Patent Publication Number: US-2019178471-A1

Title: Chromatic mirror, chromatic panel and applications thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of copending U.S. application Ser. No. 15/310,306, filed Nov. 10, 2016 (now allowed), which is a U.S. National Stage Application under 35 § U.S.C. 371 of International Application No. PCT/EP2014/059802, filed May 13, 2014. Both applications are incorporated herein by reference in their entirety. 
    
    
     DESCRIPTION 
     The present application concerns chromatic mirrors and a chromatic panel. 
     Chromatic components are used in many applications. For example, with respect to chromatic lenses, the chromatic property is mostly a disturbing artifact. Sometimes, however, the chromatic property is a wanted property of the respective component. For example, in WO 2009156347 A1 an illumination device has been presented which uses a combination of a broadband artificial light source and a chromatic diffuser in order to illuminate, for example, indoor rooms so that the resulting scene including the interior of the room results in a more pleasant appearance in that the illumination appears to be less artificial and more natural, i.e. more similar to an illumination as it would result from an illumination in outdoor environments. The chromatic diffuser described therein simulates the Rayleigh scattering process sunlight experiences on its way down to earth. 
     However, it would be favorable to have other chromatic components at hand which ease the realizations of at least some application concepts, such as the one described in the just mentioned WO 2009156347 A1. For example, in use, the mentioned chromatic diffuser is capable of simulating the illumination of the sky and the sun inside an ambient. However, for this purpose a light source should be positioned beyond the diffuser, which requires the availability of a large free volume, e.g. several m 3 , above the false ceiling, for example, if the illumination is arranged at the ceiling. Further limitations might arise from the material the diffuser is made of, in relation to mechanical resistance, fire-retardant properties, etc. 
     Accordingly, it is the object of the present application to provide such a chromatic component enabling an easier implementation of systems and concepts using such a chromatic component. 
     This object is achieved by the subject matter of the pending independent claims. 
     The present application is based on the idea that chromatic components may alleviate the usage in various applications if this chromatic component is, according to a first aspect of the present application, made-up of a mirroring surface and a diffusing layer in front of the mirroring surface, which preferentially scatters short-wavelength components of impinging light with respect to long-wavelength components of the impinging light, and if according to another aspect, the chromatic component is made up of a stratified-glass panel which comprises two glass sheets, e.g. a float glass or a tempered glass sheets, sandwiching an adhesive transparent polymeric film wherein the adhesive transparent polymeric film forms a diffusing layer which preferentially scatters short-wavelength components of light passing the stratified-glass panel with respect to long-wavelength components of this light with respect to long-wavelength components of the same. 
     In accordance with the first aspect, the underlying idea results in the combination of the reflective nature obtained by the mirroring surface, along with chromatic property achieved by the diffusing layer: in many applications, the light illuminating the chromatic component and the object to receive the chromatic component are easier to be located on the same side. With the chromatic mirror they may be positioned at the mirroring side of the mirror. For example, the object may be a room and the illuminator for illuminating the chromatic component, i.e. the chromatic mirror, is easier to be placed within the same room rather than external thereto. On the other hand, placing the diffusing layer for example immediately in front of the mirroring surface does not change the wanted chromatic property of the resulting chromatic component: light regularly reflected by the chromatic mirror maintains its initial solid-angle luminance profile with merely its spectrum being affected by the wavelength-selective scattering property of the diffusing layer, and that fraction of the impinging light which passes the diffusing layer twice, namely once when impinging onto the mirroring surface, and once when heading away from the mirroring surface, maintains its luminance profile despite the interposition of the mirroring surface because the same is diffuse, or widened compared to the regularly reflected light rays, anyway. In addition, the interposition of the mirroring surface, results in a virtual increase of the diffusing layer&#39;s thickness. Advantageously, this may help in reducing the size of the chromatic mirror in the thickness direction with respect to the size of the chromatic diffuser described in the introductory portion of the specification. 
     In accordance with the second aspect of the present application, the aim of alleviating the usage of a chromatic component is achieved by placing the diffusing layer in between two glass sheets to form a stratified-glass panel, wherein the diffusing layer concurrently assumes the role of an adhesive transparent polymeric film which fixes the two glass sheets to each other. By this measure, the diffusing layer is protected against atmospheric agents like UV light, dust, humidity and so on, which could change the chromatic and optical properties of the diffusing layers, the panel is strong enough in order to fulfill architectural requirements such as fire resistance, shock resistance, scratch resistance and the like, and the chromatic panel thus constructed may alternatively be extended to form a chromatic mirror by further depositing a mirroring layer on the chromatic component. 
     Advantageous implementations and systems using the chromatic components are the subject of the dependent claims. 
    
    
     
       Advantageous embodiments of the present application are described with respect to the figures, among which 
         FIG. 1  shows a schematic three-dimensional view of a chromatic mirror according to an embodiment; 
         FIG. 2  shows an example for a concept and system for illumination using the chromatic mirror in accordance with an embodiment; 
         FIG. 3  illustrates possible arrangements of the chromatic mirror when using the concept/system for illumination for the illumination of a room of a building; 
         FIG. 4  shows a schematic diagram of a modification of the embodiment of  FIG. 2  according to which a concave chromatic mirror is used; 
         FIG. 5 a    shows a three-dimensional view of a usage of an elongated, or cylindric concavely shaped, chromatic mirror within a concept or system for illumination in accordance with a further embodiment; 
         FIG. 5 b    shows schematically the angular luminance profile of the illuminator of  FIG. 5   a;    
         FIG. 5 c    shows schematically the appearance of the illuminator of  FIG. 5 a    when directly looking onto illuminator of  FIG. 5 a    from the direction of the mirror; 
         FIG. 5 d    shows schematically the appearance of the illuminator of  FIG. 5 a    when looking, from an on-axis position, onto illuminator of  FIG. 5 a    via reflection by the mirror; 
         FIGS. 6 a  and 6 b    show three-dimensional partial views of the illuminator of  FIG. 5  with  FIG. 6 a    showing the light source and a CPC reflector of the illuminator in accordance with one embodiment, and  FIG. 6 b    shows a light concentrator with respect to another embodiment. 
         FIG. 7  shows a plan view of the system of  FIG. 5  in accordance with a modification according to which the elongation direction of the chromatic mirror and illuminator pair is curved to result in a circular plan view arrangement; 
         FIG. 8  shows a schematic three-dimensional view of a chromatic mirror additionally having a blurring layer in accordance with an embodiment; 
         FIG. 9  shows a sectional view of a chromatic mirror in accordance with a further embodiment according to which lateral physical and/or optical thickness variation of the diffusing layer is used in order to achieve a blurring effect; 
         FIG. 10  shows a schematic three-dimensional view of an illumination system, using a transparent layer  84  downstream the chromatic mirror in accordance with an embodiment; 
         FIG. 11  shows a three-dimensional view of a portion out of an architectural object or building where a blocked area prevents visitors from directly looking into the regularly reflected light portion used to illuminate a certain interesting area within the blocked area in accordance with an embodiment; 
         FIG. 12  shows a schematic three-dimensional view of a chromatic mirror in accordance with an embodiment, where a dispersion of light-scattering centers is used to provide the diffusion layer with its diffusion property; 
         FIG. 13  shows a three-dimensional view of a chromatic mirror in accordance with an embodiment using a transparent panel or flexible polymeric film as a support member for supporting coatings or films fulfilling the task of the diffusing layer and mirroring surface, respectively, in accordance with an embodiment; 
         FIG. 14  shows a three-dimensional view of a chromatic mirror differing from  FIG. 13  in that coatings or films forming the mirroring surface and diffusing layer, respectively, are arranged at the same facet of the transparent panel or flexible polymeric film; 
         FIG. 15  shows a three-dimensional view of a further embodiment of a chromatic mirror using a stratified-glass panel composed of two float glass sheets; 
         FIG. 16  shows a three-dimensional view of a chromatic mirror in accordance with an embodiment differing from  FIG. 15  in that the adhesive transparent polymeric film in between the float glass sheets concurrently assumes the task of the diffusing layer; 
         FIG. 17  shows a three-dimensional view of a chromatic mirror using an aluminum metal foil in accordance with a further embodiment; 
         FIG. 18  shows a three-dimensional view of a chromatic mirror using a frame for holding the chromatic mirror of  FIG. 17  in place; 
         FIG. 19  shows a building façade which is partially provided with a chromatic mirror in accordance with any embodiment of the present application so as to mirror external light and enable a “hiding” of the building façade; and 
         FIG. 20  shows a three-dimensional view of a chromatic panel made on the basis of a stratified-glass panel in accordance with an embodiment. 
     
