具体实施方式：
[0034]Referring more specifically to the drawings, for illustrative purposes the present invention is embodied in the system generally shown in the preceding figures. It will be appreciated that the system may vary as to configuration and as to details of the parts without departing from the basic concepts as disclosed herein. Furthermore, elements represented in one embodiment as taught herein are applicable without limitation to other embodiments taught herein, and in combination with those embodiments and what is known in the art.
[0035]A wide range of applications exist for the present invention in relation to the collection and distribution of electromagnetic radiant energy, such as light, in a broad spectrum or any suitable spectral bands or domains. Therefore, for the sake of simplicity of expression, without limiting generality of this invention, the term “light” will be used herein although the general terms “electromagnetic energy”, “electromagnetic radiation”, “radiant energy” or exemplary terms like “visible light”, “infrared light”, or “ultraviolet light” would also be appropriate.
[0036]It is also noted that terms such as “top”, “bottom”, “side”, “front” and “back” and similar directional terms are used herein with reference to the orientation of the Figures being described and should not be regarded as limiting this invention in any way. It should be understood that different elements of embodiments of the present invention can be positioned in a number of different orientations without departing from the scope of the present invention.
[0037]Various embodiments of the invention are directed to flexible or semi-rigid light emitting structures that employ one or more arrays of interconnected compact solid-state lighting devices distributed over a surface of and attached to a flexible or semi-rigid sheet-form support substrate. The compact solid-state lighting devices may be exemplified by light emitting diodes (LEDs) or laser diodes. The embodiments presented herein are generally described upon an exemplary case where the compact solid-state lighting devices are represented by LEDs. The light emitting structures may include various additional flexible or semi-rigid layers, such as for, example, adhesive layers, reflective layers or coatings, heat or electricity-conducting layers, or encapsulation layers.
[0038]The term “flexible”, as applied to sheet-form structures (including flexible sheet-form substrates and/or layers), is generally directed to mean that such structures are capable of being noticeably flexed or bent with relative ease without breaking. It is noted that, while flexible sheet-form structures are in contrast to the ones that are rigid or unbending, the material of a sheet-form structure does not necessarily need to be soft or pliable in order to make such sheet-form structure flexible. Accordingly, the term “flexible” is directed to also include semi-rigid structures and structures that are formed by relatively hard, rigid materials such as metals or rigid plastics, when such structures have sufficiently low thickness compared to at least one their major dimension (e.g., length or width) and allow for noticeable flexing without breaking.
[0039]The LEDs may be arranged into an ordered two-dimensional array having rows and columns. The LEDs may also be distributed over a broad-area surface according to a random pattern. Each LED is mounted to the support substrate which has the ability to support the array of LEDs and associated electrical interconnects and electronic components that may be necessary for normal operation of the LED array. The sheet-form support substrate may be ordinarily formed from a rigid material, such as, for example, metal foil. Each LED may have a submount (such as, for example, a support pad or small-area rigid substrate) that is in turn attached to the sheet-form support substrate. A flexible sheet-form encapsulation layer is provided on top of the LED array to encapsulate the LEDs and optionally provide wavelength conversion. The flexible sheet-form encapsulation layer is preferably formed from an elastic material having an elastic range of at least 10%, more preferably at least 30%, even more preferably at least 50%, and still even more preferably at least 100%.
[0040]In some configurations, the encapsulation layer has a substantially uniform thickness across its entire surface. In some configurations, the encapsulation layer has a substantially uniform thickness across its surface, except for the relatively small discrete areas corresponding to individual LEDs where the thickness of the layer may be smaller than its average thickness. In some configurations, the encapsulation layer is configured as a conformal coating having a relatively constant thickness generally conforming to the relief of the LED array on the support substrate. The encapsulation layer should ordinarily provide a good bond with the support substrate so that the resulting flexible or semi-rigid structure formed by the support substrate, encapsulation layer and LEDs embedded into the encapsulation layer represents a monolithic, bendable sheet-form LED illumination panel that is resilient to repetitive bends.
[0041]In some configurations, the sheet-form support substrate is formed from a material having sufficiently high thermal conductivity to provide efficient heat spreading from LEDs. The material may be opaque and may further have a reflective surface at least in spacing areas between LEDs. The substrate may be formed from or comprise a metal foil. It may also include or be formed by a flexible printed circuit. Such flexible printed circuit may be formed by lamination of layers of a flexible plastic substrate and electrically conductive circuits. In some configurations, the sheet-form support substrate has a high-reflectance coating on the side of LEDs for recycling light that may be trapped in the encapsulation layer.
