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Patent Issued for Optical Arrangement with a Light Transmitting Layer Arranged to Cover a Portion of Light Entry Surface of Light Guide and to...

July 23, 2014



Patent Issued for Optical Arrangement with a Light Transmitting Layer Arranged to Cover a Portion of Light Entry Surface of Light Guide and to Transmit Light Diffusively

By a News Reporter-Staff News Editor at Electronics Newsweekly -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventors Ijzerman, Willem Lubertus (Eindhoven, NL); Vissenberg, Michel Cornelis Josephus Marie (Eindhoven, NL); Van Der Tempel, Leendert (Eindhoven, NL); Sabou, Florian Cosmin (Jibou, RO), filed on April 10, 2008, was published online on July 8, 2014.

The assignee for this patent, patent number 8770821, is Koninklijke Philips N.V. (Eindhoven, NL).

Reporters obtained the following quote from the background information supplied by the inventors: "As the efficacy (lm/Watt) of light emitting diodes (LEDs) increases and prices go down, it is expected that LED illumination and LED based luminaires soon will be serious alternatives to and at a competitive level with hitherto predominant tube luminescent (TL) based luminaires.

"However, one issue with LED lighting is the provision of warm white light. All today available LEDs with high lumen efficacy (.about.75 lm/Watt) produce light with a high color temperature (.about.6000 K) and are perceived as cold white. For most general illumination applications a color temperature of 3000 K or less is preferred. In addition, the light should have a good color rendering index.

"Low color temperature with a good color rendering index can be accomplished by means of phosphor in combination with illumination of a LED.

"Conventionally, the phosphor is embedded in glue that is directly attached to the LED chip. However, a problem with such a solution is that the phosphor has to withstand the temperature of the LED and the light flux at the same time. The result is often that this type of LED and phosphor solution does not meet the lifetime requirements necessary. A remedy to this particular problem is to avoid attaching the phosphor directly to the LED chip, but this results in other side effects and problems.

"For example, remote phosphor solutions of this kind result in that many solutions developed for ordinary LEDs are no longer compatible, not possible to use, not able to fulfill luminaire requirements etc. For example, professional lighting systems have to fulfill requirements with respect to the angular distribution of the light (glare regulations), see the IESNA Lighting Handbook, 9.sup.th edition. It has been shown that it is particularly difficult to fulfill these requirements with a remote phosphor solution, partly owing to that the remote phosphor conversion of light results in a larger light source with light being emitted from a larger surface.

"Another problem related to LED based luminaires is that these luminaires, and LEDs generally, provide light that is very bright. Diffusing the light from a LED based luminaire may remedy this, but makes it difficult to provide light that fulfills requirements regarding angular distribution."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "Hence, in view of the above, it is an object of the present invention to overcome or at least alleviate problems in the prior art and/or to provide an alternative luminaire arrangement. A specific object is to provide a luminaire arrangement that is particularly suitable for use in a LED based luminaire and that allows for efficiency and forming of a light beam fulfilling glare requirements.

"The invention is defined by the appended independent claim. Preferred embodiments are set forth in the dependent claims and in the following description and drawings.

"Hence, according to one aspect, the above-mentioned and other objects that will be evident from the following description, are achieved by an optical arrangement comprising a light guide having a light-entry portion with a light-entry surface, a tapering portion with a light reflecting surface, and a light-exit surface, the light-entry portion being arranged to guide light from the light-entry surface in a first direction towards the light reflecting surface, the light reflecting surface being arranged in relation to the first direction so that incident light from the light-entry portion is reflected towards the light-exit surface; and a light transmitting layer adapted to transmit light diffusively and arranged to cover at least a portion of the light-entry surface of the light guide.

"A 'wedge shaped' light guide of this kind is known from US20010046365A1, but is only described for incoupling of light by direct illumination from fluorescent tubes or light bulbs. Nothing is disclosed in US20010046365A1 about, nor teached in the direction of, incoupling of light by a light transmitting layer, and nothing is disclosed about, nor teached in the direction of using the light guide in a LED based luminaire and/or using it in luminaires targeted to solve the aforementioned problems related to such luminaires.

"In fact, the present invention is partly based on the finding that a light guide of the present 'wedge shaped' kind, advantageously may be used in a LED based luminaire and that it allows for at least alleviating the aforementioned problems.

