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(11) | EP 1 571 391 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Street lighting system |
| (57) A street lighting system, comprising a reflector (10) essentially consisting of a
series of surfaces (11-16) with an optical function, among which, in general, there
is no geometrical continuity, and arbitrary connecting surfaces (18), not optically
controlled, which serve to give continuity to the composite surface; if the reflector
(10), thus constructed, is maintained with the outlet eye parallel to the street level,
it does not disperse the light flow upwards and also produces an illumination distribution,
on the street level, corresponding to an ideal average luminosity under pre-established
photometric conditions. |
[0001] The present invention generally relates to a street lighting system and, in particular, to an optical reflector for vehicles.
[0002] The problem of correct street lighting is particularly complex due to the high visible necessity required by the driver.
[0003] The specifications for a correct illumination of the road surface are strictly defined by national provisions, each of which is inspired by the CIE publications.
[0004] Street lighting is mainly characterized by three dimensions: average luminosity, general uniformity and longitudinal uniformity.
[0005] The average luminosity value is fixed in relation to the type of visible necessity required by the driver, which, in turn, depends on the speed and traffic, or the type of road considered (urban, suburban, motorway, etc.).
[0006] In particular, the general and longitudinal uniformity coefficient values must fall within specific ranges to allow the uniformity of the light distribution of the road surface to be considered sufficient for the type of road under examination.
[0007] The CIE regulations define a region of the carriageway in which these dimensions are calculated; for example, in a straight road, the area to be considered lies between two successive streetlamps, on the same side of the road, and the spotter is in the centre of the driving lane, at 60 meters from the nearest of the two streetlamps being considered.
[0008] Normally, an ideal lighting plant produces in the area of interest a uniform light distribution equal to a minimum value required for the type of road being considered.
[0009] Furthermore, a street lighting plant is also characterized by the dazzling effect produced to the driver's detriment, but this phenomenon will not be dealt with in the following description.
[0010] If even the light distribution of the road surface is well defined, the intensity distribution of the single light point is not equally defined, firstly because in each point, the luminosity is provided by the sum of the contributions of all the single light points and, secondly, because the luminosity depends on the reflection properties of the road surface.
[0011] The CIE regulations define two types of standard surfaces, called C1 and C2, to which reference is made in illuminating engineering calculations and which respectively represent the average behaviour of a cement surface and asphalt surface.
[0012] Due to the wider diffusion of asphalted roads with respect to those made of cement, reference will be made hereunder to asphalted roads only.
[0013] The optical behaviour of the C2 surface is thus defined by the table of reduced luminance coefficients r, wherein r = (L/E).cos3(γ) and γ is the angle between the vertical to the road surface and the direction connecting the calculation point and the light point.
[0014] Once the observer and the light point have been fixed, it is possible to calculate the distribution r on the road surface.
[0015] Let us consider for the sake of convenience, the particular case of a light point L installed at a height (H) of 8 meter and an observer O at a distance D of 60 meters from the base of the light point L, as illustrated in detail in figure 1.
[0016] Figure 2 indicates the curves relating to the reduced light coefficients r; from this figure, it can be observed that the value of r is high when x<0 (m.) and 0≤y≤2 (m.) and consequently in this region a lower illumination will be necessary for obtaining the average luminosity value.
[0017] In order to define the illumination distribution necessary for obtaining the desired luminosity, all the light points of the plant must be considered; it can be assumed, however, that the contribution of two light points which delimit the calculated area is predominant and, according to this hypothesis, only two light points adjacent to the calculated area will be considered hereunder.
[0018] From the graph of figure 2, it can be deduced that, between the two light points considered, the one which is further from the observer contributes more to the luminosity of the road surface.
[0019] For this reason, a uniform luminosity is presumably required, which is equal to the average luminosity with a single light point, that which is further from the observer between the two being considered.
[0020] In this way, the relation between the photometric solid of the light point and the luminosity of the road surface is definitely biunique and invertible.
[0021] This allows the illumination required in the area of interest, produced by the single light point, to be calculated, so that the luminosity is uniformly equal to the average luminosity.
[0022] Figure 3 illustrates this light distribution assuming that the light point is situated in x = 25 m and y = 0 m and that the area of interest extends for 25 m in the longitudinal direction of the carriageway (i.e. it is assumed that the distance between successive light points is equal to 25 m) .