[0042]The present invention will now be described by way of example with reference to the accompanying drawings.
[0043]FIG. 1 schematically shows an embodiment of a flexible sheet-form LED illumination device 900. LED illumination device 900 includes a heat-spreading flexible support substrate 20, a plurality of rigid substrates (submounts) 4 bonded to flexible support substrate 20, a plurality of electrically interconnected inorganic light emitting diodes (LEDs) 2 bonded to respective rigid substrates 4, and a soft and flexible encapsulation layer 40 encapsulating and hermetically sealing the plurality of LEDs 2 and rigid substrates 4. LEDs 2 and respective rigid substrates 4 are evenly distributed over at least a substantial portion of the broad area of flexible sheet-form LED illumination device 900 and arranged into an ordered two-dimensional array having rows and columns. At least some or all of LEDs 2 may also be distributed over the area of flexible sheet-form LED illumination device 900 according to a different pattern, e.g., non-ordered pattern or random pattern.
[0044]According to an aspect of the embodiment illustrated in FIG. 1, LED illumination device 900 has a flexible, layered sheet-form construction formed by a first continuous broad-area layer (flexible support substrate 20) and a second continuous broad-area layer (soft and flexible encapsulation layer 40) laminated on top of the first broad-area layer. Both flexible support substrate 20 and flexible encapsulation layer 40 extend longitudinally and laterally to distances that are much greater than their thicknesses. According to an aspect, flexible support substrate 20 and flexible encapsulation layer 40 are formed by thin and flexible sheets. Such thin and flexible sheets are bonded together to form a monolithic sheet-form structure of flexible LED illumination device 900 which is generally free from voids or air spaces. LEDs 2 are embedded into the solid material of flexible encapsulation layer 40 and attached or otherwise mounted to flexible support substrate 20 with a good mechanical and thermal contact. According to one embodiment, LEDs 2 may be exemplified by micro-LEDs or elemental LED chips that are attached either directly or indirectly to flexible support substrate 20 and have sizes on the scale of 1 μm to 300 μm.
[0045]Flexible support substrate 20 is formed by a continuous solid sheet of tough, heat-conducting material and has a relatively low thickness so that the substrate can be easily flexed. The sheet preferably has a constant thickness across its entire area. Flexible support substrate 20 may be formed by a single material, a blend of different materials or a layered laminate of different materials. Flexible support substrate 20 is preferably formed from a rigid material or includes at least one layer of a rigid material.
[0046]According to one embodiment, flexible support substrate 20 has at least one layer that is formed from a material having a thermal conductivity of at least 50 W/mK, more preferably at least 100 W/mK, even more preferably at least 150 W/mK, and still even more preferably at least 200 W/mK. According to one embodiment, flexible substrate 20 is a laminate including a metallic heat-spreading layer which has a relatively low thickness for flexibility. The metallic layer or substrate should preferably have a thickness below 1 mm, more preferably below 0.5 mm, even more preferably below 0.3 mm, and still even more preferably below 0.2 mm. According to one embodiment, flexible support substrate 20 incorporates a thin aluminum or copper foil having a thickness between 30 μm and 150 μm.
[0047]Flexible substrate 20 is ordinarily opaque (formed by an opaque material), but may also include openings or transparent/translucent areas serving different purposes. One or more layers forming flexible substrate 20 may be transparent or perforated. According to an alternative embodiment, the entire flexible substrate 20 or at least a substantial portion of its broad area may be transparent or translucent. The entire flexible LED illumination device 900 or one or more of its portions may be made substantially transparent or translucent.
[0048]Flexible support substrate 20 is defined by a top broad-area surface 88 and an opposing bottom broad-area surface 86 extending parallel to top surface 88. Flexible support substrate 20 ordinarily has a substantially constant thickness.
[0049]Top surface 88 includes a highly reflective layer which may be of a specular or diffuse reflection type. It is preferred that surface 88 has a hemispherical reflectance considerably greater than 50%, more preferably greater than 70%, even more preferably greater than 80%, and still even more preferably greater than 85%.
[0050]When flexible substrate 20 is formed from metal, somewhat good reflectance of surface 88 may be obtained by means polishing such surface to a high gloss. Alternatively, surface 88 may be mirrored for high specular reflectance, laminated with a reflective polymeric film, or coated with a high-diffuse-reflectance material.
