Description

Device for selective distribution of luminous flux emitted by a light source.

The present patent application for industrial invention relates to a device for the selective distribution of the luminous flux emitted by a light source, which consists in a distribution body made of transparent material and shaped as an internally hollow solid of revolution, with lateral wall provided, both internally and externally, with an overlapping series of horizontal refracting ribs, each of them being formed by two inclined intersecting sides. The present invention has been devised to satisfy a need that is especially felt in the lighting of retail, production, and exhibition spaces or of any other space that requires a high level of illuminance, that is to say the need to generate a high illuminance value in the spaces where work activities are carried out, in association with the need to send a marginal portion of the light in the opposite direction.

Such a need is illustrated in fig. 1 , which represents an example of photometric distribution of the light emitted by a distribution body with light source and the reference horizontal plane passing through the photometric centre, that is to say the demarcation line between two opposite vertical sections of space to be lit. Fig. 1 describes:

- the polar representation (R. P.) of an example of luminous distribution produced by a distribution body (C) with a photometric centre (O).

- the horizontal plane (P.O.) passing through the photometric centre (O). So far, the photometric distribution of the light, with special reference to high- wattage light sources, has been controlled with dome-shaped distribution bodies with suitable profile, with the light source positioned along its central axis.

The said distribution bodies are made of non-transmitting materials with specular surface, such as metal, or transmitting materials, such as

transparent plastics, with external surface provided with a series of vertical prismatic elements; in any case, for both types of distribution bodies, light control is based on the known principle of reflection. For purposes of clarity, the operating principle of these two different models of distribution bodies is illustrated in figures 2 and 3, which show the ray emitted by the light source and the ray reflected by the wall of the distribution body.

In distribution bodies made of metal, such as for example aluminium, the reflection effect is generated by the shape and internal surface of the body, which is given a specular finish.

The above is illustrated in fig. 2, which shows a generic luminous ray (A) emitted by the light source (L) that hits the internal specular surface of the distribution body in a point (P); the reflected luminous ray (B) starts from the said point (P), being characterised by a reflection angle (α) identical to the incidence angle, comprised between the emitted ray (A) and the direction perpendicular to the tangent in point (P) to the wall of the body (C). This model of metal distribution bodies is impaired by the fact that they are not capable to diffuse a suitable quantity of luminous flux outside the distribution body or upwards. Also the models made of transmitting transparent plastics, normally acrylic material or polycarbonate, use the reflection (known as "total internal reflection") generated on the external surface of the distribution body by means of reflecting prisms (T) vertically arranged along the external surface (S. E.) of the body (C) with approximately 90° angle. In such a configuration, the vertical curvature of the prisms exactly follows the vertical curvature of the wall of the distribution body.

This effect does not allow to control the direction of the light on the vertical plane, except for the control determined by the profile of the wall of the distribution body. Deviations can be obtained on the horizontal plane, but they have a limited effect, since higher deviations tend to reduce the effect of primary reflection. The above is illustrated in fig. 3, which shows two luminous rays emitted by

the light source (L).

As illustrated in fig. 3A, which is a sectional view of fig. 3 with plane B-B, the emitted ray (a) and the emitted ray (b) pass through the transparent wall of the body (C) and hit the reflecting prisms (T) that generate the reflected rays (a1 ) and (b1 ) with reflection angles (α1 and β1 ).

Fig. 3 illustrates that the reflected rays (a1 ) and (b1 ) have different directions due to the different curvature of the wall of the body (C) in points (P1 and P2) in which the emitted rays (a) and (b) hit the wall of the body, and also due to the different direction of the incident rays (a) and (b). In these models of bodies provided with vertical reflecting prisms on the external surface, the luminous flux emitted by the light source does not propagate in the space that surrounds the bodies, in spite of the fact that they are made of transparent material; vice versa, the luminous flux is reflected inside the body and distributed downwards according to different directions. There is also a third type of distribution devices of the luminous flux emitted by a light source.

This third type uses reflecting/refracting bodies made of transparent plastics, which are provided on the external surface with vertical reflecting prismatic elements (such as in fig. 3), while the internal surface is provided with a series of horizontal inclined planes situated in the central-upper section of the body and designed to refract the light.

In such a model, the refraction generated by the internal refracting elements tends to partially modify the reflection generated by the external reflecting elements, thus permitting a partial passage of the light outwards in this limited section of surface, with partial refraction of the light.

Compared with the solutions that are exclusively based on reflecting transmissive elements, these optical solutions allow for higher selective distribution of the light. In any case, reflection is the dominant physical principle for light control also for this third type of distribution bodies, since the refracting elements situated in the central-upper section of the wall of the body modifies reflection only partially in a minor portion of the total surface of the wall of the body.

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As a matter of fact, most of the surface of the body is only provided with reflecting prismatic elements, which produce reflection, so that the photometric distribution is mainly determined and affected by the reflection generated by the external reflecting elements, which interact with the profile of the wall of the distribution body.

In conclusion, all the aforementioned traditional models are impaired by the fact that light control is strongly determined and conditioned by the profile of the wall of the distribution body. In fact, for all these models, the curvilinear profile of the wall of the distribution body determines the direction of the reflected light, since the incident flux on the curvilinear wall of the body is reflected according to an angle that varies with the variation of the incident angle comprised between the emitted ray and the direction perpendicular to the tangent of the curvilinear profile of the wall of the body. The purpose of the present invention is to obtain a device for the selective distribution of the luminous flux emitted by a light source, which allows to obtain a photometric distribution not affected by the profile of the wall of the distribution body. Another purpose of the present invention is to obtain a device for the selective distribution of the luminous flux emitted by a light source, which allows to distribute the luminous flux both above and below the horizontal plane (P. O) passing through the photometric centre (O) of the polar curve. These and other purposes have been achieved with the device of the invention, which consists in a distribution body made of transparent material and shaped as an internally hollow solid of revolution, with lateral wall provided, both internally and externally, with an overlapping series of horizontal refracting ribs, each of them formed by two inclined intersecting sides. The said body can be given the profile and shape of a dome, a bell, a cone or a cylinder.

