Artificial lighting system for simulating a natural lighting

A lighting system for illuminating an environment with a lighting that simulates natural lighting, which includes: a first light source which emits a beam of visible light; a diffused-light generator delimited by an inner surface, which receives the light beam, and an outer surface, the diffused-light generator being at least partially transparent to the light beam. The diffused-light generator transmits at least part of the light beam and emits, through the outer surface, visible diffused light, the correlated color temperature of the transmitted light being lower than the CCT of the visible diffused light. The lighting system includes a dark structure which is optically coupled to the environment via the diffused-light generator and provides a substantially uniform background to the first light source.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention is a 35 U.S.C. § 371 U.S. National Stage Application corresponding to PCT Application No. PCT/IB2013/060141, filed on Nov. 14, 2013, which claims priority to Italian Patent Application No. TO2012A000988, filed Nov. 14, 2012 and U.S. application Ser. No. 13/838,998, filed Mar. 15, 2013. The entire content of each of the aforementioned patent applications is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a system of artificial lighting. In particular, the invention relates to a system of artificial lighting that simulates natural lighting. Such lighting system may illuminate a room wherein it is inserted, with effects very similar to the effects that would occur in the same room if an aperture with sky and Sun beyond it was opened.

It is known that, as of current date, artificial lighting systems for closed environments (“indoors”) are available which aim at improving the visual comfort experienced by users. In particular, lighting systems are known which simulate natural lighting, namely the type of lighting available in open-air environments (“outdoors”) The well-known characteristics of outdoor lighting depend on the interaction between light rays produced by the Sun and the Earth's atmosphere.

In pending European patent application EP2304480, filed by the present Applicant, a lighting system is described which comprises a light source, aimed at producing visible light, and a panel containing nanoparticles. When in use, the panel receives light rays coming from the source and acts as a so-called Rayleigh diffuser, namely it diffuses light rays similarly to the Earth's atmosphere in clear-sky conditions.

Additional details relative to the panel as in pending patent EP2304480 are described in pending European patent application EP2304478, filed by the present Applicant. Moreover, pending patent application EP2304480 describes various embodiments of the panel as well as various arrangements of the panel and the light source in respect to one another, aimed at simulating various conditions of natural lighting, such as for example lighting conditions that occur in nature in case of clear sky and i) Sun at Zenith or ii) Sun close to the horizon.

The lighting system described in patent application EP2304480 simulates natural lighting in that it generates, inside the surrounding environment, direct light with low Correlated Color Temperature (“CCT”), which mimics sunlight and generates shadows in presence of lit objects; also, the lighting system described in patent application EP2304480 simulates natural lighting in that it casts diffused light with high CCT, which mimics skylight and generates shadows with a blue tinge. Nonetheless, such lighting system does not flawlessly reproduce the perceptive effects an observer would experience in presence of a sky-facing window. In particular, such lighting system does not lead an observer to experience the visual perception of unlimited depth of field.

WO 2012/140579 discloses an optical element comprising a light transmitting cell, which comprises a light transmitting channel, a light input window, a light exit window and a wall. The light input window is arranged at a first side of the light transmitting channel and receives light from a light source. The light exit window emits light with the skylight appearance. At least a part of the light exit window is arranged at a second side of the light transmitting channel opposite to the first side. The wall is interposed between the light input window and the part of the light exit window; the wall encloses the light transmitting channel. At least a part of the wall is reflective and/or transmissive in a predefined spectral range to obtain a blue light emission at relatively large light emission angles with respect to a normal to the part of the light exit window.

U.S. Pat. No. 7,722,220 discloses a lighting device including a thermal conduction element, solid state light emitters and a reflective element. The conduction element defines an opening; the emitters and reflective element are mounted on a first side of the conduction element.

U.S. Pat. No. 4,267,489 discloses a device including a diffusive transparent plate, a light homogenizing member, a fluorescent lamp and a reflection member.

BRIEF SUMMARY

Thus, the present invention aims at providing a lighting system capable of solving the known state-of-the-art limitations, at least in part.

The invention provides an artificial lighting system as set forth in the independent claims with advantageous possible implementations being subject of the dependent claims.

In general, the Applicant noticed that the capability of an observer to evaluate the distance of objects, and therefore the depth of field of the views that constitute a three-dimensional scenery, is based on multiple physiological and psychological mechanisms connected to focusing, binocular convergence, binocular parallax, movement parallax, luminance, size, contrast, aerial perspective, etc. Some mechanisms may gain significance compared to the others according to both the observing conditions (e.g., whether the observer is moving or still, watching with one or two eyes, etc.) as well as the characteristics of the scenery, these latter depending, for example, on whether objects with known size, distance or luminance are present, serving as a reference to evaluate how distant the observed element of the scenery is.

In particular, the Applicant noticed that an observer, who is watching a light projector through a window, loses the capability of estimating how far the projector is when such distance is higher than five meters (preferably, seven meters), provided that the background surrounding the projector is black and uniform. When such circumstances are met, the distance from the projector is undetermined by the observer. The capability of estimating distances is lost because i) precise focusing of a blinding light source is difficult, which prevents the observer from using the focusing mechanism to evaluate the object's distance, and ii) binocular convergence is scarcely efficient as an instrument for distance evaluation when the object is more than five meters away (preferably, seven meters); moreover, the capability to estimate is lost because the other psycho-physic mechanisms that are commonly valid and efficient in case of high distances fail, being inhibited by the absence of further points of reference.

The Applicant further noticed that, when a Rayleigh diffusion panel is interposed between the observer and the light projector, this latter being surrounded by a black, uniform background, the observer is induced to perceive the light projector virtually at infinite distance from him. More particularly, the effect of perception at infinite distance is obtained whenever the observer looks at the light projector through the Rayleigh diffusion panel, and this latter is thoroughly and uniformly lit by the projector, and the real projector-to-observer distance is five meters at least (preferably, seven meters). Such effect may be interpreted as a consequence of the so-called “aerial perspective”, a perception mechanism induced by the Rayleigh diffusion panel. As a matter of fact, the color and intensity of light scattered by the Rayleigh diffusion panel are virtually identical to the corresponding color and intensity of skylight, where intensity is evaluated as relative to the intensity of transmitted light. In particular, the so-called aerial perspective mechanism relates to the presence of an air layer interposed between any objects and the observer; the color and luminance of such air layer affect the estimation of the object-to-observer distance, the object being perceived by the observer as lying behind the air layer itself; such mechanism is dominant at high distances or, generally speaking, when the other psycho-physic mechanisms for distance evaluation are suppressed or scarcely efficient.

The Applicant further noticed that the observer is led to perceive light emitted by the Rayleigh diffusion panel as coming from a virtually infinite distance, provided that the spotlight is inside the observer's visual field. Such effect may be interpreted by considering that the Rayleigh diffusion panel acts as a secondary source of luminous radiation, and that the observer can hardly assess his distance from the emitting plane of such luminous radiation because of the high spatial uniformity of luminous radiation itself, which does not provide any visual point of reference to look upon. Thus, the presence of the light projector in the visual field at a (physical) distance of five meters (preferably, seven meters) affects the evaluation of the whole scenery's depth of field by “dragging” the estimated position of the Rayleigh diffusion panel beyond the threshold of distance perception by binocular convergence. Such effect is connected to the luminance of the light projector, and to the fact that, besides the Rayleigh diffusion panel, the light projector itself is the only spatially localized element perceived by the observer. Basically, when looking at the Rayleigh diffusion panel, the eyes of the observer are forced by the light projector to arrange themselves as if they were watching a very distant object. The mind is then pushed by such arrangement of the eyes to infer that the object in the middle of the visual field, that is light emitted by the Rayleigh diffusion panel, is very far compared to the real position of the panel itself. Also, the effect of perceiving a diffused-light source at great distance from the observer is favored by the fact that light scattered by the Rayleigh diffusion panel has the same color and luminance (compared to transmitted light) typical of skylight. Such effect, due to the aforementioned mechanism of aerial perspective, is particularly efficient, thereby causing the light projector to be perceived at virtually infinite distance. The Applicant also noticed that the described effect, that is the visual perception of an infinite depth of field (from now on called “breakthrough effect”), takes place irrespective of the direction of observation through the Rayleigh diffusion panel.

In addition, the Applicant noticed that the aerial perspective alone cannot perfectly assure the breakthrough effect, if the light projector is outside the visual field, because other psycho-physic mechanisms prevail, such as the focusing of scratches or borders of the Rayleigh diffusion panel.

Moreover, the Applicant noticed that the aforementioned breakthrough effect is reduced whenever the light projector is positioned next to the Rayleigh diffusion panel, e.g. without any mirrors or lenses to move afar its virtual image. In fact, the light projector's distance would be in this case easily estimated by the observer, which would limit the depth of field in the whole scenery despite the contribution of the aerial perspective. Similarly, the Applicant noticed that the aforementioned breakthrough effect is reduced whenever the light projector is not surrounded by a black, uniform background. In fact, an observer can determine the distance from a background other than a black and uniform background, thereby limiting the depth of field of the whole scenery, in spite of the contribution of the aerial perspective.