[0051]Surface 86 may include a high-emissivity coating configured to enhance radiative heat transfer from flexible substrate 20 to the surrounding medium (such as air). The emissivity is conventionally defined as the ratio of the energy radiated from a surface to the energy radiated from an ideal blackbody emitter under the same conditions. For example, when flexible support substrate 20 or at least its outermost layer exposed to the ambient air is made of thin-sheet aluminum, surface 86 may be anodized to increase the emissivity from 3-10% (typical for unfinished aluminum) up to 75-85%. In a further example, flexible support substrate 20 may be spray-coated with a thin layer of dielectric paint having a relatively high emissivity. According to one embodiment, the emissivity of surface 86 at normal operating conditions of flexible LED illumination device 900 is more than 85%, more preferably more than 90%, and even more preferably more than 95%.
[0052]Flexible support substrate 20 may include additional functional and/or decorative layers, which may include electrical insulation materials, electro conductive materials, heat conducting materials, paper, plastic films, PCB materials, structurally reinforcing materials, meshes, fabrics, paint, colorants, and adhesive materials. Such layers may extend over the entire area of substrate 20 or any portion of it.
[0053]Flexible support substrate 20 may include at least one electrically insulating layer disposed on top of a heat-spreading layer. The material of such electrically insulating layer should preferably have a sufficiently high thermal conductivity to effectively transfer heat from LEDs 2 (or rigid substrates 4) to the heat-spreading layer underneath. Alternatively, the electrically insulating layer should have a sufficiently low thickness to minimize a thermal resistance of the layer. In one embodiment, flexible support substrate 20 may include polyimide film.
[0054]When flexible substrate 20 is formed by multiple layers including a heat-spreading metallic layer, a total thickness of the substrate may considerably exceed a thickness of such metallic layer. Still, it is preferred that substrate 20 maintains sufficient flexibility even with all such layers employed. According to one embodiment, flexible sheet-form LED illumination device 900 is configured such that it exhibits notable flexing under gravity when suspended in a horizontal orientation and supported only in a mid-section of the respective sheet form. Flexible support substrate 20 may include a sheet material that has sufficient rigidity at the selected thickness to provide flexing in an elastic regime and allowing the substrate to restore its shape when the external force is removed. Such sheet may also provide some spring action and notable resistance to flexing.
[0055]According to an aspect of the embodiments illustrated in FIG. 1, flexible support substrate 20 is configured to remove thermal energy from individual LEDs 2 and spread such thermal energy both longitudinally and laterally in a plane of the substrate in response to thermal conduction. The thermal conductivity of flexible support substrate 20 may be selected such that at least a substantial part of the thermal energy is distributed across the entire continuous area of the substrate and can be efficiently dissipated from broad-area surface 86.
[0056]Flexible encapsulation layer 40 is formed by a broad-area sheet of an optically transmissive material and defined by a bottom surface 70 and an opposing top surface 72 extending generally parallel to surface 70. Flexible encapsulation layer 40 is configured to redistribute and spread at least a portion of light energy emitted by highly compact, discrete LEDs 2 across a much larger surface for an enhanced brightness uniformity and masking the bright spots produced by such LEDs 2. In addition, flexible encapsulation layer 40 may be configured to conduct waste heat through its volume and dissipate such heat via surface 72. Although optically transmissive dielectric materials that can be utilized for flexible encapsulation layer 40 generally provide much fewer options for efficient heat conduction compared to, for example, metallic materials that can be utilized for flexible support substrate 20, the encapsulation layer may nevertheless be configured to dissipate at least a smaller portion of waste thermal energy generated by LEDs 2.
[0057]Flexible LED illumination device 900 may be configured to dissipate heat generated by LEDs 2 using both radiative heat transfer and natural convection. Both of surfaces 72 and 86 defining the outer boundaries of the sheet-form structure of flexible LED illumination device 900 may be configured for efficient heat dissipation to the environment so that the effective heat-dissipating area of the device can be twice the area of the respective sheet-form structure.
[0058]According to one embodiment, LEDs 2 are evenly distributed over the entire light-emitting area of flexible sheet-form LED illumination device 900 and configured to consume a limited amount of electric power per unit area, within a predetermined range, and, subsequently, emit a limited amount of light energy per unit area. Such range may be selected such that flexible LED illumination device 900 emits a sufficient amount of light for the intended purpose and yet can be operated continuously without overheating when using only natural convection and direct radiation heat transfer as the primary means for heat dissipation. More particularly, the operating range of electric power consumption may be selected such that the waste heat generated by LEDs 2 can be effectively dissipated only through the exposed areas of flexible LED illumination device 900 while keeping the temperature of the device below a prescribed level (e.g., less than 20° C. above ambient, less than 30° C. above ambient, or less than 40° C. above ambient).