    
    
     In the following, embodiments of the present application are set forth with respect to the figures. In order to ease the understanding of the concepts underlying these embodiments, a general embodiment of a chromatic mirror is discussed first with respect to  FIG. 1 , and then some applications and systems using such a chromatic mirror are presented, followed by examples for producing such a chromatic mirror resulting in respective products in the form of which such a chromatic mirror may be distributed or handled. Later on, another chromatic component, namely a chromatic panel, is presented along with possible applications and systems using the same. 
       FIG. 1  shows a chromatic mirror according to an embodiment. The chromatic mirror is indicated using reference sign  10  and comprises a mirroring surface  12  and a diffusing layer  14  in front of the mirroring surface  12 . The direction into which the mirroring side of mirror  10  faces is denoted  15 . 
     It should be noted that  FIG. 1  is to be treated as a schematic representation of the chromatic mirror  10  only, and accordingly although  FIG. 1  illustrates the chromatic mirror  10  as flat panel shaped, the mirroring surface  12  may, for example, be shaped in a non-flat manner such as, for example, concavely shaped, instead of the planar configuration shown in  FIG. 1 . Likewise, although  FIG. 1  illustrates the mirroring surface  12  as a main side of a flat work piece or layer  16 , facing the diffusing layer  14 , with work piece or layer  16  laterally extending beyond the lateral circumference of layer  14 , this concept has been chosen for illustration purposes only and may not be interpreted as a restriction of the embodiment of  FIG. 1 . Similar statements are also true with respect to the thicknesses illustrated in  FIG. 1 . Further, as will be shown in the following embodiments, the mirroring surface  12  may, for example, be formed by coatings or films or panels, and layers  14  and  16  may immediately contact each other as illustrated in  FIG. 2 , or one or more layers may be positioned therebetween. For example, the mirroring surface  12  may be formed by a coating or film on work piece or layer  16 , and the diffusing layer  14  may be a film or coating deposited onto mirroring surface  16  either directly or via one or more further layers. Even in that case, the chromatic mirror  10  may be formed as a multi-layered component as illustrated in  FIG. 1 , or the work piece or layer  16  may be formed as a voluminous structure or object on the outer surface of which the mirroring surface  12  is formed. As will also become clear from the embodiments outlined below, the chromatic mirror  10  may be stiff or tensile or flexible. Any component of the chromatic mirror  10  may serve as a supporting member such as the reflective member  16 , the side facing the diffusing layer  14  of which forms the mirroring surface  12 , the diffusing layer  14  or some other layer positioned between mirroring surface  12  and diffusing layer  14  or positioned on the other side of diffusing layer  14 , i.e. to the main side  18  of diffusing layer  14  facing away from mirroring surface  12 . This supporting member may then lend the stiffness, tensibility or flexibility to chromatic mirror  10 . Whatever shape the mirroring surface  12  actually has, the diffusing layer  14  is a layer which substantially conforms to the shape of the mirror surface  12  and may have, as described below, a substantially even thickness across the mirroring surface&#39;s  12  lateral extension. 
     For the moment, any specific description of possibilities of implementing and realizing mirror  10  shall be deferred, while describing now the combined action and function of the mirroring surface  12  having the diffusing layer  14  positioned in front thereof. 
     The diffusing layer  14  is constructed so as to preferentially scatter short-wavelength components of impinging light  20  with respect to long-wavelength components of the impinging light  20 . Alternatively speaking, layer  14  lets pass long-wavelength components of the impinging light  20  without scattering at a higher probability than compared to short-wavelength components of the impinging light  20 . In even other words, the diffusing layer  14  has a scattering cross-section for impinging light  20 , which increases within the visible light spectrum from long to short wavelengths. The increase may be a monotonic increase. The way how scattered light propagates may, for example, be substantially isotropic, i.e. featuring equal intensity for all the direction, or a weak dependence of the scattered light&#39;s intensity on the scattered light&#39;s direction, i.e. the scattered light is diffuse. In the end, this means that the portion of the impinging light  20  which is regularly reflected at the mirroring surface  12  without any scattering interaction with the diffusing layer  14  within the section  22  of the light path leading within diffusing layer  14 , indicated by reference sign  24  in  FIG. 1 , has a spectrum which differs from the spectrum of the impinging light  20  in that the center of mass of the portion of the spectrum, lying within the visible region, is shifted towards longer wavelengths. Besides the light  24 , regularly reflected by chromatic mirror  10 , another portion of the impinging light  20  is subject to the just mentioned scattering by diffusing layer  14  and exits diffusing layer  14  in a diffuse manner, i.e. leading to substantially constant luminance along all the directions pointing towards the hemisphere to which direction  15  points, or at least a luminance which does not change by more than a factor  3  within a cone of at least 30°, preferably 45°, most preferably 60° HWHM aperture around the direction of specular reflection. As far as the spectrum of the just mentioned diffusely reflected light is concerned, same substantially corresponds to a spectral weighting of the spectrum of the inbound impinging light  20  with the aforementioned scattering cross-section or, in other terms, the spectrum of the scattered diffuse light substantially corresponds to a difference between the spectrum of the inbound impinging light  20  and the regularly reflected light  24 . 
     It is worthwhile to note that, as a consequence of the just outlined behavior of mirror  10 , light being emitted by mirror  10  as a consequence of its illumination at a certain direction such as the direction indicated at  24  in  FIG. 1 , is a superposition or sum of the light 1) impinging onto mirror  10  at the specular angle and having been regularly reflected by mirror  10 , i.e. light  20 , into that direction  24 , and 2) the diffuse light generated by scattering processes with light impinging onto mirror  10  from any direction and being scattered, accidentally, towards direction  24 , i.e. all light impinging onto mirror  10  contributes to the latter diffuse light, irrespective of the direction at which the light impinges onto mirror  10 . 
     A chromatic mirror as outlined with respect to  FIG. 1  might be used, for example, within a framework shown in  FIG. 2 , which in the end also shows a system in accordance with an embodiment comprising a combination of a chromatic mirror  10  and an illuminator  26  for illuminating chromatic mirror  10 . The illuminator  26  is, for example, a white light source. The illuminator  26  according to  FIG. 2  emits or casts light onto mirror  10 . In  FIG. 2  a light cone of the light emitted by illuminator  26  is exemplarily shown to completely cover and substantially match the extension of mirror  10 . That is, the area of a cross-section of light cone  28  at the plane within which mirror  10  extends may, for example, be smaller than three times the area of mirror  10 . Further, the illuminator  26  obliquely illuminates mirror  10 , i.e. mirror  10  is exemplarily shown as being flat shaped, and a projection of illuminator  26  onto the mirror&#39;s  10  plane is offset to a mid of mirror  10  by, for example, more than 50% of the square root of the area of mirror  10 . 
     With this configuration,  FIG. 2  illustrates this scene which results when looking at mirror  10  at a specular angle with respect illuminator  26 . To this end,  FIG. 2  illustrates an eye or camera  13  as being positioned at the specular angle relative to illuminator  26  with respect to mirror  10 . The picture which results in camera/eye  30  (e.g. the image sensor or the retina) is illustrated in  FIG. 2  at  32 : the outline of mirror  10  is visible, i.e.  34 , and surrounding the same, portions  26  of a wall are seen, which is exemplarily assumed to surround mirror  10  and lit by cone  28 . Within mirror  10 , a spot  38  is visible which results from the regularly reflected light portion of the light emitted by illuminator  26  and has a warmer light (lower CCT) than compared to the white light of illuminator  26 . Spot  38  is surrounded by a uniform area  40  of light being of higher CCT (correlated color temperature) than compared to the CCT of spot  38  (and compared to the CCT of the light of illuminator  26 ). The surrounding light  40  primarily stems from the diffused light generated by the scattering within diffusing layer  14 , and the dependency of this diffuse scattering is responsible for the increase in CCT relative to light  38 . The light of the surrounding scene area  40  is, for example, bluish. It is superimposed, however, by light impinging onto mirror  10  at some other angle than compared to the light output by illuminator  26 , and being regularly reflected by mirror  14 . Such light may stem, for example, from other objects within the room, with this other light travelling along paths, for example, past illuminator  26 .  FIG. 2 , for example, shows an object  42  positioned nearby illuminator  26  positioned such that the virtual image of this object  42  would be visible by camera  30 . As illustrated in  FIG. 2 , the object  42  is, for example, not directly lit by illuminator  26 . Naturally, however, due to light reflections at other objects not shown in  FIG. 2 , such as other walls or the like, object  42  may cause light to impinge onto mirror  10 . The latter light may disturb the uniformity of the diffuse light generated by diffusing layer  14  responsive to the illumination by illuminator  26 . However, preferably, the diffuse light overhelms the regularly reflected light from object  42  such that the object  42  is not visible for the observer  30 , or at least, the observer&#39;s attention is not drawn to this object. For example, imagine that observer  30  would denote an observer&#39;s eye and that the observer, owing to the sky-sun-like scene visible within mirror  10 , sets the eye to look at infinity. In that case, it may occur that owing to the overlay with the diffuse light, the observer does not “see” object  42  and retains an impression as if he or she would look into a window seeing bluish light  40  surrounding a sun-like spot  38  with experiencing an infinity depth impression. Interestingly, the illuminator  26  also resides within the same room as the observer  30 . 
     Summarizing the above,  FIG. 2  shows that a chromatic mirror  10  according to  FIG. 1  may be combined with an illuminator or light source  26  for illuminating the chromatic mirror  10  so as to form a system for illumination. The system  10  may, for example, be a system for illuminating an interior room of a building. In that case, the mirror may, for example, be fixed to a wall or a ceiling  46  of a room  48  as illustratively depicted in  FIG. 3 . As already described with respect to  FIG. 2 , the illuminator  26  may be positioned within the same room or in a wall, the ceiling  46  or the floor thereof. 
     As far as the illuminator  26  is concerned, it should be noted that same may comprise a light concentrator in order to concentrate otherwise divergently generated light of the illuminator  26  so as to form the light cone  28 , which in turn is directed towards mirror  10  so as to illuminate mirror  10 . Certain measures may be taken in order to achieve a uniform illumination of mirror  10  by illuminator  26 , as for example the use of compound parabolic concentrators (CPCs), light beam homogenizers (fly eyes, tandem arrays, etc.), as well as to obtain the formation of a light spot which matches the shape of the mirror, for example a rectangular, or an elliptic shape. 
     Although it has not yet been noted above, it should be mentioned that the diffusing layer  14  may preferably be configured such that same does not, or substantially does not, absorb light. In that case, all of the light produced by illuminator  26  is conserved for the sake of illumination. Further, although not mentioned previously, the diffusing layer may have such a wavelength-dependency in scattering cross-section that the diffusing layer scatters light in a Rayleigh or at least a Rayleigh-like regime. In that case, a just-outlined sun-sky-appearance effect is increased as the sky also predominately scatters light in the Rayleigh regime. The sun-sky-appearance, however, contributes in an higher probability that an observer looking onto mirror  10  in the specular angle relative to illuminator  26  gains an infinity depth impression so that the eyes of the observer are less likely attracted by edges in the sky-like region  40  which result from objects in the vicinity of mirror  10  other than illuminator  26 , such as  42  in  FIG. 2 . 
     That is, observer  30 , when looking onto mirror from some specular view angle, may gain a feeling as if he/she looks into the sky  40  through a window formed by mirror  10 , with concurrently seeing the sun  38  surrounded by the sky  40  through this window. It should be noted that, when looking onto mirror from some non-specular view angle, merely the light  40  is visible for the observer so that the observer may gain a feeling as if he/she looks into the sky through a window formed by mirror  10 , without seeing the sun therethrough. 
     Preferably, the combined action of the mirroring surface  12  and the diffusing layer  14  produces a haze in reflection which is greater than 10%, more preferably greater than 20%, and even more preferably greater than 30%, for impinging blue light at 450 nm. The “haze in reflection” denotes the above outlined portion of the impinging light which is effected by the scattering by diffusing layer  14 , i.e. the scattered diffuse light. In other terms, the combined action of the mirroring surface  12  and the diffusing layer  14  may be set such that a combined action produces a haze in reflection which is at least two times lower for an impinging red light at 650 nm than for an impinging blue light at 450 nm. As outlined above, this is owing to the spectral dependency of the scattering cross-section of the diffusing layer  14 . 
     In the embodiment outlined with respect to  FIG. 2 , the just outlined infinity depth impression resulting for an observer which sees the virtual image of the illuminator  26  at infinity, is disturbed by the fact that illuminator  26  is in fact arranged at a finite distance to a mirror  10 . For example, optical cues such as the eyes&#39; binocular convergence, the parallax of the illuminator  26 , and the accommodation of the observers&#39; eyes onto, for example, structural details of the illuminator  26  may distract the observer  30  from assuming this infinity depth impression. In order to alleviate this problem,  FIG. 4  shows, differing from the previously illustrated embodiments, that the mirror&#39;s  10  mirroring surface may be concavely shaped, such as having a concavely parabolic shape. In particular,  FIG. 4  amends the embodiment of  FIG. 2  in this regard and accordingly, ends-up in a system for illumination, where the illuminator  26  is positioned, for example, at a focus point of the chromatic mirror so that the light from the illuminator  26  which is regularly reflected by chromatic mirror  10  is parallelized, and the light cone  28  results, as far as its regularly reflected portion is concerned, in a parallel light stream  50  or a low-divergence light stream  50 . The obliqueness of illuminator  26  with respect to mirror  10  is maintained and translates into the fact that, for example, the chromatic mirror  10  is formed as an off-axis section of a rotational paraboloid such as a portion of a rotational parabolid which does not even contain the vertex, while keeping the light source  26  at or close to the focal point. In so doing, a collimated beam of regularly reflected rays can be obtained without having the light source in the beam path, as for the case of an on-axis lay out. However, for certain applications, the on-axis layout can be used too. 
     Shaping the mirroring surface of mirror  10  in the manner outlined above with respect to  FIG. 4  contributes to increasing the likelihood that an observer looking into the direction of mirror  10  and seeing, via mirror  10 , illuminator  26 , i.e. sees sun  38  and sky  40 , gains the just outlined infinity-depth feeling and feels as if he saw a lower CCT bright object  38 , e.g. the sun, at infinity surrounded by a sky-like atmosphere  40 . This is because the virtual image of the illuminator  26  as seen through mirror  10  is now in fact at infinity so that the binocular as well as the accommodation cues fit to the sky-sun-appearance, and possible distractions from the infinity depth impression my merely stem from visible edges of objects mirrored into the observer&#39;s field of view with the surrounding sky area  40 . 
     It may be preferred if the chromatic mirror  10  is made sufficiently wide. For example, the mirroring surface may be constructed such that a focal length thereof is smaller than a square root of the mirroring surface&#39;s  12  area or even smaller than 1.5 times the just mentioned square root of the mirroring surface&#39;s area. 
     As will become clear from the embodiment described further below, it is not necessary that the concave shape of mirror  10  of  FIG. 4  has rotational symmetry or is a portion of a rotationally symmetric surface, i.e. has a focal length equal for all translatory directions. Rather, mirror  10  may be formed like a parabolic concave cylindrical mirror, or have another concave shape along one lateral or translatory direction, hereinafter referred as y direction, and be flat or plane, i.e. have infinity focal length, along the other orthogonal lateral or translatory direction, hereinafter referred as x direction. As it will be clarified here below, in spite of the fact that the cylindrical mirror can collimate the light rays of the illuminator  26  only in the plane orthogonal to the x direction, solutions exist which guarantee the perception of the illuminator at infinite distance from the observer. 
     Such a configuration is illustrated with respect to  FIG. 5 a   .  FIG. 5 a    shows mirror  10  with its mirroring surface  12  having a concave or parabolic shape in the plane perpendicular to the x direction, i.e. within a projection onto a zy-plane, and being linearly shaped or straight along an x-axis. In other terms, said cylindrical-mirror surface is obtained by translating a concave or parabolic curve laying onto a zy plane along the x direction. Thus, mirror  10  is shown as a concave cylindric mirror having a focal line extending parallel to the x axis. A linear illuminator  26  is positioned parallel to the x-axis, at the focal line of mirror  10 , in order to more or less completely illuminate mirror  10 . Frankly speaking,  FIG. 5  represents a modification of the system of  FIG. 4  according to which, for example, the portion of the room directly illuminated by the regularly reflected portion of the light of illuminator  26  has an elongated shape, such as a rectangular shape  52  as illustrated in  FIG. 5 . As far as the zy-plane is concerned, the situation in  FIG. 5 a    is quite the same as the one outlined with respect to  FIG. 4 : The light emitted by illuminator  26  is divergent, but is parallelized by mirror  10  along a direct light direction at least as far as the regularly reflected portion of the light is concerned which impinges onto mirror  10  from illuminator  26 . 
     More specifically, from basic optics it follows that the luminance angular profile of the regularly reflected light portion, L R , as far as the dependency on the angle is concerned, may fulfil the following formula: 
     