DETAILED DESCRIPTION

That having being stated,FIG. 1shows an artificial lighting system1, which will be from now on referred to concisely as lighting system1.

In detail, lighting system1comprises a first light source2, preferably directional, i.e. designed to emit light in an emission solid angle smaller than 4π sr. Moreover, the first light source2emits light in the visible region of the spectrum, that is having wavelengths between 400 nm and 700 nm. Moreover, the first light source2emits light (visible electromagnetic radiation) with spectral width Δλ preferably higher than 100 nm, more preferably higher than 170 nm. Spectral width Δλ may be defined as the standard deviation of the first light source's wavelength spectrum.

The lighting system1also includes a first diffuser panel4, which is for example shaped as a parallelepiped. In particular, the first diffuser panel4is delimited by a first surface S1and by a second surface S2, parallel to each other; preferably, the first diffuser panel4is thin, i.e. its thickness w, measured along a direction perpendicular to the first and the second surfaces S1, S2, has square value not higher than 5%, preferably 1%, of the area of the first and the second surfaces S1, S2.

More particularly, in the embodiment shown inFIG. 1the first diffuser panel4operates as a so-called Rayleigh diffuser, i.e. as a panel which substantially does not absorb light in the visible range and which diffuses more efficiently the short-wavelength in respect to the long-wavelength components of the impinging light, e.g. a panel which substantially does not absorb light in the visible range and which diffuses light rays of wavelength λ=450 nm (blue) at least 1.2 times, preferably at least 1.4 times, more preferably at least 1.6 times more efficiently than light rays of wavelength λ=650 nm (red), wherein diffusion efficiency is given by the ratio between the diffused light radiant power respect the impinging light radiant power. Optical properties and microscopic characteristic of Rayleigh like diffusers are also described in detail in the patent application EP2304478 of the same Applicant. A further insight on the microscopic features is also provided in what follows.

In the embodiment shown inFIG. 1, the first light source2is vertically aligned to the first diffuser panel4, i.e. it lies along an axis H, which is perpendicular to the first and second surfaces S1, S2and passes through the barycenter of these latter (inFIG. 1, the barycenter of the first surface S1is designated by O). In general, except where otherwise stated, in the present description the term “barycenter” is meant in its geometric acceptation, instead of its physical acceptation (center of mass), hence it is applicable also to plane surfaces, and anyway to objects having a substantially infinitesimal thickness. Therefore, the term “barycenter” has to be meant as “geometrical center” or “centroid” and it coincides, given an object (or surface) having an infinitesimal thickness, with the center of mass of this latter, calculated under the assumption that the object has a uniform density and, precisely, an infinitesimal thickness. Moreover, the first light source2illuminates entirely the first diffuser panel4. Embodiments wherein the first light source2is arranged off-axis in respect to the barycenter of the first and second surfaces S1, S2are, however, possible, as described in what follows.

The lighting system1is optically coupled to an environment, e.g. a room6shaped as a parallelepiped and delimited by a lower wall P1, an upper wall P2and four lateral walls P1. In particular, without losing generality, it is assumed that the upper wall P2has a cavity8, which has, seen from above, the same shape of the first diffuser panel4and is filled entirely by this latter. In any case, the present invention is not restricted to the shape and/or arrangement of the cavity8; as an example, according to further embodiments (not shown), the cavity may be formed within a lateral wall. Furthermore, the present invention is not restricted to be used in indoor spaces; therefore, embodiments are possible in which the lighting device1is used as a system for outdoor day-like illumination during night time. Therefore, the lighting system1can be coupled to an outdoor environment, i.e. an environment equivalent to a room, the walls of which are either black or arranged at an infinitely large distance.

The lighting system1comprises a support element10that delimits, together with the first surface S1of the first diffuser panel4, an external volume V which is external to the room6; the first light source2is placed inside the external volume V. Although not shown, embodiments are possible in which the support element10is mechanically coupled to the room6in a manner such that the external volume V is delimited at least in part also by a wall of the room6, as an example the upper wall P2.

The support element10is internally coated by an internal layer12, made of a material capable of absorbing incident luminous radiation; such material is, for example, a material with black color and coefficient of absorption higher than 70%, preferably higher than 90%, most preferably higher than 95%, even most preferably higher than 97% in the visible range. The internal layer12is aimed ad absorbing incident radiation that comes, for example, directly from the first light source2, or from reflection and/or scattering processes by the first diffuser panel4, or from the room6through the first diffuser panel4. Preferably, the volume V is internally coated by the internal layer12in its entirety, with the exception of the first surface S1of the first diffuser panel4. In other words, the support element10and the internal layer12define a sort of dark box (or chamber), wherein the term “dark” relates to a condition of little illumination and/or to the capability of absorbing the light, so as to make the box barely visible, as described hereinbelow; therefore, in what follows, reference will also be made to a dark box10. The light can enter/exit the dark box only through the first diffuser panel4.

Again referring to the first diffuser panel4, and assuming that a light beam generated by a CIE (International Commission on Illumination) D65 standard illuminant point-like source at large distance from the first diffuser panel4(a beam, thus, constituted by light rays parallel to one another) and directed perpendicularly the first surface S1, the first diffuser panel4separates such beam in four components, particularly in:

a transmitted component, formed by light rays that pass through the first diffuser panel4and do not experience significant deviations, i.e. by light rays experiencing a deviation smaller than 0.1°, with a luminous flux which is a fraction τdirectof the overall luminous flux incident on the first diffuser panel4;

a forward diffuse component, formed by light rays exiting the second surface S2along directions that are distributed around a direction perpendicular to the second surface S2(with the exception of such perpendicular direction and of directions differing from such perpendicular direction by an angle smaller than 0.1°), with a luminous flux which is a fraction τscatteredof the overall luminous flux incident on the first diffuser panel4;

a backward diffuse component, formed by light rays exiting the first surface S1along directions that are distributed around a direction perpendicular to the first surface S1(with the exception of such perpendicular direction and of directions differing from such perpendicular direction by an angle smaller than 0.1°), with a luminous flux which is a fraction ρscatteredof the overall luminous flux incident on the first diffuser panel4; and

a reflected component, formed by light rays exiting, or originating from, the first surface S1along a direction at a mirror angle (e.g. perpendicular, or differing from the perpendicular by an angle smaller than 0.1°, in the present case) to the first surface S1, with a luminous flux which is a fraction ρdirectof the overall luminous flux incident on the first diffuser panel4.

That having being stated, the optical properties of the first diffuser panel4are such that:

τscatteredis within the range 0.05-0.5, preferably 0.07-0.4, more preferably 0.1-0.3, still more preferably 0.15-0.25;

the average correlated color temperature (“CCT”) CCT_τscatteredof the forward diffuse component is significantly higher than the average correlated color temperature CCT_τdirectof the transmitted component, namely CCT_τscattered>h*CCT_τdirectwith h=1.2, preferably h=1.3, more preferably h=1.5;

the first diffuser panel4does not absorb significantly incident light, namely the sum τdirect+τscattered+ρdirect+ρscatteredis at least equal to 0.8, preferably 0.9, more preferably 0.95, still more preferably 0.97;

the first diffuser panel4scatters mostly forward, namely τscattered>η*ρscattered, where η is at least equal to 1.1, preferably η=1.3, more preferably η=1.5, still more preferably η=2; and

the first diffuser panel4has low reflection, namely ρdirect<0.09, preferably <0.06, more preferably <0.03, still more preferably <0.02.

In greater detail, the first diffuser panel4comprises a solid matrix of a first material (e.g., a resin having excellent optical transparency, such as thermoplastic resins, thermosetting resins, photocurable resins, acrylic resins, epoxy resins, polyester resins, polystyrene resins, polyolefin resins, polyamide resins, polyimide resins, polyvinyl alcohol resins, butyral resins, fluorine-based resins, vinyl acetate resins, or plastics such as polycarbonate, liquid crystal polymers, polyphenylene ether, polysulfone, polyether sulfone, polyarylate, amorphous polyolefin, or mixtures or copolymers thereof), wherein nanoparticles of a second material (e.g. inorganic oxide such as ZnO, TiO2, ZrO2, SiO2, Al2O3) 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.

Moreover, in the embodiment shown inFIG. 1, the first diffuser panel4is uniform, in the sense that, given any point of the first diffuser panel4, the physical characteristics of the first diffuser panel4in that point do not depend on the point itself. Furthermore, the first diffuser panel4is monolithic, namely the solid matrix does not feature any discontinuity due to gluing or mechanical coupling. Such characteristics of the first diffuser panel4are not, however, necessary to the aims of the present invention, although they render the first diffuser panel4easier to be manufactured.