[0023] As the photometric solid of the single light point must be symmetrical with respect to the surface C90, i.e. to the axis x = 25 m., the graph of figure 3 can be prolonged beyond the area of interest for the illuminating engineering calculation, by simply reflecting the level curves with respect to the axis x = 25 m (figure 4).
[0024] With respect to the requirements mentioned above, an objective of the present invention is to provide a street lighting system, suitable for producing a correct illumination distribution on the road surface according to national specifications and, in particular, very similar to the ideal solution illustratively shown in figure 4.
[0025] A further objective of the present invention is to provide a street lighting system, whose reflector does not disperse a light flow upwards (γ>90°), if maintained with the outlet eye parallel to the road surface.
[0026] Another objective of the invention is to provide a street lighting system which is extremely versatile and reliable, in an extremely simple manner and with relatively limited costs, by virtue of the advantages obtained, with respect to traditional street lighting systems.
[0027] These objectives according to the present invention are achieved by providing a street lighting system according to claim 1, to which reference should be made for the sake of brevity.
[0028] The characteristics and advantages of a street lighting system, according to the present invention, will appear more evident from the following illustrative but non-limiting description, referring to the further enclosed schematic drawings, in which:
- figure 5 shows a perspective and schematic view of a first embodiment of a reflector of the street lighting system, according to the present invention;
- figure 6 schematically represents the spots produced on the ground by each of the surfaces on the reflector of the street lighting system, according to the present invention, together with a schematic plan view of the above reflector;
- figure 7 represents a second embodiment of the reflector of figure 5, designed with a continuous surface.
[0029] As already specified above, in order to produce a correct illumination of the road surface, the street lighting system according to the invention must be provided with a reflector suitable for satisfying two main requisites.
[0030] First of all, if it is maintained with the outlet eye parallel to the road level, it must not disperse its light flow upwards (γ>90°), and secondly it must produce an illumination distribution very similar to that represented in figure 4 enclosed.
[0031] In projecting a reflector which satisfies this second requisite, it should be considered that the above reflector consists of a cold moulded aluminum sheet and, as such, has a considerable light diffusion.
[0033] In the drawing of the reflector according to the invention, generically indicated with 10 in figure 5, it is assumed that the surface has an intermediate behaviour between that of a perfectly specular reflector and that of an ideal diffuser.
[0034] In any case, it is presumably not possible to neglect the diffused component of the light reflected.
[0035] In order to obtain the illumination diffusion represented in figure 4, the reflector 10 has been designed with the following technical characteristics.
[0036] The reflector 10 is first of all suitable for producing a discontinuous light distribution and with strong variations, assuming that the surface is perfectly specular; furthermore, it produces the desired illumination if the actual diffusion characteristics of the metal sheet are considered.
[0037] In practice, according to the present invention, the reflector 10 essentially consists of six surfaces with an optical function, symmetrically distributed, with respect to the axis X, on the reflector 10 and among which there is generally no geometrical continuity; figure 5 shows four of the above six surfaces, indicated with 11, 12, 13 and 14, respectively.
[0038] The reflector 10 additionally consists of arbitrary connecting surfaces (some of which are shown and indicated with 18 in figure 5), not optically controlled, which only serve to give continuity to the composite surface of the reflector 10.
[0039] Assuming that all the surfaces of the reflector 10 are specular, the spots produced on the ground by each of these are represented in figure 6; the same figure 6 indicates the calculation area 17 on the road surface and a reflector scheme 10, shown in a plan view (not in scale with the rest of figure 6 and with the other enclosed drawings), so as to indicate the correspondence between the surfaces 11-16 which form the reflector 10 and the ground spots, indicated with 21-26 respectively.
[0040] In particular, the surface 11 of the reflector 10 corresponds to the ground spot indicated with 21 in the calculation area 16, whereas the surface 12 of the reflector 10 corresponds to the ground spot indicated with 22 in figure 6.
[0041] Analogously, the same figure 6 indicates, with 23, 24, 25 and 26 respectively, the ground spots corresponding to the surfaces 13, 14, 15 and 16, which form the reflector 10.
