The present description relates to lighting devices.

One or more embodiments may be employed, for example, in streetlighting applications.

In technical lighting applications, e.g. in streetlighting, the need is felt of luminaires having design parameters or lighting patterns which may fulfil various road lighting requirements, guarantee proper lighting uniformity and avoid glaring for the drivers (called "observers") travelling along each lane, with a limited light cut off at the road edges (so called "surrounding ratio").

The target values of these parameters may vary according to the different road classifications (ME1, ME2, S1, CE0, ...) and according to various factors (pole interspacing, pole height, etc.) which may impact on performance levels.

Various implementations may involve the use of light radiation sources, e.g. solid-state LED radiation sources, combined with lenses. Each lens is adapted to provide a certain radiation pattern, with the possibility to fulfil road requirements in terms of light distribution on the road surface: by increasing the number of sources and lenses it is possible to increase the lighting flux up to the level required by the standards.

Some implementations envisage a combination of different types of lenses (e.g. with different lighting patterns) and the assembly ("convolution") of the various radiation patterns originates the required final radiation pattern.

The implementations based on the use of lenses are subjected to some drawbacks, which must be born in mind during development and production.

The first important factor is the distance of the lens from the light radiation source: factors such as the temperature of the lens and/or the blue light density, for example from a LED, may degrade the performance of the polymer which forms a polymeric lens.

The use of glass lenses may solve some of these drawbacks, but it may involve disadvantages as regards design and cost constraints.

Another factor to consider is the effect of tolerances on optical performances: for example, mechanical tolerances from the manufacturing and assembling process are comparable to the lens focal distance (around 1/10 mm in both cases); therefore, a given lens may be optimized only for a specific source of light radiation, e.g. only for one specific LED.

In addition, some lighting sources may be visible from all directions and cause discomfort to observers, with a possible undesired light spillage at high angles.

Other implementations may envisage the use of reflectors. They may be freeform reflectors for clustered solutions, or small freeform/conic shaped reflectors which are coupled to each light radiation source in distributed solutions. A drawback of these solutions regards optical efficiency, which may be reduced by multiple reflections and by the limited reflectivity of the reflector (usually about 85%). Moreover, in the case of freeform reflectors, it is necessary to consider the design complexity.

More specifically, the invention relates to a lighting device according to the preamble of claim 1, which is known e.g. from GB 2 024 397 A. Other documents of interest for the invention include, e.g.: US 6 382 803 B1, WO 2010/016118 A1, US 2007/206384 A1, US 4 694 382 A and US 2008/219008 A1.

One or more embodiments aim at overcoming the previously outlined drawbacks.

According to one or more embodiments, said object is achieved thanks to a lighting device having the features specifically set forth in the claim 1 that follows.

One or more embodiments may also refer to a corresponding method.

The claims are an integral part of the technical teaching provided herein with reference to the invention.

One or more embodiments allow the achievement of one or more of the following advantages:

• flexibility and reduced complexity in achieving a tailored radiation pattern for a specific road scenario,
• flexibility in adapting the solution to different applications, e.g. for technical street lighting,
• limited dependence on manufacturing and assembling tolerances,
• higher optical efficiency with respect to current reflectors,
• reduced light spillage and glare at high angles.

One or more embodiments will now be described, by way of non-limiting example only, with reference to the enclosed Figures, wherein:

• Figure 1 schematically shows a possible application scenario of embodiments,
• Figure 2 is the view of a reflector according to embodiments,
• Figures 3 and 4 are perspective views of a reflector according to embodiments,
• Figures 5 to 8 are various representative diagrams of implementation criteria of embodiments,
• Figures 9 to 11 exemplify the operation of embodiments,
• Figures 12 and 13 show possible implementations of embodiments, and
• Figures 14 and 15 show further embodiments.

It will be appreciated that, for a better clarity of illustration, the parts visible in the Figures are not to be considered necessarily drawn to scale.

In the following description, numerous specific details are given to provide a thorough understanding of one or more exemplary embodiments. The embodiments may be practiced without one or several specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring various aspects of the embodiments. Reference throughout this specification to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the possible appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

The headings provided herein are for convenience only, and therefore do not interpret the scope or meaning of the embodiments.

Figure 1 shows a possible application context of one or more embodiments, specifically in the field of technical street lighting.

