CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from European Patent

Application No. 17425093.6 filed on 28/09/2017, the disclosure of which is incorporated by reference

TECHNICAL FIELD

The present invention relates to an optical device for an improved lighting system capable of simulating natural lighting in two half-spaces.

BACKGROUND ART

It is known that artificial lighting systems for indoor environments are currently available that have the goal of improving the visual comfort of users. In particular, there are known lighting systems for simulating natural lighting, i.e. the type of lighting available in outdoor environments. In particular, these lighting systems aim at simulating the appearance of the Sun and/or the skylight, this latter being substantially blue.

For example, the European patent application EP2304480 describes a lighting system that comprises a light source capable of generating visible light and a panel containing nanoparticles . In use, the panel receives light rays coming from the light source and acts as a so-called Rayleigh diffuser, i.e. it scatters the light rays in a manner similar to that which occurs in the Earth' s atmosphere in clear-sky conditions. Further details regarding the panel referred to in the European patent application EP2304480 are described in the European patent application EP2304478.

In particular, the lighting system described in the European patent application EP2304480 simulates the natural lighting because it generates, inside an environment, direct light with a low correlated colour temperature (CCT) , which simulates direct light coming from the Sun and generates shadows in the presence of illuminated objects; in addition, the lighting system generates high-CCT diffused light, which simulates daylight and gives shadows a bluish tone.

The patent application PCT/IB2013/060141, filed on

14/11/2013, describes a lighting system based on the principle, given a light source that stands out on a background and is observed by an observer through a Rayleigh diffusing panel, the observer has difficulty in perceiving the effective distance of the light source, if the background is uniform. This lighting aims at inducing the observer to perceive the light emitted from the diffusing panel as coming from a virtually infinite distance, as long as the light generated by the light source falls within the observer' s field of view. In particular, the diffuser panel acts as a secondary light radiation source, which, due to the high spatial uniformity, prevents the observer from evaluating the effective distance separating him/her from the diffusing panel .

This having been said, the abovementioned lighting systems are configured to illuminate an environment, e.g. a room. In case more than one environment have to be illuminated, it is possible to provide each environment with a corresponding lighting system; however, this solution entails a duplication of the costs. Therefore, the Applicant has noted that a need is felt for a lighting system which allows to simulate the natural light in more than one environment, in a more efficient manner.

DISCLOSURE OF INVENTION

The object of the present invention is therefore to provide a lighting system that at least partly overcomes the drawbacks of the known art.

According to the invention, an optical device and a lighting system are provided, as defined in the appended claims .

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, some embodiments will now be described, purely by way of non- limitative example, and with reference to the accompanying drawings, in which:

- Figure 1 schematically shows a cross-section of a lighting system;

- Figures 2a and 2b respectively show a top plan view and a cross-section of a light source;

- Figures 3a and 3b schematically show opposite front views of an optical device;

- Figure 4 shows a picture of a portion of an optical device ;

- Figure 5 schematically shows a perspective view of an emitting surface of a light source, together with a luminance plot, as a function of an angle Θ, such a plot being illustrated in a linear arbitrary scale;

- Figures 6, 8 and 15 schematically show cross-sections of optical devices;

- Figure 7, 9-14 and 17 schematically show cross- sections of lighting systems;

- Figure 16 schematically shows a block diagram of an optical system;

- Figures 18-19 schematically show front views of portions of optical devices.

BEST MODE FOR CARRYING OUT THE INVENTION

Figure 1 shows a lighting system 1, which includes a light source 2 and an optical device 4; in addition, Figure 1 shows a first and a second orthogonal reference system (respectively designated by xyz and XYZ) .

The light source 2 emits visible light (i.e., with a wavelength in the range of between 400nm and 700nm), hereinafter referred to as direct light 16. In greater detail, the light source 2 emits a beam of direct light 16.

As shown in Figure 2a, the light source 2 comprises an emitting surface 8, not necessarily physical, which is arranged parallel to the plane xy and has a circular shape, with center 0. In addition, as shown in Figure 2b, the direct light 16 is emitted from the emitting surface 8 with a divergence DIV, parallel to either the x axis and the y axis, which is lower than 30°, preferably 20°, even more preferably 10° (under the assumption of an emission with circular symmetry or, in case of lack of circular symmetry, in any plane containing the axis of the beam of direct light 16, herein designated by H) ; purely by way of example, the axis H is perpendicular to the emitting surface 8 and passes through the center 0. The optical device 4 has the shape of a parallelepiped; in particular, and without any loss of generality, the optical device 4 is delimited by a first and a second surface SI, S2, opposite to one another and parallel to the plane XY . In addition, the abovementioned parallelepiped has a width, measured parallel to the Z axis, which is negligible, to a first approximation, with respect to the size along either the X axis and the Y axis.

Preferably, the area of the emitting surface 8 of the light source 2 is not greater than 30% (preferably 15%, more preferably 10%) of the area of the first surface SI.

The optical device 4 comprises a number of reflecting portions 41 and a number of transmitting portions 42. In particular, each reflecting portion 41 may be formed by a corresponding mirror (e.g., a planar mirror), whereas each transmitting portion 42 may be formed, as an example, by glass or PMMA.

Each reflecting portion 41 forms a corresponding portion SRI of the first surface SI, hereinafter referred to as reflecting surface S _RI . Each transmitting portion 42 forms a corresponding portion STI of the first surface SI, hereinafter referred to as input transmitting surface STI.

