Abstract:
There is provided an arrangement for spot illumination ( 14 ). The arrangement provides an improved collimation and color mixing unit comprising a LED array ( 1 ), a convex shaped reflector ( 15   a ), a field lens ( 21 ) and an additional cylindrical reflector ( 15   b ) at the exit aperture of the system. In combination with an optical projection system which may comprise at least two additional zoom lenses and a gate (in which several maskers, gobos or shutters could be inserted) the system allows color mixing in an extended operational range including out of focus zoom settings often used to get soft edge spots.

Description:
FIELD OF THE INVENTION 
     The present invention relates in general to an arrangement for spot illumination. More particularly the present invention relates in general to an arrangement for spot illumination having a tubular reflector with two sections. 
     BACKGROUND OF THE INVENTION 
     Colored light is used in many applications where scene setting and atmosphere creation is important. Examples of applications exist inter alia in the fields of theatre lighting, architecture lighting (inter alia for city beautification), shops, hotels, restaurants, hospitals, schools, office spaces. Today this is mostly accomplished by combining white light sources with colored filters in order to obtain desired colors. 
     As an alternative, systems with multi-colored LEDs can be used. Such systems are attractive because they generate the desired colors without filters. This has an efficiency advantage and, more importantly, colors can be changed by the electronics: there is no need to change filters in order to change color; all colors are directly available by combining inter alia a number LEDs of different prime colors. Having electronically regulated colors allows various automatic programming methods to be used to control the lighting system and the fact that filters are omitted results in easier supply chain (no filters needs to be removed) and color consistency (replaced filter might introduce variation). The market for these systems is quickly growing as LED performance improves. 
     In multi-channel, high flux LED applications such as e.g. CDM replacement spots and multi-color entertainment spots (for theatre/touring/stage/studio applications) a large number of LEDs may be needed and the LEDs should be packed on a small array in a robust way. The performance of an assembly of individual LED packages, such as Rebels, is often limited. On the other hand dedicated large LED arrays, such as fabricated by the company Enfis, LEDEngine have intrinsically a low yield and they are too expensive for many applications. There is thus a need for a scalable solution than can be manufactured and/or assembled with a high yield and high alignment robustness. 
     U.S. 60/200,002 disclose a so-called collimating trumpet reflector, which provides excellent color mixing for a LED light source and efficient collimation for inter alia hard edge spot fixtures as used in theatre spots. However, lighting designers may wish to use the same fixture to project an out of focus diaphragm to get a soft edge. Particularly in stage lighting, there is often a need to create a controlled beam of light having sharp edges. This is often realized using a so called hard edge spot luminary (also called a profile lantern or an ellipsoidal profile spot). The hard edge spot luminary may comprise obstructions arranged in the optical path or axis, which obstructions can be projected onto a target surface by a lens or optics of the hard edge spot luminary. These obstructions may comprise shutters or a so called gobo, e.g., a piece of material with patterned holes through which light passes, which piece of material is placed in the beam of light such that only the desired ‘shape’ of light or pattern is passed through the piece of material, while the rest of the light is blocked, thereby achieving a specific shadow/light pattern in the illuminated plane. Often in the same application, there is additionally often a need or desire to create a wash beam, i.e. a beam of light having soft edges. This is often realized by bringing the lens or optics of the hard edge spot luminary out of focus, whereby soft edge effects can be provided. However, color mixing performance often deteriorates when the lens or optics of the hard edge spot luminary is brought out of focus, which may result in undesired color fringes in the shadow/light pattern projected onto the target surface, i.e. undesired fringes of color along boundaries separating bright and darker areas in the projected pattern. 
     SUMMARY OF THE INVENTION 
     It has been noticed that lighting systems according to prior art does not provide sufficient color mixing which may result in unacceptable color fringes. It is an objective of the current invention to provide an arrangement for spot illumination that can give a good color mixing and a homogeneous spot at any focusing settings of the arrangement. Further, it may be desirable to use the same arrangement also to generate a wash beam, in other words to project an out of focus diaphragm to get a soft edge. 