At any rate, the reference to such a possible application field is merely exemplary and not limitative of the embodiments.

Specifically, Figure 1 shows a part of a road S, of indefinite length, having a width w and being lit by luminaires 10 mounted e.g. on poles P. We may assume for example that luminaires 10 may be separated by distance i, may be placed at a height h and may be mounted on poles P having the base at a certain distance from the edge of the road.

In one or more embodiments, luminaires 10 may comprise (e.g. mounted in a respective housing, not visible in the Figures) a reflector body 12, e.g. of a molded material, such as a lightweight metal material or plastic.

Reflector 12 is designed to be coupled to a light radiation source L adapted to comprise for example an electrically powered light radiation source.

According to the invention the source is an LED source mounted on a PCB (Printed Circuit Board, not visible in the drawings).

In any case, the specific features of the light radiation source L destined to be associated to reflector 12 are not in themselves a compulsory aspect of the embodiments.

In one or more embodiments, light radiation source L may be designed to be placed in a given position, marked by point F. For simplicity of illustration, source L will hereinafter be identified with point F, therefore assuming for simplicity the presence of a point-shaped light radiation source.

The reflector 12 may have the function of reflecting the light emitted from light radiation source L, arranged in position F, towards an illumination space adapted to be identified, for instance, with road surface S.

According to the invention, reflector 12 has an internal reflective surface having a substantially ribbon-like shape, possibly of a constant or substantially constant height.

Said reflective surface is therefore ideally enclosed between two end planes.

According to the invention, light radiation source L (point F) is placed at one of such end planes, i.e. it may lie in one of such planes or in the vicinity thereof.

Due to such placing in an end position, the light radiation emitted from source L may propagate towards said reflective surface, in order to be reflected thereby (according to ways described in the following), so as to be projected out of luminaire 10 towards the illumination space, i.e. the space that must be lit (for example road surface S of Figure 1).

In one or more embodiments, as exemplified in the Figures, reflector 12 may have itself a generally ribbon-like shape. Said ribbon-like reflective surface may then be simply comprised of the inner surface of reflector body 12, shaped and/or treated (e.g. with an aluminising treatment) so as to have (high) reflectivity.

According to the invention, said reflective surface is a multi-faceted surface, comprising several reflective sides or facets.

In one or more embodiments, said multi-faceted reflective surface may comprise:

• a first and a second opposed reflective sides, respectively front side 120 and back side 122, and
• two further end sides joining opposed sides 120 and 122 to each other.

The denomination of opposed sides 120 and 122 as "front" and "back" sides (ideally referred to a possible orientation of reflector 12 with respect to road surface S in the Figures) is merely exemplary, and it only aims at facilitating the description and the comprehension of the embodiments. It must not therefore be interpreted as limitative of the embodiments.

As better explained in the following, each of the front 120, back 122 and end 124 sides is shaped and/or oriented so as to reflect the radiation coming from radiation source L, while directing it in a different direction of the illumination space.

In one or more embodiments, as exemplified in the annexed Figures, said multi-faceted reflective surface comprising sides or facets 120, 122 and 124 may be an annular surface, e.g. with the shape of a closed loop.

In one or more embodiments, all said multi-faceted surface may be reflective. In one or more embodiments, said multi-faceted surface may comprise separating portions between reflective portions.

In one or more embodiments, as exemplified in Figures 2 to 12, the front 120 and back 122 sides, on one hand, and the end sides 124, on the other hand, may constitute respectively the major and the minor sides of a multi-faceted reflective surface the plan view whereof is an approximately rectangular broken curve, the light radiation source L (point F) being arranged approximately in the middle (see for example the plan view of Figure 2), i.e. in a central symmetry plane of the reflective surface.

In one or more embodiments, as exemplified in Figures 14 and 15, the multi-faceted reflective surface comprising facets or sides 120, 122 and 124 has on the contrary a substantially asymmetrical plan view.

In one or various embodiments, each of the sides 120, 122, 124 constitutes a portion of the (internal) reflective surface of reflector 12, being able to reflect the light radiation of source L towards the illumination space in an independent way, i.e. via a single reflection: for example, a ray emitted by radiation source L meets the reflective surface only once.

In one or more embodiments, the front side 120, the back side 122 and each of the end sides 124 of the reflective surface is so to say "dedicated" to sending the light radiation reflected thereby towards a direction of the illumination space which corresponds to a respective area of road surface S.

