Abstract:
In various embodiments, a street lighting device with a first light source for illuminating the street plane from above is provided. The device may include a second light source located at a closer position to the street plane than said first light source; a sensor sensitive to the occurrence of conditions of reduced ambient visibility; and a controller connected to said sensor and capable of activating said second light source in the presence of said conditions of reduced ambient visibility.

Description:
TECHNICAL FIELD 
       [0001]    The present description relates to street lighting devices. The description is particularly concerned with the possible application to street lighting in conditions of poor ambient visibility, caused for example by the presence of fog. 
       DESCRIPTION OF THE RELEVANT PRIOR ART 
       [0002]    A street lighting device of the most commonly used type (such as a lamp post) comprises a structure  10  which supports at a certain height a light source  12  intended to project light radiation downward toward the street plane S. 
         [0003]    As shown schematically in  FIG. 1  of the appended drawings, this form of lighting is such that, in conditions of reduced visibility, for example in the presence of fog or other atmospheric precipitation such as rain, snow or smoke, the lighting of the street plane S is far from optimal. It may even be the case that visibility at the level of the street plane S is worsened by the effect of the lighting. Even on lighted stretches of road, drivers may therefore always prefer to use any fog lamps which are available on their vehicles. 
         [0004]    The inventors have observed that any worsening of visibility as a result of the switching on of street lighting is due to the fact that, in these conditions, the degree of visibility of the street plane S by an observer O (such as a driver) can be modeled as the superimposition of two components, namely:
       a “signal” component, corresponding to the light emitted from the observed scene, which diffuses (back) toward the observer O the light radiation originating from the source  12  and from any vehicle headlights that may be present;   a “noise” component, corresponding to the light from the source  12  diffused by diffusion sources DS such as fog droplets, raindrops, snowflakes or particles of smoke.       
 
       OBJECT AND SUMMARY OF THE INVENTION 
       [0007]    The object of the invention is to overcome the problems arising from the unsatisfactory operation of street lighting devices in the conditions described above. 
         [0008]    According to the invention, this object is achieved by means of a device having the characteristics specifically claimed in the claims below. 
         [0009]    The claims form an integral part of the technical teachings provided herein in relation to the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE APPENDED DRAWINGS 
         [0010]    The invention will now be described, purely by way of non-limiting example, with reference to the appended drawings, in which: 
           [0011]      FIG. 1  has been described above, 
           [0012]      FIG. 2  shows one embodiment, 
           [0013]      FIGS. 3 to 5  show the operating principles of one embodiment, and 
           [0014]      FIGS. 6 and 7  show some developments of embodiments. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0015]    The following description illustrates various specific details intended to provide a deeper understanding of the embodiments. The embodiments may be produced without one or more of the specific details, or may use other methods, components, materials, etc. In other cases, known structures, materials or operations are not shown or described in detail, in order to avoid obscuring various aspects of the embodiments. 
         [0016]    The reference to “an embodiment” in this description is intended to indicate that a particular configuration, structure or characteristic described in relation to the embodiment is included in at least one embodiment. Therefore, phrases such as “in an embodiment”, which may be present in various parts of this description, do not necessarily refer to the same embodiment. Furthermore, specific formations, structures or characteristics may be combined in a suitable way in one or more embodiments. 
         [0017]    The references used herein are purely for convenience and therefore do not define the scope of protection or the extent of the embodiments. 
         [0018]    In the drawings, the reference  10  indicates the whole of a street lighting device which, in the embodiment considered here, takes the form of a pole or lamp post provided at its upper end with a light source  12  which can, for example, be an LED lighting module (lamp or luminaire). 
         [0019]    In various embodiments, the lamp  12 , which is a first light source for lighting the street plane S from above, operates by projecting a light beam  12 A downward toward the street plane. For this purpose, the lamp  12  can be supported by a pole or column  14 . It will be appreciated that the use of this specific suspension or support structure is not essential: various embodiments may, for example, make use of suspension on an overhead line, mounting on a gateway, support by means of a bracket affixed to the facade of a building, or other arrangements. 
         [0020]    The reference  16  indicates another light source, which can also be an LED lighting module for example, and which is intended to serve as a further source of light radiation located in the lower part of the device  10  so as to be at a position closer to the street plane S than the first light source  12 . In other words, the second light source is at a lower position than the first source  12 . 
         [0021]    It will be evident from  FIG. 2  that, by comparison with the lighting beam  12 A of the first source  12  (which is projected onto the street plane S from a position which can be considered azimuthal or approximately azimuthal), the beam of radiation  16 A produced by the second source  16  reaches the street plane S from a lesser height and travels in a much more inclined, quasi-horizontal direction. 
         [0022]    The inclination of the beam  16 A depends on the height of mounting of the second light source  16 . In some embodiments, this height is set at rather low levels, of the order of several tens of centimeters, for example at levels approximately equal to the height at which the fog lamps of motor vehicles are located with respect to the street plane. The values concerned may therefore fall within the range of 15 to 60 cm, for example. 
         [0023]    The reference numeral  18  indicates a sensor capable of identifying the occurrence of conditions of reduced ambient visibility. The sensor can therefore be of the type known as a “twilight sensor”, used to switch on lighting systems in the area of buildings in conditions of reduced ambient light levels. 
         [0024]    While it can also be used to detect the occurrence of conditions of reduced ambient visibility and cause street lighting to be switched on (although this function may be served by a central “twilight” system controlling a plurality of devices), in various embodiments the sensor  18  is mounted at a certain distance from the first source  12  (in the proximity of the second source  16 , for example), at a position such that it can be impinged upon by the radiation emitted by the first light source  12 . Thus the sensor  18  can detect—when the source  12  is switched on—the fact that the light radiation emitted by the source  12  is subject to diffusion, for example by fog, smoke or other diffusion sources DS. 
         [0025]    By adjusting the threshold of sensitivity of the sensor  18  (according to known principles), it is therefore possible to distinguish between:
       the situation shown schematically in  FIG. 3 , in which the lamp  12  is assumed to be switched on, for example at night, in normal ambient and atmospheric conditions (in the absence of fog or other phenomena having a negative effect on visibility); and   the situation shown schematically in  FIG. 4 , in which it is again assumed that the lamp  12  is switched on, but this time in the presence of fog or other DS phenomena having a negative effect on visibility: this is because these phenomena invariably cause a reduction in the intensity of the light radiation which impinges upon the sensor  18 , regardless of the intensity of radiation emitted by the source  12 .       
 