       
         
           
             
               
                 fwhm 
                 y 
               
                
               
                 = 
                 def 
               
                
               
                 
                   FWHM 
                    
                   
                     { 
                     
                       
                         L 
                         R 
                       
                        
                       
                         ( 
                         
                           ϑ 
                           y 
                         
                         ) 
                       
                     
                     } 
                   
                 
                 ≈ 
                 
                   q 
                   * 
                   2 
                   * 
                   
                     arctan 
                      
                     
                         
                     
                     [ 
                     
                       
                         w 
                         y 
                       
                       
                         2 
                          
                         f 
                       
                     
                     ] 
                   
                 
               
             
             , 
           
         
       
     
     wherein
         w y  is the width of the illuminator  26  along the y axis,   f is the focal length of mirror  10  relative to the mirror curvature in the zy plane,   ϑ y  is the angle of a direction in the zy plane with respect to the direct light direction, i.e.       

     z, and
         q is a quality factor which has a value d=1 in an ideal system, and which here is assumed to preferably fulfill 1≤d≤3, more preferably 1≤d≤2, even more preferably 11.5
 
and wherein the formula is valid for any position, x,y, and for any angular direction in the xz plane, ϑ X , for which the luminance L R  (x, y, ϑ x , ϑ y ) is larger than 10% of the maximum luminance value. In summary, the formula above simply says that the system for illumination is arranged to collimate the light in the yz plane with a precision no more than preferably 3, more preferably 2, even more preferably 1.5 far from the optical limit for the case of a Lambertian emitter of width w y  
       

