FIELD OF THE INVENTION

[0001] The invention relates to an illumination system, which is arranged to illuminate at least one illumination object, the system comprising at least one illumination object and at least one light-emitting unit.

[0002] The invention also relates to a method for illuminating at least one illumination object, in which method light is emitted.

[0003] Further, the invention relates to an electronic device comprising at least one illumination object and at least one light-emitting unit.

BACKGROUND OF THE INVENTION

[0004] Currently keypads in electronic devices more and more often comprise a keypad illumination functionality which makes the device easy to use also in dim light. Especially the keypad of a mobile station is typically illuminated by connecting a light source to a relatively thick photoconducting plate placed under a circuit board, from which plate the light is switched to give light out to key edges and touch surfaces, for instance, through a translucent keypad mat.

[0005] US publication 2004/174339 discloses a solution for keypad illumination of an electronic device, in which a light control layer placed under a circuit board is used as a photoconducting plate. Light is arranged to transfer optically through the light control layer from a common light source, such as a LED component, to the keypad. The solution of the above-mentioned publication has a drawback, however, that the structure comprises a separate light control layer that is arranged on a separate substrate. This structure increases the thickness of the electronic device by up to a few millimetres, which is a considerable disadvantage, particularly in mobile stations, PDA devices and in other small electronic devices. Moreover, the area of the light control layer utilized in the keypad illumination is typically only a small portion of the total area of the light control layer, but the intensity of the light to be transferred to the light control layer, however, must be high to be sufficient for keypad illumination. Thus, the efficiency of the light control layer is poor in applications of this kind, which causes unnecessary energy consumption, particularly in battery- operated electronic devices. A complicated structure and consumption of material cause further manufacturing costs.

BRIEF DESCRIPTION OF THE INVENTION

[0006] The object of the invention is to provide a novel and improved illumination system, a method for illuminating an illumination object, and an electronic device.

[0007] The invention is based on the idea that an illumination system comprises at least one illumination object, such as a key in an electronic device, and at least one light-emitting unit, such as a light-emitting diode, i.e. a LED component, or any other light-emitting component adaptable to an electronic device. The illumination system also comprises at least one discrete light channel, which is operationally connected to the at least one light-emitting unit and the at least one illumination object and which is arranged to transfer emitted light from at least one light source to at least one illumination object.

[0008] According to a first embodiment of the invention a discrete light channel is arranged in a circuit board, for instance, by integrating it inside the circuit board or on the surface thereof.

[0009] According to a second embodiment of the invention the illumination object is a keypad comprising one or more keys.

[0010] According to a third embodiment of the invention the light- emitting unit is arranged in the discrete light channel.

[0011] According to a fourth embodiment of the invention the discrete light channel is arranged to produce a desired illumination area in response to determining a physical dimension, such as size or shape, of the discrete light channel.

[0012] According to a fifth embodiment of the invention the discrete light channel is arranged to produce one or more colours in response to colour selection of the material of the light outlet point.

[0013] According to a sixth embodiment of the invention in operational connection with the discrete light channel there is arranged one or more light sources that are arranged to emit two or more light components of different colours in total.

[0014] The arrangement of the invention has a substantial advantage that an electronic device, such as a mobile station, a PDA (Personal Digital Assistant) device, a portable computer, a PC (Personal Computer), a remote control, a wristwatch or a control panel of an instrument, can be manufactured thinner and thinner, because light is arranged for transfer to the keypad via discrete light channels, whereby in the electronic device there is no

need for a relatively thick, separate light control layer of prior art for the transfer of light. One embodiment has an advantage that the discrete light channels can be integrated to be part of a circuit board, whereby the electronic device can be manufactured even thinner. One embodiment has an advantage that the discrete light channels enable considerable energy saving over a light control layer with typically low efficiency. Hence, the solution of the invention makes it possible to reduce the light intensity considerably, for instance, by using less LED components. One embodiment has a further advantage that the discrete light channels also enable features that can be utilized in various ways. For instance, the shape and/or the surface structure of the discrete light channel can be designed such that it permits various patterns or text to be provided for the electronic device, or that by controlling the width of the discrete light channel illumination areas of different sizes can be provided. One embodiment has a further advantage that, for instance, some of the keys may be illuminated in a different manner from the other keys, for instance by using different colours or light intensities, which will find use in game applications, for instance.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In the following the invention will be described in greater detail in connection with some embodiments with reference to the attached drawings, wherein

Figure 1 shows an illumination system according to an embodiment of the invention,

Figure 2 shows an electronic device according to a second embodiment of the invention,

Figure 3 shows an arrangement of a third embodiment of the invention, and

Figure 4 shows an arrangement according to a fourth embodiment of the invention.

[0016] For the sake of clarity, the figures show the embodiments of the invention in a simplified manner. Like reference numerals refer to like parts in the figures.

