Embodiments of the present invention relate generally to the field of illumination systems, and, more specifically, to optical modules for providing light output having narrow beam size and high lumen output.
As the efficacy (measured in lumens per 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 until now predominant tube luminescent (TL) based luminaires.
WO 2008/126023 describes a luminaire comprising a light source positioned within a source cavity in a collimating structure arranged for providing predefined light distribution from the luminaire. The light source includes a plurality of LEDS. The number of LEDS that can be included within the source cavity depends on the size of the cavity. In turn, the intensity of the light produced by the luminaire depends on the number of LEDS included. Thus, in order to increase lumen output of such a luminaire, a larger source cavity capable of accommodating a larger number of LEDs should be used.
One drawback of the proposed structure is that increasing the size of the source cavity also increases the beamwidth of the output light.
These absolute light levels can be too low for a range of applications where narrow beam spotlights with high light output are needed, such as surgical lighting, outdoor lighting, entertainment, etc. Therefore, it is desirable to provide a luminaire capable of providing light having both a narrow beamwidth and a high lumen output.
According to one aspect of the invention, an optical module is disclosed. The module includes two or more segments positioned around an axis of symmetry of the module. Each segment includes a light collimating structure for providing a predefined light distribution of light exiting the optical module and a light source, preferably a LED or a laser diode, assembled in a cavity within the light collimating structure. A center of the cavity coincides with the optical axis of the light collimating structure and is at a distance d from the axis of symmetry of the optical module.
As used herein, the term “center of a cavity” refers to a point of symmetry (e.g. the center of a circle or a regular polygon, or the axis of symmetry), or a focus point lying on such an axis of symmetry (e.g. one of the foci of an ellipse or parabola).
Providing an optical module that includes two or more segments where each segment comprises its own light source allows obtaining higher lumen output compared to prior art luminaires having only one light source. Within each segment, a light source is positioned within its own source cavity. Arranging the segments in such a manner that the center of each source cavity coincides with the optical axis of the collimating structure of the segment allows preserving narrow beamwidth collimation of the light exiting the optical module.
According to another aspect of the invention, a light output device or a luminaire comprising such an optical module is provided.
Embodiments of claims 2-5 advantageously allows guiding light provided by each of the light sources towards the light collimating structure of the corresponding segment. Placing specular mirrors at certain key positions, such as e.g. in the back of the cavities, may aid in directing the light from each light source into the proper corresponding collimating optics, resulting in a dramatic increase of the luminaire efficiency.
Embodiment of claim 6 specifies that the collimating structure may comprise a light guide, such as e.g. a wedge-shaped light guide, and a re-direction layer, such as e.g. a redirection foil. In one embodiment, the light guide may be substantially rotational symmetric in a plane, with the center of symmetry of the light guide coinciding with the center of the cavity. Rotational symmetry enables for provision of a symmetric light beam which often is desirable in lighting applications, such as in downlighting applications.
Embodiment of claim 7 specifies an advantageous structure for the light guide.
Embodiment of claim 8 provides that the optical module may further include 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. 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.
Embodiment of claim 9 provides that 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).
Embodiment of claim 10 specifies that the light source may be arranged to directly or indirectly illuminate the light transmitting layer and the optical module may further include 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. allows 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.
Embodiment of claim 11 provides that 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 light rays, emitted by the light emitting layer and 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.
Hereinafter, an embodiment of the invention will be described in further detail. It should be appreciated, however, that this embodiment may not be construed as limiting the scope of protection for the present invention.
In all figures, the dimensions as sketched are for illustration only and do no reflect the true dimensions or ratios. All figures are schematic and not to scale. In particular the thicknesses are exaggerated in relation to the other dimensions. In addition, details such as LED chip, wires, substrate, housing, etc. have been omitted from the drawings for clarity.
In the following description, numerous specific details are set forth to provide a more thorough understanding of the present invention. However, it will be apparent to one of skill in the art that the present invention may be practiced without one or more of these specific details. In other instances, well-known features have not been described in order to avoid obscuring the present invention.
In the shown embodiment there is a second light guide 157 shaped as a tube, or cylinder with a cylindrical through-hole 132 in the center, concentrically located in the cylindrical through hole 102. The second light guide 157 has a light input surface 158 facing the center of the through-hole 132 and a light output surface 168 facing the light emitting layer. The second light guide further has lateral surfaces 159, i.e. the end surfaces of the cylinder which are perpendicular to the light input and output surfaces 158, 168. These surfaces are preferably not in optical contact with neighboring objects, but instead interfacing an optically less dense medium, preferably air, i.e. are in optical contact with a medium of lower refractive index than the second light guide 157. The light emitting layer 113 is shown at a distance from the light output surface 168 i.e. in non-optical contact with the second light guide, but may in alternative embodiments be in optical contact.