By suitably designing the inclination of the sides of the internal refracting ribs (obtained on the wall of the body that sides the light source) and of the

interfaced sides of external refracting ribs (obtained on the wall of the body opposite the light source), it is possible to generate a series of combinations of refracting elements designed to deflect the luminous flux upwards, above the horizontal plane, and downwards, below the horizontal plane, without being affected by the profile of the lateral wall of the distribution body.

This optical solution is exclusively based on the refraction of the light, providing the entire internal and external surface of the lateral wall only with refracting transmission elements, unlike all the other traditional models that are only provided with reflecting prisms or reflecting prisms partially associated with refracting transmissive elements.

According to the said optical solution, multiple combinations of angular inclinations of the inclined sides of the said external and internal refracting ribs are obtained for each point of the profile of the wall of the distribution body, so that numerous directional results of the refracted light can be designed on the vertical plane, unlike reflection-based models that are limited by the impact angle with the wall of the distribution body, as well as by the angle of the reflecting prisms, which must be approximately 90° (with slight differences according to the material used). For purposes of clarity, the description of the device according to the present invention continues with reference to the enclosed drawings, which only have an illustrative, not limiting purposes, wherein:

- figure 4 is a diagrammatic perspective view of an example of distribution body of the invention;

- figure 4A is a sectional view of a section of the lateral wall of the distribution body of fig. 4 with a vertical plane;

- figure 5 diagrammatically illustrates an example of how the luminous flux is refracted by the distribution body of the invention;

- figures 5A, 5B and 5C are three enlarged views of fig. 5 that illustrate how three different refracted rays are obtained from the same luminous ray that hits the same point of the distribution point because of a different inclination/combination of the inclined sides of the overlapping series of internal and external refracting ribs;

- figures 6 and 7 illustrate two different photometric distributions generated by the device of the invention.

With reference to figs. 4 and 5, the device of the invention is applied in an example of distribution body (C) made of transparent material and shaped as a dome with two openings at the vertical ends (B1 and B2).

The said body (C) has a lateral wall (P. L.), an internal surface (S.I.) of the lateral wall (P. L.) and an external surface (S. E.) of the lateral wall (P. L.).

As shown in figs. 4 and 4A, the lateral wall (P. L.) is provided both on the internal (S.I.) and external surface (S. E.) with an overlapping series of horizontal refracting ribs, each of them formed by two intersecting inclined sides.

The internal refracting ribs are identified with (N.R.I.) and the external refracting ribs are identified with (N. R. E.).

In fig. 5 the two inclined sides that form each rib (N.R.I.) and (N. R. E.) are identified with letter "F".

Figure 5 shows the refraction of a luminous ray (R. E) emitted by a light source (L) that hits the wall (P. L.) in a point (H) associated with an opposite pair of refracting ribs (N.R.I, and N. R. E.).

The inclination of the refracted ray (R. R.) that propagates outside the lateral wall (P. L.) depends on the inclination given to the inclined sides of the refracting ribs (N.R.I, and N. R. E.) associated with point (H).

The above is illustrated by a comparative examination of the three figures 5A,

5B and 5C, in which three different refracted rays (R. R.1 , R. R.2 and R. R.3) are generated with the same incident angle of the emitted ray (R. E.) using three different combinations of inclined sides of the refracting ribs (N.R.I and

N.R.E.).

Evidently, numerous combinations are possible for each point of the lateral wall (P. L) of the body (C).

The comparative examination of figures 5A, 5B and 5C illustrates that the different direction of the refracted light does not depend on the profile of the lateral wall (P. L.) of the body (C), which may not be curvilinear, such as in the case of a conical or cylindrical body (C).

To clarify the concept further, it can be noted that the device according to the present invention allows to generate the same photometric result from distribution bodies (C) with different profile or vice versa generate different photometric results from the same body (C). According to a preferred simplified embodiment of the present invention, the inclination of the sides of the opposite pairs of refracting ribs (N.R.I and N. R. E.) has a constant value.

In such a version, the lateral wall (P. L.) is provided both internally and externally with an overlapping series of horizontal circular uniform ribs. In this case, the photometric distribution will be identical for any radial plane passing through the vertical axis that intersects the centre of the light source

(L).

Therefore, a rotational circular shape will generate a circular projection having the photometric distribution shown in fig. 6. According to a more complex embodiment of the invention, the inclination of the inclined sides of the opposite pairs of refracting ribs (N.R.I and N. R. E.) remains constant only for a section of circumference, so that the inclination has different values in different radial planes, as shown in fig. 7A, which indicates two different radial planes (π.1 and π.2) that correspond to opposite pairs of refracting ribs (N.R.I, and N. R. E.) with sides having a different inclination.

In such a version, the lateral wall (P. L.) is provided, both internally and externally, with an overlapping series of horizontal circular ribs, each of them having consecutive sections of different configuration in terms of inclination of the inclined sides of each section.

In this second version, regardless of the presence of a distribution body (C) with rotational circular shape, a non-circular projection of the photometric distribution can be obtained, as shown in fig. 7.