In addition, each reflecting portion 41 forms a corresponding portion SR2 of the second surface S2, hereinafter referred to as back surface SR2. Furthermore, each transmitting portion 42 forms a corresponding portion ST2 of the second surface S2, hereinafter referred to as output transmitting surface ST2.

Without any loss of generality, given any reflecting portion 41, the corresponding reflecting surface S RI and back surface S R2 have the same shape and are laterally staggered only parallel to the Z axis. The optical properties of the back surface S R2 are not relevant in this example.

Without any loss of generality, given any transmitting portion 42, the corresponding input transmitting surface S TI and output transmitting surface S T2 are equal and are laterally staggered only parallel to the Z axis.

From a practical point of view, each transmitting portion 42 of the optical device 4 is at least partially transparent. In particular, the term "transparent" has to be construed like in PCT/IB2013/060141, i.e. as indicating the so-called "see through" optical property, i.e. the property of an optical element of transmitting image-forming light. Furthermore, from an optical point of view, and to a first approximation, the input transmitting surface S TI and the output transmitting surface S T2 of each transmitting portion 42 may be regarded as one and the same surface.

As an example, Figures 3a and 3b show an example of the optical device 4. In this case, the optical device 4 comprises a single reflecting portion 41 and a plurality of transmitting portions 42, arranged in rows and columns, the transmitting portions 42 being equal. In practice, the reflecting portion 41 is patterned with a plurality of through holes 43 laterally staggered, each hole 43 housing a corresponding transmitting portion 42 of the optical device 4. In addition, the reflecting surface S RI and the back surface S R2 are depicted in a different manner, to make clear that they have different optical behaviors. From another point of view, the reflecting portion 41 forms a frame which houses the transmitting portions 42, such a frame being reflective, on one side, and (as an example) black on the other side.

Irrespective of the arrangement of reflecting and transmitting portions 41, 42, the optical device 4 delimits two half-spaces. From a geometrical point of view, these half-spaces are delimited by assuming that the first and second surface SI, S2 coincide and have infinite size. From a practical point of view, the optical device 4 may be interposed between a first and a second environment .

The light source 2 is arranged on one side of the optical device 4, i.e. in one of the abovementioned half- spaces (hereinafter referred to as first half-space) . The light source 2 is thus arranged in one of the first and second environments. In greater detail, the light source 2 is arranged so that the first surface SI of the optical device 4 gives out onto the light source 2.

The light source 2 is oriented so that the H axis forms an angle δ with the axis Z, this angle δ being comprised, as an example, in the range of between 0° and 90°. Furthermore, the light source 2 is arranged so that the beam of direct light 16 illuminates the whole first surface SI. In particular, considering any one of the points of the first surface SI of the optical device 4, it is illuminated by all the points of the emitting surface 8. In order to achieve this feature, the light source 2 is arranged at a distance from the optical device 4, such a distance being greater than a minimum distance which depends on the divergence of the direct light 16.

In use, the beam of direct light 16 impinges onto the first surface SI of the optical device 4; therefore, portions of the beam of direct light 16 which impinge onto the reflecting surfaces S RI are back reflected by the reflecting surfaces S RI, thereby generating corresponding direct reflected beams BR1, at least locally non-overlapped (in particular, nearby the first surface SI of the optical device 4, i.e. in a portion of the first half-space adjacent to the first surface SI) . Portions of the beam of direct light 16 which impinge onto the input transmitting surfaces S TI pass through, to a first approximation, the corresponding transmitting portions 42 of the optical device 4, without experiencing any angular deviation; therefore, to a first approximation, each of these portions of the beam of direct light 16 is then transmitted by the corresponding output transmitting surface S T2 , thereby generating a corresponding direct transmitted beam BT2 propagating in the second half- space. The direct transmitted beams BT2 are at least locally non-overlapped (in particular, nearby the second surface S2 of the optical device 4, i.e. in a portion of the second half-space adjacent to the second surface S2.

From a practical point of view, an observer looking at the second surface S2 of the optical device 4 and arranged in a position in which no overlap occurs between direct transmitted beams BT2, can perceive the image shown in Figure 4. In particular, the observer sees, through a first hole (designated by 43'), a bright spot 50, which simulates the Sun, as if this latter was arranged behind a (as an example) dark frame (as an example, like a pergola) formed by the back surface S R2 of the reflecting portion 41. In case the observer moves in the second half-space, he perceives the bright spot 50 as moving accordingly; in particular, the observer may happen to see the bright spot 50 as arranged in a hole 43 other than the first hole 43' . Therefore, the observer is induced to perceive the artificial Sun represented by the bright spot 50 as arranged at an infinite distance, thanks to the so-called motion parallax, because the bright spot 50, formed by a corresponding direct transmitted beam BT2, is coherently seen though more than one hole 43, when the observes moves.

In a similar way, if the observer looks at the first surface SI of the optical device 4, he will be induced to perceive once again a bright spot simulating the image of the Sun. In this case (not shown), the bright spot is formed by a direct reflected beam BR1 and is perceived as arranged in the corresponding reflecting surface S RI .

From a practical point of view, the lighting system 1 allows to induce the perception of an artificial Sun in a couple of environments, physically separated from one another by the optical device 4, but optically coupled to one another by means of the transmitting portions 42 of the optical device 4. In addition, no duplication of the light source is required.