[0059]The heat energy generated by LEDs 2 and received by the laminate of flexible support substrate 20 and flexible encapsulation layer 40 is defined by the amount of electric energy consumed by LEDs 2 and the efficiency with which such LEDs 2 and the overall structure of flexible LED illumination device 900 converts electrical power into optical power. Accordingly, a maximum allowed density of the heat flux flowing through heat-dissipating surfaces may be determined by the design of flexible LED illumination device 900 and the electric power consumed by the device per its unit area.
[0060]The electric consumption of flexible LED illumination device 900 or any its portion may be expressed in terms of an operational areal electric power density and measured in watts of consumed electric energy per square meter of the respective light emitting area. For example, when flexible LED illumination device 900 is configured as a thin broad-area sheet with a continuous light emitting area having a length and width dimensions of 0.5 m and 1 m, respectively, and is further configured to consume 100 W of nominal electric power when in normal operation, an average operational areal electric power density of the device is 200 W/m2. Considering that LEDs 2 may be dimmable, a nominal electric power consumed by flexible LED illumination device 900 may be defined as a product of electric current and voltage delivered to the device without any dimming.
[0061]According to one embodiment, an average operational areal electric power density of flexible LED illumination device 900 is between a minimum of 50 W/m2 and a maximum of 1500 W/m2. According to one embodiment, the average operational areal electric power density is between 75 W/m2 and 1000 W/m2. According to one embodiment, the average operational areal electric power density is between 100 W/m2 and 500 W/m2.
[0062]According to one embodiment, the operational areal electric power is substantially constant across the entire light emitting area of flexible LED illumination device 900. Local operational areal electric power density at a specific point location of flexible LED illumination device 900 may be defined as an average of operational areal electric power density of a sampling area surrounding such point location. The dimensions of the sampling area may be selected based on the size of flexible LED illumination device 900. In one embodiment, the sampling area may have dimensions that are about 1/10th of the respective dimensions of flexible LED illumination device 900. For example, when the entire active light emitting area of flexible LED illumination device 900 has a size of 500 mm by 500 mm, the sampling area may have dimensions of 50 mm by 50 mm. Each sampling area and may include a relatively large number of LEDs 2 (e.g., 50, 100 or more).
[0063]The number of LEDs 2 and the amount of light produced by each LED 2 may be selected such that the operational areal electric power density does not exceed the prescribed values, as described above. Depending on the luminous efficacy of LEDs 2 (commonly expressed in lumens per Watt) and optical efficiency of the sheet-form light emitting structure formed flexible support substrate 20 and flexible encapsulation layer 40, a luminous emittance of flexible LED illumination device 900 may also be limited by a practical range. Luminous emittance (luminous exitance) is commonly defined as the luminous flux emitted from a surface per unit area and is conventionally measured in lumens per square meter (lm/m2). According to one embodiment, flexible LED illumination device 900 is configured to have a luminous emittance between 2500 lm/m2 and 250000 lm/m2. According to one embodiment, flexible LED illumination device 900 has a luminous emittance between 3000 lm/m2 and 150000 lm/m2. According to one embodiment, flexible LED illumination device 900 has a luminous emittance between 5000 lm/m2 and 75000 lm/m2. According to one embodiment, flexible LED illumination device 900 has a luminous emittance between 10000 lm/m2 and 50000 lm/m2. According to one embodiment, flexible LED illumination device 900 has a luminous emittance between 10000 lm/m2 and 25000 lm/m2.
[0064]According to one embodiment, flexible LED illumination device 900 is configured as an opaque, continuous, monolithic solid sheet emitting light from one side through surface 72. Flexible LED illumination device 900 may be further configured such that there are generally no optical boundaries between at least some of LEDs 2 embedded into flexible encapsulation layer 40. Each individual LED 2 may be disposed in energy exchange relationship with respect to one or more adjacent LEDs 2. According to one embodiment, each individual LED 2 is disposed in energy exchange relationship with respect to at least several other LEDs 2 surrounding such individual LED 2. The optically transmissive material of flexible encapsulation layer 40 can be configured to operate as a light-carrying medium and conducting light from one LED 2 to another. Flexible LED illumination device 900 may be further configured such that it can be flexed, bent or folded in spacing areas between LEDs 2 disposed in energy exchange relationship with each other.
