Illumination device and luminaire comprising such an illumination device

FIELD OF THE INVENTION

The invention relates to an illumination device. The invention also relates to a lamp fitting comprising such an illumination device.

BACKGROUND OF THE INVENTION

In the field of lighting, in particular lighting for offices and homes or for the illumination of sales displays, in practice a number of known light sources are used, such as filament lamps, halogen lamps, low-pressure and high-pressure gas discharge lamps and of late also light-emitting diodes (LEDs). By means of such light sources and sometimes by mixing multiple individual sources it is possible to produce lamp systems of widely varying light colorations, light outputs and color renditions. In addition to the suitable choice of light coloration, light output and color rendition combined with high efficiency, variable-color lamp systems have recently been proposed, which allow a user, at least to some extent, to control in particular the light coloration of the lamp systems. To this end, Philips has developed a dynamic lighting system, also known as the Carpe Diem lighting system, comprising two TL5 lamps contained by a reflective luminaire. The Carpe Diem lighting system has the capacity to animate a space by changing the very character of light - the light can be adjusted in level and color temperature - providing a pleasing, natural lighting rhythm that will stimulate and inspire both home and office users. However, this solution in dynamic lighting reduces light output to about 50% compared to the light output of the individual TL5 lamps to realize a satisfying color-mix and color uniformity.

It is an object of the invention to provide an illumination device having an increased efficiency.

SUMMARY OF THE INVENTION

This object can be achieved by providing an illumination device according to the preamble, comprising: at least one first light source, said first light source comprising: an at least partially light-transmissive discharge vessel filled with an ionisable substance, and discharge means for maintaining a gas discharge in the discharge vessel during operation of

the first light source, light-guiding means surrounding the discharge vessel of the first light source at least partially, said light-guiding means being made of an optically substantially transparent material; and at least one second light source optically coupled with the light- guiding means such that light emitted by the at least one second light source is coupled into the light-guiding means during operation of the second light source, wherein at least one surface of the light-guiding means is provided with at least one optical emission structure for mixing light emitted by the at least one first light source and by the at least one second light source such that said mixed light is emitted by the illumination device. Reflection of light within the hybrid illumination device according to the invention is reduced significantly with respect to the reflections required within the known Carpe Diem lighting system, as a result of which the hybrid illumination device according to the invention is adapted to realize an increased overall mixed light output in a relatively efficient manner, which makes the improved illumination system relatively beneficially and versatilely. By varying the output of the first light source(s) and/or the second light source(s), a user can influence the overall light output and hence also the color temperature of the illumination device as such. Moreover, a relatively homogeneous mixing of light emitted by the first light source(s) and the second light source(s) can be achieved by means of the illumination device according to the invention. A further advantage of the illumination device according to the invention is that the illumination device does not require a particularly shaped luminaire, and may hence be constructed in a relatively simple manner. The illumination device will commonly be applied as lighting for offices and homes, for the illumination of sales displays, and/or for the illumination of public places both indoor and outdoor. The discharge means comprise multiple electrodes inside the discharge vessel for maintaining a gas discharge, or multiple external electrodes for maintaining a gas discharge, or a coil provided outside the discharge vessel with a winding of an electric conductor.

The light-guiding means or light conductor will commonly act as a waveguide for light emitted by the second light source(s) to guide this light in the direction of the discharge vessel of the first light source to enable efficient mixing of light emitted by both light sources. The light-guiding means may partially surround the discharge vessel to realize partial color-mixing, wherein commonly a part of the light emitted by the first light source will be mixed by light coupled into and subsequently out of the light-guiding means. It may be conceivable that a part of the discharge vessel not being covered by the light-guiding means is covered by a reflective layer to reflect this light towards the light-guiding means to improve the color-mixing efficiency. More preferably, the light-guiding means substantially

