Patent Description:
Traditional incandescent light bulbs are available in various designs such as plain functional bulbs with different glass finishes (e.g. transparent, diffuse or colored) and decorative bulbs with complex filaments, wherein the filament itself serves a decorative purpose. However, due to demands on power saving in lighting devices, driven by eco awareness and legislation, traditional incandescent light bulbs are being replaced by more power efficient light sources such as fluorescent lamps and LED (light emitting diode) lamps. Such conventional eco-friendly lamps do not provide the same various designs as traditional incandescent light bulbs.

A solution of how to provide a lighting device resembling a carbon filament lamp is disclosed in <CIT>. The document shows a lighting device comprising a solid state light source optically coupled to an optical fiber having an out-coupling surface. A drawback with such a lighting device is that it does not provide a sufficiently energy-efficient functional lighting (such as e.g. general lighting or task lighting).

Thus, there is a need for providing alternatives and/or new devices that would overcome, or at least alleviate or mitigate, at least some of the above mentioned drawbacks. It is with respect to the above considerations that the present invention has been made. An object of the present invention is to provide an improved alternative to the above mentioned technique and prior art.

More specifically, it is an object of the present invention to provide a lighting device enabling both decorative lighting and functional lighting with improved efficiency. It is also an object of the present invention to provide a method of manufacturing such a lighting device.

These and other objects of the present invention are achieved by means of a lighting device having the features defined in the independent claim.

Preferable embodiments of the invention are characterized by the dependent claims.

Hence, according to a first aspect of the present invention, a lighting device is provided. The lighting device comprises a first light emitting element being optically coupled to a light guide having an out-coupling surface for illumination via the light guide. Further, the lighting device comprises a second light emitting element dedicated for direct illumination from the lighting device.

The basic idea of the invention is that the light emitted from the first light emitting element is emitted out of the lighting device via the light guide and the light emitted from the second light emitting element is emitted out of the lighting device directly from the second light emitting element. As a result, decorative lighting is provided by the light guide and the first light emitting element, and a direct illumination (suitable for functional lighting) is provided by the second light emitting element.

In this respect, with the term "direct illumination" it is meant that most of, or at least a considerable part of the light emitted from the second light emitting element is emitted from the lighting device without passing a light guide. The inventor has realized that the lighting device according to prior art suffers from energy-losses when the light emitted from the solid state light source is coupled into the optical fiber and then out again. Hence, the lighting device according to prior art may be improved with respect to functional lighting (such as e.g. general lighting or task lighting). Functional lighting may be defined as a type of lighting wherein it is desirable to output from the lighting device as much of the light emitted from the solid state light source as possible.

The present invention is advantageous in that the lighting device provides both a decorative appearance (look) and functional illumination, and is still energy-efficient since the light emitted from the second light emitting element is directly emitted from the second light emitting element without unnecessary energy-loss.

Further, the present invention is advantageous in that a double functionality (decorative lighting and functional lighting) is provided within a single lighting device, enabling an extended field of use since the lighting device may be used both in a decorative purpose and e.g. for general lighting or task lighting.

According to an embodiment of the present invention, the illumination from the lighting device via the light guide and the first light emitting element may be dedicated to a first type of lighting. Further, illumination from the lighting device from the second light emitting element without any light guide may be dedicated to a second type of lighting. Accordingly, the first type of lighting and the second type of lighting are functionally and structurally separated such that each type of lighting can be optimized in terms of energy-efficiency.

According to an embodiment of the present invention, the first light emitting element may be dedicated to decorative lighting (via the light guide, i.e. the first type of lighting as defined in the preceding embodiment) and the second light emitting element may be dedicated to functional lighting (without any light guide, i.e. the second type of lighting as defined in the preceding embodiment).

According to an embodiment, the light intensity of the second light emitting element may be adjustable relative to the light intensity of the first light emitting element. Preferably the light intensity of the second light emitting element may be adjustable relative to the light intensity of the first light emitting element in response to an input signal to the lighting device. The input signal may be received at the lighting device from a dimmer connected to the lighting device (wherein the actual receiver of the dim signal is on the mains voltage). Alternatively, the input signal may be received at e.g. a low voltage circuitry of the lighting device (further described below) via a remote control (operated by a user of the lighting device). Preferably, a transfer function may be used such that the input voltage is correlated to a specific relationship or ratio between the intensity of the first light emitting element and the intensity of the second light emitting element. The present embodiment is advantageous in that it provides at least two different operation modes of the lighting device, a decorative mode for which the light intensity of the second light emitting element is lower than the light intensity of the first light emitting element and a functional mode for which the light intensity of the second light emitting element is higher than the light intensity of the first light emitting element. In other words, the light guide will become more visible and stand for a greater part of the total light-output from the lighting device when the light intensity of the second light emitting element is lowered in the decorative mode compared to when the lighting device is in the functional mode. In the functional mode, the light intensity of the second light emitting element will dominate the total light-output from the lighting device.

