This invention relates to a lighting device comprising one or more solar cell and light emitting diode (LED).

The use of solar panels which collect sunlight and convert it into clean, emissions-free electricity has gained an increasing interest over the recent years, for various reasons. Solar panels are silent collectors of energy available in nature, which cast no shadow that has an umbra. Energy collected by the solar panel may be stored and used to energize a wide variety of devices amongst which road markers, "lighted message panels", lighting etc. Usually, the solar panels are installed at the location where energy collection possibilities are optimal, while the devices to be powered by the solar panels are positioned at another location where the energy is needed.

US 5905356 describes a solar powered charger for recharging portable units such as battery powered hand tools and cellular phones. The solar powered charger comprises a transparent front-side panel constructed from plexiglass or tempered glass and a transparent back-side panel constructed from half-inch thick acrylic. One or more solar panels are housed in the empty space between the front-side and the back side panel. The solar panels are cushioned and immobilised by pads, which provide a shock absorbing buffer for the delicate solar panels. Once the components of the solar powered charger are assembled, a rubber coating is applied to provide a protecting and sealing exterior that will completely cover the side of the charger and the entirety of the back-side panel. Thus only the front-side panel is available for collecting light.

US 2005/0244225 describes a solar powered illuminated road marker. Often used road markers have a small, rectangular housing with a reflective material arranged such that light from the headlights from an approaching motor vehicle are reflected back to the driver. Since such reflective road markers do not function well under adverse weather conditions, US 2005/0244225 proposes to provide the marker with an internal light source. The marker disclosed by US 2005/0244225 includes a one-piece housing formed of a plastic abrasion material, for example polycarbonate having a top plate and perimeter sides, where at least one perimeter side has a light transmission surface through which light can be transmitted, and where the top plate and the sides define a cavity in the housing. At least one LED is positioned within the cavity such that light produced by the LED is transmitted through the light transmitting surface. The road marker also includes a long life battery for energizing the LED. The battery is positioned within the cavity at a position adjacent to the top plate. The cavity further contains at least one solar cell for recharging the battery and an electrical circuitry configured to control charging of the battery. Typically, the marker will be placed on concrete or asphalt paving materials and will be fixed with a strong adhesive.

US 2006/0101685 describes an illuminated display device which is internally powered and suitable to be positioned in areas that are not limited by the requirement of available electricity. The device comprises an upper display layer which contains text and/or graphics. The display layer is mounted on top of and connected to a substrate layer. The substrate layer comprises a power source, a plurality of light devices, for example LEDs interconnected to the power source, and a controller interconnected to the power source and the light devices. The controller is provided to activate a light device to an illumination state. The power source may include a solar cell and/or a battery. The substrate layer may be formed of a flexible material for example a rubber type material of siliconized or synthetic rubber. The display layer may include transparent portions in proximity to the light devices on the substrate layer, allowing light to be visible trough the display layer.

All of the above described devices according to the state of the art have a configuration which is not aesthetically pleasing and which may need extensive modifications to permit integration in different settings.

The inventors have thus identified a need for a versatile lighting device which is aesthetically pleasing, which is suitable for use in a wide variety of applications and which can be easily integrated in different settings, while being suitable for a broad range of possible applications.

The present invention seeks to provide such a lighting device.

Thereto, lighting device of this invention lighting comprises a rigid, at least partly light-transparent front-side panel and a backside panel, which front- and back-side panel sandwich between them a layer of an at least partly light-transparent encapsulation material connecting the front-side and back-side panel, wherein at least one solar cell and at least one light element are encapsulated in the encapsulation material, the at least one solar cell and at least one light element being electrically interconnected.

The inventor has found that a lighting device having such a configuration allows for a seamless integration of one or more solar cells for capturing and converting sunlight into electrical energy, as well as seamless integration of one or more lighting elements which are electrically powered by the solar cells. The lighting elements may be powered by the solar cells in a direct manner thereby using light impinging the solar cells in the lighting device directly for illumination purposes, or in an indirect manner using a chargeable battery, which may be mounted either into or outside of the device. By the presence of at least one rigid panel in the device a self- supporting device is provided. The invention thereby permits to eliminate the need for the use of a support structure, which could have complicated integration of the lighting elements and could have limited the number of applications. By the presence of the encapsulation material, the position of the solar cells and the light elements may be fixed and a protective, shock resistant environment is provided.

The presence of at least one transparent panel provides a versatile lighting device with an aesthetically pleasing appearance and a functional operation. The simple design of the device keeps production costs low and the production process lean. The long lifetime of the device and the low maintenance requirements positions the lighting device according to the invention as an attractive solution for a wide variety of illumination applications in need for sustainability.