More particularly, the nanoparticles may be monodisperse. The nanoparticles may be spherically shaped or shaped otherwise. The effective diameter D of the nanoparticles (for a definition in the case of non-spherical shape, see below) falls within the range [5 nm-350 nm], preferably [10 nm-250 nm], more preferably [40 nm-180 nm], still more preferably [60 nm-150 nm], where the effective diameter D is given by the diameter of the nanoparticles times the first material's refractive index.

Moreover, nanoparticles are distributed inside the first diffuser panel4so that their areal density, namely the number N of nanoparticles per square meter, i.e. the number of nanoparticles within a volume element delimited by a portion of the first surface S1having an area of 1 m2, satisfies the condition N≥Nmin, where:

Nmin=υ⁢10-29D6·m2+2m2-12
wherein ν is a dimensional constant equal to 1 meter6, Nminis expressed as a number/meter2, the effective diameter D is expressed in meters and wherein m is equal to the ratio of the second material's refractive index to the first material's refractive index.

Preferably, the nanoparticles are distributed homogenously, at least as far as the areal density is concerned, i.e. the areal density is substantially uniform on the first diffuser panel4, but the nanoparticle distribution may vary across a direction perpendicular to the first and second surfaces S1, S2. The areal density varies, for example, by less than 5% of the mean areal density. The aerial density is here intended as a quantity defined over areas larger 0.25 mm2.

Alternatively, embodiments are possible wherein the areal density varies, so as to compensate illumination differences over the first diffuser panel4, as lit by the first light source2. For example, the areal density N(x,y) at point (x,y) within S1may be related to the illuminance I(x,y) produced by the first light source2at point (x,y) via the equation N(x,y)=Nav*Iav/I(x,y)±5%, where Nay and Iavare the averaged illuminance and areal density, these latter quantities being averaged over the first surface S1. In this case the luminance of the first diffuser panel4is equalized on the first diffuser panel4, in spite of the non-uniformity of the illuminance profile of the first light source2on the first diffuser panel4. To this regard, it is reminded that the luminance is the luminous flux of a beam emanating from a surface (or falling on a surface) in a given direction, per unit of projected area of the surface as viewed from the given direction, and per unit of solid angle, as reported, as an example, in the standard ASTM (American Society for Testing and Materials) E284-09a.

In the limit of small D and small volume fractions (i.e. thick panels) an areal density N≈Nminis expected to produce scattering efficiency of about 5%. As the number of nanoparticles per unit area gets higher, the scattering efficiency is expected to grow proportionally to N, until multiple scattering or interferences (in case of high volume fraction) occur, which might compromise color quality. The choice of the number of nanoparticles is thus biased by the search for a compromise between scattering efficiency and desired color, as described in detail in the patent application EP2304478. Furthermore, as the size of nanoparticles gets larger, the ratio η=τscattered/ρscatteredof the forward to backward luminous flux grows, such ratio being equal to one in the Rayleigh limit. Moreover, as η grows, the aperture of the forward scattering cone gets smaller. Therefore, the choice of η is biased by the search for a compromise between having light scattered at large angles and minimizing the flux of backward scattered light. However, in a per se known manner, an antireflection layer (not shown) may be deposited on the first and the second surface S1and S2, with the aim of minimizing ρdirect; by doing so, the luminous efficiency of the lighting system1is raised and the visibility of the first diffuser panel4(as a physical element) from an observer in the room6is diminished.

Embodiments are however possible wherein nanoparticles do not have spherical shape; in such case, the effective diameter D can be defined as the effective diameter of the equivalent spherical particles, namely the effective diameter of spherical particles having the same volume as the aforementioned nanoparticles.

Furthermore, embodiments are possible wherein the nanoparticles are polydispersed, i.e. their effective diameters are characterized by a distribution N(D). Such distribution describes the number of nanoparticles per surface unit and unit interval of effective diameter in a neighborhood of the effective diameter D (that is, the number of particles per surface unit having an effective diameter between D1e D2is equal to

ND2-D1=∫D1D2⁢N⁡(D)⁢⁢dD).
These effective diameters may fall in the range [5 nm-350 nm], i.e. the distribution may be non-null within this range. In this case, considering that scattering efficiency grows approximately, i.e. in the limit of small particles, with the sixth power of the nanoparticle's diameter, the polydisperse distribution behaves approximately as a monodisperse distribution with a representative diameter D′effdefined as:

D′effmay by selected so as to lie within the range [5 nm-350 nm], preferably [10 nm-250 nm], more preferably [40 nm-180 nm], still more preferably [60 nm-150 nm].

Moreover, the first diffuser panel4is at a distance d from the first light source2, measured along the axis H. Such distance d may be varied according to an expected position of the observer inside the room6, so that the distance between the expected position of the observer and the first light source2is equal to at least five meters, preferably seven meters. For example, in the case of a ceiling-type application, distance d may be equal to three meters. As a precaution, distance d may be equal to five meters, in case the observer is very close to the second surface S2.

According to a different embodiment shown inFIG. 2, the first light source2is once again arranged inside the external volume V, but it is arranged off axis, i.e. laterally with respect to the first diffuser panel4, i.e. it is not intercepted by any line that passes through the first diffuser panel4and is parallel to the axis H. Furthermore, the lighting system1includes a reflective system20, which includes a first mirror22and forms a light path that connects the first light source2to the first diffuser panel4; in other words, the light rays generated by the first light source2are conveyed by the reflective system20onto the first surface S1. The first mirror22causes a last deviation (i.e. a last change of direction) of the light path before the first diffuser panel4.

In addition, the first light source2and the reflective system20are such that the first diffuser panel4is lit thoroughly by the light rays coming from the first light source2. Furthermore, for reasons that will be described more accurately later on, the first diffuser panel4and the reflective system20are arranged so that they satisfy the following geometric condition. There are no couples composed by a light ray RL1and a light ray RL2such that:

the light ray RL1passes through the first diffuser panel4(as an example, coming from the room6) or originates from the first diffuser panel4; and

the light ray RL2is the reflection of the light ray RL1by the reflective system20and it is directed so as to impinge again on the first surface S1.

The abovementioned geometric condition on light rays RL1and RL2is equivalent to stating that no light ray generated inside the room6and intersecting the first surface S1in a first point can be subsequently reflected by the reflective system20in a manner such that it hits again the first surface S1in a second point. Even alternatively, the reflective system20is arranged such that all inbound light rays emanating from the first surface S1and impinging onto the reflective system20, irrespective of the position within the first surface S1from which the inbound light rays emanate, are reflected onto the internal layer12.

The aforementioned geometric condition on light rays RL1and RL2leads to reducing the volume occupied by the lighting system1, mainly in terms of the volume occupied outside room6, without damaging the quality of lighting. In particular, the lighting system1features a reduction of the space occupied vertically, i.e. measured along the axis H. Given that a reduced vertical encumbrance is a prerequisite for a large number of applications, the abovementioned geometric condition allows to obtain the breakthrough effect in a great number of situations of practical interest. For the sake of brevity, from now on the reference to the vertical dimension of the occupied space will be generally omitted.

In greater detail, besides leading to a reduction of the occupied space, the reciprocal arrangement of the reflective system20and the first diffuser panel4prevent the occurrence of two phenomena which could spoil the natural quality of the lighting.

As shown inFIG. 3, should the aforementioned geometric condition on the light rays RL1and RL2be violated, the following would happen:

a light ray IR1generated by the first light source2hits the reflective system (here designated by30) and is conveyed onto the first diffuser panel4, crosses the first diffuser panel4and reaches the observer; and

a light ray IR2generated by the first light source2hits the reflective system30a first time, is conveyed a first time onto the first diffuser panel4, is partially reflected due to Fresnel reflection by the first surface S1, hits the reflective system30a second time, is conveyed a second time onto the first diffuser panel4, crosses the first diffuser panel4and reaches the observer from a different direction with respect to the light ray IR1.

In this case, the observer would experience the vision of two different images of the first light source2, that are seen under different directions. The first image is the image formed by IR1and by all the light rays close to IR1, i.e. the light rays that have crossed only one time the first diffuser panel4. The second image is the image formed by the light ray IR2and by all the light rays close to IR2, i.e. the rays which, having been partially reflected by the first surface S1, are redirected by the reflective system30toward the observer. Since Fresnel reflection redirects only a portion (e.g. about 4% per each surface of the first diffuser panel4, for incidence nearly perpendicular and for PMMA material), the second image of the first light source2is weaker than the first one. Nevertheless, its luminance is still very high; therefore, an observer would perceive the difference with natural lighting, which is evidently characterized by the presence of only one image of the Sun.