The second light guide 157 provides a collimating effect which increases efficiency. However, it can be noted that the second light guide is not required for the function as such of the luminaire arrangement in
At the lower or bottom part of the cylindrical through hole 132 there is a light source 117, preferably a light emitting diode (LED), which may be omnidirectional. The light source may be attached to a substrate (not shown), such as a PCB. In other embodiments there may be one or many light sources also at other positions, such as at various positions in the mixing cavity 132. For example, to produce white light a blue LED or LEDs 117 can be used in combination with a yellow or orange phosphor layer 113.
Opposite to the light source 117, at the top end of the cylindrical hole 102, there is a mirror 115 covering the opening of the cylinder. The mirror 115 presents an inclined surface for reflecting light from the light source 117 towards the light emitting layer 113, light which else would escape via the cylinder opening. Since the light source is arranged so that it also illuminates the light emitting layer directly, the mirror 115 is not necessary, although it increases efficiency. Alternatively the mirror may be flat (not inclined) and/or may have diffusely reflective properties for light spreading. In
The light entering the light guide 101 via the light-entry surface 105 is first guided in a light-entry portion 103 of constant thickness, here equal to the thickness t1g of the light guide 101. Light that fulfills the conditions of TIR in inner surfaces 109, 110 of the light guide 101 will be guided towards a tapering portion 107 of the light guide 101, which portion 107 presents a reflecting surface 111 that is inclined and facing in the direction of the light-entry surface 105. The reflecting surface 111 is arranged with an angle [beta] in relation to the normal direction of the light-entry surface 105 and the plane x-y of the light guide.
The reflecting surface 111 reflects light incident from the light-entry portion 103, i.e. from the x-direction in
To ensure that light does not leave the reflecting surface 111 via refraction, a mirror layer 119 may be provided to cover the outside of the reflecting surface 111. Preferably the mirror layer 119 is arranged at a small distance from the light guide surface so that there is no optical contact.
In the plane (x-y) of the light guide 101 there is an angular distribution of the light. Owing to that the light emitting layer 113 will emit light into the light guide via the light-entry surface 105 at a distance of about R1 from the central axis CA, not all light will be incident on the reflecting surface 111 at 90 degrees in the x-y plane as would have been the case without the cylindrical hole and instead a “point like” light source on the central axis CA of the light guide. Note that this applies in the shown x-y plane and not when light is incident on the reflecting surface from directions that are not in this plane. When light from the light emitting layer is entering the light guide at the distance R1 from the center, a largest angle [phi] of light incident on the reflecting surface in the plane of the light guide occurs where the tapering portion 107 and the reflecting surface 111 begin, i.e. at a distance R2 from the central axis CA. It can be noted that non-optical contact between the light emitting layer 113 and the light-entry surface 105 typically will make the largest angle smaller than the angle [phi] indicated in the figure when light is refracted into the light guide 101 via the light-entry surface 105.
Still referring to
A light ray leaving the light-exit surface 109 of the light guide 101 will thus first be refracted at a light guide to air interface, pass the air filled “valley” between adjacent triangular elements, be refracted in the first surface 125 of a triangular element 123 at an air to re-direction layer interface, and then be reflected by TIR in the second surface 127 of the triangular element 123 at a re-direction layer to air interface. The last reflection directs the light ray towards the opposite surface of the redirection layer 121, which it passes by refraction at a re-direction layer to air interface. The re-direction layer may thus have a collimating and/or focusing effect on the light from the light guide.
It may be noted that the redirection layer 121 shown in
Moreover, in
The material of the light guide 101 and the second light guide 157 may in general and advantageously have an optical absorption less than 0.3/m, provide low haze and scattering, contain particles smaller than 200 nm and be able to sustain an operational temperature higher than 75 degrees Celsius. Since the optical path in the light guide typically is relatively large (e.g. about 50 mm), the material should preferably have high optical transparency and be of good optical quality so that absorption still can be low. The material of the re-direction layer 121 may generally and advantageously have an optical absorption of less than 4/m, provide low haze and scattering, contain particles smaller than 200 nm, be able to sustain an operational temperature higher than 75 degrees Celsius. The redirection layer may be similar to a so-called re-direction foil, such as the transmissive right angle film (TRAF) as currently is available under the name Vikuti™ from 3M. Furthermore, in the first detailed example the light guide 101 has a thickness t1g=5 mm and the re-direction layer 121 a thickness t11=3 mm. The light-entry surface 105 is located at a distance R1=20 mm from the central axis CA of the light guide, the tapering portion 107 and the reflecting surface 111 begin at a distance R2=30 mm from the central axis CA, and the light guide 101 and the reflecting surface 111 end at a distance R3=55.5 mm. The angle [beta] of the reflecting surface 111 is thus about 11 degrees and the area of the light-entry surface 105 and the light emitting layer covering it, is about 600 mm2. The light source 117 is a LED of less than 10 W having an area of 3 mm2. The light emitting layer is a phosphor layer, such as YAG:Ce (Cerium-doped Yttrium Aluminum Garnet) which is arranged as close as possible to the light-entry surface 105 without optical contact. There are about 100 adjacent triangular elements concentrically arranged about the central axis CA of the light guide 101. The first angle [alpha1] of each triangular element 123 is 9 degrees and the second angle [alpha2] is 31 degrees. The first detailed example results in a light beam with a beam width of about 2*30 degrees.