completely surrounds the discharge vessel to facilitate mixing of light of the different light sources. In a particular preferred embodiment, the light-guiding means comprises at least one (transparent) jacket surrounding the discharge vessel at least partially. In an alternative preferred embodiment the light-guiding means comprises multiple jackets oriented concentrically with respect to each other. In this orientation e.g. a first jacket may enclose a second jacket. Commonly, each jacket will be optically coupled to a separate (second) light source, which light sources may have mutually different characteristics. In this manner, different optical dynamic and/or static optical effects can be realized in a relatively efficient manner. Although the first light source may have an arbitrary shape, the first light source preferably comprises an elongated light source discharge vessel. Tubed light sources, like for example TL5 lamps, are well known and relatively cheap. Moreover, this kind of lamp is commonly well suitable to allow (close) covering of its discharge vessels by the light-guiding means. In a particular preferred embodiment the first light source is a low- pressure discharge lamp which will commonly not affect and deteriorate the light-guiding means and/or the second light source(s). An important advantage of a low-pressure discharge lamp is a relatively low operating temperature of the lamp. Customarily a tubular low- pressure mercury- vapor discharge lamp, for example one or more cold-cathode fluorescent (CCFL), hot-cathode fluorescent lamps HCFL), or external electrode fluorescent lamps (EEFL) may be employed as the first light source in the illumination device according to the invention. Beside QL lamps (induction lamps) may be employed as first light source in the illumination device. In such an induction lamp the means for maintaining a gas discharge are situated outside the discharge space surrounded by the discharge vessel. Generally said means are provided by a coil provided with a winding of an electric conductor, with a high- frequency voltage, for example having a frequency of approximately 3 MHz, being supplied to said coil in operation. In general, said coil surrounds a core of a soft-magnetic material. Commonly, a phosphorous coating is applied for allowing low-pressure mercury vapor discharge lamps being able to convert UV light to visible radiation for the specific illumination purpose. In a preferred embodiment the at least one second light source is optically coupled to an end surface of the light-guiding means. Coupling light emitted by the second light source(s) via an end surface into the light-guiding means will be an efficient manner to couple light into the light-guiding means, wherein the second light source(s) can be oriented adjacent to an electrode of the first light source. It is, however, also conceivable that

particular provisions are employed to couple light emitted by the second light source(s) via another surface and/or element into the light-guiding means.

Light of a single second light source may be coupled into the light-guiding means at least partially. However, it will commonly be preferable that light of multiple second light sources is coupled into the light-guiding means. Preferably, the second light source is formed by a light emitting diode (LED). A LED is a relatively small light source, wherein the LED commonly has a relatively durable life expectancy. Moreover, merely a small voltage is required for LED operation. In a particular preferred embodiment the at least one LED is adapted to emit light with a substantially blue color to generate mixed light with a cool white or warm white color temperature. Application of one or more LEDs as second light source will commonly lead to a relatively broad color temperature mixing range of approximately between 2700 and 17000 Kelvin, depending on the initial color temperature of the first light source. Beside monochromatic LEDs it is also imaginable to apply polychromatic (multicolor) LEDs. Other kind of light sources, like e.g. an organic LED (OLED) or a laser may also be employed as second light source.

In order to achieve a position-selective light emission of the illumination device, the light-guiding means is preferably partially provided with a reflective layer. By means of this reflective layer emission of light at the location of said reflective layer can be prevented, while emission of light at an opposite side or part of the light-guiding means can be optimized.

Since the luminance of light emitted by the second light source, preferably a LED, will be relatively high close to the second light source and will decrease in a direction away from said second light source. Hence, it is commonly advantageous in case the position-selective light emitting capacity of the optical emission structure increases in a direction away from the at least one light source to realize a relatively uniform and homogenous light output along the light-guiding means, and hence along the illumination device.

To facilitate emission of light by the light-guiding means, the optical emission structure preferably comprises at least one outcoupling element. The outcoupling element can be of various nature and is preferably chosen from the group of outcoupling elements consisting of: prism-rings, gravures, in particular grooves, or scattering dots printed (coated) onto an inner surface and/or outer surface of the light-guiding means. More preferably, the optical emission structure comprises multiple outcoupling elements to enhance the light outcoupling capacity of the light-guiding means. The outcoupling elements may even form a

diffuse-reflective character, which may be an image or a symbol. In this manner, e.g. advertorials or other commercial expressions may be visualized.

The light-guiding means, preferably one or more jackets, is preferably made of glass or plastic, in particular polymethylmethacrylate (PMMA) or polycarbonate (PC). Both materials have or may have the characteristic to be at least partially transparent for light. The light-guiding means may be positioned at a distance from the first light source. However, in a preferred embodiment the light-guiding structure and the discharge vessel are mutually coupled to provide a relatively solid construction of the illumination device according to the invention. Coupling may be achieved by means of a transparent adhesive and/or by conventional mechanical means.

In an alternative preferred embodiment the light-guiding structure and the discharge vessel are mutually integrated. Since the discharge vessel is commonly made of (quartz) glass, the light-guiding means will also be made of (quartz) glass according to the embodiment. Integration of the discharge vessel and the light-guiding means would lead to a further simplification of the construction of the illumination device according to the invention.