     However, things are different as far as the xz plane is concerned. Within this plane, the light emitted by illuminator  26  and regularly reflected by mirror  10  retains its divergence stemming from the illuminator  26 . Accordingly, illuminator  26  is, as shown in  FIG. 5 a   , especially configured to show 1) a fairly low divergence in the xz plane. More precisely, given ϑ x  as the angle of a direction in the zx plane with respect the z axis, the illuminator  26  is configured to produce a luminance angular profile, L(ϑ x ), having a width which matches the width of the reflected luminance L R (ϑ y ) in the orthogonal direction. With reference to the FWHM of said luminance angular profiles, the concept becomes: 
       fwhm x   FWHM{ L (ϑ x )}≈fwhm y  
 
     wherein the formula is valid for any position, x,y, and for any angular direction in the yz plane, ϑ y , for which the luminance L(x, y, ϑ x , ϑ y ) is larger than 10% of the maximum luminance value. In order to obtain this result, the illuminator divergence in the xz plane should be tailored according to the actual values of the illuminators width, w y , of mirror  10  focal length, f, and on quality factor, q. Beyond that, the luminance profile should be 2) substantially independent, i.e. uniform, as far as the dependency on x coordinate is concerned, i.e. L x=x     1    (ϑ x , ϑ y )=L x=x     2    (ϑ x , ϑ y ) for any pair of different points along axis x. The uniformity, however, may merely be fulfilled at a granularity corresponding to the angular resolution of the observer&#39;s eyes, that is, for any integrals of the luminance over x within two different regions of, for example, 10 mm 2 . How this may be achieved is illustrated later with respect to  FIGS. 6 a  and 6 b   . However, before this, firstly, the special thoughts relating to the luminance profile of the illuminator  26  of  FIG. 5 a    so as to address the cylindrical shape of mirror  10  is explained in more detail and, secondly, the functionality and appearance of the illumination generated by the system of  FIG. 5 a    shall be explained. 
     The linear illuminator  26  is characterized by its luminance profile, L(x,y, ϑ x , ϑ y ), wherein the luminance is defined as the luminous flux in a beam, emanating from a surface, in a given direction, per unit of projected area of the surface as viewed from that direction, per unit solid angle (ASTM, E 284-09a, Standard Terminology of Appearance) and wherein ϑ x , ϑ y  are the directions as measured in the z,x and in the z,y planes, respectively. With this respect, the linear illuminator  26  is configured to have a luminance which substantially does not depend on the x coordinate, i.e. which is uniform along the x direction, and which is typically not isotropic for what concerns the angular dependence (it can be isotropic in some exceptional case), in the sense that said luminance generally depends weakly on ϑ y  while it shows a narrow peak with respect to its dependence on ϑ x . For example, said luminance angular profile has a FWHM (full width at half maximum) larger than 60°, preferably larger than 90°, most preferably larger than 120° with respect to the dependence on ϑ y , L(ϑ y ), and has a FWHM smaller than 45°, preferably smaller than 30°, most preferably smaller than 15° with respect to the dependence on ϑ x , L(ϑ x ), as schematically depicted in  FIG. 5   b.    
     Imagine briefly, an observer was looking directly onto illuminator  26  (i.e. in  FIG. 5 a    from the view point of the mirror downwards). That is, the observer would be positioned in front of the linear illuminator  26  at a certain distance from the illuminator, e.g. 1 m, looking directly into the center of the linear illuminator  26  from a direction ϑ x =ϑ y =0°. In this circumstance, he/she would see a bright spot under angular aperture Δϑ y  which is limited by the angular width of the illuminator, in the y direction (for example Δϑ y =3° for a width of ˜5 cm of the illuminator for the given 1 m distance), and which is limited by the FWHM of the L(ϑ x ) luminance angular profile, in the x direction, i.e. Δϑ x =fwhm x , assuming the linear illuminator being fairly long (e.g. several m) in the x direction. In other terms, an observer looking directly into the source when it is on may perceive a flashed area or a luminous spot which, for a typical observation distance, is strongly elongated in the x direction. For example, the observer may perceive the source flashed area under an angle Δϑ x =10°, or less. An example of the appearance of the linear illuminator  26  and the flashed area as seen by an observer directly looking into the source is given in  FIG. 5 c   . In what follows, it is assumed that the linear illuminator is configured so that only the flashed area is perceived by an observer which is looking into the source. 
       FIG. 5 d    shows the appearance of the linear illuminator  26  and its flashed area as seen by an observer who looks at said illuminator  26  via the reflection of the cylindric parabolic chromatic mirror  10 , i.e. by an observer positioned within the regularly reflected light beam. Owing to the fact that the linear illuminator  26  is positioned in the focus line of the parabolic mirror  10 , the image of the linear illuminator may be magnified along the y direction. More precisely, the angular width Δϑ y ′ under which the observer sees the flashed area does not depend on the observer-source distance anymore, as described with respect to  FIG. 5 c   , but only on the width of the source in the y direction and on the focal length of the parabolic mirror. For example, a focal length of ˜30 cm leads, in the ideal condition, the observer to perceive the flashed area under an angle Δϑ y ′˜10°, for a ˜5 cm width linear illuminator. In contrast, the angular width under which the observer perceives the flashed area in the orthogonal, z,x, plane is not modified by the presence of the cylindric parabolic chromatic mirror  10 , since the mirror has infinite focal length in the z,x plane, leading therefore to Δϑ x ′=Δϑ x =10° This means that, for any observatory-source distance, and for a give source width in the y direction and source Luminance profile, the condition of substantially isotropic or at least not-elongated appearance of the source flashed area, i.e. the condition Δϑ x ′=Δϑ y ′, can be met by properly choosing the parabolic mirror focal length. Therefore the present invention allows to produce the appearance of a sun image equally wide along y and x direction having an illumination device which may have an arbitrarily large length in the x direction. 
     It is worth noticing that the observer looking at the linear illuminator  26  via the reflection of the cylindric parabolic chromatic mirror  10  will perceived the flashed area or the source, i.e. the flashed spot, at virtually infinite distance. In fact, for what concerns the perception related to the light ray distribution in the y,z plane, the fact that the source is in the focal position automatically ensures the perception of a source virtual position at the infinity. For what concerns the perception related to the light ray distribution in the orthogonal x,z plane, it was noticed by the inventors of present application that the observer perceives the flashed spot at infinite distance as well. This evidence follows by the chosen luminance source profile, and specifically by the fact that said luminance does not depend on the x coordinate, i.e. it is uniform along the x direction. As a consequence, the observer eye cues, e.g. the binocular parallax, the motion parallax, and the accomodation cue, do not find any support for inducing the observer to converge or accommodate her/his eyes at the physical plane where the illuminator is located, this action being in conflict with the eye convergence/accommodation at infinity supported by the virtual image of the flashed spot as perceived in the orthogonal plane. Additionally, the presence of a uniform, blue, luminous light background, which is created by the contribution of the light scattered by the chromatic parabolic mirror  10 , e.g. the light scattered in the Rayleigh regime, further contribute in inducing the observer to set his sight at the infinity, due to the so called “aerel perspective” cue, i.e. the eye cue by which the distance of an object from the observer is perceived to increase with the increase of bluish haze, this bluish haze being normally due to the amount of air interposed between the object and the observer, which in turn is proportional to the object observer distance. 
     Summarizing, all the above mentioned factors, i.e. the focusing power in the y,z plane, the anisotropic angular luminance profile of the illuminator, the uniformity of said angular profile in the x direction, the fact that the chromatic mirror  10  has a cylindrical parabolic shape and that the linear illuminator  26  is positioned at the mirror focal line and, last but not least, the capability of the chromatic mirror  10  of scattering the short wavelength of the impinging light, concurrently contribute in creating the appearance of a blue sky and a bright sun spot at infinite distance, wherein the size of the produced sky window along the x direction can be made arbitrarily large, differently from rotational symmetric mirrors, for which the size of the produce sky cannot be larger than a few focal lengths. 
     Thus, the system of  FIG. 5 a    could, for example, be installed in a ceiling of a room, thereby illuminating a rectangular area  52  on the floor by way of the regularly reflected low-divergence direct light portion of the light generated by illuminator  26 , while other portions of the room are also illuminated by way of the diffuse light caused by the scattering within the diffusing layer of mirror  10 . As described with respect to  FIG. 4 , any light which could directly illuminate the room, i.e. is not directed onto mirror  10 , could, optionally, be blocked by a light blocker or a light concentrator which is schematically indicated in  FIG. 5 a    using reference sign  54  as a concavely shaped cylinder arranged on the other side of illuminator  26  relative to mirror  10  so as to prevent any light of illuminator  26 , which is not directed onto mirror  10 , i.e. heads downwards, so as to not directly illuminate the room. 
       FIG. 5 a    illustrates a layout which ensures the effect of above. By way of the schematically indicated camera or observer eye  30 ,  FIG. 5 a    illustrates the appearance of the illumination system of  FIG. 5 a    when an observer looks onto mirror  10  in a manner so that his/her eyes  30  are directly hit by the regularly reflected light of illuminator  26 , but the observer&#39;s eyes  30  are offset from the zx plane, i.e. the eye is underneath the projection of mirror  10  onto directly lit portion  52 , but at a fraction thereof offset from the projection of illuminator  26  onto area  52 . That is, the bright disc  38  moves, as far as x and y coordinates are concerned, i.e. the plane perpendicular to the direct light direction, along with the observers&#39; eyes  30 , in the same speed as th latter, just as the sun does relative to a window&#39;s frame when seen therethrough. That is, the observer would, for example, look upward onto the ceiling where the mirror  10  and the illuminator  26  are, standing within area  52 . Due to the elongated shape of mirror  10 , he/she would see an elongated bluish, i.e. higher CCT, background light portion  40  within which, along the elongated direction, the backside of light blocker  54  is visible as indicated by the dashed portion  56 . However, directly above him/her (in the direct light direction, here parallel to z, i.e. at angles ϑ y  and ϑ x  equal to zero), the observer sees the bright, lower CCT spot  38  resulting from the low divergence regularly reflected light, the low divergence along the x-axis stemming, as just mentioned, from the specific design of illuminator  26 , while the low divergence along the y-axis stems from the concave/parabolic shape of mirror  10 . 
     Summarizing, in  FIG. 5 a   , the illuminator  26  and the chromatic mirror  10  are formed in an elongated manner along an elongation axis x wherein the mirror  10  is concavely shaped in a plane perpendicular to the elongation axis x, wherein the illuminator  26  has a luminance profile which is divergent, i.e. wide, such as having a FWHM as great as, or even greater than, the angular width of mirror  10  when seen from illuminator  26 , as far as the luminance profile&#39;s dependency on the first angle is concerned, and substantially uniform as far as the luminance profile&#39;s dependency on x, and substantially collimated i.e. narrow such as having a FWHM smaller than three times the FWHM pertaining ϑ y , as far as the luminance profile&#39;s dependency on ϑ x  is concerned. FWHM pertaining ϑ x  may be in the range of a*2*arctan(½w y /f) to b*2*arctan(½w y /f), both inclusively, with preferably a=0.5 and b=6, or more preferably or a=0.7 and b=3, or even more preferably a=0.8 and b=1.5, for example. 
       FIGS. 6 a  and 6 b    show examples of a construction of the illuminator  26  of  FIG. 5 .  FIG. 6 a    shows a fraction of illuminator  26  along the elongation direction, i.e. the x-axis. Specifically, the illuminator  26  of  FIG. 6 a    comprises a linear array of couples of anisotripic emitters  58  and CPC reflectors  60  wherein each anisotropic emitter  58  comprises, for example, a LED such as, for example a rectangular white light LED, and each CPC reflector  60  such as, for example, a rectangular CPC (compound parabolic concentrator) reflector, is optically coupled with, and positioned downstream, the LED of the respective couple, i.e. has an input aperture which matches the LED&#39;s emitting surface. Each CPC reflector  60  comprises two first parabolic reflecting facets  62 , one facing the other, having a curvature that is designed for reducing the LED divergence in the x,z plane, for example for reducing the divergence down to, for example, 10°, or less. Each CPC reflector  60  may further optionally comprise two second parabolic reflecting facets  64 , one facing the other, having a curvature that is designed for reducing the LED divergence in the y,z plane, for example for reducing the divergence down to 90°. 