"In the present luminaire arrangement, the light transmitting layer allows for controlled and efficient incoupling of diffuse light transmitted from a comparatively large area into the light guide. Dimensioning of the light guide allows for forming the incoupled light into a light beam having predetermined properties when leaving the light guide, which properties allow for fulfillment of luminaire requirements, e.g. as regards to angular distribution and glare.

"The light transmitting layer may be a light transmissive layer adapted to diffuse incident light and output the diffused light from the side of the layer facing the light-entry surface. Hence, problems related to light source brightness can be remedied or alleviated without using a diffuser at the luminaire output.

"The light transmitting layer may also be a light emitting layer adapted to emit light in response to excitation. The light emitting layer may thus be a layer that can generate light and not a translucent layer that merely forwards light through the layer. The light emitting layer may be a layer adapted to emit light in response to excitation by light, preferably a phosphor layer. It has been found that increased efficiency is particularly desirable/needed in slim luminaires (large light output area compared to thickness) from which a uniform and 'non-glare' light is desirable to provide. In such luminaires the active phosphor area for re-generating the light will be relatively small compared to the total light output area of the luminaire (in order to be able to provide collimated light within glare requirements and still keep the luminaire thin).

"The optical arrangement may further comprise a light source, preferably a light emitting diode (LED) or a laser diode, arranged to directly or indirectly illuminate the light transmitting layer.

"The optical arrangement may comprise a re-transmitting light source arranged to illuminate the light transmitting layer in response to illumination by the light source. The re-transmitting light source may be adapted to emit light in response to excitation by light, preferably by comprising a phosphor material. This e.g. allow a phosphor layer to be used to generate light, e.g. by illumination from a LED, without arranging the phosphor to cover the light-entry surface, and thus the phosphor can be shielded from being visible via the light-exit surface. One advantage from this is that a colored appearance, such as yellow, can be avoided when e.g. a luminaire comprising the optical arrangement is in a off-state.

"The light transmitting layer may cover the light-entry surface in such way that the light transmitting layer substantially shields the light-entry surface from direct illumination by the light source.

"The light-entry surface and the light transmitting layer may encircle a space. By 'encircle a space' is meant that there exists at least one plane that intersects said space and which plane, in virtually all directions from a position in the space, also intersects the light emitting layer and the light-entry surface. As a result, the light transmitting layer will emit light towards the light guide side or towards the space side. In the latter case, owing to the encircled space, light from the light transmitting layer may be incident either on another portion of the light-entry surface and/or the light transmitting layer, which means the light can be efficiently utilized and it reduces the risk of light escaping the light guide in an undesirable manner. Another result is that the light transmitting layer, despite being a layer, may act as a single centrally placed light source emitting light omnidirectionally into the light guide, and that the reflecting surface will be able to reflect light to cover a large light-exit surface area. In case there is a light source, such as a LED, arranged to directly or indirectly illuminate the light transmitting layer, the light source may be arranged in the space, or at least so that it illuminates the light emitting layer via the space.

"The light guide may be substantially rotational symmetric in a plane, preferably substantially circular symmetric, with the center of symmetry located in the encircled space. Rotational symmetry enables for provision of a symmetric light beam which often is desirable in lighting applications, such as in downlighting applications.

"The light transmitting layer may be arranged less than 1 mm, preferably substantially equidistantly, from the light-entry surface, and more preferably as close as possible to the light-entry surface without being in optical contact. An advantage from non-optical contact is that refraction of light rays emitted by the light emitting layer and that are coupled into the light guide, will be refracted with a collimating effect.

"Alternatively, the light transmitting layer may be in optical contact with the light-entry surface. This has another advantage, viz. that light more efficiently can be coupled into the light guide since reflections in the light-entry surface can be avoided.

"The reflecting surface may be obliquely arranged in relation to the light-exit surface at an angle in a range of 1.degree.-20.degree., preferably 4.degree.-12.degree..

"The light-entry portion may increase in thickness from the light-entry surface towards the tapering portion. An increase of the thickness, for example by a linear slope, reduces the angle of incidence on the inner light guide surfaces of light being coupled in via the light-entry surface, and is thus beneficial for accomplishing total internal reflection (TIR) avoiding that light that entering the light guide is coupled out undesirably.

"The light-entry portion may have at least a sub-portion of substantially constant thickness along the first direction. Constant thickness and thus parallel opposite surfaces where reflection and refraction of light can occur inside the light guide, have a collimating effect of the light being guided and that eventually will be coupled out via the light-exit surface.