DETAILED DESCRIPTION OF THE INVENTION

[0017] Figure 1 shows an illumination system according to an embodiment of the invention in a simplified cross-sectional view, in which the keys

100, 100' of an electronic device, such as a mobile station, a PDA device, a portable computer, a PC, a remote control, a wristwatch or a control panel of an instrument, are arranged on the surface of a circuit board 102 preferably on top of a flexible and transparent element 104. The light-emitting unit 106 is implemented in this embodiment by a LED component that is integrated into a circuit board 102. Alternatively a discrete light channel 108 may be located on the surface of the circuit board 102. There may be one or more light-emitting units 106 and they may illuminate one or more illumination objects 100, 100'. The LED component 106 is arranged to emit light into the discrete light channel 108 integrated inside the circuit board, which light channel in turn is operationally connected to both the LED component 106 and the keys 100, 100'. The illumination system may also comprise a plurality of discrete light channels 108 or the discrete light channel 108 may be branched to illuminate a plurality of illumination objects 100, 100' as is the case in this example. By using discrete light channels 108 it is possible to omit the prior art light control layer in the electronic device altogether, which allows the electronic device to be manufactured clearly thinner and, due to the simplified structure, also more economical. Also with regard to assembly the illumination system integrated in the circuit board, instead of a separate illumination configuration, brings considerable cost savings. The emitted light is transferred via the discrete light channel 108 from the LED component 106 towards the keys 100, 100' advantageously illuminating the edges and the touch surface of the keys 100, 100', which enables the use of the mobile station also in the dark.

[0018] To produce discrete light channels on the circuit board it is possible to use all known methods, such as lithography in its various forms, direct writing, various etching methods and photolithography methods. The materials may be both wet and dry films and their chemical base may be any spreadable light-conducting material. The most typical material bases include epoxies, acryls, imides and siloxanes, but it is also known to manufacture light channels on a thermoplastic or ceramic circuit board substrate or on silicon, quartz and glass substrates, whereby a wide variety of material bases may constitute a discrete light channel.

[0019] In the discrete light channels and the input and output connections thereof it is possible to use various light beam refracting structures. Advantageously the discrete light channel is manufactured to comprise three layers such that an optically denser core layer is located between optically less

dense substrate and surface layers. The layers are typically manufactured of the same material such that their optical densities have been modified with a suitable additive, for instance. Hence, the different layers of the discrete light channel have different refractive indexes, which enables sinuous refraction of light along the discrete light channel. The difference between the refractive indexes may be, for instance, from 1 to 2% or even larger. The larger the difference of the refractive indexes the sharper the turns the light is made to reflect.

[0020] According to one embodiment the width of the discrete light channel is 50 to 200 μm. The discrete light channel also allows, even within one single light channel, creation of illumination areas of different sizes in the electronic device by selecting a dimension, such as width, of the discrete light channel to be suitable to produce the desired illumination area. According to a second embodiment the discrete light channel allows production of specific illumination areas, such as various patterns or texts, in the electronic device, for instance, by determining a suitable shape for the discrete light channel and suitable outlet points for the light. In addition, the illumination objects can be manufactured of materials of different colours, whereby lights of different colours can be produced. For instance, each side of a multifunction key in a mobile station can be illuminated differently or a pattern symbolizing a desired function can be created on the key, which facilitates the usability of the mobile station. In addition, the discrete light channels can also be utilized in connection with various software applications, for instance, such that some of the keys are illuminated in a manner that differs from the other keys, whereby the dialling keypad of a mobile station will be better adapted to a gaming keypad.

[0021] According to a preferred embodiment in operational connection with the discrete light channel there is arranged one or more light sources that are arranged to emit in total two or more light components of different colours into the discrete light channel. For instance, one RGB component may emit red, green and blue light components and LED components of different colours may be connected in parallel. In the discrete light channel light components of different colours will quickly mix, because several reflections take place in a narrow channel.

[0022] Figure 2 shows a simplified explosion view of the essential parts of the electronic device according to an embodiment of the invention, in which explosion view a top layer 110, a keypad membrane layer 112 and a

circuit board 102 are shown apart from one another. The keys 100, 100' are located in the keypad membrane layer 112 that may be made of tinted or non- tinted, translucent, transparent or opaque material. Under the keys 100, 100' there are arranged discrete light channels such that each key 100, 100' to be illuminated is in operational connection to the discrete light channel 108 or a branch thereof advantageously such that the light is able to transfer from the light-emitting unit 106 via the discrete light channel 108 as close as possible to the key 100, 100' to be illuminated. As it can be seen in Figure 2, the discrete light channels occupy remarkably little space on the circuit board and they do not significantly increase the thickness of the electronic device. The efficiency of the discrete light channels is good, because the light will be efficiently transferred therethrough to the illumination object 100, 100', unlike in the prior art solutions based on light control layers, in which a substantial amount of light is transferred to the entire light control layer, whereby the intensity of light must be significantly higher than in the solution of the invention.

[0023] Figure 3 shows a top view of a circuit board 102 in accordance with a preferred embodiment of the invention. On the surface of the circuit board 102 there are arranged two light-emitting units 106, 106', discrete light channels 108, 108' and keys 100, 100' to be illuminated. The light can be directed from the light-emitting unit to the keys to be illuminated, for instance, via a direct or a branched discrete light channel, or the light can be arranged for being directed to its target through a chainlike structure consisting of discrete channels and other keys to be illuminated or any light-conducting component.

[0024] Figure 4 shows an illumination system in accordance with a preferred embodiment of the invention, in which the light-emitting unit 106 is arranged on the surface of the circuit board 102 or in the discrete light channel 108 integrated in an inner layer. In this model it is possible to further increase the amount of light to be switched to the discrete light channel and thus the performance will be improved. With the arrangement the structure will also be thinner.

[0025] It is apparent to a person skilled in the art that as technology progresses, the basic idea of the invention can be implemented in a variety of ways. In some cases, features presented in this document may be used as such, irrespective of other features. On the other hand, features presented in this document may be combined, when necessary, to obtain various combina-

tions. The invention and the embodiments thereof are thus not restricted to the above-described examples that are intended to illustrate the invention, but the invention may vary within the scope of the claims.