A second detailed example differs from the first detailed example in that R2=80 mm and R3=151 mm, whereby [beta] is about 4.0 degrees. The second detailed example results in a light beam with a beam width of about 2*10 degrees. A third detailed example differs from the first detailed example in that the first angle [alpha1] of each triangular element 123 is 2 degrees and the second angle [alpha2] is 36 degrees. In comparison with the light beam of the first detailed example, the third detailed example results in a light beam with a reduced “tail”, i.e. with less light flux at angles between half the beam width (at FWHM) and the cut-off angle. Furthermore, in linear systems it has been found that, at least in the range of a reflecting surface having an angle [beta] in the interval 2 degrees-15 degrees, the beam angle being provided is, as a design rule of thumb, about 5 times the angle [beta].
The number of triangular elements 123 disposed between the center and the perimeter of the light guide 101, i.e. along any radial direction in the x-y plane, is typically not crucial, however, more elements 123 (at constant layer thickness t1g), means smaller dimensions of the elements 123, which has the advantage that the elements will be more discrete and virtually invisible. On the other hand, when the dimensions become too small, there is a risk that imperfections in the triangular surfaces 125, 127, e.g. caused by manufacturing, will have increasing and eventually detrimental impact on the light beam to be provided. Hence, care should be taken when increasing the number of and downsizing the triangular elements.
In another embodiment there is a transmissive diffuser layer 113 instead of the light emitting layer 113. Light that pass through the diffuser is being diffused, i.e. here light incident on the inner side becomes diffused light that leaves from the side facing the light-entry surface. The diffuser may diffuse light in directions corresponding to those being provided by the light emitting layer and the diffuser layer may be arranged in relation to the light-entry surface similarly to the light emitting layer. In yet another embodiment, there is a light emitting layer, such as a phosphor layer, instead of the mirror 115, and instead of the light emitting layer 113 covering the light-entry surface there is a diffuser layer arranged to cover the light-entry surface 105. In this embodiment, the light source 117 emits light that is converted with a re-emitting effect by the light emitting layer at the top end of the cylindrical hole 102 thus forming a re-transmitting light source. The re-transmitted light then is incident on the diffuser layer. The diffuser layer may be shielded from direct light from the light source 117.
Most is the same in luminaire arrangements 100 and 169. However, a difference is that there is no second light guide 157 present and also that the mirror layer 119 has been replaced by a reflecting layer 118 covering not only the outer side of the reflecting surface 111 of the light guide, but also an outer surface side of the surfaces 110, 112 in the light-entry portion 103 and the bottom opening of the cylindrical hole 102. It is understood, however, that a second light guide may be used also with the luminaire arrangement 169. Furthermore the light source 117 is here arranged on the side of the reflecting layer 118 facing the through-hole 102. The reflecting layer 118 has a mirror or a specularly reflecting surface facing the light guide 101, and is preferably not in optical contact with the light guide 101.
Another difference between the embodiments of
When the sub-portion 106 reaches the thickness t1g of the light guide 101, at a distance R2′ from the central axis CA, there is a second sub-portion 108 of constant thickness, between distances R2′and R2 from the central axis CA, before the tapering portion 107 begins. The reason for the first sub-portion 106 of increasing thickness is to reduce the risk of undesirable refraction out from the light guide. The sloped surfaces 112 of the sub-portion 106 reduce the angle of light incident directly from the light-entry surface 105, and thus facilitate TIR. A sloped first sub-portion 106 may be particularly advantageous when the light-emitting layer is in optical contact with the light-entry surface. (In a situation with optical contact and without the sloped first sub-portion 106, some light would be incident by approximately 90 degrees in surfaces 109, 110.)