"The light guide may be a flat structure, preferably in a plane substantially perpendicular to the light-entry surface.

"'Flat' in this sense is when the dimensions in one plane of the light guide is magnitudes greater, such as at least 3 times greater, than the dimension along a normal to that plane. The reflecting surface allows for outcoupling of light covering a large part of the plane of flatness of the light guide. Typically the light-exit surface is parallel to the plane of flatness. A flat light guide and a flat luminaire based on this light guide, which are able to provide light via the plane of flatness, can be made with a very discrete appearance.

"The arrangement may further comprise a light transmissive re-direction layer covering at least a portion of the light-exit surface of the light guide. By 'transmissive redirection layer' is meant a layer with low optical absorption that has the ability to change direction of light passing through the layer in a predetermined manner.

"The re-direction layer may thus make secondary adjustments to the light, such as final tuning of the light beam to be provided, typically by focusing or diffusing the light leaving the light guide. The splitting of the 'beam-shaping' functionality into separate parts allows each part to solve separate sub-problems, which facilitate design and implementation. For example, it may be enough that the light leaving the light guide via the light-exit surface is collimated only to a certain degree since the re-direction layer can take care of the last focusing, which i.a. means that the output from the light guide can be more permissive allowing for greater freedom in the design of the light guide. A separate redirection layer also allow for convenient adaptation, e.g. by replacing only the re-direction layer when requirements of the light beam to be provided changes.

"The re-direction layer may comprise at least one triangular element formed in the surface of the layer, said element may have a first triangle surface facing towards the light-entry surface side of the light guide arranged at a first angle in relation to the normal to the plane of the layer, and may have a second triangle surface facing away from the light-entry surface side of the light guide arranged at a second angle in relation to the normal to the plane of the layer, said first and second triangle surfaces may meet at a tip of the triangular element.

"The at least one triangular element may encircle a point in the plane of the re-direction layer, and the re-direction layer may be is substantially rotational symmetric in the plane of the layer, preferably circular symmetric, with the center of symmetry being the encircled point. This may be particularly advantageous in combination with a rotational symmetric light guide, and in such case the center of symmetry is preferably the same and the symmetry planes parallel.

"The at least one triangular element may be formed on the side facing the light guide with the triangular element tip pointing towards the light guide. The first angle added to the second angle may be in the range of 35.degree.-45.degree., preferably in the range of 38.degree.-42.degree., more preferably about 40.degree.. The first angle preferably is more acute than the second angle. The first angle may be in the range 1.degree.-17.degree., preferably 2.degree.-12.degree. and the second angle may be in the range 28.degree.-44.degree., preferably 30.degree.-38.degree..

"The optical arrangement may further comprise a second light guide arranged to guide light to the light transmitting layer, said second light guide being adapted to guide light in its interior along a guide direction using reflections in lateral surfaces of the second light guide, which surfaces are substantially parallel to said guide direction, the second light guide having a light input area for in-coupling of light and a light output area for output of light to the light transmitting layer, wherein the light output area is arranged at a distance from the light input area in the guide direction. The second light guide allows for improved efficiency with more reaching the light transmitting layer. It also provide means for distributing and mixing light in a controlled manner before it reaches the light transmitting layer.

"The second light guide may be of a dielectric material capable of guiding light inside the material and the light input area and the light output area may correspond to a respective input surface and output surface of said light guide. By 'surface' is included both inner and outer surfaces of the light guide. A 'surface' may further be a full surface, e.g. a full edge surface, or a portion thereof.

"A light source may be arranged opposite to the input surface to provide light in the guide direction towards the light input surface. Except from being a straightforward and efficient way of coupling light into the light guide, this allows for coupling light into the light guide from the side via end surfaces perpendicular to the guide direction, which in turn allows for keeping electronic components such as LEDs away from the internal, or inner parts of light guide and luminaire.

"The first input surface may be is convex, preferably with linear slope and/or it may have undulations, preferably with linear slope. Owing to the convex or undulated input surface light that is emitted straight along the axis of the light guide become directed towards the lateral surfaces which increase the amount of light incident on the light transmitting layer.

"The optical arrangement may further comprise a second light source, preferably a LED, arranged to provide light to a second light input surface arranged opposite to the first light input surface in the guide direction, whereby light can be coupled into the second light guide from opposite directions, preferably the first and second light input surface and respective thereto adjoining portions of the second light guide are of substantially same shape.