     Generally, the above objectives are achieved by an arrangement for spot illumination according to the attached independent claim. According to a first aspect of the invention, this and other objects are achieved by an arrangement for spot illumination, comprising a tubular reflector having a reflective inner surface, the tubular reflector comprising a first section having an entrance aperture and an exit aperture being larger than the entrance aperture, and a second section having an entrance aperture and an exit aperture being substantially identical in size, the entrance aperture of the second section being positioned adjacent the exit aperture of the first section; a light source array comprising a plurality of light sources arranged to emit light into the first section of the tubular reflector at the entrance aperture of the first section; and an optical focusing element arranged proximate the second segment of the tubular reflector, wherein the first section, the second section, the light source array and the optical focusing element thereby are arranged to form a collimated beam of homogeneous color mixed light to be outputted at the exit aperture of the second section. 
     Advantageously such an arrangement may provide a good color mixing and a homogeneous spot at any focusing settings of the arrangement. The same arrangement may also be used to generate a wash beam. 
     According to a second aspect of the invention, the above object and other objects are achieved by a luminaire comprising an arrangement as disclosed above. 
     According to a third aspect of the invention, the above object and other objects are achieved by light system, comprising an arrangement as disclosed above. 
     It is noted that the invention relates to all possible combinations of features recited in the claims. Thus, all features and advantages of the first aspect likewise apply to the second and third aspects, respectively. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various aspects of the invention, including its particular features and advantages, will be readily understood from the following detailed description and the accompanying drawings, in which: 
         FIG. 1  illustrates an LED array according to an embodiment. 
         FIGS. 2-5  illustrate arrangements for spot illumination according to embodiments; and 
         FIG. 6  illustrates an illumination pattern for an arrangement according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled addressee. Like reference characters refer to like elements throughout. 
     Multi-channel, high brightness LED light source platforms to serve the needs of various entertainment lighting applications (inter alia in the fields of theatre, touring and TV studios) are currently being developed. Such LED light source platforms may have a light output of about 10 000 lm and at least four different color channels (from a highly dense packed LED array with a diameter of less than 30 mm). Such a high brightness light source offers many advantages for spot applications. Especially it may allow to realize a hard edge spot (also referred as profile) together with on gel matching functionality.  FIG. 1  illustrates a highly dense packed LED array  1 . The illustrated LED array, which is attached to a substrate  3 , has a diameter D of 29 mm and comprises six color channels and has 120 LEDs  2 . 
     One or more LED arrays  1  as illustrated in  FIG. 1  may be used in an illumination system for spot illumination.  FIG. 2  is a perspective view of a high brightness LED light source based arrangement  4 . The arrangement  4  is suitable for spot illumination. The arrangement comprises a highly dense packed LED array  1  and a mixing and/or collimating tubular reflector  5  (also known as a trumpet reflector). The tubular reflector  5  has an entrance aperture  6   a  and an exit aperture  6   b . Light from the LED array  1  is received at the entrance aperture  6   a  and mixed and/or collimated light is emitted at the exit aperture  6   b . According to the embodiment illustrated in  FIG. 2  a first optical element  7  is attached to the entrance aperture  6   a  and a second optical element  8  is attached, via a ring  9 , at the exit aperture  6   b . The second optical element  8  may for example be fixed to the ring by means of a screw arrangement  10   a - d  or the like. The LED array  1  is operatively connected to a heat sink  11 . Heat generated by the LED array  1  may thereby be transmitted from the LED array  1  to the heat sink  11 . In turn the heat sink  11  is operatively connected to a fan  12 . The fan  12  may provide forced air cooling. The LED array  1  may be electrically connected to a LED driver or the like by means of one or more electrical connector  13   a - d.    
       FIG. 3  is an exploded view of an arrangement  14  for spot illumination according an embodiment. The arrangement  14  of  FIG. 3  is similar to the arrangement  4  of  FIG. 2 . The arrangement  14  comprises two sections  15   a ,  15   b  forming a tubular reflector (or trumpet reflector). The body of the tubular reflector may be fabricated from a polymeric material by assembly multiple pieces together or as a single piece inter alia by injection moulding or rapid prototyping. The tubular reflector has a reflective inner surface  16  so that light received by the tubular reflector is reflected at the reflective inner surface  16  and thereby results in output light emitted from the tubular reflector being mixed and/or collimated. For example, a highly reflective foil such as Miro foil may be attached (e.g. glued) onto the inner surface  16  of the tubular reflector. 