Although not shown, cases are possible in which the holes 43 are empty, in which case the input and output transmitting surfaces S TI and S T2 are immaterial.

In addition, it is possible that the ratio between the sum of the areas of the reflecting surfaces SRI and the area of the first surface SI is equal to at least 20%, preferably 30%, even more preferably 50%.

Furthermore, it is possible that the ratio between the sum of the areas of the transmitting surfaces STI and the area of the first surface SI is equal to at least 20%, preferably 30%, even more preferably 50%.

Although not shown, at least part of at least one of the first and second surface SI, S2 may be curve. Accordingly, the parallelism of SI and S2 with respect to the XY plane and with respect to each other may not be fulfilled in every portion of the surfaces SI, S2.

In order to strengthen the above effect of inducing the perception of an infinite distance between the light source 2 and the observer, the arrangement of the reflecting portions 41 and the transmitting portions 42 of the optical device 4 may be such that at least one line 51 (see Figure 3b) exists, such a line 51 being given by the intersection between the reflecting surfaces SRI and a plane and being such that, along this line 51 (which is straight if the reflecting surfaces SRI are coplanar, but may be curve in case the reflecting surfaces SRI are curve) , at least three transitions between a reflecting surface SRI and a portion not occupied by any reflecting portion occur, the direction of the transition (either from the reflecting surface S _RI to the non-occupied portion, or vice versa) being irrelevant. As an example, along the straight line 51 shown in Figure 3b, ten transitions occur.

Without any loss of generality, advantageously the light source 2 is arranged in a portion of the first half- space wherein no direct reflected beam BR1 is present, so that the light source 2 is less visible to the observer.

As shown in Figure 5, the light source (here designated by 122) may be configured to generate the direct light 16 so that it has the following features.

In detail, across the emitting surface (designated by 108 and having, as an example, a rectangular shape) , the direct light 16 has a luminance profile Ldirect (x, y, θ , cp ) which is, to a first approximation, locally uniform (i.e, with respect to the spatial dependence) and has a narrow peak 30 (i.e., with respect to the angular dependence) along a direct-light direction 32, wherein x and y are the transverse coordinates along axes x and y spanning the emitting surface 108, Θ is the polar angle measured relative to the direct-light direction 32, and φ is the azimuthal angle .

The luminance profile Ldirect (x, y, Θ , cp ) substantially does not depend on cp . Furthermore, the term "narrow" might be interpreted as implying that the luminance profile Ldirect (x, y, Θ , cp ) has a peak, at (i.e., the abovementioned direct-light direction 32), the width of which (as an example, meant as the half-width half-maximum, HWHM) which is significantly smaller than 2n sr, e.g. smaller than 0.4 sr, preferably smaller than 0.3 sr, more preferably smaller than 0.2 sr.

In addition, the above term "locally", referred to the spatial uniformity of the luminance profile Ldirect (x, y, Θ , cp ) of the direct light 16, has to be meant in the following way: across each circular area 55 within the emitting surface 108 having a diameter at least equal to 10cm, preferably 30cm, more preferably 50cm, the peak angle 9 _ma x(x,y) (i.e., the direct-light direction 32) doesn't vary, parallel to a single direction (e.g., the x axis or y axis) or to a couple of orthogonal directions (e.g., the axes x and y) for more than 5° (preferably, 2°), compared to a reference angular direction. Along the direction or directions of invariance, also the width of the luminance profile Ldirect (x, y, θ, cp) is substantially constant.

In particular, in case of invariance along a single axis, the light source 122 may be implemented as taught in PCT/EP2014/059802 or PCT/EP2016 / 001943 ; in case of invariance along two orthogonal axes, the light source 122 may be implemented as taught in PCT/EP2012/072648.

As an example, assuming that the abovementioned narrow peak of the luminance profile Ldirect (x, y, Θ, cp) has a width smaller than 0.2 sr, this implies that, along the abovementioned direction or directions of invariance, the divergence of the beam of direct light 16 is lower than 30°.

Figure 6 shows a further example of the optical device (designated by 104), which may be optically coupled to any of the light sources described above (not shown) .

In detail, the optical device 104 includes a transparent panel 105 with the shape of a parallelepiped. One side of the parallelepiped is coated in part by one or more reflecting layers 106, each of which forms a corresponding reflecting surface, designated by SRI'. The reflecting surfaces SRI' are coplanar and lie on the first surface SI of the optical device 4, which is partially immaterial; the opposite side of the parallelepiped forms the second surface S2 of the optical device 4. In addition, portions of the abovementioned side of the transparent panel 105 not coated by the reflecting layers 106 form corresponding input transmitting surface S TI', which are coplanar and lie in a plane laterally staggered with respect to the plane of the reflecting surfaces S RI ' .

Figure 7 shows an embodiment, wherein the light source may be of the type shown in Figure 1 or in Figure 5. In addition, the optical device, here designated by 204, includes a diffuser 210, which has the shape of a parallelepiped. A first side of the parallelepiped is coated in part by one or more reflecting layers (here designated by 206), each of which forms a corresponding reflecting surface, designated by S RI". Portions of the abovementioned first side of the diffuser 210 not coated by the reflecting layers 206 form corresponding input transmitting surfaces S TI"; portions of a second side of the diffuser 210, opposite to the first side, form corresponding output transmitting surfaces S T2 " . In addition, portions of the second side of the diffuser 210 opposite to portions of the first side coated by the reflecting layers 206 form corresponding back surfaces, here designated by S B .