     Thus, according to  FIG. 6 a   , the illuminator  26  comprises an elongated line-like light source  58  composed of a one-dimensional array of individual emitters  58  arranged in line along the x axis and emitting, for example, anistropically light towards to mirror  10 . Downstream each emitter  58 , a CPC reflector  60  is arranged which reduces the emitter&#39;s divergence perpendicular to the x axis. Each CPC reflector  60  comprise an input aperture for receiving light from, and facing, emitter  58 , and a output aperture for emitting the light received from its emitter  58  via the input aperture and guided within the respective CPC reflector  60  by way of its reflective inside faces  62  and  64  to illuminate a respective portion of mirror  10 . Preferably, the output aperture of all CPC reflectors  60  seamlessly adjoin each other so as to from a continuous face of CPC reflector  60 , facing mirror  10 . 
     Each CPC reflector  60  has a cross section which continuously widens from the input aperture towards the output aperture. The widening parallel to the x axis corresponds to a parabolic or similar light concentrating widening. In particular, each CPC reflector  60  may comprise four internal reflective facets  62  and  64 : two facets  64  extending parallel to the x-axis, both facing each other, and two oppositely arranged, mutually facing facets  62  which are, relative to a completely planar extension in a plane perpendicular to the x-axis, bent towards each other in a direction from the output aperture towards the input aperture in the form of a parabola, for example, so that each CPC reflector  60 , owing to the concave or parabolic shape of reflective facets  62 , reduces, in the xz plane, the diffuseness of the light down to a low divergence, the low divergence fitting to the low divergence achieved in the zy-plane by way of mirror  10  as described above. The concave or parabolic curvature of facets  64 , or even their presence, is merely optional, i.e. they could be left off. 
       FIG. 6 b   , for example, shows the case wherein said second parabolic facets  64  are replaced by plane reflectors. In this case, the divergence in the x,z plane maintains the natural divergence of the emitters  58 . 
     In a certain embodiment, each emitter  58  comprises an LED which might be equipped with a dome lens such as, for example, a cylindrical lens for reducing the divergence in the x,z plane. In certain embodiments, each emitter  58  comprises a LED and a total-internal-reflector (TIR) lens instead of the CPC, or a combination of TIR lens and CPC. 
     In a different embodiment, a beam homogenizer is positioned downstream the array of emitters  58 , for the purpose of improving the uniformity of the linear illuminator  26  in the x direction. For example, the beam homogenizer comprises comprise a fly-eye micro lens tandem array, configured to produce the desired light source divergence in the x,z and y,z planes, respectively. 
     It is worth noticing that some of the described layout for the linear illuminator may generate a rectangular angular divergence which, in turn, may cause the observer to perceive a rectangular (or square) disc  38  when he/she looks at the image of the source reflected by the chromatic mirror  10 , instead of a circular one, as desired. With this respect, the layout in  FIG. 6 b    may perform better than the layout in  FIG. 6 a   , due to the fact that it does not produces a sharp cut-off in the source angular profile, at least in the x,z plane. 
     In a certain embodiment, an improvement for what concerns the generation of round symmetric angular divergence of the light reflected by the chromatic mirror is obtained by implementing onto the chromatic mirror a low-angle white-light diffusing layer, which acts as a low-band pass filter and therefore blooms any image, including the image of the source, by convolving it with a circularly symmetric function with this possibility being further outlined with respect to  FIGS. 8 and 9 . 
     Thus, in other words,  FIGS. 5 to 6   b  show that the concept of  FIG. 4 , i.e. the system for illumination, could be modified so as to result in a system where the illuminator  26  and the chromatic mirror  10  are formed in an elongated manner along elongation axis x, wherein the illuminator  10  has a radiation characteristic, i.e. luminance profile, which is divergent perpendicular to the elongation axis x and collimated parallel to the elongation axis x. 
     It should be noted that the elongation axis x does not necessarily correspond to a straight line as illustrated in  FIG. 5  and  FIG. 6 a    and  FIG. 6 b   . Rather, the elongation axis x may, for example, be bent in the plane perpendicular to the z-axis. For example, the whole setup of  FIG. 5  may be bent, when seeing in a top view, so as to result in a circular shape so that the mirroring surface  12  of mirror  10  would assume the form of a donut cut along a horizontal plane with the illuminator  26  then being arranged along the circular focal line defined by mirror  10 . The explanations given above would then, however, remain the same by replacing the x-axis to define the tangential direction of the circular extension of the donut shape when seen in the plan view, and the y axis corresponding to the radial direction thereof. Such a plan view is illustrated in  FIG. 7 . 
     As described above, the concept of forming the mirroring surface  12  of mirror  10  in the form of a concave or even parabolic shape helps in increasing the stability of the achievement of the sun-sky-appearance along with the associated infinity depth impression within the observer&#39;s eyes by lowering the divergence of the regularly reflected direct light portion back-emitted by mirror  10 . However, as noted above, irrespective of using this concave/parabolic shape concept, there are still aspects which may attract the observer&#39;s attention at the time the observer directly looks into the regularly reflected direct light portion, thereby distracting the observer from experiencing the infinity depth impression. For example, all edges of objects, such as object  42  in  FIG. 2 , the image of which is within the field of view of the observer&#39;s eyes via reflection at mirror  10 , cause spatial luminance gradients in the sky-like background portion  40  and as the eyes of the observer are especially prone to such irregularities, the following embodiments seek to provide measures to avoid the described distraction. 
     A first possibility is described with respect to  FIG. 8 .  FIG. 8  shows mirror  10  as comprising, in addition to the elements of  FIG. 1 , a further layer  76  which is, in comparison to diffusion layer  14 , designed to, as far as the visible spectrum range is concerned, show a substantially uniform interaction cross-section with respect to wavelength for the impinging light  20 , but an interaction property according to which each interaction event with an inbound impinging light ray merely leads to relatively small propagation direction change of the light ray from before to after the interaction. Accordingly, in the embodiment of  FIG. 8 , the regularly reflected light  24  substantially has the same spectrum as in the case of  FIG. 1 , but some of its energy is smeared-out around the specular angle direction as illustratively indicated in  FIG. 8  by way of a dotted circle  78 . 
     Although  FIG. 8  shows layer  18  as being arranged at side  18  of diffusing layer  14 , according to an alternative, layer  18  may be positioned, for example, between diffusing layer  14  and mirroring surface  12 . As will be described further below when discussing possible implementations for implementing and fabricating mirror  10 , a possibility to provide diffusing layer  14  with its ability to have a spectrally dependent scattering cross-section and to provide blurring layer  76  with its characteristic to smear-out the regularly reflected light rays is to use a first dispersion of light-scattering centers of an average size smaller than 250 nm for the diffusing layer  14  and a second dispersion of light-scattering centers for layer  76  of an average size which is, for example, exactly or more than 5 times larger, preferably exactly or more than 10 times larger, more preferably exactly or more than 15 times larger or even exactly or more than 50 times larger than the average size of the light scattering centers forming the first dispersion. In a certain embodiment, the size of the light scattering centers forming the second dispersion for layer  76  will be designed so as to be larger than 1 micron, preferably larger than 2 micron, more preferably larger than 3 micron or even larger than 10 micron. Both layers  18  and  76  may use a transparent polymer layer as the matrix for the dispersion. In this regard, both dispersions may be provided within the same matrix layer, e.g. a transparent polymer layer, so that the just outlined blurring characteristic described with respect to layer  76  could, according to an alternative embodiment, be included by layer  14  itself, i.e. layer  14  itself could have this characteristic in addition to its wavelength-dependent scattering cross-section leading to the diffuse scattering. 
     When using the mirror of  FIG. 8  in the embodiments shown in  FIGS. 2 to 7 , the effect is that, in the observer&#39;s eye  30 , the resulting perceived scene, i.e. the image, is blurred, i.e. is effectively low-pass filtered so that the previously mentioned steep brightness gradients in the sky-like region  40  of the image, which might distract the observer from experiencing the infinity depth impression, are effectively reduced. For example, the size of the light scattering centers forming the second dispersion  76  and the numbers of said scattering centers per unit of surface of the chromatic mirror  10  may be configured in order to obtain a blurring angle of about 30°, preferably 20°, more preferably 10° or even 3° only and a blurring efficacy&gt;50%, preferably &gt;70%, more preferably &gt;90%, in the sense that at least 50%, 70% or 90% of the imping rays experience a deviation within the specified blurring angle. 
     Another possibility of achieving the just mentioned blurring effect is discussed with respect to  FIG. 9 . According to  FIG. 9 , the mirror of  FIG. 1  is modified in that the diffusing layer  14  comprises a physical and/or optical thickness which varies laterally. The effect of said thickness variation is that of providing scattering centers which, due to the effect of refraction and/or diffraction, are capable of providing an efficient bending of the impinging light rays. For what concerns the amount of produced angular deviation, i.e. the burring angle, it is well known by elementary scattering theory how this can be computed as a function of the transverse size and of the depth of the thickness modulation (intuitively: smaller size and larger depth produce larger angular deviation). For what concerns the blurring efficiancy, the present approach based on the thickness modulation allows to obtain large figures more easily than the previous approach based on usage of a second dispersion of scattering centers, because said thickness modulation can be easily configured in order to minimize and almost avoid the presence of flat profiles, i.e. of non-modulated portions of the diffusing-layer  14  optical thickness. However, in spite of the fact that the thickness-modulation approach is routinely used at the industrial level for blurring filter production, the cost of the technology may be higher than for the previous case based on the second dispersion. Therefore, in a way which is known to the expert of the filed, the profile of the thickness modulation can be configured in order to obtain a blurring angle of about 30°, preferably 20°, more preferably 10° or even 3° only and a blurring efficacy&gt;50%, preferably &gt;70%, more preferably &gt;90%, or even higher than 97%. For example, the thickens modulation may have an average spatial frequency in the range of 10-200, preferably 20-1000, more preferably 40-500 modulations/mm, and a ratio between the depth and the transverse size of the thickness modulation in the range 0.05-2, preferably 0.1-1. However, different examples concerning modulation depth and spatial frequency are also possible, the quoted values being only indicative of the most frequent figures currently used in blurring-filter technology. 
     The mechanism by which the thickness modulation produces the bending of the impinging light rays as schematically illustrated in  FIG. 9 , is exemplarily limited to the effect of refraction, which is the dominant one when the transverse width of the thickness variation exceeds the tenths of micron. However, diffraction effects may be exploited, too, as mentioned above. Owing to the optical thickness variation, incident light  20  experiences different minor directional changes  80  and  82  when entering into, and exiting from, diffusion layer  14  with this being true for the regularly reflected light portion  24 , i.e. the one not scatter-interacting with the first dispersion in the diffusion layer  14 , as well as, less significantly, the diffused, scattered light portion. Compared thereto, in case of a completely even thick layer  14 , the directional change at entering and exiting layer  14  would compensate each other so that the regularly reflected light path would be at the specular angle with respect to the light path of the incident light  20 . Owing to the varying inclination of diffusing layer  14  facing away from mirror surface  12 , however, the directional changes  80  and  82  do not compensate each other. Rather, depending on the exact location where ray  20  impinges onto diffusing layer  14 , the direction at which the regularly reflected, non-scattered light leaves layer  14  deviates more or less, or is merely accidentally equal to, the specular angle direction which would occur if the diffusing layer  14  was flat as shown in  FIG. 1 . Thus, the varying thickness presented in  FIG. 9  is able to generate the blurring effect previously described with respect to  FIG. 8  and may, accordingly, be likewise used in order to alleviate the distraction problem with respect to the infinity depth impression. 
     It should be noted that there are also some further advantages of exploiting the just-outlined blurring effect discussed above with respect to  FIGS. 8 and 9 . In addition to the aim of
         1) hiding object contours of objects such as object  42  using the low angle wide scattering, further advantages are, for example:   2) a more uniform appearance of the inner of spot  38 ,   3) a smoothening of the outline of spot  38  so that deviations from a circular appearance may be rendered less visible, as discussed above,   4) the appearance of the sun-like disc  38  is enlarged and therefore its glare is reduced,   5) an unevenness of the illumination of the directly lit portion of the illuminated room (compare  52  in  FIG. 5 , for example) due to, for example, imperfections of the mirroring surface&#39;s concave shape, is compensated.       