In a similar way, should the aforementioned geometric condition on light rays RL1and RL2be missing, light rays coming from the room6and with any color could cross the first diffuser panel4, be reflected by the reflective system30and re-enter the room6after crossing again the first diffuser panel4. In such case, an observer would perceive the presence of luminous objects having colors different from the color of the first diffuser panel4, as if they were arranged beyond the first diffuser panel4. Furthermore, due to the so-called backscattering, the first diffuser panel4itself would be seen by the observer not only directly, but also trough the reflective system30; in practice, the first diffuser panel4would generate a luminous spot, spatially limited by the mirror frame, which would spoil the uniformity of the background. In addition, an observer could notice the presence of the reflective system30because of swift change in luminance that could take place at mirror edges. All these effects would cause the lighting to appear unnatural, the image of the first diffuser panel4being different from that of natural sky. Moreover, the perception of objects or mirrors in the background of the first diffuser panel4would prevent from obtaining the breakthrough effect.

That having being stated, embodiments are possible where, as shown inFIG. 2, the first mirror22is plane and parallel to the first diffuser panel4(namely parallel to the first and second surfaces S1, S2), so that the occupied volume is minimized.

Moreover, irrespective of the shape and the angle of inclination of the first mirror22, the first light source2and the first mirror22are arranged in such a way that, if the surface of the first mirror22is referred to as the reflecting surface Sr, the barycenter O of the first surface S1and the barycenter O′ of the reflecting surface Srcan be connected by a line, having an angle of incidence AO with respect to the axis H which is between 40° and 65°, preferably between 42° and 50°, more preferably in a neighborhood of 45°. In such a way, a compromise is reached between minimizing the space occupied vertically by the lighting system1, which decreases as the angle of incidence AO gets larger, and minimizing the light losses due to the partial reflection which occurs at the first diffuser panel4, which grows as the angle of incidence AO gets larger, in the hypothesis that the first diffuser panel4has refractive index basically equal to 1.5 and that the angle of incidence AO is higher than 45°. It is worthwhile noting that the benefit of illuminating the first diffuser panel4at an angle of incidence AO substantially equal to 45° holds true for all possible embodiments, including those described later and those without any mirror.

The Applicant also verified that, when the first mirror22is plane, the vertical space occupied by the lighting system1is minimized for any angle of incidence AO, provided that the first mirror2is parallel to the first diffuser panel4.

Before moving on to describe, it is defined the “carrier ray” as the folded light path that connects the barycenter O″ of the emitting surface Sf(defined later on) of the first light source2to the barycenter O of the first surface S1, via the reflective system20, or the shortest among these light paths, if more than one light path exists; only one light path exists if the reflective system20is designed as an imaging-optic component.

Moreover, a Cartesian reference system is introduced, such a reference system having an origin in the barycenter O of the first surface S1, and including an x-axis and an y-axis lying in the plane defined by the first surface S1and arranged in such a way that the y-axis is perpendicular to the plane of incidence of the carrier ray onto the reflecting surface Srof the first mirror22(i.e. the plane containing the two segments of the carrier ray that contact the first mirror22, as well as the line perpendicular to the reflecting surface Srin the contact point).

Irrespective of the shape and the angle of inclination of the first mirror22, embodiments are possible wherein the first surface S1has a rectangular or at least an elongated shape, with its largest axis being coincident with the y-axis. The Applicant has verified that these embodiments allow to fulfill the geometric condition on the light rays RL1and RL2with a smaller height of the lighting system1along the axis H, with respect to the cases in which the first diffuser panel4is not elongated or is elongated along the x-axis, the area of the first diffuser panel4and the angle of incidence AO being the same. In other terms, these embodiments allow to maximize the area of the first diffuser panel4for a given height of the lighting system1and a given angle of incidence AO. In fact, the Applicant has noted that, for a given angle of incidence AO, the maximum width of the first diffuser panel4along the x-axis is proportional to the minimum height of the lighting system1along the axis H, the proportionality coefficient being close to 1 when the angle of incidence AO is close to 45°.

The Applicant also noticed that the natural quality of lighting is further improved if the first light source2features a circular (FIG. 4a) or elliptic (FIG. 4b) emitting surface Sf. Given that the first light source2is directional, it is characterized by a main direction, which is the direction of the absolute maximum of the luminous intensity, and by a main plane, here defined as the plane, perpendicular to the main direction, in which the absolute maximum of the luminance occurs. That having being said, the emitting surface Sfis the portion of the main plane where the luminance along the main direction is higher than 10% of this absolute maximum of the luminous intensity. The emitting surface Sfis called circular or elliptic if there exists a circumference or ellipse enclosing it and having an area greater than the area of emitting surface Sf, by no more than 30%, preferably 20%, more preferably 10%.

All that being said, the light rays hit the first surface S1in corresponding points of incidence and form corresponding angles of incidence with the lines perpendiculars to the first surface S and passing through the points of incidence. That having being said, the reflective system20and the arrangements of the first light source2and of the first diffuser panel4are such that, given:

a light ray RL3that connects, via the reflective system20, the barycenter O″ of the emitting surface Sfto the barycenter O of the first surface S1, and forms an angle θ1in respect to a line perpendicular to the first surface S1and passing through the barycenter O of this latter; and

a light ray RL4that connects, via the reflective system20, the barycenter O″ of emitting surface Sfto a point of the first surface S1which is spaced apart of a distance X from the barycenter O of this latter, and that forms an angle θ2in respect to a line perpendicular to the first surface S1and passing through this point;

it thus happens that:
|tan(θ1−θ2)|≤X·cos(θ1)/L

where L is at least equal to three meters and, preferably, X<<L, e.g. X<10 cm. Preferably, L is at least equal to four meters; still more preferably, L is at least equal to five meters. Note that such condition is satisfied also by the embodiment shown inFIG. 1, provided that the aforementioned distance d of the first diffuser panel4from the first light source2is equal to L.

In such a way, the light rays impinge on the first surface S1with almost parallel directions, in a way similar to what happens in nature. Furthermore, this condition can be met even when the first light source2is at a physical distance from the first diffuser panel4lower than L, provided that the reflective system20comprises converging mirrors, i.e. mirrors designed to form a virtual image of the first light source2at a distance greater than the physical distance.

The Applicant has further noticed that, in certain applications (e.g., in the case where the first diffuser panel4is set apart of a small distance from the observer), it is sufficient that L is at least equal to 50%, preferably 70%, even more preferably to 100%, of the maximum distance between any two points of the first surface S1.

Irrespective of the above details on the distance of the first diffuser panel4from the first light source2, embodiments are however possible, wherein the light source2is arranged so that the illuminance profile on the first surface S1varies between a minimum value ILLUminand a maximum value ILLUmax, wherein ILLUmax≤3*ILLUmin, in order to limit the illuminance variations on the first diffuser panel4. Such a condition on the illuminance uniformity may be achieved by interposing a free-form optics between the first light source2and the first surface S1and/or by spacing the light source2apart from the first surface S1of a suitable distance. As an example, embodiments are possible, wherein the illuminance produced by the first light source2on the first surface S1is substantially uniform, owing to the fact that the following relationship holds true:
|tan(θ1−θe)|≤0.5·cos(θ1)

wherein θeis the angle at which a further light ray, which originates from the barycenter O″ of the emitting surface Sfof the first light source2, impinges on a point of the boundary of the first surface S1, this point being the point among the points of the boundary having maximum distance from the barycenter O of the first surface S1. The Applicant has further noticed that, also in this case, if the observer is set apart from the first diffuser panel4by a small distance, it is sufficient that L is at least equal to 50%, preferably 70%, even more preferably to 100%, of the maximum distance between any two points of the first surface S1.

The Applicant further noticed that the natural quality of lighting improves whenever the maximum luminance of the first light source2is greater than 106cd/m2, preferably 0.1*106cd/m2, more preferably 1*106cd/m2, still more preferably 10*106cd/m2. For such values, as a matter of fact, the first light source2generates enough glare for the source itself to be difficult to look at, thereby preventing the observer from evaluating the source's distance by means of the mechanism of eye focusing. These luminance values thus contribute to obtain the infinite breakthrough effect. Moreover, glare makes it difficult to detect possible non-uniformities in the luminance profile of the first light source2, thus making it difficult to detect differences between the image of the first light source2and the image of the Sun.

The Applicant also verified that the natural quality of lighting improves if the size and shape of the first light source2are such that, given a light ray that connects the perimeter of emitting surface Sfto the barycenter O of the first surface S1, the angle it forms with the abovementioned light ray RL3is lower than 4°, preferably 3°, more preferably 1.2°, and still more preferably 1.0°. As a matter of fact, the natural quality of lighting improves when the lower values of such angle are associated to the higher values of luminance, this condition allowing to obtain a more natural perception.

As shown inFIGS. 5aand 5b, independently from the details of the first diffuser panel4, the first mirror22may be a concavely curved mirror, such as a concavely curved mirror having a parabolic curvature. In particular, as shown inFIGS. 5aand 5b, the first mirror22may be shaped as a portion of a circular paraboloid, i.e. a surface obtained by rotating a generator parabola around its axis A, such that the intersection with any plane including the axis A defines the same generator parabola. In particular, the portion of circular paraboloid is obtained by splitting a portion of the circular paraboloid surface with a secant plane that crosses the axis A forming an angle different from 90°. For the sake of brevity, from now on, reference is made to the circular paraboloid, without mentioning explicitly that the mirror is formed by a portion of the circular paraboloid.