In greater detail, the diffuser 201 is at least partially light-transparent, the term "semi-transparent" having to be construed as in PCT/IB2013/060141. In addition, the diffuser 201 may be like the diffuser panel mentioned in PCT/IB2013/060141. In this case, the diffuser 210 comprises a solid matrix of a first solid material, wherein nanoparticles of a second material are dispersed, this second material having a refractive index different from the first material's refractive index. Both the first and the second material basically do not absorb electromagnetic radiation in the visible wavelength range.

From a practical point of view, the portions of the beam of direct light 16 which impinge on the reflecting surfaces SRI" generate corresponding direct reflected beams BR1, in the same way as the Figure 1. In addition, owing to the fact that the diffuser 210 is at least partially light- transparent, at least parts of the abovementioned portions of beam of direct light 16 which impinge onto the input transmitting surfaces S TI" pass through the diffuser 210 without experiencing any angular deviation, thereby forming corresponding direct transmitted beams, here designated by BT2", which exit from the output transmitting surfaces S T2 " .

In addition, the portions of the beam of direct light 16 which impinge onto the input transmitting surfaces S TI " are partially diffused by the diffuser 210, thereby forming diffused light. In particular, for each pair of input and output transmitting surfaces S TI " , S T2 " , a forward diffused light FDL and a rear diffused RDL are generated, which are shown by means of corresponding luminance intensity distributions (LID) . In general, in the Figures, the notation LID_kk is used, to indicate the luminance intensity diagram of a corresponding kk light. In greater detail, the luminance intensity distribution represents the light power emitted by a source in a particular direction per unit solid angle (weighted by the luminous efficiency functions) . The luminous intensity distribution depends on two angular coordinates cp.

In detail, given a pair of corresponding input and output transmitting surfaces STI", ST2", which delimit a part of the diffuser 210, and referring to the portion of the beam of direct light 16 which impinges onto the input transmitting surface STI" as the direct sub-beam, the corresponding forward diffused light FDL is formed by the part of direct sub-beam which is scattered by the abovementioned part of the diffuser 210 in virtually all forward directions; such a forward diffused light FDL is substantially uniform across the output transmitting surface ST2". AS an example, the forward diffused light FDL is emitted, by the output transmitting surface ST2", over a solid angle which is at least four times larger, preferably nine times larger, more preferably sixteen times larger than the solid angle subtending the narrow peak 30. Referring to the rear diffused light RDL, it is formed by the part of direct sub-beam which is scattered by the abovementioned part of the diffuser 210 in virtually all rear directions; such a rear diffused light RDL is substantially uniform across the input transmitting surface STI". AS an example, the rear diffused light RDL may be emitted by the input transmitting surface STI" over a solid angle which is at least four times larger, preferably nine times larger, more preferably sixteen times larger than the solid angle subtending the narrow peak 30.

The rear diffused light RDL and the forward diffused light FDL have the same correlated colour temperature (CCT) . In addition, the diffuser 210 is configured so that the direct light 16 generated by the light source 2, 122 has a CCT which is lower (e.g. at least 1.2 times lower, preferably 1.3 times lower, more preferably 1.4 times lower) than the CCT of the rear/forward diffused light RDL, FDL.

In greater detail, in the first half-space, downstream the diffuser 210, the following light distribution occurs.

Each reflecting surface SRI" emits a corresponding direct reflected beam BR1, which has a luminance intensity diagram LID_BR1, qualitatively shown in Figure 7. In addition, each input transmitting surface S TI" emits, towards the first half-space, a corresponding rear diffused light RDL.

In the second half-space, downstream the diffuser 210, the following light distribution occurs.

To a first approximation, no light comes from the back surfaces SB. In addition, referring to the forward outer light to designate the light emitted by each output transmitting surface S T2 " towards the second half-space, this forward outer light includes the corresponding forward diffused light FDL and the corresponding direct transmitted beam BT2".

In greater detail, the forward outer light emitted by any output transmitting surface S T2 " , and in particular by any point of the output transmitting surface S T2 " , comprises:

- a respective first light component, which features a peak in the luminance angular profile along a transmitted direct-light direction, when the beam of direct visible light impinging on the first surface SI features a peak in the luminance angular profile along a directed-light emitting direction; and

- a respective second light component which propagates along directions spanning at least 30% of the angular region outside a cone with axis directed along the abovementioned transmitted direct-light direction and half-aperture three times larger than the half-width half-maximum (HWHM) polar angle of the peak along the transmitted direct-light direction.

In greater detail, the first light component of the forward outer light is formed by the parts of the corresponding direct transmitted beam BT2" and of the corresponding forward diffused light FDL which propagate along the abovementioned directions contained within the corresponding narrow peak. The second light component of the forward outer light is formed by the part of the forward diffused light FDL which propagates along the abovementioned directions spaced apart from the corresponding narrow peak.

In addition, the first light component has a CCT which is lower than the CCT of the second light component (e.g. at least 1.2 times lower, preferably 1.3 times lower, more preferably 1.4 times lower) .

From a practical point of view, an observer located in the first half-space perceives the input transmitting surfaces S TI" as portions of a blue sky, because the diffuser 210 acts as a Rayleigh diffuser. In addition, an observer located in the second half-space and hit by one direct transmitted beam BT2" perceives the output transmitting surface S T2 " which emits such a direct transmitted beam BT2" as a bright spot simulating the Sun, possibly (depending on the apparent size of the output transmitting surface S T2 " and the emitting surface of the light source) surrounded in part by a blue region, which simulates the skylight. Furthermore, the observer located in the second half-space perceives the other output transmitting surfaces S T2 " as corresponding portions of blue sky. The back surfaces S B are perceived as a pergola.