According to a preferred embodiment of the invention, the back-side panel is at least partly light-transparent. Not only does this preferred embodiment allow harvesting more light with the two sides being exposed and functionally operational, it also gives the device a greater versatility in use, allowing its smooth integration in a wide variety of settings.

Preferably the back-side panel is rigid, to ensure the strength and self-supporting capacity of the panel.

Within the framework of the present invention, a solar cell (also called photovoltaic cell or photoelectric cell) is understood to include a solid state electrical device that converts the energy of light and sunlight directly into electricity by the photovoltaic effect. Materials presently used for photovoltaic solar cells include monocrystalline silicon, polycrystalline silicon, amorphous silicon, cadmium telluride, and copper indium selenide/sulfide. Many currently available solar cells are made from bulk materials that are cut into wafers between 180 to 240 micrometers thick that are then processed like other semiconductors. Other materials used for photovoltaic cells are made as thin-films layers, organic dyes, and organic polymers that are deposited on supporting substrates. A third group are made from nanocrystals and used as quantum dots (electron-confined nanoparticles). To date, silicon is still the only material that is well-researched in both bulk and thin-film forms. By varying the size and the number of solar cells, greater or lesser amount of electrical power may be produced. For aesthetical reasons, a coating may be applied on the surface of the solar cells.

In the framework of the present invention, a light element is meant to include any electric powered light source known to the skilled person which may be sandwiched between the a front-side rigid at least partly light-transparent panel and a back-side rigid at least partly light- transparent panel and may be powered by the one or solar cells in the lighting device. Such light elements may be for example incandescent light sources such as conventional light bulbs or halogen lamps or electroluminescent lamps such as LEDs. A LED is a semiconductor light source, which consists of a chip of semiconducting material doped with impurities to create a p-n junction. The wavelength of the light emitted, and thus its color depends on the band gap energy of the materials forming the p-n junction. The materials used for the LED have a direct band gap with energies corresponding to near- infrared, visible, or near-ultraviolet light. For lighting applications, LEDs with band-gap energies corresponding to visible light are used. LEDs present many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved robustness, smaller size, and faster switching.

The electrical interconnection between the at least one solar cell and the light source will usually comprise the means to transform the electrical power supplied by the solar cell(s) into electrical power which is compatible with the electrical power requirements of the light source.

The front-side panel may be constructed in many different ways, but is usually built of an electrically insulating material and/or materials resistant to a number of environmental conditions such as sunlight, weathering, temperature variations, chemical exposure and mechanical impact. Examples of such materials include those which are not significantly degraded by sunlight, for example (tempered) glass, laminated glass and plate shaped plastic materials, but any other material deemed appropriate by the skilled person may be used as well. Glass may be understood to comprise conventional glass, but also reinforced glass and electrically conductive glass.

Examples of plastic materials which may be shaped into plates and are suitable for use with the present invention include polycarbonate or poly(methyl methacrylate) (PMMA), also known as plexiglas. The front-side rigid at least partly light-transparent panel function as a cover and protection shield for the fragile solar cells and provides at least one bearing surface for the lighting device.

Similar to the front-side panel, the back side panel may also be constructed of a wide variety of materials, in particular an electrically insulating material or materials resistant to a number of environmental conditions, for protecting the solar cells from for example moisture ingression. It is possible to use for the back-side panel the same rigid material(s) as those that are used for the front-side panel, but a different rigid material may be used as well. In addition to this the back-side material may be made of a different type of material for example a flexible, electrically insulating polymer film. Examples of suitable polymer materials besides the rigid glass, polycarbonate and PMMA materials, include the more flexible thermal polymer olefins (TPO). TPO includes any olefins which have thermoplastic properties such as polyethylene, polypropylene, polybutylene, etc. Other polymer materials which are not significantly degraded by sunlight such as fluoropolymers such as ethylene tetrafluoroethylene (ETFE) or poly ethylene terephthalate (PET), acrylics or silicones as well as multilayers and co-extrusions may also be used. When using a flexible back side panel, the mechanical support for the panel is provided by the front-side rigid panel.

The at least partly light-transparent encapsulation material which is sandwiched between the front-side and backside panel and connects the front and back-side panel, may be made of a wide variety of materials, as long as they are at least partly transparent to light. The encapsulation material may comprise a resin, in particular a resin selected from the group of at least partly transparent polyurethane, polyesters and epoxy resins and silicones or polysiloxanes. The at least partly light- transparent encapsulation material may also comprise an adhesive composition, which is at least partly transparent to light, such as polyethyl vinyl acetate (EVA) or polyvinyl butyral (PVB), but many other adhesive compositions may suitably be used.