     In more detail the tubular reflector has two sections; a first section  15   a  and a second section  15   b , each having a respective entrance aperture  17   a ,  18   a  and a respective exit aperture  17   b ,  18   b . A light source array  1  may be arranged to emit light into the first section  15   a  of the tubular reflector at the entrance aperture  17   a  of the first section  15   a . An optical axis  19  may thus be formed from the light source array  1  towards the exit aperture  18   b  of the second section  15   b.    
     The tubular reflector may have a beam shaping functionality transforming the Lambertian light distribution from the light source array  1  into the required beam shape of 10°-40° FWHM) and providing color mixing. As noted above the first section  15   a  (of the tubular reflector) has an entrance aperture  17   a  and an exit aperture  17   b . The first section  15   a  is preferably arranged and/or orientated such that incident light is received at the entrance aperture  17   a  and output light is emitted at the exit aperture  17   b . The exit aperture  17   b  of the first section  15   a  is larger than the entrance aperture  17   a  of the first section  15   a . According to a preferred embodiment the first section  15   a  has substantially a trumpet shape. More particularly, the first section  15   a  may have a convex shape as seen from the optical axis  19 . The first section  15   a  may further comprise multiple facets  20   a - c  arranged to form a polygonal cross section along the optical axis  19 . The entrance aperture  17   a  of the first reflector  15   a  may thus have a polygonal cross section, such as a hexagonal, a heptagonal or an octagonal cross section. In  FIG. 3  the entrance aperture  17   a  of the first reflector  15   a  has a heptagonal cross section. 
     Likewise, as also noted above the second section  15   b  (of the tubular reflector) has an entrance aperture  18   a  and an exit aperture  18   b . The second section  15   b  is preferably arranged and/or orientated such that incident light is received at the entrance aperture  18   a  and output light is emitted at the exit aperture  18   b . According to an embodiment the second section  15   b  has substantially a cylindrical shape cross section as seen from the optical axis  19 . However, according to another embodiment the second reflector  15   b  also has a polygonal cross section, preferably similar to the shape of the first section  15   a  of the tubular reflector. More particularly the second section  15   b  may have a cross section shape which corresponds to the cross section shape of the first section  15   a.    
     The entrance aperture  18   a  of the second section  15   b  and the exit aperture  18   b  of the second section  15   b  are substantially identical in size. The wording “substantially identical in size” should here be interpreted as being different only within a predetermined margin (such as the diameters of the apertures in question not differing more than 1-5%, or being within factory specifications). In other words, the first section  15   a  may have a tubular shape whereas the second section  15   b  may have a cylindrical shape. The second section  15   b  and the first section  15   a  are preferably arranged such that the entrance aperture  18   a  of the second section  15   b  is positioned adjacent the exit aperture  17   b  of the first section  15   a . Preferably the entrance aperture  18   a  of the second section  15   b  and the exit aperture  17   b  of the first section  15   a  have the same diameter and/or shape. 
     The arrangement  14  further comprises an optical focusing element  21 . The optical focusing  21  element may be a field lens. Preferably the optical focusing element  21  is arranged proximate the second segment  15   b  of the tubular reflector. For example, the optical focusing element  21  may be attached to the second segment  15   b . Alternatively the optical focusing element  21  and the second segment  15   b  may be separated by a ring (not shown) or another separating element(s). According to an embodiment optical focusing element  21  is arranged in the optical path (i.e. along the optical axis  19 ) tightly between the first section  15   a  (i.e. the tubular section of the reflector) and the second  15   b  section (i.e. the cylindrical section of the reflector), as is disclosed in the illustrative example of  FIG. 3 . More generally the optical focusing element  21  may be positioned between the entrance aperture  18   a  of the second section  15   b  and the exit aperture  17   b  of the first section  15   a.    