Although not shown in detail, in the embodiment shown in Figure 7, the nanoparticles are uniformly dispersed in the whole volume of the solid matrix of the diffuser 210. However, as shown in Figure 8 purely by way of non-limitative example, embodiments are possible in which the optical device (here designated by 304) includes a transparent support 310 having the shape of a parallelepiped, one side of which is coated by the reflecting layers, here designated by 306, the opposite side being coated by a scattering layer 311, like the diffusing layer disclosed in PCT/EP2014/059802. The optical behavior stays the same as the one of Figure 7; although not indicated in Figure 8, the output transmitting surfaces S T2 " and the back surfaces S B are formed by the scattering layer 311.

Figure 9 shows a further embodiment, in which the optical device (here designated by 404) includes an optically guiding structure 410, which is at least partially transparent for the beam of direct-light 16. In this embodiment, the guiding structure 410 is free of nanoparticles and has the shape of a parallelepiped, one side of which is coated by the reflecting layers 206, the opposite side of which features a microstructure, such as a micrometric roughness 412.

In addition, a secondary illuminator 466 is present. The secondary illuminator 466 is arranged on top of the top base of the parallelepiped of the guiding structure 410.

The secondary illuminator 466 configured to emit a secondary light 467, which is optically fed to the top base of the guiding structure 410. The secondary light 467 then propagates along the guiding structure 410, in a guided mode, but for side leakages due to the micrometric roughness 412. To this regard, although not shown, embodiments are possible in which the microstructure is implemented at least in part inside the bulk of the guiding structure 410, as opposed to only one side of this latter. As an example, alternative leakage processes could be achieved by putting micro- particles inside the guiding structure 410. In general, all processes that result in light scattering and therefore light extraction from the guiding structure 410 may be implemented. These processes may take place on the surface and/or in the bulk of the guiding structure 410.

The secondary light 467 may have a CCT higher with respect to the first beam of direct light 16. Possible values of the CCT for the secondary light 467 may be greater than 8000K, preferably greater than 15000K, even more preferably greater than 30000K. Typically, at such CCTs, most of the energy in the visible spectral domain is contained along high frequency domain of the visible spectrum. For example, more than 60% of the visible energy is contained under the visible spectrum for wavelength greater then 450nm, 500nm, 550nm .

In greater detail, the embodiment of Figure 9 differs from the embodiment of Figure 7 in that the back surfaces, here designated by SB' , and the output transmitting surfaces (here designated by S T2 ' ' ' ) feature the micrometric roughness 412. In Figure 9, the reflecting surfaces and the input transmitting surfaces are designated, respectively, by S RI ' ' ' and S TI " ' .

In use, to a first approximation, the rear and forward diffused light RDL, FDL may be the same as the ones of Figure 7, because of the spectral content of the secondary light 467; also the direct transmitted beams BT2" are substantially the same as the ones of Figure 7. In addition, each back surface SB' emits, towards the second half-space, an additional forward diffused light AFDL, which is substantially the same as the forward diffused light FDL. Therefore, when the observer is located in the second half- space, she/he perceives the back surfaces S B' as corresponding portions of blue sky.

As shown in Figure 10, the optical device (here designated by 504) may include an organic light-emitting diode (OLED) 510, acting as support for the reflecting layers 206, which are arranged on one side of the OLED 510. The OLED 510 uniformly emits diffused light from the portions of its respective side not covered by the reflecting layers 206.

The OLED 510 forms the back surfaces, here designated by S B", and the output transmitting surfaces, here designated by T2' ' ' ' , as well as the input transmitting surfaces, here designated by S TI' ' ' ' . In Figure 10, the reflecting surfaces are designated by S RI ' ' ' ' .

In use, to a first approximation, the OLED 510 emits the rear and forward diffused light RDL, FDL, as well as the additional forward diffused light AFDL. Therefore, the optical behavior is the same as the one of Figure 9, without the use of the secondary illuminator 466.

From another point of view, in the embodiments of Figures 9 and 10, the diffused light is generated by means of an active optical generator (i.e., the secondary emitter 466 or the OLED 510) , as opposed to, as an example, the embodiment shown in Figure 7, wherein, aside from the light source, no other active element is present, the diffuser 210 being optically passive and operating in the Rayleigh-like regime, as defined, as an example, in WO 2009/156348 Al .

Figure 11 shows a further embodiment, in which the optical device, designated by 604, comprises the transparent support, here designated by 610, one side of which is coated by the reflecting layers, here designated by 606. In turn, the reflecting layers 606 are coated by corresponding scattering layers 611, which are delimited by corresponding front surfaces S F, which give out onto the light source 2, 122.

In use, the optical device 604 emits the direct transmitted beams BT2.