This possible operating mode is schematically exemplified in Figures 9 to 11, wherein:

• the terminal or end sides 124 may be designed to reflect the radiation of source L towards two end regions S3 of the lit road surface S below luminaire 10 (Figure 9),
• back side 122 may be designed to reflect the radiation of source L towards a portion S2 of road surface S on the side opposite the side where luminaire 10 is mounted on respective pole P (Figure 10), and
• front side 120 may be designed to reflect the radiation of source L towards a portion S1 of the road surface S on the same side where luminaire 10 is mounted on the respective pole P (Figure 11).

In order to be clearly understood and without limiting purposes, one or more embodiments as exemplified herein may be used in a context as the one explained with reference to Figure 1, wherein the height h of poles P approximately corresponds to the width w of road S, and the distance i separating poles P (i.e. luminaires 10) is approximately 3-4 times the height h.

By observing Figures 9 to 11 it is moreover possible to understand that, in one or more embodiments, a reflecting mechanism may be implemented whereby at least some of the light beams reflected by the various facets or sides 120, 122 and 124 may cross each other on the propagation path in the illumination space.

For example, as schematically shown in Figure 9, illumination beams L3 reflected by sides 124 and directed towards the end regions S3 may cross while exiting luminaire 10, so that (referring by way of example only to the arrangement of Figure 9):

• light radiation L3 reflected by plane 124 on the right is directed towards region S3 of road surface S disposed on the left, and
• light radiation L3 reflected by plane 124 on the left is directed towards region S3 of road surface S disposed on the right.

In a similar way, as schematically shown in Figures 10 and 11, illumination beams L1 and 12 reflected by front side 120 and back side 122 may cross while exiting luminaire 10, too, so that, always referring by way of example only to the relative arrangement shown in Figures 10 and 11:

• light radiation L2 reflected by back plane 122 is directed towards the upper region S2 of road surface S (i.e. the region farther away from luminaire 10), and
• light radiation L1 reflected by front plane 120 is directed towards the lower region S1 of road surface S (i.e. the region closer to luminaire 10).

Figures 6 to 8 exemplify various criteria which may be used, in one or more embodiments, to implement sides 120, 122 and 124 of the multi-faceted reflective surface of reflector 12 according to parametric curves (ellipsoids, parabolas, spheres).

For example, in one or more embodiments, the reflective surfaces which correspond to the end sides 124 may be implemented so as to have a parabolic surface (a paraboloid), the focus of the parabola being disposed at point F where light radiation source L is arranged, and the axis of the parabola/paraboloid which describes the profile of said parabolic surface being oriented so as to direct the reflected radiation for example towards the areas S3 of the road surface which are farthest away from the mounting position of luminaire 10.

In one or more embodiments, one or more parabolic profiles may be used, according to the space which must be lit, with the possibility of aiming each parabolic profile towards a different target area.

The Figures exemplify moreover, with reference to the front side 120 and the back side 122, the possibility to give the sides of the reflective surface a further multi-faceted shape, wherein one or more sides 120, 122 and 124 of the multi-faceted reflective surface comprise in turn several portions or parts.

For example, front side 120 may have a general gull-wing shape, with two symmetrical portions (referring to an ideal plane passing through point F) each of which comprises:

• a proximal part 120a,
• a middle part 120b, and
• a distal part 120c.

As used herein, the terms "proximal" and "distal" refer to the relative arrangement with respect to source L.

A similar relative arrangement is also visible in Figures 14 and 15, wherein the reflective surface has an asymmetrical shape.

In one or more embodiments, at least one of the sides (e.g. the back side 122, in the embodiments exemplified in the Figures) may be implemented as a Fresnel reflector, i.e. with a reflective surface divided into various facets F1, F2, F3, ... each of which may be named a "Fresnel facet".

In one or more embodiments, various facets F1, F2, F3, ... may be oriented vertically with respect to the lying plane of source L.

In one or more embodiments, the profile of the facets of the Fresnel reflector may be described by a parametric curve.

For example, the profile of each Fresnel facet may be described by a parabolic equation, wherein the focus of the parabola may be arranged at point F, where the light radiation source L lies, and the axis of the parabola/paraboloid describing the profile of the facet surface may be oriented so as to direct the reflected radiation towards a respective portion SF1, SF2, SF3 (see Figure 5 above) of road surface S, i.e. in a respective direction of the illumination space.