The invention also relates to a luminaire comprising an illumination device according to the invention, wherein the illumination device will be mounted in the luminaire. The hybrid illumination device can be mounted in various manners. A conventional TL5 luminaire may be used to mount the illumination device, provided that said luminaire also incorporates drivers for the second light source. Preferably, the luminaire comprises a control unit for controlling the first light source and the second light source independent of each other to regulate the color temperature and light intensity of the illumination device. Since the second light source is commonly formed by a LED, the illumination device and hence the luminaire may act as a night lighting in case the first light source, preferably a low-pressure discharge lamp, is switched off, while the LED('s) is/are switched on by the control unit.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated by way of the following non- limitative examples, wherein:

Fig. 1 shows a cross section of a first embodiment of an illumination device according to the invention,

Fig. 2a shows a side view of a second embodiment of an illumination device according to the invention,

Fig. 2b shows a side view of a third embodiment of an illumination device according to the invention,

Fig. 2c shows a side view of a fourth embodiment of an illumination device according to the invention, and Fig. 3 shows a perspective view of a fifth embodiment of an illumination device according to the invention.

DDETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 shows a cross section of a first embodiment of an illumination device 1 according to the invention. The illumination device comprises a fluorescent tube 2, which tube 2 comprises a discharge vessel 3 and multiple electrodes 4a, 4b connected to said vessel 3, between which electrodes 4a, 4b a discharge extends during operation of the fluorescent tube 2 leading to emission of light. The discharge vessel 3 is enclosed by a substantially cilindrical jacket 5 being made of a substantially transparent material, preferably PMMA. The jacket 5 is adapted to act as a waveguide for light (indicated with arrows) emitted by multiple LEDs 6 positioned adjacent to the electrodes 4a, 4b of the fluorescent tube 2. Light emitted by the LEDs 6 is coupled into the jacket 5 via end surfaces 7a, 7b of the jacket 5. An outer surface of the jacket 5 is provided with multiple outcoupling elements 8, in particular grooves, which are adapted to allow light to exit the jacket 5 in a predefined direction. Since light of both the LEDs, after being led through the jacket 5, and the fluorescent tube 2 are emitted in more or less the same direction (radially away from the illumination device 1), an efficient mixing of light will occur. The distance between neighboring outcoupling elements 8 is relatively large close to the LEDs 6 and is relatively small in the central region of the discharge vessel 3 to establish a relatively homogeneous light output of LED light out of the jacket 5. By varying the output of the fluorescent tube 2 and/or the LEDs 6, the overall light output and hence also the color temperature of the illumination device 1 as such can be regulated. Moreover, a relatively homogeneous mixing of light emitted by the fluorescent tube 2 and the LEDs 6 can be achieved by means of the illumination device 1 according to the invention. Fig. 2a shows a side view of a second embodiment of an illumination device 9 according to the invention. This illumination device 9 is constructively substantially similar to the illumination device 1 shown in Fig. 1. The illumination device 9 shown in this figure comprises an elongated discharge lamp 10 being surrounded by a transparent housing 11. Two LEDs 12 are provided to couple light emitted by said LEDs 12 via an end surface 13 of

the housing 11 into said housing 11. An optical emission structure (not shown) is used to realize an efficient mixing of light emitted by the LEDs 12 and discharge lamp 10. In this figure it is clearly shown that the LEDs 12 are positioned relatively close to each other and are not positioned regularly with respect to the end surface 13 of the housing 11, in contrary to the four LEDs 14 of the illumination device 15 shown in Fig. 2b.

Fig. 2c shows a side view of an alternative embodiment of an illumination device 16 according to the invention, wherein a tubular discharge lamp 17 is partially surrounded by two concentrically oriented transparent jackets 18a, 18b. An inner jacket 18a is optically coupled via both end surfaces 19 of said jacket 18a with a first set of LEDs 20a. The outer jacket 18b is optically coupled via particular grooves 21 applied to said jacket 18b with a second set of LEDs 20b. Light coupled into the jackets 18a, 18b can be emitted by the jackets 18a, 18b via optical structures 22a, 22b applied to the jackets 18a, 18b respectively. A part of the discharge lamp 17 not being covered by the jackets 18a, 18b is provided with a reflective layer 23 to optimize the mixing efficiency of the illumination device 16. Fig. 3 shows a perspective view of a fifth embodiment of an illumination device 24 according to the invention. The illumination device 24 shown in this figure comprises a discharge lamp 25. The discharge lamp 25 comprises a relatively thick- walled discharge vessel 26 made of glass, and multiple electrodes 27 coupled to said vessel 26. LEDs 28 are provided at end surface 29 of the discharge vessel 26 to couple light into the wall of the discharge vessel 26. Diffuse-reflective symbols 29 are provided to the discharge vessel 26 via which symbols 29 light initially emitted by the LEDs 28 will be emitted and mixed with light emitted by the discharge lamp 25.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.