The scattering layers 611 are at least partially light- transparent, therefore, given any scattering layer 611, at least a part of the direct light 16 passes through the scattering layer 611 (in forward direction), is backwards reflected by the adjacent reflecting layer 606 and passes again through the scattering layer 611, without experiencing any angular deviation; such a part of direct light 16 forms a corresponding direct reflected beam, here designated by BR1". To a first approximation, the direct reflected beams BR1" may have the same divergence, luminance profile and direct-light direction as the direct reflected beams BR1 shown, as an example, in Figure 7. From a more quantitative point of view, in view of the Lambertian behavior of the scattering layers 611, which allows to generate the blue light simulating the skylight, the amplitude of peak of the luminance profile of the direct reflected beams BR1" is slightly reduced with respect to the case of Figure 7, although the width of the peak of the luminance profile has not changed.

In addition, each front surface SF emits an additional rear diffused light ARDL, which is formed by the part of direct light 16 which is scattered by the scattering layer 611 in virtually all rear directions (either when it propagates towards the reflecting surface 606 or when, afterwards, it propagates back towards the first half- space) .

To a first approximation, the additional rear diffused light ARDL may be have the same properties (meant as solid angle of emission and CCT) as the abovementioned rear and the forward diffused light RDL, FDL.

In view of the above, referring to the rear outer light to designate the light emitted by each front surface S F, this rear outer light includes the corresponding additional rear diffused light ARDL and the corresponding direct reflected beam BR1".

In greater detail, the rear outer light emitted by any front surface SF, and in particular by any point of the front surface SF, comprises:

- a respective first light component, which features a peak in the luminance angular profile along a reflected direct-light direction, when the beam of direct visible light impinging on the first surface SI features a peak in the luminance angular profile along a direct-light emission direction; and

- a respective second light component which propagates along directions spanning at least 30% of the angular region outside a cone with axis directed along the abovementioned reflected direct-light direction and half-aperture three times larger than the half-width half-maximum (HWHM) polar angle of the peak along the reflected direct-light direction.

In greater detail, the first light component of the rear outer light is formed by the parts of the corresponding direct reflected beam BR1" and of the corresponding additional rear diffused light ARDL which propagate along the abovementioned directions contained within the corresponding narrow peak. The second light component of the rear outer light is formed by the part of the additional rear diffused light ARDL which propagates along the abovementioned directions spaced apart from the corresponding narrow peak. In addition, the first light component of the rear outer light has a CCT which is lower than the CCT of the second light component of the rear outer light (e.g. at least 1.2 times lower, preferably 1.3 times lower, more preferably 1.4 times lower) .

The rear outer light emitted in the first half-space by the front surfaces SF may be substantially equal to the forward outer light emitted by the output transmitting surfaces S T2 " in the second half-space. Therefore, an observer located in the first half-space perceives the front surfaces SF as portions of a blue sky, one of which (i.e., the one which emits the direct reflected beam BR1" which hits the observer) includes a bright spot simulating the Sun .

Although not shown, embodiments are possible, which differ from the embodiment shown in Figure 11 in that the transparent support 610 is replaced by i) the guiding structure 410 and the secondary illuminator 466, or ii) the OLED 510; in these cases, the light generated in the second half-space is the same as the one described with reference to Figures 9 and 10, and the light generated in the first half-space includes the rear diffused light RDL.

Figure 12 shows a further embodiment, in which the optical device, designated by 704, is the same as the one shown in Figure 11, but the transparent support 610 is replaced by the diffuser shown in Figure 7, here designated by 710. In this case, the second half-space is illuminated as in Figure 7; in addition, the optical device 704 emits also the rear diffused light RDL.

In addition, the thicknesses of the diffuser 710 and the scattering layer 611 and/or the respective concentrations of nanoparticles and/or the mismatch between the refractive indexes of the nanoparticles and the hosting matrixes may be chosen so that the additional rear diffused light ARD L has the same properties (meant as solid angle of emission, scattering amplitude and CCT) as the rear and the forward diffused light RD L , FDL.

Figure 13 shows an embodiment including an optical system 1000 which includes the optical device 204 and an additional diffuser 1210, as an example equal to the diffuser 210 and arranged so as to contact the reflecting layers 206, which are thus interposed between the diffuser 210 and the additional diffuser 1210, which gives out onto the light source 2, 122. By tuning the diffuser 210 and the additional diffuser 1210, the illumination of the second half-space may stay the same as the one of Figure 7.

In addition, referring to the first side of the additional diffuser 1210 arranged opposite to the side contacting the reflecting layers 206, this first side includes i) respective first portions which are opposite to corresponding reflecting layers 206 and form corresponding front surfaces (here designated by S F' ) and ii) respective second portions, coplanar to the first portions and laterally staggered with respect to these latter, these respective second portions acting as input transmitting surfaces S TI '

Therefore, the illumination of the first half-space includes, besides the additional rear diffused light ARD L and the direct reflected beams BR1" emitted by the front surfaces S F' , also the rear diffused light RD L emitted by the input transmitting surfaces STI''''' .

Figure 14 shows an embodiment comprising an optical system 2000 which includes the optical device 404 shown in Figure 9 and the secondary illuminator 466. In addition, the optical system 2000 comprises an additional secondary illuminator 2466 and an additional guiding structure 2410, which may be respectively equal to the secondary illuminator 466 and the guiding structure 410. The additional secondary illuminator 2466 is configured to feed the additional guiding structure 2410 with an additional secondary light 2467, in the same way as the secondary illuminator 466 feeds the guiding structure 410 with the secondary light 467. The additional secondary light 2467 may have the same spectral content as the secondary light 467.