[0065]Surface portions of rigid substrates 4 may be exposed to light propagating within flexible encapsulation layer 40. Accordingly, such exposed surface portions may be made reflective to reduce the light loss within flexible LED illumination device 900. According to one embodiment, surface area surrounding each LED 2 may be configured to receive light emitted by one or more other LEDs 2, such as the adjacent LEDs 2.
[0066]According to one embodiment, each LED 2 is represented by an individual inorganic LED chip or die. Such inorganic LED chips or dies are distributed over a broad area of flexible substrate 20 and bonded or otherwise mounted to surface 88 with a good mechanical and thermal contact that allows for efficient heat transfer from the LED chips to the substrate.
[0067]According to one embodiment, each LED 2 may also include a cluster of LED chips or dies. In one implementation, each LED chip in the cluster may be configured to emit light in the same color, such as “royal blue” for example. In an alternative implementation, each LED chip in the cluster may be configured to emit light in a different color. In a non-limiting example, each individual LED 2 may be configured as an RGB LED and include a multi-color cluster of 3 LED chips (Red, Green, and Blue). At least one of the LED clusters may also include a white-color LED.
[0068]According to one embodiment, the plurality of LEDs 2 is formed by a large two-dimensional array of inorganic LED chips evenly distributed over surface 88 and having alternating colors. For example, the alternating colors may be red, green, blue, and white. The multi-color LED chips may be distributed according to any suitable pattern. In a non-limiting example, each white-color LED may be surrounded by red, green, and blue LEDs or LED chips disposed equidistantly from such white-color LED.
[0069]Referring further to FIG. 1, each LED 2 is mounted (e.g., bonded) to rigid substrate 4 with a good mechanical and thermal contact. In turn, rigid substrate 4 is bonded to the reflective side (surface 88) of flexible substrate 20 with a good mechanical and thermal contact. According to an aspect of the embodiments illustrated in FIG. 1, each rigid substrate 4 represents a generally undeformable (under normal operation of flexible LED illumination device 900) pad upon which LED 2 is residing.
[0070]According to one embodiment, each rigid substrate 4 supports a single LED 2. Each rigid substrate 4 may have a width and length dimensions approximating those of the respective LED 2. Alternatively, rigid substrates 4 may have slightly or considerably greater dimensions than those of LED 2.
[0071]According to one embodiment, each rigid substrate 4 supports multiple LEDs 2. For example, two, three, four, or more LED chips may be mounted to substrate 4 at different locations of its surface. According to one embodiment, such LED chips may have the same light emission color. According to an alternative embodiment, such LED chips may have different light emission colors.
[0072]Each rigid substrate 4 should preferably have a considerably greater stiffness than flexible support substrate 20. It may be also configured to have a sufficient thickness to prevent its deformations when flexible substrate 20 is bent or flexed during the normal operation of LED illumination device 900 or during normal handling of the device. By way of example, each rigid substrate 4 can be made from a rigid and stiff ceramic material such as alumina, aluminum nitride, or silicon carbide and should preferably have a high thermal conductivity. Various layers of rigid substrate 4 may include crystalline materials such as sapphire or silicon, various polymeric or metallic layers, and/or a printed circuit board (PCB).
[0073]Each rigid substrate 4, as a whole, is ordinarily opaque. However, it may also be transparent, translucent or incorporate one or more optically transmissive layers. According to one embodiment, each rigid substrate 4 has a highly reflective surface. In one embodiment, each rigid substrate 4 incorporates one or more other substrates, pads or submounts that have various thicknesses. In one embodiment, each rigid substrate 4 incorporates a solder mask. In one embodiment, each rigid substrate 4 incorporates two or more electrical contacts used for interconnecting LEDs 2 in the array.
[0074]It is noted that LEDs 2 may be represented by unpackaged (uncased) LEDs or LED chips that are attached or otherwise mounted to flexible support substrate 20 either directly or indirectly using any suitable method. For example, flexible support substrate 20 may be formed by a flexible circuit board (PCB) having a 0.3-1 mm thickness and LEDs 2 may be bonded directly to such PCB using a Chip-On-Board (COB) technique. In a further non-limiting example, flexible support substrate 20 may be formed by a film-thickness flexible PCB substrate having a 0.03-0.3 mm thickness and LEDs 2 may be mounted directly to such flexible PCB substrate using a Chip-On-Film (COF) technique. According to an aspect of such exemplary implementations, the sheet-form structure formed by LED illumination device 900 may represent a single, large-area, flexible package for otherwise unpackaged LEDs 2.