In an embodiment, at least one of the second light emitting element and the first light emitting element may be dimmable, which is advantageous in that it provides a step-less transition between the two above-mentioned operation modes of the lighting device. Moreover, the first light emitting element and the second light emitting element may be simultaneously and/or separately (individually) dimmed. For example, when the light intensity of the first light emitting element is increased, simultaneously, also the light intensity of the second light emitting element may be increased. Such a kind of regulation may be implemented using a single dimming device common to all light emitting elements (making the lighting device relatively technically simple). Hence, when both the first light emitting element and the second light emitting element are operated at a low dimmed level (i.e. at a low light intensity) the total light-output from the lighting device is low, thereby rendering visible the light guide which may provide a decorative appearance. In contrast, when the light emitting elements are driven at a high power level (i.e. at a high light intensity) the total light-output from the lighting device is high, thereby providing a functional lighting. It will be appreciated that such a kind of regulation with a common dimmer resembles the function of a traditional incandescent lighting device.

According to another example, wherein the light emitting elements are individually dimmed, the light intensity of the first light emitting element is increased while the light intensity of the second light emitting element is decreased. The above-mentioned effects (for resemblance to the function of a traditional incandescent lighting device) may be achieved and even enhanced, when the first light emitting element and the second light emitting element have different light intensities.

According to an embodiment, a wavelength (color) of the light emitted from the first light emitting element is adjustable, preferably in response to an input signal to the lighting device. For example, the color of the first light emitting element may be adjusted to be red/amber in the decorative mode and yellow/white in the functional mode.

In an embodiment, the input signal to the lighting device may be a current or a voltage supplied to the lighting device. Further, lighting device may comprise a circuitry with a transfer function correlating the input signal with a light-output and/or the light color of the first and second light emitting element. As an illustrating example, for a low input signal (such as in a dimmed traditional incandescent lamp), the first light emitting element may provide a red/amber color and have a relatively low light intensity, while the light intensity of the second light emitting element may preferably be turned off. The stronger the input signal is, the more the first light emitting element may become yellow/white (and the more the light output from the first light emitting element is increased) and, at some threshold value of the input signal, the second light emitting element switches on and light-output is slowly increased.

According to the present invention, the light guide comprises a light guide plate, which may be designed in any desired way. For example, the light guide may be designed in any three-dimensional shape.

According to the present invention, the light guide is provided with diffusing means for out-coupling light. The diffusing means enhances the out-coupling of the light guided into the light guide and thus, renders the light guide more clearly visible. In an embodiment of the invention, the structure of the out-coupling surface (e.g. the roughness of the surface) may be selected to adjust the scattering of the light. Further, the light guide may comprise (scattering or diffusing) particles and/or vacuum/gas bubbles for out-coupling light. In other words, distortions of the optical characteristics of the light guide are provided for scattering out some of the light. These distortions may be located on the surface/edge of the light guide and/or inside of the light guide. Generally, any optical distortion resulting in a change of the internal light angles may result in that part of the light is coupled out of the light guide. Distortions in a 3D-shaped light guide may for example be obtained by local laser heating.

According to the present invention, at least one of the first light emitting element and the second light emitting element may comprise at least one light emitting diode (LED), which is advantageous in that LEDs are high-efficient point-like light sources available in several different colors, thereby allowing various designs of the lighting device. Further, the LED may be a laser-LED, which is advantageous in that it improves the coupling of light to the light guide.

According to an embodiment of the present invention, the lighting device may further comprise an envelope encapsulating the first light emitting element, the second light emitting element and the light guide, which is advantageous in that the light emitting elements and the light guide will be protected against damage and dust. Additionally, the lighting device will resemble a traditional incandescent light bulb.

According to an embodiment of the present invention, the lighting device may further comprise a base at which the first light emitting element and the second light emitting element are arranged.

Optionally, the lighting device may further comprise a diffusing/scattering element arranged on top of the second light emitting element e.g. in the form of a plate covering the second light emitting element(s). Such a diffusing/scattering element is advantageous in that an individual light emitting element will be less visible and provide a more even light distribution than without a diffusing/scattering element.

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 realize that different features of the present invention can be combined to create embodiments other than those described in the following.

The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and nonlimiting detailed description of preferred embodiments of the present invention, with reference to the appended drawings, in which:.