The additional guiding structure 2410 and the guiding structure 410 are arranged symmetrically with respect the reflecting layers 206, which thus contact one side of the additional guiding structure 2410, the opposite side of the additional guiding structure 2410 forming the input transmitting surfaces (here designated by STI""") and the front surfaces (here designated by SF") .

From a practical point of view, the embodiment shown in Figure 14 allows to achieve the illumination of the first half-space shown in Figure 13 and the illumination of the second half-space shown in Figure 9.

As shown in Figure 15, a further embodiment is possible, which optically behaves like the one shown in Figure 14. In this embodiment, the optical device 3000 is the same as the one of Figure 10, but further includes an additional OLED 3510. The OLED 510 and the additional OLED 3510 are arranged symmetrically with respect the reflecting layers 206.

Figure 16 shows a further embodiment, including an optical structure 4000, which includes an inner structure 4001, which may be formed by any of the optical devices 104, 204, 304, 404, 504, 604, 704 or the optical systems 1000, 2000, 3000 previously described. As schematically shown in Figure 16, the optical structure 4000 is delimited by the first and the second surface SI, S2, which may be at least in part immaterial. In particular, the first surface SI may be construed as:

A) the surface wherein the reflecting surfaces lie, in case the scattering layers 611, the additional diffuser 1210 and the additional guiding structure 2410 are absent; or B) the surface wherein the front surfaces SF lie, in case the scattering layers 611 are present (see Figure 12) ; or

C) the surface wherein the front surfaces SF' and the input transmitting surfaces STI'''' lie, in case the additional diffuser 1210 is present (see Figure 13) ; or

D) the surface wherein the front surfaces SF" and the input transmitting surfaces STI""" lie, in case the additional guiding structure 2410 is present (see Figure 14) ; or

E) the surface defined by the side of the additional

OLED 3510 opposite to the reflecting layers 206, in case of the embodiment shown in Figure 14.

The second surface S2 may be construed, according to the embodiments, as the side, opposite to the side giving out onto the reflecting surfaces, of any of the transparent panel 105, the diffuser 210, 710, the scattering layer 311, the guiding structure 410, the OLED 510 and the transparent support 610.

In addition, the optical structure 4000 includes a first outer device 4002 and a second outer device 4003, which are arranged, respectively, i) between the first half-space and the inner structure 4001, and ii) between the inner structure 4001 and the second half-space.

Although in Figure 16 the first and second outer devices

4002, 4003 are depicted as contacting the first and the second surface SI, S2, respectively, they may be separated from the inner structure 4001. Furthermore, the sides of the first and second outer devices 4002, 4003 which are opposite to the inner structure 4001 respectively, define a first and a second output surface Sout_l , Sout_2.

Each of the first and second outer devices 4002, 4003 may be formed, alternatively, by a corresponding electrochromic layer or a corresponding polymer dispersed liquid crystal (PDLC) layer. Therefore, the first and second outer devices 4002, 4003 act as electrically tunable optical layers .

Irrespective of whether the first and the second outer device 4002, 4003 are constituted by electrochromic layers or PDLC layers, in case the first and the second outer device 4002, 4003 are turned on, they are optically transparent, therefore, to a first approximation, they are not perceived by the observer.

In addition, in case the first and the second outer device 4002, 4003 are turned off, the first and the second output surface Soutj , S _ou t_2 appear white, if the first and the second outer device 4002, 4003 are constituted by PDLC layers, or else black, if the first and the second outer device 4002, 4003 are constituted by electrochromic layers.

In case the first outer device 4002 is on and the second outer device 4003 is off, and assuming that both the first and the second outer devices 4002, 4003 are constituted by PDLC layers, the second output surface S ₀ ut_2 appears white, whereas the first output surface S ₀ ut_i appears like a pergola through which the Sun (simulated by the reflected light) is seen; on the contrary, assuming that that both the first and the second outer device 4002, 4003 are constituted by electrochromic layers, the second output surface S ₀ ut_2 appears black and provides a black optical background to the input transmitting surfaces, thereby preventing objects possibly arranged in the second half-space from spoiling the appearance of the input transmitting surfaces, for an observer arranged in the first half-space.

In case the first outer device 4002 is a PDLC layer, in the off-state, the first output surface S ₀ ut_i appears white and at least partially prevents light from reaching the second half-space; analogously, assuming that the first outer device 4002 is an electrochromic layer, in the off- state the first output surface S _ou t_i appears black, thereby also at least partially preventing light from reaching the second half-space.

From what has been described and illustrated previously, the advantages that the present solution affords are evident .

Finally, it is clear that modifications and variations may be made to what has been described and illustrated herein, without thereby departing from the scope of protection of the present invention, as defined in the annexed claims.

As already mentioned, one or more of the cited surfaces may be curve. Furthermore, it has to be noted that the function of light source may be performed by the Sun.

Further embodiments are possible, which comprise, each, a mirror featuring holes and acting as a support for, as an example, passive diffusing regions or OLEDs.

In that concerns the diffuser, it may include, instead of or along with the nanoparticles , nanoscatterers , as described in WO2017084756. Therefore, the term nanoscatterer refers, in general, to either the nanoparticles and optically equivalent liquid or gaseous phase nanoscale elements such as liquid or gas phase inclusions (e.g. nanodroplets , nanometric voids, nanoinclusions , nanobubbles, etc.) having nanometric size and embedded in the host materials.

