiral or a helix. Preferably, the LEDs are arranged on an elongated carrier like for instance a substrate, that may be rigid (made from e.g. a polymer, glass, quartz, metal or sapphire) or flexible (e.g. made of a polymer or metal e.g. a film or foil).

Claim 1:
A light emitting diode, LED, filament (<NUM>) for providing LED filament light (<NUM>'), comprising:
- a first linear array of LEDs (<NUM>) arranged on a first surface (<NUM>) of a carrier (<NUM>) including only first LEDs (<NUM>) configured to emit first white light (<NUM>).
- a second linear array of LEDs (<NUM>) arranged on a second surface (<NUM>) of the carrier (<NUM>), opposite to said first surface (<NUM>), including only second LEDs (<NUM>) configured to emit color controllable light (<NUM>),
characterized in that:
- the LED filament light (<NUM>') comprises the first white light (<NUM>) and the color controllable light (<NUM>)
- the first LEDs (<NUM>) comprise UV LEDs (<NUM>) emitting UV light (<NUM>) and/or blue LEDs (<NUM>) emitting blue light (<NUM>), the UV LEDs (<NUM>) and/or blue LEDs (<NUM>) being covered by a first encapsulant (<NUM>) comprising a luminescent material (<NUM>) configured to at least partly convert the UV light (<NUM>) and/or the blue light (<NUM>) into converted light (<NUM>), wherein the white light (<NUM>) comprises (i) the converted light (<NUM>) and optionally (ii) the non-converted UV light (<NUM>) and/or the non-converted blue light (<NUM>), and
- the second linear array of LEDs (<NUM>) comprises a plurality of M groups (<NUM>), each group (<NUM>) comprising a red LED (119a), a green LED (119b) and a blue LED (119c).