         [0028]    In the latter case (that is to say, when the sensor  18  detects the occurrence of conditions of reduced visibility), a control device  20  which receives the output signal of the sensor  18  acts on the light sources  12  and  16  by switching on the light source  16 , as shown schematically in  FIG. 5 . 
         [0029]    As mentioned previously, the source  16  is closer to the street plane S than the source  12 , and it can therefore light the street plane S more effectively, being assisted in this by the orientation of the beam  16 A which it produces. These factors are also relevant for the possibility of making the edges of the street easier to identify, for example by drivers traveling along a street to which the plane S corresponds. 
         [0030]    In various embodiments, the light radiation  16 A emitted by the source  16  can have characteristics which are at least marginally different from those of the radiation  12 A produced by the main light source  12 . 
         [0031]    In various embodiments, the auxiliary source  16  can generate a “warm” white radiation or a radiation having a colored component, such as a red component, which can be perceived as such and is therefore easier to distinguish as originating from a light source intended to improve visibility and safety in adverse atmospheric conditions. 
         [0032]    In various embodiments, the module  20  can switch on the source while keeping unchanged the intensity of the radiation produced by the first light source  12 . 
         [0033]    Since, as has been mentioned, the diffusion of this radiation, by fog for example, is one of the causes of the possible worsening of visibility, in various embodiments the module  20  can act to reduce the intensity of the radiation produced by the source  12  when the source  16  is switched on. 
         [0034]    In various embodiments, the light sources  12  and  16  can be two separate light generators (such as two LED-type “light engines”) which can be switched on selectively (with emission levels which can be controlled, depending on the embodiment, in on/off mode or with an emission intensity control or “dimming” function). 
         [0035]    In various embodiments, the light sources  12  and  16  can be two different diffusion points for the light radiation produced by a single light generator, located for example in the device  10 . In various embodiments, this single light generator can be connected to the two sources  12  and  16  by optical waveguides, with the provision of an optical switch that can be actuated to vary selectively (in a complementary way, for example) the intensity of the radiation sent toward the first source  12 , located at the “high” position, and the intensity of the radiation sent toward the second source  16 , located at the “low” position. Optical switches of this type are known in the technical field of fiber optic communications. However, it is not essential to use fiber optics, since the propagation of optical radiation from a single generator toward two (or more) different diffusion sources  12  and  16  with selective variation of the corresponding levels of relative intensity of the radiation sent to the two diffusion points can also be achieved by the propagation of optical radiation in free air. The switching function can be provided according to various principles, for example by using an electro-optical device (such as a liquid crystal device) or by means of a mirror and/or prism structure which is motorized and is therefore selectively orientable. 
         [0036]    Different choices may also be made regarding the possible location of a single light radiation generator capable of supplying a plurality of light sources  12  and  16 . 
         [0037]    In various embodiments, this generator can be located in the upper part of the device  10 , and can even form part of the source  12 , with provision for “tapping off” from the source  12  a selectively controllable quantity of radiation to be sent toward the source  16 . 
         [0038]    In various embodiments, this generator can be located in the lower part of the device  10 , and can even form part of the source  16 , with provision for “tapping off” from the source  16  a selectively controllable quantity of radiation to be sent toward the source  12 . 
         [0039]      FIGS. 6 and 7  refer to various embodiments in which part of the device  10  between the upper light source  12  and the lower light source  16  can be made from an optically diffusive (or illuminable) material which, in conditions of reduced visibility, can be activated, for example by diverting toward it some of the radiation produced by the light generator or generators which supply the sources  12  and  16 , thereby making the structure of the device  10  luminous and thus more visible, as shown schematically in  FIGS. 6 and 7 . 
         [0040]    Consequently, various embodiments can increase visibility, in the presence of fog or smoke for example, by preventing or at least minimizing the phenomenon of diffusion (scattering) of the light radiation produced by the light source  12  located at the upper end of the device  10 . In the embodiments shown in  FIGS. 6 and 7 , the illumination of the support structure of the device  10  makes it possible to provide information on the direction of a street on which a plurality of devices  10  are located to a driver who has to drive a vehicle along the street, without directly interfering with his direction of view. 
         [0041]    Naturally, the principle of the invention remaining the same, the details of construction and the forms of embodiment may be varied significantly with respect to those illustrated in the form of non-limiting examples only, without thereby departing from the scope of protection of the invention as defined in the attached claims.