According to this embodiment, the first light source2is arranged in the focus of the circular paraboloid; more precisely, the barycenter O″ of the emitting surface Sfof the first light source2is arranged in the focus of the circular paraboloid, so that the light rays coming from that barycenter and reflected by the circular paraboloid hit the first surface S1with directions of propagation all parallel to the axis A. In this way, the observer perceives the first light source2as if it were arranged at a virtually infinite distance, similarly to what happens with the Sun, thereby enhancing the natural quality of lighting. In other words, the virtual image of the first light source2is at infinite distance from the observer.

Furthermore, the size of the first light source2perceived by the observer is given by the size of the image of the first light source2on the retina, and depends only on the physical dimension of the first light source2and on the magnification of the optical telescope system formed by the eye lens (the crystalline) and by the circular paraboloid; such optical telescope system has an image plane and an object plane which are arranged, respectively, in the focus of the eye lens and in the focus of the circular paraboloid. The abovementioned magnification is given by the ratio of the eye lens focal length to the circular paraboloid focal length; therefore, the size of the first light source2as perceived by the observer does not depend on the distance of the observer from lighting system1. Thus, this additional condition contributes in creating a natural lighting effect, because the Sun's perceived size do not depend on the observer's position.

The Applicant also noticed that, if the emitting surface Sfis shaped as a circle, the image of the first light source2perceived by the observer is still circle shaped, because the optical system shown inFIG. 5adoes not twist the image.

The embodiment shown inFIG. 5ais characterized in that the vertical space occupied by the lighting system1is almost equal to the size of the first diffuser panel4along the x-axis, in case the light rays reflected by the circular paraboloid hit the first diffuser panel4at450, and the abovementioned geometric condition is met.

According to a variant, shown inFIG. 5a, the first and second surfaces S1and S2of the first diffuser panel4have an elliptic shape, such a shape being encompassed by the projection of circular paraboloid22on the xy plane along the direction given by the axis A. Therefore, the first and second surfaces S1and S2can be circumscribed by the luminous spot SP formed by the circular paraboloid in the xy plane, thereby reducing light losses. Moreover, the first mirror22is cut so as to accept a light beam having circular divergence, i.e. is cut in a way that its projection on the plane orthogonal to the line connecting the barycenter O″ of the emitting surface Sfand the vertex of the circular paraboloid has a circular shape, or at least circumscribes a circle with good approximation. However, other shapes of the first mirror22are also possible, e.g. an elongated shape along the y direction.

The use of the circular paraboloid implies that the light entering the room6through the first diffuser panel4projects on the floor of the room6a light spot having the same shape and size as the first diffuser panel4, as it happens with sunlight through a window, thereby contributing to the natural lighting effect. Moreover, since the observer is capable of evaluating the distance of a generic light source based on the divergence of the light beam it generates, the lighting system1shown inFIG. 5acreates an effect of large depth of field even if the first light source2is not directly in the observer's visual field.

As shown inFIG. 6, the first mirror22may be shaped as the portion of a paraboloid with cylindrical symmetry, i.e. as a portion of a parabolic cylinder, this portion being obtained by intersecting the parabolic cylinder with three secant planes. In detail, it is known that, given a generator parabola and a reference line R, the parabolic cylinder is the ruled surface formed by lines parallel to the reference line R and incident on the generator parabola; in other words, the parabolic cylinder is obtained by translation of the generator parabola along the reference line R. In what follows, the reference line R is also called cylindrical axis.

In the embodiment shown inFIG. 6, the parabolic cylinder is obtained by translation of the generator parabola in a direction parallel to the x-axis. Moreover, the generator parabola has its vertex in the xH plane and its axis A oriented along a line which is specular to the line that connects the barycenter O of the first surface S1and the barycenter O′ of the reflecting surface Srof the first mirror22. In this embodiment, a plane tangent to the parabolic cylinder at the vertex of the generator parabola is parallel to the xy plane. Moreover, two out of three secant planes are, for example, parallel to yH plane, whereas the third plane is, for example, substantially parallel to plane xy. All that having being said, from now on, for the sake of brevity reference will be made to the parabolic cylinder, without mentioning explicitly that the mirror is formed by a portion of the parabolic cylinder.

In the embodiment shown inFIG. 6, the parabolic cylinder is laterally spaced apart along the x-axis, with respect to the axis H, so that the angle of incidence AO is substantially equal to 45°.

In greater detail, the barycenter O″ of emitting surface Sfis arranged in the xH plane, close to the line formed by the foci of the parabolae forming the parabolic cylinder, at the position which ensures the best collimation of the light rays directed toward the first diffuser panel4, for what concerns the ray propagation in the plane containing the y-axis and the barycenter of the parabolic cylinder, and more generally what concerns ray propagation in all the planes that intersect the first diffuser panel4along lines parallel to the y-axis. In the following, the average divergence in these latter planes is referred for simplicity as divergence along the y-axis direction.

The embodiment shown inFIG. 6allows to use a first diffuser panel4which is considerably longer along the y-axis than along the x-axis, thereby maximizing the area of the first diffuser panel4and so the angles under which the observer perceives the breakthrough effect. More precisely, such a large elongation of the first diffuser panel4is possible because the embodiment relies upon the usage of a mirror which features a large elongation in the y-axis direction, while preserving a limited (output) divergence in the same y-axis direction. More specifically, the Applicant has noticed that the perceived size of the first light source2along the y-axis direction, i.e. the diameter of the perceived emitting surface Sfalong the y-axis direction, does not depend on the distance between the observer and the first light source2, or it depends from this distance very weakly. Regarding the size of the first light source2perceived by the observer along the x-axis direction, it depends on the position of the observer and decreases with distance. Therefore, with the aim of assuring that a circular shape of the first light source2is perceived, a light source with an elliptic emitting surface Sfcan be adopted, wherein the eccentricity of the ellipse is fixed according to the expected point of observation inside the room6.

A further advantage given by using a parabolic cylinder is the fact that such a kind of mirrors are easy to be manufactured, since they can be obtained by a plane-mirror foil, e.g. an Aluminium mirror foil. Furthermore, referring to an observer standing in vertical position and looking at the first light source2from a central position, i.e. through the barycenter O of the first surface S1, and hence having the eyes aligned along the y-axis direction, he will perceive the first light source2at far distance, due to the fact that his eye-convergence operates only in planes containing both eyes (i.e. the y-axis direction), where high convergence occurs. That happens no matter the ray divergence in the orthogonal direction is.

In a different embodiment (not shown), the lighting system1is mounted in such a way that the first diffuser panel4is parallel to a vertical wall, instead of a ceiling, in such a way that the light beam from the first light source2enters the room6being parallel to floor and at an angle of about 45° with respect to the vertical wall. In this embodiment, the parabolic cylinder is obtained by translation of the generator parabola in a direction parallel to the y-axis, rather than the x-axis, this being the configuration that allows the largest depth perception for an observer, whose eyes are aligned in the x-axis. Also in this case, given a height of the lighting system1beyond the vertical wall, the largest area of the first diffuser panel4can be obtained by adopting a shape elongated in the y-axis direction.

In a different embodiment, the reflective system20may include a second mirror24, as shown for example inFIG. 7. That is, the aforementioned first mirror22may be one mirror of a plurality of mirrors of the reflective system20, which causes the last deviation of the light path along which the light rays generated by the first light source2are conveyed onto the first diffuser panel4.

The second mirror24is optically interposed between the first mirror22and the first light source2. In this case, the abovementioned geometric condition does not change, because this condition refers to the overall reflective system20. It is thus irrelevant if the light ray RL2is generated by reflection of the light ray RL1on just the first mirror22, or on the first and second mirrors22,24. Similarly, the reflective system20may include additional reflective elements (not shown).

Any of the first and second mirrors22,24may be plane or have different shape. In particular, as shown inFIG. 8, embodiments are possible wherein both the first and second mirrors22,24are shaped as portions of two corresponding parabolic cylinders, that are generated by generator parabolae that lie in orthogonal planes, and that are translated along orthogonal directions and thus perform light collimation in orthogonal panes. In the present embodiment, for example, the first mirror22is similar to the parabolic cylinder shown inFIG. 6, whereas the second parabolic cylinder, which forms the second mirror24, is obtained by taking a second generator parabola in the xH plane and by translating it along the y-axis direction, thus obtaining a beam-divergence reduction in the xH plane. Moreover, the Applicant has verified that a good collimation in all the directions for the light rays reflected by the second mirror24towards the first mirror22is obtained when the second generator parabola has its axis oriented in a direction substantially parallel to the axis of the generator parabola of the first mirror22, provided that the two parabolic cylinders are arranged so that they share a common focus (or, more precisely, so that the generator parabolae share a common focus, where the position of the focus of the generator parabola of the first mirror22accounts for the reflection by mirror24) and the first light source2is arranged substantially in such a common focus.