[0042] Bearing in mind the light scattering phenomenon on the part of the metal sheet of the reflector 10, the light distribution on the ground becomes much more continuous, even if it is not necessarily what is requested.
[0043] In order to obtain the desired result, an empirical procedure can be adopted by exploiting three degrees of liberty, whereby:
1) it is possible to move the ground spots indicated with 21, 22, 23 and 24 (and consequently 25 and 26 by symmetry) on the road surface;
2) it is possible to vary the light distribution within the single spot;
3) it is possible to vary the area of the optical surfaces corresponding to the regions 11, 12, 13, 14, 15 and 16 of the reflector 10.
[0044] These three operations create changes in form and extension of the single optical surfaces 11-16, but not their positioning inside the reflector 10 or correspondence between optical surfaces 11-16 and luminous spots 21-26 illustrated in figure 6.
[0045] Finally, in order to make the surface of the reflector 10 more continuous, to avoid the formation of live edges in the cold moulding process of the metal sheet, the connecting surfaces 18 of the optical surfaces 11-16 can be designed arbitrarily, without varying the overall optical behaviour of the reflector 10.
[0046] Figure 7 shows an example of a reflector 10 with a continuous surface projected in the manner described above.
[0047] The characteristics of the street lighting system, object of the present invention, as also its advantages, are evident from the above description.
[0048] Finally, numerous variants can obviously be applied to the lighting system in question, all included in the novelty principles inherent in the inventive concept. It is also evident that, in the embodiment of the invention, the materials, forms and dimensions of the details illustrated can vary according to the demands and can be substituted with other technically equivalent alternatives.
1. A street lighting system, of the type comprising at least one reflector (10) characterized in that said reflector (10) has a composite surface essentially consisting of a series of
first surfaces (11-16) with an optical function, and arbitrary connecting surfaces
(18) between said first surfaces (11, 16), said connecting surfaces (18), not optically
controlled, being envisaged to give continuity to the composite surface, so that said
if said reflector (10) is maintained with the outlet eye parallel to the street level,
it does not disperse the light flow upwards and also produces an illumination distribution
corresponding to an ideal average luminosity under pre-established photometric conditions.
2. The street lighting system according to claim 1, characterized in that said pre-established photometric conditions envisage the use of at least one light
point (L) adjacent to a calculation area (17) on the road surface, so that the relation
between the photometric solid of said light point and the luminosity of the road surface
is biunique and invertible, in order to calculate the illumination within said calculation
area (17), produced by a single light point (L), which is such that the luminosity
is uniformly equal to a pre-established average luminosity value.
3. The street lighting system according to claim 2, having a photometric solid symmetrical
with respect to the orthogonal surface to the axis of the carriageway, characterized in that the calculation area (17) extends in a longitudinal direction of the carriageway
for a distance which is double the distance between two successive light points (L)
of the plant.
4. The street lighting system according to claim 1, characterized in that said reflector comprises a cold moulded aluminum sheet, surface-treated to increase
its reflectance specular component, but that in spite of this it has a considerable
diffused component.
5. The street lighting system according to claim 4, characterized in that said reflector (10) has a surface with an intermediate behaviour between that of
a perfectly specular reflector and that of an ideal diffuser, said reflector (10)
also having at least one reflected light diffused component.
6. The street lighting system according to claim 1, characterized in that said reflector (10) essentially consists of six surfaces (11-16) with an optical
function, between which there is no geometrical continuity.
7. The street lighting system according to claim 6, characterized in that said surfaces (11-16) are symmetrical with respect to an axis (X) of said reflector
(10) and are specular, said surfaces (11-16) also being in biunique correspondence
with the spot (21-26) produced on the ground by each of these.
8. The street lighting system according to claim 7, characterized in that said spots (21-26) produced on the ground can be moved on the road surface and/or
each single spot (21-26) can internally vary the light distribution.
9. The street lighting system according to claim 8, characterized in that said optical surfaces (11-16) of the reflector (10) have varying forms and extensions,
but their positioning inside the reflector (10) and the correspondence between said
optical surfaces (11-16) and said luminous spots (21-26) are fixed.
10. The street lighting system according to claim 1, characterized in that said reflector (10) is produced with a continuous surface.