Figure 8 exemplifies how such a parametric criterion may be applied to different sides, so that for example the radiation reflected by one of the end sides 124 and the radiation reflected by the distal portion 120c of front side 120 are directed towards respective portions S3 and S31 of road surface S, therefore, once again, in respective directions of the illumination space.

In one or more embodiments, one or more sides of the reflective surface (e.g. the facets of the Fresnel reflector of the back side 122) may optionally be filled with so-called "pillows" in order to broaden and smooth the light distribution.

In one or more embodiments it is therefore possible to light the whole road surface S in a uniform way.

As exemplified in Figures 12 and 13, in one or more embodiments the reflector body 12 may be formed by two parts 12a, 12b, which may be adapted for example to be coupled on a plane which is parallel to the lying plane of a PCB on which the light radiation source L is mounted.

The joining of both parts 12a, 12b may take place for example by ultrasonic welding, hot melting or gluing. Alignment pins 12c may optionally be provided which may insert in corresponding openings 12d, as exemplified in Figure 12.

Figures 12 and 13 further highlight the broken line shape of the plan profile of parts 12a and 12b.

In one or more embodiments it is possible to join both parts 12a, 12b by snap-fit formations, e.g. comprising spring teeth 12e engaging corresponding eyelets or openings 12f.

Similar solutions may be adopted in one or more embodiments, for reflectors 12 having an asymmetrical structure, as exemplified in Figures 14 and 15.

One or more embodiments as exemplified herein overcome possible limitations due to the distance from the light radiation source, because they enable an arrangement of the reflective surfaces at a farther distance from the light radiation source than it would be possible with a lens. The consequence is a lower irradiation of the optical surfaces, with a lower operating temperature and a lower light absorption in the blue range.

In one or more embodiments, the use of a reflector may be competitive in terms of cost as compared to the use of lenses, both in extended light radiation sources and in clustered or spread sources.

In one or various embodiments, the light radiation emitted by the source is optically masked by the reflector, i.e. it is not visible by an observer practically from all viewpoints. This is particularly true for angles of 75-90° with respect to the reflector axis, which reduces the glare perceived by the observers as compared with lenses.

One or more embodiments may show a reduced sensitivity towards manufacturing and assembling tolerances, for example because the parametric focal distance is higher in comparison with mechanical tolerances.

In one or more embodiments, the possibility to implement reflective sides 120, 122, 124 as parametric reflectors may simplify the design from an optical point of view, because it requires the handling of fewer parameters (focus, curvature, aiming direction), therefore simplifying the designing activity. Moreover, explicit equations are available to determine the projection of source L in the illumination space (e.g. on the lit road surface) given the position of the radiation source.

In one or more embodiments, the fractioning of the reflective surface, e.g. the creation of Fresnel facets that are oriented vertically with respect to the light radiation source F, allows for tailoring the light source in the different areas of the lighting space, e.g. on the road surface to be lit.

In one or more embodiments it is possible, for example, to modify each surface portion (e.g. each Fresnel facet) according to the application scenario.

One or more embodiments achieve a high optical efficiency as well, because the reflector does not cover the light radiation source completely.

In one or more embodiments, the reflective source acts mainly through single reflection interactions, with the possibility for example to use the various elements of the reflector (e.g. various Fresnel facets) to direct the light radiation in controlled directions in the illumination space, enabling to direct a higher amount of light towards the illumination space.

One or various embodiments offer a high level of flexibility in tailoring the radiation pattern: providing independent reflective portions (for example independent Fresnel facets, each operating on a respective portion of the radiation pattern) makes it easier to adapt to different road scenarios.

For example, one or more embodiments may be used in contexts wherein, as previously mentioned, the mounting height h of luminaires 10 approximately corresponds to the width w of road surface S, and the distance i between neighbouring luminaires 10 amounts for example to 3.5 times the height h. Moreover, the possibility is given to adapt the amount of "overhang" of luminaire 10 projecting above the road surface (which is given by distance o of Figure 1) and of a possible tilting.

Of course, without prejudice to the basic principle, the details and the embodiments may vary, even appreciably, with respect to what has been described herein by way of non-limiting example only, without departing from the extent of protection.

The extent of protection is defined by the annexed claims.