The embodiment shown inFIG. 8enables to use a diffuser panel having a length along the y-axis which is considerably larger than the length along the x-axis, and therefore enables to maximize the area of the first diffuser panel4, the vertical space occupied by this embodiment being equal to the one occupied in case of square panel. Moreover, this embodiment enable to generate a light beam that impinges on the first surface S1with a reduced divergence along both the x-axis and the y-axis (i.e. along planes that intersect the xy plane along lines that are parallel to the x-axis and the y-axis, respectively). Therefore, the transmitted light rays have a divergence similar to sunrays. This condition contributes in creating a large depth of field perception even when the first light source2is not in the observer's visual field. Moreover, since the first light source2is arranged close to the common focus, the size of the first light source2as perceived by the observer does not depend on the distance. Finally, the illumination of a diffuser panel elongated along the y-axis direction is here made possible by starting from a light beam which impinges on the second mirror24with substantially a same divergence both in the plane of incidence and in the orthogonal plane, i.e. by efficiently using a light source that generates a light beam having a square-like cross-section. This result, that is achieved by performing the reduction of the initial beam divergence in two separate steps in the two orthogonal directions, represents an advantage respect to the case of a single parabolic cylinder, for which asymmetric beams are required, as described below.

Irrespective of the details of the first diffuser panel4and the reflective system20, the first light source2may have, as explained before, an emitting surface Sfwith a circular or elliptic shape. In particular, the emitting surface Sfmay have an elliptic shape whenever the reflective system20includes at least one paraboloid with cylindrical symmetry, so that the different magnifications introduced along the x-axis and y-axis are compensated, thus allowing for the creation of a circle-shaped light spot on the observer's retina.

As shown inFIGS. 9aand 9b, the first light source2may be formed by a set of emitting devices50. Each emitting device50is formed by a LED source52and a corresponding compound parabolic concentrator (“CPC”)54of rectangular type, which features an input aperture IN and an output aperture OUT; the input aperture IN and the output aperture OUT may be respectively shaped as a first and a second rectangle, parallel and aligned to each other, the first rectangle having an area smaller than the second rectangle. Moreover, the first rectangle has a different ratio between the lengths of its axes of symmetry than the second rectangle. For example, the first rectangle has a greater ratio, i.e. it is more elongated, than the second one. The LED source52may be formed by an array of LED emitters (not shown) and is arranged close to the corresponding input aperture IN, in such a way that radiation emitted by the LED source52is coupled to the CPC concentrator54through the input aperture IN, and exits the output aperture OUT. Other types of reflective concentrators are however possible; similarly, light emitting devices other than LEDs may be used.

The light beam generated by each emitting device50has a rectangular cross-section, its divergence being maximum in the plane containing the axis of the beam itself, i.e. containing the optical axis56of the pair formed by the concentrator54and the corresponding LED source52, and the greater of the symmetry axes of the rectangle defined by the output aperture OUT, designated by57inFIG. 9a. In case of a different output aperture OUT, the plane of maximum divergence would be spanned by the elongation direction, i.e. the direction of maximum extension of the outlet OUT, and the optical axis56.

The amount of the beam divergence in each of the maximum-divergence plane and its orthogonal plane (also this latter containing the optical axis56) scales with the ratio between the lengths of the corresponding side of the input rectangle, dIN, and of the corresponding side of the output rectangle, dOUT, and it is in particular equal a to twice the arcsine of this ratio, i.e. arcsin(dIN/dOUT) In this regard, not only the areas, but also the shapes of the input and output apertures have to be different, in order to ensure different divergences in the two orthogonal planes.

The size of the input aperture IN should be chosen so that it encloses the LED source52. In the embodiment ofFIGS. 9aand 9b, each concentrator54has a funnel-like shape and is formed by four parabolic reflective surfaces, each of which is one-dimensionally curved and has a generator parabolas lying either in the maximum-divergence plane or in its orthogonal plane, all the generator parabolae having their focuses in the input plane in which the input aperture IN lies. Moreover, the four parabolic reflective surfaces have the same length along the direction of the optical axis56.

According to an embodiment, all the emitting devices50are equal, and the concentrators54are arranged so that the input apertures IN lie in the same input plane P_IN, and the output apertures OUT lie in the same output plane P_OUT. In particular, the concentrators54are arranged one next to the other, with output apertures OUT adjacent to each other, i.e. they are tightly packed, so that the maximum average luminance of the emitting surface Sfis assured; moreover, the number and arrangement of the concentrators54are such that the surface composed by the union of all the output apertures OUT approximates a circular surface, although embodiments are possible in which the composed surface approximates an elliptical shape. Finally, all the emitting devices50are arranged so as to have their axis56oriented in the same direction. In this circumstance, the first light source2has an own “plane of greater divergence”, which is the plane that contains the barycenter O″ of the emitting surface Sfand that is parallel to the planes of maximum divergence of the emitting devices50; furthermore, the first light source2has an “axis of greater divergence”58, given by the intersection between the plane of greater divergence of the first light source2and the emitting surface Sfof the first light source2. Even if the axis of greater divergence has been introduced for the case of a plurality of rectangular concentrators54, it is evident that other shapes of funnel-like concentrators54having output apertures elongated along parallel axes57lead to a light source still having an axis of greater divergence, which is parallel to the axes57.

The first light source2shown inFIGS. 9aand 9ballows to decouple the light beam characteristics, and in particular the shape of its cross-section and its divergence, from the shape of the emitting surface Sf, without introducing any loss. In the present case, wherein the emitting devices50generate identical “unit light beams” having rectangular cross-section, the distances between the centers of output apertures OUT are small compared to the width of the composite light beam formed by the summation of all the unit light beams, this summation occurring because of the propagation of the composite beam and the divergence of each unit light beam. In practice, the unit light beams melt into one composite light beam that has the same rectangular cross-section and the same divergence as a single unit light beam. In other words, at distances which are great in respect to the diameter of the emitting surface Sf, the composite light beam has the same shape and divergence of the beam generated by a single emitting device50, since it is formed by a plurality of identical unit light beams which are slightly shifted one respect to the other. Therefore, the embodiment shown inFIGS. 9aand 9ballows for a composite beam to be generated, having a section, in a plane perpendicular to the axis of the composite beam itself and at a desired distance from the first light source2, which is a rectangle of desired area and shape. Furthermore, this embodiment enables to create a light source having an emitting surface Sfwhich can have any shape, e.g. a circular or an elliptical shape. In what follows, this light source is referred to as “rectangular-beam source”. It should be stressed that the result is not obtained by relying upon a knife-cut aperture and imaging optics as performed, e.g., for standard, theater-like, stage-light projectors, where the beam cut causes high transmission losses. Therefore, the rectangular-beam source allows to minimize the overall energy consumption.

Although not shown, a different embodiment is possible, in which the first light source comprises a plurality of emitting devices, each of which is formed by a LED source having square shape, and a corresponding compound parabolic concentrator of a square type, which features a square input aperture and a square output aperture. In such a way, each emitting device generates a square beam, which has the same divergence in the two orthogonal directions (i.e. in the two planes containing the concentrator axis and, respectively, the two axes of the output aperture that are parallel to the sides of the output aperture). In particular, the present embodiment allows to generate a square beam with a desired divergence, for an arbitrary shape of the emitting surface Sf. In what follows, this first light source will be referred to as the “square-beam source”.

In a further different embodiment (not shown), the first light source comprises a plurality of emitting devices, each of which s formed by a LED source having a circular, and a corresponding compound parabolic concentrator of a circular type (not shown), which features a circular input aperture and a circular output aperture. In this case, the first light source generates a beam with a circular symmetry. Therefore, this first light source allows to generate a circular beam with a desired divergence, for an arbitrary shape of the emitting surface Sf. In what follows, this first light source will be referred to as the “circular-beam source”.

In case the reflective system20is made of one or more plane mirrors, or in case the reflective system20includes a single mirror having the shape of a parabolic cylinder, the rectangular-beam source allows to obtain a luminous spot SP which is elongated along the y-axis, i.e. a luminous spot SP which circumscribes the first surface S1of the first diffuser panel4, the first surface S1having the shape of a rectangle elongated along the y-axis. In both cases, the rectangular-beam source is oriented so that its axis of greater divergence58is “mapped” by the reflective system20onto the y-axis, so as to reduce the complexity of the lay-out of the reflective system. In the context of the present invention, the reflector system is said to map the axis of greater divergence onto the y-axis if, given a narrow bundle of light rays including the carrier ray, originating at barycenter O″ of the emitting surface Sfand lying in the plane of greater divergence, the reflective system20causes the ray bundle to cross the first diffuser panel4along a line tangent to the y-axis. For example, if the reflective system20is such that the carrier ray is folded in a single plane, the rectangular-beam source is oriented with the axis of greater divergence58parallel to the y-axis.