In addition, although the previous embodiments referred to the case in which no further optical elements are present between the light source and the first surface SI of the optical device, or the first output surface S ₀ ut_i (if present), i.e. to the case in which the beam of direct light 16 generated by the light source impinges onto the first surface SI or the first output surface Sout_i after propagating exclusively in free space, further embodiments are possible, in which further optical elements are interposed between the light source and the first surface SI or the first output surface S ₀ ut_i .

In addition, further embodiments are possible, each of which corresponds to one of the previously described embodiments, but in which each reflecting portions of the optical device (i.e., the reflecting layers) forms, besides the corresponding reflecting surface which acts as a front reflecting surface, a back reflecting surface, arranged symmetrically with respect to the reflecting surface; therefore, each back reflecting surface may have the same shape as the corresponding reflecting surface. Purely by way of non-limiting example, Figure 17 shows a variant of the embodiment shown in Figure 7, wherein each reflecting layer 206 forms back reflecting surface S RR .

The back reflecting surface SRR may receive an additional beam of direct light 197, which has been emitted by an additional light source 199 (as an example, the Sun, in which case the second half-space may be the outside of a building) arranged in the second half-space, which has propagated through the diffuser 210. The back reflecting surface SRR reflects the additional beam of direct light 197, thereby generating an additional direct reflected beam BRRl" which passes through the diffuser 210 and then propagates in the second half-space. The additional direct reflected beam BRRl" may have the same optical properties as the direct reflected beam BR1", if the additional beam of direct light 197 emitted by an additional light source 199 has analogous properties as the beam of direct light 16.

In addition, further embodiments are possible, each of which corresponds to one of the previously described embodiments, but includes the following features.

Irrespective of the implementing details, the reflecting and transmitting portions have small areas and are spatially mixed so as to achieve a high spatial uniformity .

In detail, as shown in Figure 18, the reflecting portions (here designated by 6041) are such that their reflecting surfaces (here designated by SRIX) have the following features.

Each reflecting surface S RIX is such that, given the barycenter (i.e., the geometrical center) and a local line normal to the reflecting surface SRIX at the barycenter thereof and passing through the barycenter, the projected surface of the reflecting surface S RIX onto a plane orthogonal to the local normal line (such a projection being carried out parallel to the local normal line) has an area not greater than 10cm ² , preferably 5cm ² and more preferably 2cm ² ; furthermore, the diameter of the maximum circumference inscribed within the projected surface is smaller than 20mm, preferably 5mm and even more preferably 2mm.

In addition, by defining a main normal line as an angular average of the abovementioned local normal lines, and projecting the reflecting surfaces S RIX onto a plane orthogonal to the main normal line (such a projection being carried out parallel to the main normal line) , and referring to the new projected surfaces to designate the projections of the reflecting surfaces S RIX onto a common plane orthogonal to the main normal line, the maximum distance between adjacent new projected surfaces (i.e., between couples of new projected surfaces whose geometrical centers lie on a corresponding straight line which does not intersect any other new projected surface) is not greater than 5cm, preferably 2cm and even more preferably 1cm.

In such a way, an observer at a distance of at least 2m from the geometric center of the first surface SI perceives the first surface SI substantially as homogenous, for the following reasons. The angular size parallel to at least one direction of the reflecting and transmitting portions is substantially sub resolution for human sight and, therefore, bare eye perception of a region of the optical device does not allow to identify, as an example, the details of the reflecting surfaces.

In particular, at any point of the first surface SI, the observer perceives averaged properties of the reflecting/transmitting surfaces of the optical device, and in particular perceives an averaged diffuse reflectance (i.e., the ratio of the reflected flux to the incident flux, where the reflection is at all angles within the hemisphere bounded by the plane of measurement except in the direction of the specular reflection angle) , in case of passive diffused light generator implementation, or an averaged LID of the diffused light emittance, in case of active diffused light generator implementation, the averages occurring over an area (e.g., a circular area) having geometrical center in the considered point and diameter greater than 300mm, 80mm or even preferably 30mm. In addition, the abovementioned averaged properties may be substantially homogeneous (i.e., shift-invariant); in facts, they may stay substantially the same for any point of the first surface SI.

As an example, Figure 19 shows an embodiment forming reflecting and transmitting surfaces 7041 and 7042, which lie in a plane parallel to the plane XY, have the shape of stripes elongated along the X axis and are arranged alternately. In addition, the size of each of the reflecting and transmitting surfaces 7041 and 7042, measured parallel to the Y axis, is not greater than 3mm, 1mm, 0,5 mm.

Moreover, embodiments are possible, in which one or more of the corresponding elements which have been previously defined as at least partially transparent are replaced by corresponding elements which are still light transmitting in the visible range, but introduce a higher amount of optical deviation, i.e. have a behaviour which tends to be more diffusive. As an example, the replacing elements may be constituted by the same elements to be replaced, which are integral with, or in case optically coupled to, low-angle diffusing elements, i.e. elements creating a statistical small variation of the direction of the impinging light. In this case, the amplitude and the width of the luminance peaks of the direct reflected beams and direct transmitted beams may be respectively reduced and increased with respect to the case of original corresponding embodiment. By way of an example, acceptable low angle diffusers have a FWHM not greater than 30°, preferably 10° or even more preferably 5°.

In addition, hybrid embodiments are possible, which derive from the combinations of elements of the previously described embodiments. As an example, embodiments are possible, in which the diffused light is generated either actively and passively.

Finally, embodiments are possible which include the optical guide, and in which the light is scattered out towards only one side of the optical guide.