Some relations regarding the angular distribution in the plane of the light guide will now be given with reference to the two embodiments disclosed in the foregoing. With optical contact between the light-entry surface and the light emitting layer, the following equations may be used in the design of the light guide:
sin [phi]=R1/R2 (Eq. 2A)
The angle [phi] may be considered a good approximation for the cut-off angle for rule-of-thumb estimates. R1, R2 and [phi] are in accordance with
Without optical contact between the light-entry surface and the light emitting layer, the following equation replaces Eq. 2A:
sin [phi]=R1/(n1g*R2) (Eq. 2B)
with n1g being the refractive index of the light guide.
However, since the re-direction layer 121 may give a small but adverse contribution to the cut-off angle, it may be advised to have some margin when designing the light guide using the equations above.
For example, in a design with a cut-off of 10 degrees in air, a light guide with a refractive index of 1.5 and a light-entry surface arranged at R1=20 mm from the center, Eq. 2B results in that R2 should be about 77 mm. In practice R2 may need to be larger than this to accomplish a cut off not exceeding 10 degrees. It should be noted that the angle [beta] can be considered to determine the beam width in the direction orthogonal to the direction of [phi] and that thus both [phi] and [beta] must be considered in order to have a narrow beam, i.e. for a narrow beam both [phi] and [beta] should be small. In the foregoing the refractive indices of the light guide and the re-direction layer have been about 1.5. Other refractive indices may be used, preferably in the range of 1.4-1.8. However, as will be recognized by the skilled person, the hitherto discussed dimensions, angles, etc. may need to be adapted accordingly, which the skilled person will be able to do based on the information disclosed herein.
The pie-shaped sections, or segments, of the rotational symmetric luminaire arrangements that have been discussed in the foregoing may advantageously be used in assembling an optical module according to embodiments of the present invention. In the following, the term “cavity” refers to a through-hole 102 described above, the term “light source” refers to the light source 117 described above, and the term “collimating structure” refers to all of the elements of the luminaire arrangements shown in
As shown in
The corner axis of the segment 197 where the planes 194 and 195 intersect, shown in
First, the number of segments to be present in the future optical module should be selected. As previously described herein, the number of segments define the number of light sources that will be present in the optical module. Since the total light output of the optical module is the combination of the light outputs of each light source, the greater the number of light sources, the greater the lumen output of the optical module. Since, as will be described in greater detail below, the segments will be arranged in a “daisy” pattern around an axis of symmetry of an optical module, when N segments are selected to be included in the optical module, each segment spans an angle of 360/N degrees:
=360°/N
In
The distance d is selected to be such that the segment 197 includes the whole cavity. Therefore, for N segments, the minimal distance d can be determined as:
d
min
=R1/sin(180°/N)
Any distance d greater than dmin can be selected. The greater the distance d, the greater the diameter of the optical module. In one embodiment, it may be preferable to select the distance d to be as small as possible in order to e.g. keep the overall luminaire footprint as small as possible. In other embodiments, it maybe be preferable to select a larger distance d because an additional through-luminaire center hole would allow for the placement of extra optical equipment, such as e.g. a central camera in medical lighting equipment.
In step 182, N segments identical to the segment 197 defined in the previous step are produced (one such segment is shown in
In step 184, a first segment is arranged so that the axis of symmetry of the cavity of that segment (i.e., the intersection of planes 192 and 193, equivalent to the central axis CA of
The method ends in step 186, where other (N−1) segments are arranged around the axis of symmetry of the optical module so that, for each segment, the axis of symmetry of the cavity of that segment is at a distance d from the axis of symmetry of the optical module. A complete optical module 200 arranged in this manner is shown in
In case the azimuthal portion of the light ray angle differs from zero, it will be directly translated into a similar output light beam angle, since the redirection layer 121 does not provide collimation action for the azimuthal part of the light rays. Hence, in one embodiment, the azimuthal angle portion should be lower and preferably significantly lower than the intended final output light beam angle.
Optionally, the optical module may further include at least partially reflective structure (a mirror) configured, for each of the segments, to direct [at least some of] the light produced by the light source towards the collimating structure of that segment. (i.e., so that the light of each light source is guided only in the optics of its own segment).
In one embodiment, a mirror is used to close the top of all cavities, which could be done e.g. with a flat circular (diffusively reflecting) mirror 202 illustrated in
While the embodiments described above illustrate cavities having a circular cross-section in the x-y plane, in other embodiments such cross-sections of cavities may have other shapes, such as e.g. a regular polygon, en ellipse or a parabola.
One advantage of the present invention is that light output beam having high lumen output as well as narrow band width may be provided. Therefore, optical modules that have been discussed in the foregoing may advantageously be used in a downlighting application, particularly in surgical lighting.
While the forgoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. Therefore, the scope of the present invention is determined by the claims that follow.
Number | Date | Country | Kind |
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10177884.3 | Sep 2010 | EP | regional |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IB11/54065 | 9/16/2011 | WO | 00 | 3/14/2013 |