In case the reflective system20comprises two mirrors having the shapes of parabolic cylinders having orthogonal cylinder axes, the use of the square-beam source is advantageous. In this case, in fact, it is possible to rely upon the fact that the initial divergence of a square beam is reduced at two different distances from the first light source2, for the purpose of obtaining a luminous spot SP elongated along the y-axis. This embodiment allows to achieve an optimal coupling between commercially available LED emitters, that are typically square-shaped, and the concentrators.

Furthermore, in case the reflective system20comprises a mirror having the shape of a circular paraboloid, the use of the circular-beam source is advantageous. In this case, however, the light source2may be made of a single circular CPC, which is coupled to a circular LED assembly, this solution allowing to obtain a circular emitting surface Sf.

FIG. 10shows an additional embodiment where the first light source2is again formed by identical CPC concentrators54, their input apertures IN and output apertures OUT being again, exemplarily, rectangular-shaped. In this case, however, a mask60is applied on the overall aperture formed by the output apertures OUT; the mask60, which lies in the output plane P_OUT, defines a mask aperture62, having a shape which is a rounded rectangle with an area larger than the area of a single output aperture OUT. In particular, the mask60may be formed by a layer of optically absorbing material, so that the radiation can cross the output plane P_OUT only through the mask aperture62. In this way, the first light source2is still perceived as having basically a circular emitting surface Sf. The Applicant further noticed that the mask60does not substantially distort the shape of the luminous spot SP formed in the plane of first surface S1.

Independently from the number and the shape of the mirrors which form the reflective system20, the lighting system1may include a second light source, which comprises a diffused-light emitting layer, this layer being transparent, or at least partially transparent. In use, the additional light source emits diffused light from the emitting layer independently from being illuminated by the first light source2, while an observer that looks through the diffused-light emitting layer of the second light source can see the first light source2beyond this emitting layer. In the present description, the term “transparent” is used for indicating the so-called “see through” optical property, i.e. the property of an optical element of transmitting image-forming light. More specifically, considering a light beam generated by a point-like D65 standard illuminant source set at a great distance from the diffused-light emitting layer (a beam, thus, constituted by light rays parallel to one another) and directed perpendicularly to the diffused-light emitting layer, so that a portion of the diffused-light emitting layer is illuminated by a certain bundle of rays generated by the D65 standard illuminant, the diffused-light emitting layer is defined as partially transparent if at least 50%, preferably 70%, more preferably 85% of the light rays of the bundle are transmitted by the diffused-light emitting layer within a cone with a FWHM angular aperture not larger than 8°, preferably 4°, most preferably 2°. For the sake of completeness, it has further to be noted that also the first diffuser panel4is partially transparent.

From a practical point of view, given a standard illuminant (e.g. a D65 source) which emits light uniformly from a circular emitting surface, and given a standard observer who sees the emitting surface under a conical solid angle of 8°, preferably 4°, most preferably 2°, the luminance of the emitting surface as perceived by the observer when the partially transparent diffused-light emitting layer is interposed between the observer and the emitting surface is hence at least 50%, preferably at least 70%, more preferably at least 85% of the corresponding luminance perceived by the observer when the diffused-light emitting layer is absent.

All that having being said, as shown in FIG.11, the second light source (designated by68) may be arranged parallel to the first diffuser panel4, e.g. above it, and for example in direct contact with it.

The second light source68may comprise a second diffuser panel64and an illuminator66, the second diffuser panel64being shaped as a light guide side-lit by the illuminator66, the illuminator66being formed, as an example, by a linear stripe of LEDs or a fluorescent tube lamp, so that light emitted by the illuminator66propagates in guided-mode inside the second diffuser panel64, which diffuses it homogeneously. The second diffuser panel64may be, for example, a commercial diffuser suitable for side-lighting as, e.g., “Acrylite® LED” or “Plexiglas® LED EndLighten”. Moreover, as shown inFIG. 11, the thickness along the axis H of the second diffuser panel64is negligible compared to thickness along a direction K perpendicular to the axis H.

In a particular configuration, the second diffuser panel64is formed by a third material (e.g., a material chosen from among the materials previously listed with reference to the first material), wherein microparticles of a fourth material (e.g., ZnO, TiO2, ZrO2, SiO2, Al2O3) are dispersed; such third and fourth material do not absorb light with wavelengths in the visible range. In particular, the diameters of microparticles may range from 2 μm to 20 μm.

When in use, part of the radiation guided by the second diffuser panel64exits the second diffuser panel64while propagating along the second diffuser panel64, due to diffusion by microparticles of the fourth material. Since the second diffuser panel64has negligible thickness along the axis H compared to the direction K, the second diffuser panel64is basically transparent to radiation propagating along the axis H, but works as a diffuser for radiation propagating along the direction K.

Moreover, assuming that the second diffuser panel64is delimited on the upper and the lower side by a third and a fourth surface S3, S4, at least one out of such third and fourth surface S3, S4may be surface finished to introduce roughness. Such roughness contributes to the diffusion by the second diffuser panel64of the light generated by the illuminator66, the diffusion process being virtually homogeneous along any direction parallel to the direction K. In a per se known manner, roughness may be designed so that great part of the light generated by the illuminator66is scattered mainly through one between the third and the fourth surface S3, S4, and in particular towards the first diffuser panel4. In case at least one between the third and the fourth surface S3, S4features roughness, no microparticles need to be dispersed in the second diffuser panel64. In any case, roughness may be present on both the third and the fourth surface S3, S4of the second diffuser panel64.

In a different configuration, the second light source68includes a substantially transparent emitting surface, which is made of an OLED film. The OLED film is also capable to generate diffused light with controlled color and intensity, being at the same time transparent to the light that crosses it along a direction perpendicular to its surface.

The second light source68allows to change the color and intensity of the diffused-light component generated by lighting system1, basically without changing the color and intensity of the transmitted component. For this aim, it is possible to act on the color and intensity of the light emitted by the second light source68.

For example, aiming at reproducing the characteristics of late afternoon light, a lamp with low CCT, e.g. 2500 K, may be used as the first light source2; in this way, the color of the transmitted component is similar to the color of sunlight before sunset. Without the second light source68, the color of the component scattered by just the first diffuser panel4would be different from the color of the corresponding natural component. As a matter of fact, what happens in nature is that the sky above the observer is lit by white sunlight, i.e. by sunlight that has not crossed the atmosphere yet, having a CCT which is equal approximately to 6000 K, a much higher value than the lamp's CCT. As a consequence, the CCT of the light scattered by the sky above the observer in the late afternoon hours is significantly higher than the CCT of the light scattered by the first diffuser panel4, in case the first light source2that illuminates this latter has low CCT. However, if the second light source68is used, and particularly if the second diffuser panel64is used together with the illuminator66, and this latter is made of an ensemble of red, green, blue (“RGB”) LED emitters, it is possible to adjust the luminous flux for each of such three elements; this allows for the second diffuser panel64to generate a scattered component having color and intensity which are such that the overall component that exits the first diffuser panel4and is scattered by the first and the second diffuser panel4,64, has the desired color. In other words, the second source68allows for decoupling the color of the transmitted component from the color of the scattered component. Moreover, if a lamp with adjustable CCT is used as the first light source2, the variation of natural lighting at different times of the day can be reproduced.

Other embodiments are also possible where the second light source68is placed under the first diffuser panel4, in such a way that the light generated by the first light source2passes through the first diffuser panel4before passing through the second diffuser panel64. Moreover, additional embodiments are possible where the first and second diffuser panels4,64are physically separated.

Embodiments are also possible where the second light source68is used in the absence of the first diffuser panel4, i.e. in the absence of the Rayleigh panel. In this case the axis H is a line perpendicular to the diffuse-light emitting layer and crossing the barycenter of the diffuse-light emitting layer.

In view of the above, all the disclosed embodiments refer to a system including a first light source, a diffused-light generator and a dark chamber, wherein the diffused-light generator is shaped as a layered component delimited by an inner surface (facing the dark chamber) and an outer surface (facing the room), and the first light source is configured to emit a visible-light beam, and the dark chamber is optically coupled to the room via the diffused-light generator. Moreover, the diffused-light generator is configured to receive the visible-light beam, and to be at least partially transparent to the visible-light beam, and to transmit at least part of the visible-light beam, and to emit visible diffused light from the outer surface, and to generate a transmitted light having CCT lower than the CCT of the visible diffused light. The diffused-light generator may be substantially free from chromatic absorption or reflection, i.e. from preferentially absorbing or reflecting a limited portion of the visible-light spectrum with respect to another portion.