     Other positions of the optical focusing element  21  are equally possible. The optical focusing element  21  may, for example, be positioned proximate the exit aperture  18   b  of the second section  15   b  of the tubular reflector. For example, the optical focusing element  21  may be positioned directly at the exit aperture  18   b . Alternatively the optical focusing element  21  and the exit aperture  18   b  may be separated by a ring (not shown) or another separating element(s). Such an arrangement  22  is illustrated in  FIG. 4 . The arrangement  22  of  FIG. 4  is thus similar to the arrangement  14  of  FIG. 3 . Hence the arrangement  22  comprises inter alia a light source array  1 , a tubular reflector having a first section  15   a  and a second section  15   b , where each one of the first section  15   a  and the second section  15   b  has an entrance aperture  17   a ,  18   a  and an exit aperture  17   b ,  18   b , and an optical focusing element  21 . An optical axis  19  is formed from the light source array  1  through the optical focusing element  21  towards the exit aperture  18   b  of the second section  15   b.    
     As noted above the arrangements  14 ,  22  comprises a light source array  1  which comprises a plurality of light sources  2 . The light source array  1  is arranged to emit light into the first section  15   a  of the tubular reflector at the entrance aperture  17   a  of the first section  15   a . The light source array  1  may therefore be positioned close to or adjacent (the entrance aperture  17   a  of) the first section  15   a  of the tubular reflector. 
     The arrangements  14 ,  22  (including the first section  15   a , the second section  15   b , the light source array  1  and the optical focusing element  21 ) are thereby are arranged to form a collimated beam of homogeneous color mixed light to be outputted at the exit aperture  18   b  of the second section  15   b.    
       FIG. 5  illustrates an arrangement  24  according to an embodiment. The arrangement  24  of  FIG. 5  is similar to the arrangements  14 ,  22  of  FIGS. 3 and 4 . Hence the arrangement  22  comprises inter alia a light source array  1 , a tubular reflector having a first section  15   a  and a second section  15   b , where each one of the first section  15   a  and the second section  15   b  has an entrance aperture  17   a ,  18   a  and an exit aperture  17   b ,  18   b , and an optical focusing element  21 . An optical axis  19  is formed from the light source array  1  through the optical focusing element  21  towards the exit aperture  18   b  of the second section  15   b.    
     The arrangement  24  further comprising a lens assembly  25 . The lens assembly  25  is arranged to controllably focus/defocus light emitted at the exit aperture  18   b  of the second section  15   b . The lens assembly comprises at least two lenses  25   a ,  25   b  arranged in spaced relation to each other. Particularly the lens array  25  may be placed along the optical axis  19  beyond the exit aperture  18   b  of the second section  15   b  of the tubular reflector. At least one lens  25   a ,  25   b  of the lens assembly  25  is controllably moveable towards and/or away from another lens  25   a ,  25   b  of the lens assembly  25  and/or towards the second section  15   b  of the tubular reflector. Such an arrangement may achieve a high contrast with limited blur and limited colored edges. In more detail, by such an arrangement  24 , a zoom lens can substantially be maintained in focus independently of the value of the zoom factor (i.e. the degree of zooming) or even be completely maintained in focus independently of the value of the zoom factor. 
     Thus, according to one aspect there may be provided a method for controlling an arrangement (or an optical system) as disclosed above, a luminaire and/or a light system comprising at least one arrangement as disclosed above. In other words, an illumination system may comprise a light source array  1 , color mixing means, such as the disclosed tubular reflector, and an adjustable optical system (e.g. zoomable and/or (de-)focusable projection system) such as the disclosed lens assembly  25 . The optical system may comprise two sections along its optical axis  19 ; a first segment, such as section  15   a  and/or section  15   b , in which colors are mixed (spatial and angular) and a segment section, such as section  15   b  and/or lens array  25 , in which colors are mixed at all position in the optical system of the second part. The projection system may thereby be controlled by moving the first segment and the second segment in relation to each other such that at any state the projection system projects a focal plane that is within the second segment, in which the colors are mixed, even if the projection system is defocusing to the extremes (i.e. independently of the value of the zoom factor). 