With reference to <FIG>, there is shown a lighting device in accordance with an embodiment.

<FIG> shows a lighting device <NUM> comprising a first light emitting element <NUM> and a second light emitting element <NUM>. The first light emitting element <NUM> is optically coupled to a light guide <NUM> having an out-coupling surface <NUM>. The optical coupling can be provided e.g. via an optical element (not shown) arranged between the first light emitting element <NUM> and the light guide <NUM> or by linking the first light emitting element <NUM> directly to the light guide <NUM>, as shown in <FIG>.

Optionally, the lighting device may be provided with additional first light emitting elements being optically coupled to the light guide <NUM>. For example, one first light emitting element may be coupled to a first end of the light guide <NUM> and another first light emitting element may be coupled to another end of the light guide <NUM> (opposite to the first end).

Further, the lighting device may be provided with additional second light emitting elements <NUM> for providing functional lighting.

The first light emitting element <NUM> and/or the second light emitting element <NUM> may for instance be light emitting diodes, LEDs, such as e.g. laser LEDs. For example, an amber colored LED, providing a warm light, may be used as the first light emitting element <NUM>, thereby resulting in a light guide resembling a warm glowing filament (when the first light emitting element is activated/on). An alternative is to provide e.g. phosphor (or any other wavelength converting material) on top of the light guide (i.e. at the out-coupling surface of the lightguide) and select a phosphor providing a warm colored light. According to another example, the first light emitting element <NUM> may comprise a red LED, a green LED and a blue LED, thereby together providing a white light, which may be modulated into different colors by controlling the red, green and blue LED.

Further, an LED of a colder color (which may be more efficient), such as white, may be used as the second light emitting element <NUM>, thereby providing light being suitable for functional lighting. According to another example, the second light emitting element <NUM> may comprise a red LED, a green LED and a blue LED, thereby together providing a white light, which may be modulated into different colors by controlling the red, green and blue LED. However, it will be appreciated that the invention is not limited to such color configuration, the light emitting elements <NUM>, <NUM> in the lighting device may be of any desired color.

The light guide <NUM> may comprise an optical fiber (like an optical wave guide) made of a suitable material such as plastics or glass-fiber. The use glass-fiber material is advantageous because of its optical quality and material characteristics (e.g. sensitivity to heat). The optical fiber may be of a shorter or longer length allowing a simple or more complex design. For example, the optical fiber may be spirally wound in order to resemble a traditional retro-filament.

The out-coupling of light from the out-coupling surface <NUM> of the light guide <NUM> may be achieved (and/or enhanced) in different ways. Some of the light may be out-coupled due to curvatures of the light guide <NUM>. Moreover, the light guide <NUM> may be provided with diffusing means for out-coupling the light. In general, any optical distortion added to the light guide will provide out-coupling of light. The diffusing means may be provided e.g. by making the out-coupling surface <NUM> rough (e.g. by sand-blasting, scratching, or molding in a texture in the surface), or by providing indents or small protrusions in the out-coupling surface <NUM>. Further, particles (e.g. white paint) and/or vacuum/gas bubbles (e.g. created by local laser heating) may be provided on or inside the light guide such that light is scattered out of the light guide.

According to an embodiment, the light guide <NUM> may comprise at least one connecting port <NUM> to which the first light emitting element <NUM> may be optically coupled. The present embodiment is advantageous in that it allows a great part of the light emitted from the first light emitting element <NUM> to be received and out-coupled by the light guide <NUM>, thereby serving a decorative purpose, and still a great part of the light emitted from the second light emitting element <NUM> provides an illumination without unnecessary considerable energy-losses in any light guide.

However, some (i.e. a relatively small part) of the light emitted from the second light emitting element(s) <NUM> may be coupled into the light guide <NUM> via the out-coupling surface <NUM>, and thus, coupled out again via the out-coupling surface <NUM>, thereby contributing to the illumination out of the light guide <NUM>.

With reference to <FIG>, there is shown a design of a light guide according to an embodiment of the invention. <FIG> shows a light guide in the form of a light guide plate <NUM> being optically coupled to a first light emitting element <NUM>. Some of the light emitted from the first light emitting element <NUM> is coupled out via an edge <NUM> which may be curved (and optionally rough), thereby resulting in the appearance of a filament such as in a traditional light bulbs. Further, light may be coupled out via diffusing means provided inside the light guide plate <NUM> or on the surface of the light guide plate <NUM>.

It will be appreciated that the light guide may be designed in any desired three-dimensional shape, such as a spherical or prismatic shape. Further, the diffusing means may be provided at any desired position in or on the light guide. For example, the diffusing means may form a pattern (such as a filament-resembling pattern).