More in particular, the CCT of the diffused light is higher than the CCT of the transmitted light; still more in particular, the CCT of the transmitted light is not greater than the CCT of the light beam generated by the first light source. Furthermore, as already said, in the context of the present invention, the light “transmitted” by an optical element is meant as the portion of the light rays impinging onto the optical element which cross the optical element without suffering significant angular deviation, e.g. being deviated by an angle smaller than 0.1°. Therefore, an optical component is said to “transmit at least a portion” of an impinging light beam whenever it produces a transmitted light component.

As explained above, the diffused-light generator may be formed by a Rayleigh diffusing layer, i.e. a layer which selectively diffuses the short-wavelength component of the luminous radiation coming from a main light source, this Rayleigh diffusing layer being shaped, e.g. as a flat panel (as in the case of the first diffuser panel4), or as a curved panel (not shown). In addition, or alternatively, the diffused-light generator may be formed by a diffused-light source, i.e. a light source that emits diffused light from an extended layer orthogonal to the axis H, independently from the light received from the main light source. In the case of using just the diffused-light source, this source does not operate for correcting the color of the diffused light as produced by, e.g., the first diffuser panel4, but for generating the entire diffused component of the light emitted by the lighting system. In certain embodiments, the diffused-light generator may have an elongated shape, in the sense that a first circle inscribed into the inner surface has a diameter at least 1.5 times smaller, preferably two times smaller than a second circle circumscribed to the same inner surface.

Furthermore, the considerations regarding the presence of a Rayleigh diffusing layer and/or a light source emitting diffused light apply also to the variants which will be described in the following.

The advantages brought by the present lighting system are made evident by the previous description.

In detail, the present lighting system allows for an observer to perceive the existence of an unlimited space beyond the diffused-light generator, similarly to what happens in nature when the sky and the Sun illuminate a room through a window. Such result is due to the presence of the dark chamber, which is coupled to the room by means of the diffused-light generator. The dark chamber allows for perceiving an homogeneous black background for every direction along which the first and/or second diffuser panels are observed. Moreover, such effect is improved by adopting a suitable observer-to-source distance (and thus, a first and/or second panel-to-source distance), and/or by using a reflective system which reflects light rays in such a way that they feature a limited range of slopes.

Furthermore, some embodiments of the present invention give rise to the aforementioned breakthrough effect while limiting the space occupied by the lighting system. In particular, the embodiment shown inFIG. 2is an off-axis lighting system, namely a system wherein the light source and the first diffuser panel are not aligned, which allows to reducing the space occupied by the system itself, without spoiling the quality of the illumination.

Eventually, it is evident that modifications and variations can be made to the present lighting system without departing from the scope the present invention, as defined by the appended claims.

For example, the position of the light source with respect to the focus/focuses of the optical elements of the reflective system can be different than those described. Furthermore, instead of, or in addition to a converging mirror, the reflective system may comprise a diverging mirror. In addition, in order to achieve full divergence removal, at least along the y-axis direction, more complex shapes of the mirrors (e.g. free-form shapes) can be considered.

Furthermore, the form of the dark structure may be different from what has been previously shown. In fact, in order to provide a substantially uniform background, it is sufficient to form a dark structure the geometrical and/or light absorbing characteristics of which are such that, when the first light source2(and the illuminator66, if present) is on, a first structure condition applies, described hereinbelow, with reference to theFIG. 12. For simplicity, and without any loss of generality, inFIG. 12the first light source of the point-like type; furthermore, the dark structure is designated by300and is without corners, without that implying any loss of generality. The first structure condition described hereinbelow is in any case applicable also to the embodiments previously described, as an example by referring it to the characteristics of the support element10and the inner layer12. Furthermore, inFIG. 12angles are shown in a qualitative manner.

In detail, the abovementioned first structure condition provides that, given a direction sheaf (e.g., a conical sheaf)200with a top angle of at last 0.1 sterad and a sheaf axis210, at any first point220of at least a portion of the second surface S2having an area equal to at least 50%, preferably 80%, even more preferably 100%, of the area of the entire second surface S2, a first and a second luminances of the first point220, which hereinafter will be referred to as the first and second background luminances, differ from one another by no more than 50% of the first background luminance. In greater detail, the first and second background luminances are measured in a first and second observation directions230,240, respectively, the first observation direction230being parallel to any of the directions of the direction sheaf200and being non-parallel to any of the local dazzling directions250, the second observation direction240being set apart from the first observation direction230by an angular distance in the range between 0.3° and10and being non-parallel to any of the local dazzling directions250, the local dazzling directions250being the directions which are set apart by less of30from any direction260under which any point of the first light source2is seen from the first point220(given the assumption of point-like source, only one direction260is present). In greater detail, each of the first and second background luminances is formed only by the light rays which have hit the dark structure and have never passed through the room6(not shown inFIG. 12), hence which have never crossed the second surface S2coming from the room6.

As an example, referring to any of the first and second background luminances, it can be measured under the assumption of coupling the first diffuser panel4to a first anechoic chamber in the visible range, namely by assuming that the room6absorbs the 100% of the impinging light, and by carrying out the steps of:

after substituting the dark structure300with a second anechoic chamber in the visible range, measuring the luminance L1of the abovementioned first point220, in the first observation direction230; and afterwards

removing the second anechoic chamber and providing the dark structure300; and afterwards

measuring the luminance L2of the first point220, still in the first observation direction230; and

computing the difference between the luminance L2and the luminance L1.

As shown inFIG. 12, the sheaf axis210may coincide with the direction260under which the first light source2is seen from the first point220. Furthermore, the direction sheaf200and the attitude thereof relative to the first diffuser panel4are invariant with respect to the position of the abovementioned first point220on the second surface S2.

As previously mentioned, the first structure condition may be fulfilled also by the other embodiments. Therefore, it is possible, as an example, that the support element10and the inner layer12are different from what has been shown, but anyway such as to fulfill the first structure condition. As an example, the inner layer12may coat only a portion of the support element10, which in turn may be formed in more than one piece. To this regard, at least part of the dark structure may be formed by a housing of the first light source2, or by one or more screens; similarly, the support element10may feature one or more optical apertures, as an example closed by corresponding elements which are matt in the visible range, or overlain by brickworks elements.

The dark structure300may further be configured to fulfill a second structure condition, and namely to prevent that, when the first light source2is on, the abovementioned first background luminance is greater than a luminance threshold value equal to 30% of the total luminance of the first point220in the first observation direction230, this total luminance being measured under the assumption of absence of light rays coming from the room6, and hence by means of the abovementioned first anechoic chamber. Furthermore, embodiments are possible, wherein the second structure condition is fulfilled, but the first structure condition no. Furthermore, the second structure condition may be fulfilled also by the other embodiments. Therefore, as an example it is possible that the support element10and the inner layer12are different from what has been shown, but such as to fulfill, in any way, the second structure condition.

A further example of dark structure, applicable to all the embodiments previously described, is shown inFIG. 13. In this example, only a portion of the support element10is coated by a corresponding portion of the inner layer, which is referred to as the absorbing patch310. The absorbing patch310has an absorbing coefficient in the visible range substantially uniform and/or an absorbing coefficient in the visible range at least equal to 70%, preferably 90%; furthermore, the absorbing patch310is preferably edge-free and has an area at least equal to 50%, preferably 80%, of the first surface S1.

A further embodiment is shown inFIG. 14, wherein, for simplicity, reference is made to the case in which the second diffuser panel64and the illuminator66are absent; furthermore, inFIG. 14the dark structure and the reflective system are not shown. In this embodiment, a visual reference element is arranged downstream the first diffuser panel4, such, as an example, a reflecting surface320, which is delimited by an edge and is arranged so that at least one portion of it is lit, together with a corresponding portion of the edge, by the light generated by the first light source2and transmitted by the first diffuser panel4. This portion of the reflecting surface320has an area at least equal to 50%, preferably 70%, even more preferably 100%, of the area of the entire reflecting surface320. Furthermore, this portion of the reflecting surface320is such that the shortest path among the optical paths connecting the first light source2to the reflecting surface320has a length equal to at least 50%, preferably 70%, even more preferably 100%, of the maximum distance between any two points of this portion of the reflecting surface320.

As shown inFIG. 15, the visual reference element may be formed by a diaphragm350between two rooms, which delimits a corresponding aperture, which puts the two rooms in optical communications. This aperture thus forms an immaterial surface (with the exception of the edge) and has a respective portion, delimited by a corresponding portion of the edge, which fulfills the requirements mentioned a little while ago with reference to the abovementioned portion of the reflecting surface320.

In practice, referring to the embodiments shown inFIGS. 14 and 15, it occurs that, the closer to one is the ratio of the speed at which the observer moves to the speed at which he sees the first light source2moving with respect to the visual reference (the edge of the abovementioned portions of the reflecting surface320and the aperture of the diaphragm350), i.e. the closer to the visual reference is the observer, the greater is the depth effect induced by the so-called motion parallax. Furthermore, the abovementioned portions of the reflecting surface320and of the aperture of the diaphragm350may have narrow areas, as an example equal to 1/10, preferably 3/10, even more preferably ½, of the area of the second surface S2.