"The light input area may intersect the guide direction, preferably substantially perpendicularly, and the light input surface may be in optical contact with a dielectric medium of lower refractive index, such as air, whereby any light provided to be incident on the light input surface will pass through this medium and be coupled into the second light guide at angles within a determined angular interval that is more narrow than an angular interval of the incident light. The difference in refractive index between the second light guide and the dielectric medium may be at least what is required to reach total internal reflection in the lateral surfaces for substantially all light within the angular interval. The difference in refractive index between the second light guide and the dielectric medium is preferably at least about 1.4. This promotes total internal reflection (TIR) in the lateral surfaces for any input angle (i.e. a maximal first angular interval of .+-.90.degree.) when the lateral surfaces are perpendicular (or at a larger angle) in relation to the input surface and in optical contact with a medium having the same or less refractive index as for the input surface, e.g. as is the case when both are in optical contact with air. It is understood that if the angular interval is more narrow than .+-.90.degree., the refractive index can be less than the above and still total internal reflection for all incoupled light can be accomplished. It should be noted that parts can be in mechanical contact without there being optical contact, e.g. the second light guide may have a lateral surface in contact with an object although there is no, or substantially no, optical contact in between, instead, e.g. if the mechanical contact is made in an air atmosphere, there can be a sufficiently small gap inbetween whereby the optical contact instead is with the air.

"The light output surface may be a portion of one of the lateral surfaces, which portion is in optical contact with and at least partially covered by the light transmitting layer. The light transmitting layer is hence arranged in a parallel relationship to the guide direction of the second light guide. Light will thus be guided and reach the light transmitting layer by reflections in the lateral surfaces, which facilitates shielding of the light transmitting layer from direct illumination by a light source. It also allows light to distribute and spread in the light guide before output, for example in case multiple light sources are used to produce the light being coupled into the light guide.

"A fully reflecting reflector layer may be arranged opposite to the light transmitting layer on an opposite side of the second light guide, preferably in non-optical contact with the second light guide. The reflector layer may be a wall portion of a reflector housing at least laterally enclosing the second light guide to prevent undesired outcoupling of light via the lateral surfaces of the light guide, and the housing is preferably in non-optical contact with the second light guide and provided with an opening for the light transmitting layer.

"The light guide may have additional spaced apart light output surfaces, each of which may be a respective portion of one of the lateral surfaces and which respective portion may be in optical contact with and at least partially covered by a respective light transmitting layer. Hence the light in the light guide, such as coupled into the second light guide by one or a few light sources, can be used to illuminate multiple light transmitting layers, with the light first distributing and spreading in the light guide.

"The light entry portion may comprise a funnel-shaped portion with a wider end of the funnel facing the tapering portion and a narrow end of the funnel comprising the light-entry surface. Lateral surfaces of the funnel, in relation to the first direction, may be in optical contact with a dielectric medium of lower refractive index, such as air. The light entry portion and the tapering portion may belong to separate parts of the light guide in optical contact with each other.

"The light entry portion may comprise several such funnel shaped portions lined up with parallel wider funnel end surfaces in substantially the same plane.

"According to another aspect:

"The light output surface may intersect the guide direction, preferably perpendicularly, the light output surface being in optical contact with a dielectric medium of lower refractive index, such as air, whereby light leaving the second light guide via the light output surface will pass through this medium. This means that also light being backscattered from the light transmitting layer and directed towards the light output surface will pass through the medium, which promotes that back-scattered light reenters the second light guide at TIR angles.

"The light output surface may be arranged substantially perpendicularly in relation to the light transmitting layer. As a result, only some light from the light output surface, i.e. light that is directed towards the light transmitting layer when leaving the light output surface, will be incident on the light transmitting layers, i.e. light is 'portioned out' to the light transmitting layer. The light that is not incident can thus be used for other purposes, e.g. to continue further in the guide direction to additional light transmitting layers, e.g. after being coupled into another light guide.

"The output surface may face a light output cavity, the light transmitting layer being at least part of a lateral closing surface to said cavity.

"The optical arrangement may further comprise a reflector layer arranged as at least part of a lateral closing surface to said cavity opposite to the light transmitting layer, preferably the reflector is arranged to reflect back-scattered light from the light transmitting layer back towards the light transmitting layer, such as by being a specular reflector directly facing the light transmitting layer.