     In particular, the lateral variation may be such that light which crosses the layer  14  in the outward direction experiences a low-angle diffusion so that red light rays at 650 nm which cross layer  14  in the inward direction and are reflected by the mirroring surface  12  and cross again layer  14  in the outward direction have—assuming a spatial even probability of incidence, i.e. an isotropic illumination—at least 50%, preferably 70%, more preferably 90% or even 97% probability of experiencing an angular deviation in the range of 0.1° to 15°, preferentially 0.1° to 10°, more preferentially 0.1° to 5° or even 0.1° to 1.5° from the direction of specular reflection. 
     Further, speaking differently, the physical and/or optical thickness variation of the layer of varying thickness may be configured such that the chromatic mirror  10  has finally a regular reflectance, i.e. the reflectance at the specular angle, smaller than 50%, preferentially smaller than 30%, even more preferentially smaller than 10% or even smaller than 3% with respect to the case of a flat diffusing layer  14  which comprises only the first nanoparticle dispersion. 
     Even further, it should be noted that alternatively to the description of  FIG. 9 , instead of using diffusing layer  14 , another layer could be provided in addition to layer  14  which is transparent and has the described variance in physical and/or optical thickness variation. Accordingly, such a transparent layer of varying thickness could be positioned at the side  18  of diffusing layer  14  just as layer  76  in  FIG. 8  was added to diffusion layer  14 . 
     Another possibility to achieve a reduction in distraction probability is presented below with respect to  FIG. 10 .  FIG. 10  merely exemplarily forms a modification of  FIG. 5 , but the usage of a semitransparent layer outlined with respect to  FIG. 10  could alternatively also be used in combination with any of the other systems of combinations of an illuminator and a mirror  10 . In the context of present application, “semitransparent layer” shall denote something which
         (i) transmits without disturbance a portion of the impinging light, for example. has a regular transmittance preferably in the range 5-50%, more preferably 10-40%, even more preferably 15-30%,   (ii) scatters the rest of the light over arbitrary directions, preferentially in an isotropic way or at least ensuring that more than 30%, preferentially 50%, more preferentially 70% of the scattered light is deviated by more than 5°, preferably more than 10°, more preferably more than 15° from the direction of the impinging light.       

     Additionally, in a certain embodiments it is beneficial that the scattering occurs preferentially in the forward direction, e.g. it is preferred that the semi-transparent layer show a ratio between forward and backward scattering efficiency&gt;1.1, preferably &gt;1.5, more preferably &gt;2 or even &gt;5. 
       FIG. 10  shows a semi-transparent layer  84  as being positioned downstream mirror  10 , i.e. between the area  52  lit by the regularly reflected light where the observer&#39;s eyes are expected to be. In other words, the semi-transparent layer  84  is arranged, and is held, in a position between observer on the one hand and mirror  10  on the other hand. The semi-transparent layer may be a fabric tent. In the case where mirror  10  along with illuminator  26  is arranged at the ceiling of a room, the semi-transparent layer  84  may be suspended beneath illuminator  26 . Independently from the position of mirror  10  and illuminator  26  inside the room, the effect of the semitransparent layer  84  may be the typical effect of a tent in front of a window, as for example the effect of producing a screen which
         (i) is illuminated by the direct warm light of the sun, which casts onto the tent a luminous and sharply defined spot of warm light which, in turn, illuminates the room by diffused light,   (ii) is illuminated by the bluish and diffused light from the sky, which produces a bluish tinge onto the tent and particularly in the surrounding of the projected warm sun spot, thus leading to an easy perception of the beautiful combined action of the light from the sun and the sky.       