     According to embodiments the light source array  1  may, furthermore, comprise at least one set of light sources  2  arranged to emit light of a first color and at least one set of light sources  2  arranged to emit light of a second color different from the first color. A set of light sources  2  may be defined by a single light source. Similarly, a set of light sources  2  may comprise two or more light sources arranged together in a group. For example, a set of light sources  2  may be provided in the form of a line of light emitting diodes (LEDs). According to an embodiment the light source comprises a plurality of LEDs. Preferably the light source comprises between 5 and 250 LEDs. More preferably the light source comprises between 20 and 200 LEDs. Even more preferably the light source comprises between 70 and 150 LEDs. Increasing the number of light sources may increase the flux (in lm) of the outputted light. Increasing the number of light sources may also increase the number of different colors obtainable by the arrangement. 
     According to an embodiment of the invention the light source comprises LEDs of 2-8 different colors. For example, the LEDs may have white (W), red (R), green (G), blue (B), amber (A), cyan (C), deep red (dR) and/or deep blue (dB) emission spectrum. By combination thereof, any desired light spectrum is obtainable that falls within the color space made up by the color coordinates of the WRGBAdRdB starting LEDs. According to an embodiment the light source thus comprises a plurality of colors such as (RGB), (NW+WW), (RGBA), (RGBAW), (RGBW), (RGBAC), (RGBAdR), (RGBACdR), (RGBACdRW), (RGBACdRdB), or the like. 
     In addition, it may desirable that the light source occupies an area which is as small as possible whilst still allowing a large number of LEDs to be present. It may thus be desirable to have a high densely packed LED array. According to embodiments the plurality of light sources comprises an LED array having an EPI density between 5% and 70%. Preferably the plurality of light sources comprises an LED array having an EPI density between 15% and 50%. Under EPI density is understood the overall area of the light emissive parts of the LEDs with respect to the area of the light source. 
       FIG. 6  illustrates an illumination pattern  23  for an arrangement  14 ,  22  as disclosed with references to  FIG. 3  or  4  according to an embodiment. A gobo (or GOBO; derived from “Go Between” or GOes Before Optics originally used on film sets between a light source and the set) is a physical template slotted inside, or placed in front of, a lighting source. A gobo may thereby be used to control the shape of light emitted from a light source and/or illumination system. Such a gobo may be located at the exit of the collimation and color mixing optics of the disclosed arrangements  14 ,  22 . Preferably the gobo is located close to the field or collimation lens and will be projected by an optical projection system attached to the rest of the illumination system on a scene, e.g. on a wall. Alternatively or in addition to the gobo there may be provided a photo mask, a wavelength conversion element and a beam shaping element configured to reflect, refract, absorb and/or diffract light. As a very good color mixing has been achieved at the exit aperture (i.e. close to the field or collimation lens) the illumination pattern shows a sharp pattern  23  without color fringes or collared edges. 
     In summary there has been disclosed an illumination system for spot illumination. The system comprises a tubular reflector with a reflective inner surface. The tubular reflector comprises two sections; a first sections (preferably with a convex shape as seen from the optical axis of the system) having an entrance aperture and an exit aperture being larger than the entrance apertures and a second sections adjacent to the first sections, the second sections having an entrance aperture and an exit aperture being substantially identical in size. The system further comprises a light source array comprising a plurality of light sources arranged to emit light (preferably of different spectral content and/or different colors) into the first sections of the tubular reflector at the entrance aperture The system further comprises an optical focusing element (such as a field lens) attached to the second sections of the tubular reflector. The light source array, the field lens, the first section and the second sections of the tubular reflector are thereby configured such that a collimated beam enabling homogeneous color mixing (special and angular) in the output light beam is formed. 
     The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, the disclosed arrangement may be part of a luminaire. Thus, a luminaire may comprise one or more arrangements as disclosed above. Similarly, the disclosed arrangement may be part of a light system. As noted above, at least one of the plurality of light sources may comprise a solid-state light source such as at least one light-emitting diode (LED). Such a LED may be inorganic or organic. The plurality of light sources may alternatively or optionally comprise one or more compact fluorescence lamps (CFL), high-intensity discharge (HID) lamps and/or halogen lamps. According to the embodiment illustrated in  FIG. 5 , the lens assembly  25  comprises two lenses  25   a ,  25   b . Embodiments comprising any number of lenses in the lens assembly  25   a ,  25   b , such as three, four, five, six lenses or more or even a single lens are equally envisaged.