The encapsulation material generally functions to fix the position of the solar cells and the light elements and to protect the cells and light elements from the environment (e.g. wind, rain, snow, dust and the like) and from mechanical shocks. The encapsulation material may also function to both encapsulate the solar cells and laminate them to the front- side and/or back-side panel. The encapsulation material is preferably selected such that it is chemically stable, electrically insulating, elastomeric and easily processable. When selecting the encapsulation material, the skilled person will be capable without undue burden, to identify those materials which are compatible with the materials used for the front- and back-side panel and do not cause degradation thereof. Either one single layer or several layers of encapsulation material may be applied using either the same or different encapsulation materials for different layers. For example a first layer of encapsulation material e.g. polyethyl vinyl acetate (EVA) which is transparent to sunlight, may be utilized as an adhesive, to adhere the front-side panel to a series of interconnected solar cells. A second layer of encapsulation material may then be applied onto the first layer of encapsulation material and interconnected solar cells. The second layer of encapsulation material may be an additional layer of the same material as used for the first encapsulation material or a different encapsulation material. A wide variety of materials have been proposed for use as solar cell encapsulation materials. Common examples include films of ethylene-vinyl acetate copolymer (EVA), Tedlar® from E.I. Dupont de Nemours & Co of Wilmington Del. and UV curable urethanes, ethylene methyl acrylate (EMA), acrylic laminating film, poly-n-butyl acrylate (InBA), aliphatic polyester urethane, silicone elastomer, and polyvinyl butyral (PVB). The encapsulation materials are generally supplied in the form of films and are laminated to the cells, front-side and back-side panel. Prior art examples include the lamination of photovoltaic cells using adhesives as exemplified in U.S. Pat. No. 4,331 ,494 and the application of an acrylic polymer and a weather resistant layer as described in U.S. Pat. No. 4,374,955. The lighting device of this invention may be connected to an electrical energy storage means such as a (rechargeable) battery or a capacitor. According to a preferred embodiment of the invention, the electrical energy generated in the one or more solar cells is communicated or conveyed to an electrical energy storage means such as a (rechargeable) battery or a capacitor, electrically connected to the at least one solar cell and the lighting element for powering the light element. In this manner, the electrical energy storage means may be charged by the solar cells in order to power the light elements during periods when the solar cell is not generating (enough) power, such as during low light conditions. Examples of rechargeable batteries include nickel-cadmium, lithium polymer, nickel-metal hydride and lithium ion batteries. Electrical energy storage means may also include a capacitor that is capable of holding a relatively large charge that may be used to power the light elements for an appropriate time period. For example a super capacitor may provide such power for a significant time period.

The present invention is further elucidated in the appending figures and the figure description below.

Figure 1 shows a view to the front-side of a preferred embodiment of a lighting device according to the invention.

Figure 2 shows a view to an upright side of a preferred embodiment of a lighting device according to the invention.

Figure 3 shows a cross-section of a preferred embodiment of the lighting device according to the invention, in longitudinal direction.

Figure 4 shows an example of a lighting device of this invention.

As shown in the preferred embodiments of Figures 1-3, the lighting device 1 may be configured as a generally rectangular laminar panel, which is sized and shaped in accordance with the environment and the setting, in which it is meant to be installed. The lighting device 1 may therefore take any size and shape suitable for a certain application and context. Depending on the application the lighting device 1 may be flat or bent. Figure 3 and 4 show an example of such a bent device 1. The bending radius may vary within wide ranges and may suitably be chosen by the skilled person taking into account the dimensions of the panel and the nature of the material or materials from which the panel is made.

The lighting device 1 comprises a rigid, at least partly transparent front-side panel 2. The thickness of the front-side panel 2 will usually be chosen by the skilled person taking into account the size of the lighting device 1 , the degree of bending and the load it has to bear. The thickness of the front-side panel 2 will usually be chosen such that a sufficiently rigid, self-standing device may be obtained. Suitable materials for the front-side panel are for example (tempered) glass, laminated glass and plate shaped rigid plastic materials. Examples of plastic materials which may be shaped into plates and are suitable for use with the present invention include polycarbonate or Poly(methyl methacrylate) (PMMA), also known as plexiglas. Solar energy is permitted to pass through the front-side panel 2. The material from which the front-side panel is made may comprise a dye or any other additives to change the colour and light absorbing properties of the panel if needed. The dye may be applied throughout the panel or it may be applied to certain areas only. An outer and/or inner face of the front-side panel may be partly or entirely coated with a coating. A wide range of coating materials may be used, depending on the envisaged function of the coating and the panel and the intended aesthetic effect. For example, a satin finish or similarly opaque coating may be applied. The purpose of such a coating is to conceal the interior components and workings of the lighting device 1. Other surface coatings are possible, for example abrasion resistance coatings. Examples of such coatings include without limitation, silicone based coatings, fluorinated epoxies, fluorinated urethanes and fluorinated polyol coatings.