     In a certain embodiment, semi-transparency of semi-transparent layer  84  shall describe the semitransparent layer  84  characteristic, so as to, in a fine granular manner, be partitioned into portions being completely transparent for light crossing layer  84 , and other portions which are not, i.e. deviate the light seeking to cross layer  84 . For example, there may be openings in layer  84 , with the material of layer  84  otherwise acting as a white-light diffuser, as for the case of a white fabric. In a certain embodiment, the semitrasnparerent diffuser may also be colored, or partially colored, as it is often the case for domestic fabric tents. In different embodiments, the semitransparent diffuser may have a regular transmittance which varies from one point to another, as it is suited for the purpose of exhibiting aesthetical figurative effects. In all the embodiments, the fact that the semitransparent diffuser has a non-zero regular transmittance ensure that the observer has always the possibility of perceiving the flashed portion of the light source beyond semitransparent diffuser and, according to the configured distance between the observer and the real/virtual image of the light generator she/he might gain the perception of the existence of an infinitely deep space beyond the semitrasnparerent diffuser, for the same reason and by means of the same mechanisms outlined above for the case in the absence of the semitransparent diffuser. 
     In a certain embodiment, the semitransparent layer  84  may produce the following effect: an observer looking onto mirror  10  within the direct light portion  52  is prevented from seeing all of the details of the reflected light generator or, more relevantly, of the reflected room, which might spoil the experience of infinite depth perception. In fact, her/his visual attention may be now more attracted by the luminous spot onto the semitransparent layer, e.g. the tent, and by the mentioned contrast between warm and bluish light onto the same diffuser, i.e. the attention is attracted by effects naturally occurring at finite distance from the observer, instead of being attracted by the room reflection into the mirror, which leads to a non-natural effect. As a result, the observer is less likely distracted from experiencing the infinity depth impression. 
     Before describing some embodiments for realizing and fabricating a chromatic mirror  10  according to any of the above embodiments, it should be noted that the systems for illumination described above with respect to  FIGS. 2 to 7 and 10  might be used in the form of an array of such systems, such that the light which is regularly reflected by the chromatic mirrors of these systems forms an array of light beams oriented in the same direction. For example, the illumination system of  FIG. 5  could be positioned side by side so as to cover, for example, the whole ceiling of a room instead of merely a portion thereof. 
     Beyond that, it should be noted that all of the illumination systems described above form, along with optional surrounding building elements such as walls, ceilings and the like, an architectural object, i.e. a building, such as a house or the like, which participates in the advantages of the embodiments outlined above. 
     Further, in this respect, it should be noted that the advantages provided by the embodiments using the concave or even parabolic shape of the mirroring surface do not have to be necessarily used. In some applications, e.g. even in conditions where the light generator is positioned so close to the chromatic mirror that the observer will unavoidably perceive it a finite distance, as well as in condition where to the usage of a plurality of illumination devices may cause the observer to perceive simultaneously, i.e. from a single observation position, the presence of more than one light generator, i.e of more than one sun. Even in these cases architectural measures may have been taken in order to prevent people from directly looking into the direct light beam formed by the regularly reflected light from mirror  10 .  FIG. 11  shows such an example for an architectural object.  FIG. 11  shows two walls  86   a  and  86   b  of the room of the architectural object, wherein the mirror  10  is hung up on wall  86   a  for illustration purposes. Mirror  10  is illuminated by illuminator  26  which, in turn, is, for example, suspended at the ceiling of the room. The direct light, regularly reflected by mirror  10 , is shown as exemplarily lighting a certain area of the room where, for illustration purposes, a sculpture is shown to be positioned. In order to prevent people from accidentally directly looking onto illuminator  26  via mirror  10 , the area  88  directly lit by the direct light is shown to be included within a blocked area, blocked against human visitors seeking to enter the blocked area. In  FIG. 11 , the blocked area is exemplarily defined by a fence  90  surrounding the area  88  lit by the direct light. Accordingly, any visitor or observer  92  outside the blocked area defined by fence  90  is prevented from directly looking into the illuminator  26  via mirror  10 , but merely sees the sky-like diffuse light and the direct sun-like rays illuminating a scene, and may accordingly feel as if mirror  10  would be a window permitting a view into the sky, all these effect being perceived without directly seeing the sun. Notably, this setting may be used in order to release the constraint about the perceivable shape of the light generator or of its flashed area, which can be of any shape in this case. 
     After having described certain embodiments for a chromatic mirror and concepts and systems using the same in an advantageous manner, some specific implementation examples and examples of fabricating such a chromatic mirror are described in the following. 
     As has already been described above, the diffusing layer  14  may be a coating or a film, e.g. a layer having a preferably a thickness&lt;0.2 mm, more preferably &lt;0.1 mm, even more preferably &lt;0.05 mm or, for a certain embodiments, even &lt;0.01 mm, deposited onto the mirroring surface  12 .  FIG. 12  illustrates that the diffusing layer  14  may be provided with its wavelength dependent scattering cross-section by forming the diffusing layer  14  as a transparent polymer layer having a dispersion of light-scattering centers, i.e. nanoparticles, of an average size smaller than 250 nm embedded therein. The light-scattering centers or nanoparticles are indicated using reference sign  94 .  FIG. 12  also illustrates that the transparent layer of the diffusing layer  14  may, optionally, also have a second dispersion of other light-scattering centers  96  embedded therein, with an average size of the light-scattering centers  96  being, for example, greater than 5 microns. See also the above notes concerning a relationship between the average size of the light-scattering centers of the first and second dispersions, and further examples for absolute minimum average sizes. While the dispersion of light-scattering centers  94  provokes the above outlined wavelength-dependent diffuse scattering, the second dispersion of light-scattering centers  96  provokes the blurring effect outlined with respect to  FIG. 8  and layer  76 , respectively. Insofar,  FIG. 12  is an example for the above mentioned alternative to  FIG. 8 , according to which both characteristics, i.e. wavelength-dependent diffuse scattering and low-angle white light blurring, are unified within the same layer  14 . 
     In construing mirror  10 , transparent polymer layer  14  with dispersion  94  and optionally dispersion  96  may be fabricated first so as to result in a film which is then applied onto mirroring surface  12 , or onto which the mirroring surface  12  is then formed, or alternatively, the dispersion  94  and optionally dispersion  96  along with the transparent polymer material of layer  14  are directly deposited onto mirroring surface  12  such as, for example, by way of spraying, inkjet method, film spinning, deep coating, coil coating, metal vacuum deposition, molecular beam epitaxy, plasma coating, or the like. 
     The density of first and second diffusions may be selected such that the diffuse reflectance of the chromatic mirror is, for example, greater than 50%, greater than 80% or even greater than 90%. That is, virtually all the iminging light may be scattered, either at low angles at the second dispersion or at large angles at the first dispersion, leaving a negligible regularly reflected light portion. 
       FIG. 13  shows a further embodiment of realizing a mirror  10 . According to  FIG. 13 , a transparent panel  98  is positioned between a coating or film  100  forming mirror surface  12 , and another coating or film  102  forming the diffusing layer  14 . Coatings or films  100  and  102  may comprise the dispersions outlined with respect to  FIG. 12 . In other words, the transparent panel which may be a polymeric, e.g. an acrylic, polycarbonate, a mylar, a PVC or the like, panel or a glass or a stratified-glass panel, has two main sides or facets, with coating or film  100  being positioned on one facet, and the coating or film  102  being deposited onto the other facet. 
     Accordingly, in case of  FIG. 13 , mirror  10  may be stiff or flexible or even tensile, with a stiffness/flexibility/tensibility provided by the transparent panel  98 . Note that the term panel in the context of the present invention is just used to mean a layer of any possible thickness, therefore it may be also a film or a coating and may be not necessary rigid. 
       FIG. 14  shows a variation of the embodiment of  FIG. 13  according to which both coatings or films  100  and  102  are positioned on the same side or facet of transparent panel  98 . For example, coating or film  102  is positioned between coating or film  100  and transparent panel  98  with the coating or film  100  or the side thereof facing diffusing layer  14  forming the mirroring surface  12 . 
     Interestingly, the embodiment of  FIG. 14  enables the avoidance of using the tin side of a glass panel in the case of using such a float glass panel as transparent panel  98 . In other words, in case of  FIG. 14 , the transparent panel  98  may be embodied as a float glass panel and in that case, the tin side may be used as the side facing away from coatings or films  100  and  102 , whereas the air side of the float glass panel  98  contacts coating or film  102 . By this measure, the effects resulting from the tin used for the production of the float glass panel are prevented from negatively affecting films or coatings  102  and  100 . 
     For illustration purposes, the tin side is illustrated in  FIG. 14  using hatching and indicated using reference sign  104 . 
       FIG. 15  explains how the embodiment of  FIG. 13  may be construed by way of float glass sheets, avoiding depositing any of films or coatings  100  and  102  onto any tin side of the float glass sheets. In particular, in accordance with  FIG. 15 , the chromatic mirror  10  comprises a stratified-glass panel composed of two float glass sheets  104  and  106  sandwiching, and affixed to each other, by way of an adhesive transparent polymeric film  108 , e.g. an EVA or PVB film, wherein the facet of the two glass sheets  104  and  106  facing, and attached to each other via the adhesive polymeric film  108  are the glass tin sides of float glass sheets  104  and  106 , and the coating or film  100  forming the mirroring surface  12  is deposited onto the air side of float glass sheet  104 , whereas the coating or film  102  forming the diffusing layer  14  is deposited onto the air side of float glass sheet  106 . By this measure, the mirror  10  of  FIG. 15  behaves also as a “safety glass panel”, and fulfills many requirements imposed onto the usage of elements in buildings such as shock resistance (e.g. the fact that the panel does not separate in many parts when it eventually got broken), fire resistance and the like. 