With reference to <FIG>, there is shown another design of a light guide according to yet another embodiment. <FIG> shows a light guide <NUM> in the form of a continuous optical element <NUM> in which a string of a plurality of LEDs <NUM> is arranged. The LEDs <NUM> may be mounted on a small flexible PCB (printed circuit board) <NUM> with the continuous optical element <NUM> on top of it (or encapsulating it).

Turning again back to <FIG>, further embodiments of the invention will be described. The lighting device <NUM> may further comprise an envelope <NUM> encapsulating the first light emitting element <NUM>, the second light emitting element <NUM> and the light guide110. Preferably, the envelope <NUM> is transparent (or at least semi-transparent) such that the light guide <NUM> is visible for providing a decorative effect. Further, the envelope <NUM> may be formed as a bulb resembling a traditional incandescent light bulb. The lighting device <NUM> may further comprise a base <NUM> at which the first light emitting element <NUM> and the second light emitting element <NUM> are arranged. The base <NUM> may comprise a bayonet base or a screw base <NUM> (e.g. of the type E14, E26 or E27), which is advantageous in that the lighting device can be fitted in conventional lamp fittings and used as a replacement for a traditional incandescent light bulb (retro-fitting). The base <NUM> may further comprise a heat-sink <NUM> for cooling the light emitting diodes <NUM>, <NUM>. Optionally, the light emitting elements <NUM>, <NUM> may be arranged such that an upper portion of the heat-sink <NUM> (or an upper portion of the base <NUM>) hides the light emitting elements <NUM>, <NUM> (as shown in <FIG>) for reducing the risk of direct view of them. Further, the inside of the upper portion of the heat-sink <NUM> may be reflective such that all (or at least almost all) light emitted from the light emitting elements <NUM>, <NUM> can be output from the lighting device.

The lighting device may further comprise a diffusing/scattering element (not shown) in form of a plate on top of the second light emitting elements <NUM>. For example, such plate may be arranged on top of the base <NUM>. The plate may be provided with a hole where light emitted from the first light emitting element <NUM> may go through to be coupled into the light guide <NUM>.

The lighting device <NUM> may further comprise electronic driving means <NUM> provided with a power supply for converting the mains voltage supply into an output signal suitable for driving the light emitting elements <NUM>, <NUM>. The electric driving means <NUM> may further comprise an electronic circuitry configured to control the light intensity of the first light emitting element <NUM> and/or the second light emitting element <NUM> such that the light intensity of the second light emitting element <NUM> is adjustable relative to the light intensity of the first light emitting element <NUM>. Further, the electronic circuitry may be configured to slightly modulate the brightness (or color) of the first light emitting element <NUM>, or to sequentially switch on and off the first light emitting element <NUM>, for providing a flame and flickering effect of the light guide <NUM>. The electronic circuitry may further contain a transfer function for correlating an input signal (such as input current or input voltage) with a light output and/or an emission color of the first and second light emitting elements. The electric driving means <NUM> may be controlled by a remote control unit, by buttons on the base <NUM> or by any other type of user interface.

In an embodiment of the invention, the first light emitting element <NUM> and/or the second light emitting element <NUM> may be dimmable. In an embodiment of the invention, the lighting device supports traditional incandescent light dimmers such that the light emitting elements can operate in a dimmed mode.

With reference to <FIG>, a method of manufacturing a lighting device according to an embodiment of the present invention will be described. <FIG> shows the general outline of a method <NUM> of manufacturing a lighting device. The method comprises a step <NUM> of providing a first light emitting element, a step <NUM> of providing a light guide having an out-coupling surface, and a step <NUM> of optically coupling the first light emitting element to the light guide. Further, the method <NUM> comprises a step <NUM> of providing a second light emitting element dedicated for direct illumination from the lighting device.

While specific embodiments have been described, the skilled person will understand that various modifications and alterations are conceivable within the scope as defined in the appended claims.

Claim 1:
A lighting device for providing decorative lighting comprising:
a first light emitting element (<NUM>) comprising at least one light emitting diode and being optically coupled to a light guide (<NUM>) having an out-coupling surface (<NUM>) for decorative illumination via the light guide;
a second light emitting element (<NUM>) comprising at least one light emitting diode and dedicated for direct illumination suitable for functional lighting from the lighting device;
the light guide comprising a light guide plate (<NUM>) and being designed in a three-dimensional shape, wherein the light guide comprises an edge (<NUM>) which is curved, and
diffusing means provided in or on the light guide and arranged to form a filament resembling pattern.