[0075]The thickness of flexible encapsulation layer 40 is preferably greater than the height of individual LEDs 2. According to different embodiments, the thickness of flexible encapsulation layer 40 is at least two times, at least three times, and at least four times greater than the height of individual LEDs 2.
[0076]The thickness of flexible encapsulation layer 40 may also be greater than the size of individual LEDs 2 measured in a plane parallel to the surface of flexible sheet-form LED illumination device 900. According to one embodiment, a combined thickness of flexible encapsulation layer 40 and flexible support substrate 20 is greater than such size of individual LEDs 2.
[0077]According to an aspect of the embodiments schematically illustrated in FIG. 1, the array of LEDs 2 assembled on a common flexible support substrate 20 forms elevated mesa structures on otherwise smooth and planar surface 88. Flexible encapsulation layer 40 fully covers/encapsulates such mesa structures, covering the exposed sides of the respective LED dies, and levels the surface of flexible LED illumination device 900.
[0078]The material of flexible encapsulation layer 40 is disposed in contact with the bodies of each LED 2 on all sides so that there is generally no air spaces between such LED 2 and the material of flexible encapsulation layer 40. The material of flexible encapsulation layer 40 is also particularly disposed in contact with the light emitting surface of each LED 2. When LED 2 is formed by a LED die mounted to a substrate and protruding away from the mounting surface of such substrate, flexible encapsulation layer 40 should fully encapsulate such LED die so that the is substantially no air gap between LED die and the material of flexible encapsulation layer 4.
[0079]According to an aspect, flexible encapsulation layer 40 having a good, gapless optical contact with the light emitting area of LED 2 may improve light extraction from the light emitting layer(s) of LED 2, e.g., by suppressing TIR within such light emitting layer(s) at least for some light propagation angles.
[0080]According to one embodiment, flexible encapsulation layer 40 is configured as a gapless conformal coating over flexible support substrate 20 and mesa structures formed by LEDs 2. In this case, top surface 72 of flexible encapsulation layer 40 may have a generally constant or near-constant thickness over its entire area featuring somewhat smoothened surface bumps corresponding to LEDs 2. Such surface bumps (not shown in FIG. 1, but see, e.g., FIG. 17) may have the shape of spherical or quasi-spherical lenses. Such lenses may be configured to assist in light extraction from flexible encapsulation layer 40 and/or redistributing light emitted from surface 72 (e.g., collimating the emergent light rays).
[0081]The thickness of flexible encapsulation layer 40 is preferably very low compared to its major dimensions (e.g., length and width for a rectangular shape or a diameter for a round shape). According to one embodiment, a thickness of flexible encapsulation layer 40 is less than 0.01 of a smallest major dimension of the layer. According to one embodiment, a thickness of flexible encapsulation layer 40 is less than 0.001 of a major dimension of the layer.
[0082]Flexible encapsulation layer 40 is made from a heat-resistant, optically transmissive dielectric material. The material may be optically clear but may also have some tint or haze while providing some transparency. Such material should also preferably be relatively soft, highly flexible, and have good elasticity.
[0083]Flexible encapsulation layer 40 is preferably configured to allow for its reversible distortion or deformation when bending or folding flexible LED illumination device 900. In one embodiment, the material is silicone. In alternative embodiments, the material of flexible encapsulation layer 40 may be selected from various elastomeric compounds or resins that provide sufficient flexibility, softness, gas/moisture impermeability and resistance to high temperatures associated with LED encapsulation.
[0084]According to one embodiment, a hardness of the material of flexible encapsulation layer 40 is between durometer hardness values of 10 Shore A and 90 Shore A (as measured in accordance with ASTM D2240 type A scale). According to one embodiment, the material of flexible encapsulation layer 40 has a hardness between 25 Shore A and 85 Shore A. According to one embodiment, the material of flexible encapsulation layer 40 has a hardness between 30 Shore A and 65 Shore A.
[0085]Flexible encapsulation layer 40 may include a light diffusing material. For example, such light diffusing material may incorporate light scattering particles distributed throughout its volume and causing light rays propagating through encapsulation layer 40 to randomly change their propagation directions.
[0086]Flexible encapsulation layer 40 may further include a luminescent material or phosphor used to change the light emission spectrum. For example, the light emitting chips of LEDs 2 may be configured to emit a blue light and a YAG phosphor may be employed to convert such blue