     Another embodiment is shown in  FIG. 16 . Here, the embodiment of  FIG. 15  is modified in that the diffusing property of the diffusing layer is transferred from the separate film or coating  102  of  FIG. 15  towards the transparent layer  108  between float glass sheets  104  and  106  which, accordingly, serves as both adhesive transparent polymeric film as well as the diffusion layer. For example, the adhesive transparent polymeric film may concurrently serve as a matrix for the dispersion of light-scattering centers  96  depicted in  FIG. 12 . Thus, the mirror of  FIG. 16  may be fabricated very easily by way of processes which occur anyway in case of fabricating a two-sheet stratified glass panel with merely the film or coating  100  needing depositing onto the air side of one of the float glass sheets  104  or  106  ( 104  in the case of  FIG. 16 ). 
     In case of the embodiments of  FIGS. 13 to 16 , the transparent panel and glass sheets, respectively, assumed the role of the supporting member, or supporting layer. In the case of the glass sheet and glass panel examples, same provide the mirror  10  thus construed with stiffness. 
     Embodiments of  FIG. 17  show an example where the mirroring surface is formed by an aluminum metal mirror foil having e.g. very high-reflectivity (e.g. with reflectivity&gt;95%, and even &gt;98%) as the ones nowadays used, e.g. for fluorescent-tube light reflectors, or for solar light reflection in the outdoor, and produced by means a several industrial process such as, for example, electrophoreses, metal vacuum deposition, organic and/or inorganic material coating, including the usage of micro and nanoparticles, as suited, for example to control the index mismatch and so increase reflectivity or to enhance the mechanical and chemical resistance of the mirror to external agents, such as to atmospheric agents for the case of outdoor applications. In a certain embodiment, the diffusing layer  14  may be formed by a coating or film  102  deposited directly onto the finished aluminum mirror foil, indicated using reference sign  110  in  FIG. 17 . Alternatively, the diffusing layer  14  may be deposited in the course of the industrial process suited for the Al mirrofoil production. This second solution implies a more complex and costly process, but it may lead to a better finishing of the chromatic mirror  10 , especially for outdoor applications. 
     In both cases, accordingly, the aluminum metal mirror foil  110  may provide the resulting mirror  10  with suitable flexibility as necessary for being processes by means of coil-coating technique and for being stored in coils. For illustration purposes,  FIG. 17  shows the mirror  10  as being furled into a coil  112  such as, for instance, for the sake of delivery or transport. 
     In any of the above outlined embodiments, the diffusing layer or the film or coating  102  forming the same may be a transparent polymer layer with a dispersion of the aforementioned light-scattering centers  96 . The latter light-scattering centers may, for example, be organic nanoparticles or, in the aim of obtaining the largest scattering efficiency an so the smallest possible thickness for the scattering layer  14 , also inorganic nanoparticles, such as TiO 2 , ZnO nanoparticles, which feature a larger index mismatch with respect to the organic matrix, and have an average diameter of smaller than 250 nm. These inorganic nanoparticles may be protected against photo-catalysis introduced by near-UV and/or visible light radiation, as it is currently done by industrial nanoparticle suppliers. 
     In a different embodiment, the diffusing layer  14  my comprise nanoparticles, e.g. inorganic nanoparticles, dispersed into an inorganic matrix, such into a glass of silica-based material, such as a sol-gel based material. This option may imply the use of large industrial plants, as it is typical the case for the glass production industry, but will have the benefit of reducing the number of steps and thus simplifying the industrial process and reducing the cost, making the new process to differ very slightly from the standard industrial process for the glass, tempered glass, stratified glass and glass mirror production. 
     Further,  FIG. 17  shows rather representatively for all of the above-outlined embodiments for mirror  10  that a protective layer  112  made of a transparent material and resistant to atmospheric agents may protect the diffusing layer  14 . In the case of  FIG. 17 , for example, the diffusing layer  14 , i.e. film or coating  102 , is sandwiched between the aluminum metal mirror foil  110  and the protective layer  112 . The protective layer  112  may, for example, be an inorganic film or a sol-gel film such as a silica sol-gel film or a film comprising silica micro or nanoparticles. 
     As has already been mentioned above with respect to  FIG. 17 , the mirror  10  according to  FIG. 17  is flexible. In accordance with an embodiment shown in  FIG. 18 , the mirror  10  is thus held in a fixed position by way of a frame  114  which surrounds the outer circumference of mirror  10  which processes a foil-like flexibility in accordance with the embodiment of  FIG. 17 . 
     By way of the frame  114 , the mirror  10  may be held, for example, at a fixed position with respect to a wall or the like. In a certain embodiment, the chromatic mirror  10  based on a Al mirror foil support may feature a plurality of perforations, e.g. perforations having a size in the range of 1-100 mm, preferably in the range 5-50 mm, as it is convenient for applications of the chromatic mirror  10  for the construction of building coats acting as chromatic ventilated facades. Hover, some application of the chromatic mirror  10  for ventilated façades, or even for aesthetical building façades, does not necessary require the perforation to be made. 
     With respect to  FIGS. 13 and 14 , it is noted that the transparent panel  98  shown therein may be replaced by flexible members such as a transparent flexible polymeric film so that the resulting mirror  10  is provided with tensibility, i.e. it can be kept in tension by a suitable frame, e.g. a tensile structure as the one used for shade-making tents in the outdoor. Accordingly, when using a flexible polymeric film  98  in  FIGS. 14 and 13 , the resulting chromatic mirror  10  forms a tensile structure which is bendable into various shapes such as, for example, a concave or even parabolic shape as discussed above. This feature can be used, for example, for construing large sky-like ceiling in sport holes, SPAs, entertainment parks, etc., wherein not only the vision of the sky is ensured but also that of the sun. 
     Instead of using a metal foil in order to form the mirroring surface, alternatively a fabric coated with a reflective coating could be used. This option can be used, e.g., in the fashion industry in order to crate sky-sun clothes featuring an appearance that changes with the type of illumination, and specifically with the tipe of directionality of the illumination, which in turn means with the change of atmospheric condition from the case of a clean deay, ensuring strongly directional light, and the overcast day, wherein all the light is diffused. 
     Finally,  FIG. 19  shows an embodiment where a building façade, here exemplarily the façade of a skyscraper  116 , is provided with one or more chromatic mirrors  10 , wherein  FIG. 19  illustratively shows merely a portion of the façade as being provided with mirrors  10 , namely portion  118 . According to this application, the building façade may be made to behave as a piece of sky when it is lit by some directional light, as the light from the sun in a clean day or even in a partially overcast day, thus allowing to substantially modify the appearance of the building and its aesthetical interplay with the surrounding nature and the sky. Although any of the above examples of mirrors  10  may be used to form, at least partially, the façade (with the mirroring side facing outwardly),  FIG. 19  illustrates the case that portion  118  is filled by an array of mirrors of the type of  FIG. 18 . This circumstance shall, however, not be interpreted as excluding any of the other embodiments of mirror  10  to be used for providing portion  118  of the façade with the mirroring effect. 
     The effect of providing portion  118  of skyscraper  116  with mirror  10  can be further explained as follows: usually sunlight illuminates the façade of skyscrapers  116 . Owing to the diffusing property of the diffusing layer of mirror  10 , however, an observer looking onto skyscraper  116  will feel as if the sky behind skyscraper  116  would be visible at portion  118  covered by mirror  10 . By this measure, the skyscraper  116  may accordingly be almost rendered to disappear at least as far as portion  118  is concerned and this measure may be used for many purposes such as, for example, aesthetic aspects. 
     Finally,  FIG. 20  shows an example of a chromatic panel formed as a stratified-glass panel. It differs from  FIG. 16  merely in that the coating or film  100  is left off. That is,  FIG. 20  shows a chromatic panel which is easily extendable to result in a chromatic mirror according to  FIG. 16 , and which has the same advantages with respect to its usage within architectural and building environments: it is easily fabricated as there is, in principle, no additional construction step necessary in order to form the stratified-glass panel with layer  100  concurrently assuming the affixation of glass sheets  104  and  106  to each other as well as the wavelength-dependent diffuse scattering functionality. The glass sheets may be of float or tempered glass. Interestingly, within a building, chromatic panel of  FIG. 20  may be used both in transmission as well as “in reflection” as far as the half of the diffuse light is concerned, which exits the chromatic component at the same side as the incident light. Thus, when replacing, for example, the mirror  10  at the side wall of  FIG. 3  with the chromatic panel of  FIG. 20 , and illuminating this chromatic panel from the neighboring room to the left of room  48  then an observer standing within room  48  would be able to obtain a sun-sky appearance similar to the one outlined with respect to  FIG. 2  with the difference being that the illuminator is positioned in the neighboring room. An observer being within the neighboring room illustrated by dashed lines in  FIG. 3 , in turn, would see a plane sky without sun. The usage of the chromatic component within a building comprising the two rooms would be of no problem due to the stratified-flat panel construction. 
     As to the possibility of construing/fabricating the diffusing layer, reference is made to the above embodiments and in particular the statement made above with respect to  FIG. 12 .