"The optical arrangement may further comprise an additional light guide having substantially the same properties and shape as the second light guide, the additional light guide may have a light output surface forming at least part of a closing surface to said light output cavity opposite to the output surface of the second light guide. It should be generally understood that the light output cavity can be closed by different combinations of light output surfaces, reflectors and light transmitting layers. Although in principle also a light source surface can take part in closing a light output cavity, this would mean that light will not be able, as is typically desirable, to mix and distribute before being incident on the light transmitting layer.

"The light entry portion may comprise a funnel-shaped portion with a wider end of the funnel facing the tapering portion and a narrow end of the funnel comprising the light-entry surface. Lateral surfaces of the funnel, in relation to the first direction, are in optical contact with a dielectric medium of lower refractive index, such as air.

"The light entry portion and the tapering portion may belong to separate parts of the light guide in optical contact with each other.

"The light entry portion may comprise several such funnel shaped portions lined up with parallel wider funnel ends in substantially the same plane.

"All cavity surfaces perpendicular to the light transmitting layer may be light output surfaces of the second light guide. The second light guide may be formed as a plate, the cavity being formed by a hole in said plate.

"The light transmitting layer may be a portion of a larger light transmitting layer covering the plate and multiple cavity holes therein.

"The light guide may be in the form of a layer comprising multiple funnel-shaped light guide elements, the light entry portion may comprise narrow end portions of the funnel-shaped light guide elements and the tapering portion may comprise wider end portions of the funnel-shaped light guide elements, the light exit surface comprising end surfaces of said wider end portions.

"A light source surface comprising a light source, preferably a light emitting diode (LED), may be arranged substantially perpendicular in relation to the light input surface.

"The input surface may face a light input cavity, the light source surface being at least part of a lateral closing surface to said cavity.

"The optical arrangement may further comprise a reflector layer arranged as at least part of a lateral closing surface to the light input cavity opposite to the light source surface, preferably the reflector is arranged to reflect light towards the light input surface, such as by being a diffusive reflector and/or by having a sloped surface. Hence light that is not directly incident on the light input surface or reflected therefrom, is promoted to be indirectly incident thereon, which increase efficiency.

"Moreover, the optical arrangement may further comprise an additional light guide having substantially same properties and shape as the second light guide, the additional light guide having a light input surface forming at least part of a closing surface to said cavity opposite to the input surface of the second light guide.

"It is understood that sides of the light input cavity generally can be closed by different combinations of light input surfaces, reflectors and light source surfaces. However, what specifically is possible depends on how the optical arrangement is used. Although in principle also the light transmitting layer can take part in closing a light input cavity, this means that light will not be able, as is typically desirable, to mix and distribute before being incident on the light transmitting layer.

"The light guide, the light transmitting layer and the second light guide may encircle a space in a plane with the light input surface facing the space, whereby the guide direction is a direction in said plane. The light guide, the light transmitting layer and the second light guide may be substantially symmetrical in the plane, preferably circular symmetric, with the center of symmetry located in the encircled space.

"The light input surface may be arranged opposite to the light output surface in the guide direction, and the light output surface may be facing the light transmitting layer.

"The light input surface and the light output surface may be substantially perpendicularly arranged in relation to the plane.

"The light output surface may be in optical contact with a dielectric medium of lower refractive index, such as air, which light to/from the light transmitting layer has to pass. An advantage here is that light being back-scattered from the light transmitting layer towards the light output surface will enter the light-guide at angles promoting TIR, however, as a result also more light may be reflected in the interface and not reach the light transmitting layer in the first place. Alternatively the light output surface may be in optical contact with the light transmitting layer. This has the advantage that light is promoted to be coupled out from the light output surface and not reflected back in the first place, however, there is at the same time an effect of increased amount of light being scattered back from the light transmitting layer into the second light guide at non-TIR angles.

"A luminaire and/or a light output device may comprise the optical arrangement. The light output device may be a lighting application, preferably a downlighting application.

"It is noted that the invention relates to all possible combinations of features recited in the claims."

For more information, see this patent: Ijzerman, Willem Lubertus; Vissenberg, Michel Cornelis Josephus Marie; Van Der Tempel, Leendert; Sabou, Florian Cosmin. Optical Arrangement with a Light Transmitting Layer Arranged to Cover a Portion of Light Entry Surface of Light Guide and to Transmit Light Diffusively. U.S. Patent Number 8770821, filed April 10, 2008, and published online on July 8, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8770821.PN.&OS=PN/8770821RS=PN/8770821

Keywords for this news article include: Electronics, Light-emitting Diode, Koninklijke Philips N.V..

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