As illustrated in Figure 1-3, the lighting device 1 comprises a back-side panel 3. The back-side panel has preferably substantially the same shape and size as the front-side panel 2. The thickness of the back-side panel 3 may vary within wide ranges and will usually be chosen taking into account the nature of the material used. Suitable materials for the back-side panel are the same materials as used for the front-side panel 2. The front- and back-side panel may be made of the same material or of a different material. Where the front-side panel is made of a rigid material, it is possible to use a flexible polymer material for the backside panel 3. Examples of suitable flexible polymer materials include thermal polymer olefins (TPO). TPO includes any olefins which have thermoplastic properties such as polyethylene, polypropylene, polybutylene, etc. Other suitable polymer materials are fluoropolymers such as ethylene tetrafluoroethylene (ETFE) or poly ethylene terephthalate (PET), acrylics or silicones as well as multilayers and co-extrusions may also be used. Depending on the material used, solar energy may be permitted to pass through the back-side panel 3 and here as well a coating, similar to the coating described for the front-side panel 2 may be applied on at least part of one or both sides of the back-side panel 3.

Sandwiched between the front-side panel 2 and the back-side panel 3 is a layer of an at least partly light-transparent encapsulation material 4. The at least partly light-transparent encapsulation material may comprise a resin, in particular a resin selected from the group of at least partly transparent polyurethane, polyesters and epoxy resins and silicones or polysiloxanes. The at least partly light-transparent encapsulation material may also comprise an adhesive composition, which is at least partly transparent to light. The encapsulation material is used to fix the position of the solar cells and the light elements and generally functions to protect the cells and light elements from the environment (e.g. wind, rain, snow, dust and the like) and from mechanical shocks. The encapsulation material may also be used to both encapsulate the solar cells and laminate them to the front- side and/or back-side panel to form the lighting device. The encapsulation material is preferably selected such that it is chemically stable, electrically insulating, elastomeric and easily processable. Either one single layer or several layers of encapsulation material may be applied using either the same or different encapsulation materials for different layers. Additionally, any compatible dye, known to the skilled person, could be added to the encapsulation material, in order to conceal the interior components and workings of the lighting device 1. The encapsulation material should be chosen such that it adheres well to the one or more materials from which the front-side panel 2 and/or the back-side panel 3 or made of.

As may be appreciated in Figures 1 and 3, the solar cells 5 and the light elements 6 may be arranged in a certain manner. They may for example be arranged in a regular geometric pattern. The arrangement shown reflects only one possible distribution of the solar cells 5 and the light elements 6 in the lighting device 1 and many other geometric patterns or random arrangements may be used. The arrangement shown makes it easy to electrically interconnect the different components of the lighting device 1. Both the solar cells 5 and the light elements 6 may be connected to electrical energy storage means, for example a rechargeable battery (not shown) connected by electrical circuitry to the solar cells 5 and the light elements 6. The energy generated by the solar cells 5 may be stored in the rechargeable battery and released to the light elements 6. It may also be possible to transfer the electrical energy generated by the solar cells 5 directly to the light elements 6. The lighting device may comprise a controller integrated into the panel, which controls the electrical power supply by the battery to the light elements 6, taking into account the voltage and currents which ensure a normal operation of the light elements 6. The controller may be connected to a light sensor mounted to the lighting device 1 , for activating or de-activating the controller at a certain light intensity measured by the light sensor and permitting or inhibiting illumination of the light elements depending on the light intensity. Suitable light sensors include a photo-detector, such as a photo-intensity detector. In a preferred embodiment, in response to a signal from the detector, the controller can adjust the electrical power supplied to the light elements 6, and as a result adjust the light intensity emitted by the light element 1.

A panel comprising the front-side and back-side panel and the encapsulation material with the encapsulated solar cells and light elements, may be flat or curved or have a combination of shapes. The panel may for example be curved to provide a cylinder.

Thus, the lighting device of the present invention is suitable for use in a wide variety of applications, for example as a lightened wall panel separating two rooms from one another, a lightened window panel, a lightened roof panel.

The lighting device may be used as such positioned on a supporting floor or it may be supported by a carrier. The carrier may for example take the form of a pole or the foot and branches of a tree, with a cylindrical lighting device being mounted on an upper part of the foot. Thus an aesthetically pleasing lighting device is provided. With a bent panel, regions in the vicinity of the longitudinal edges of the panel may rest on supporting walls to provide a lightened, light transparent roof member. In the description above, the front-side panel may be used as back-side panel and the reverse.

Now, this invention has been fully described, the skilled person will realize that the invention can be carried out with a wide range of possibilities within what is claimed, without thereby departing from the spirit and scope of the invention. As is understood by the skilled in the art, the general invention as defined by the claims comprises other preferred embodiments, which are not specifically mentioned.