EP1709360A1

EP1709360A1 - System for illuminating large areas in an even or defined manner

Info

Publication number: EP1709360A1
Application number: EP05706675A
Authority: EP
Inventors: Matthias Stier; Werner Hoffman
Original assignee: Fresnel Optics GmbH
Current assignee: Fresnel Optics GmbH
Priority date: 2004-01-21
Filing date: 2005-01-10
Publication date: 2006-10-11
Anticipated expiration: 2025-01-10
Also published as: WO2005071310A1; ATE371145T1; DE502005001309D1; DE102004004261B3; EP1709360B1

Abstract

The invention relates to a system for illuminating large areas in an even or defined manner. The aim of the invention is to provide a system with which large areas having the defined parameters can be illuminated in an inexpensive and variable manner, said system comprising at least one reflective element that is relatively compact. According to the inventive system, light (1') collimated by a light source (1) is directed onto at least one reflecting element (2) having a Fresnel structure reflecting surface. The reflecting element is provided at least in some areas with a disturbance flank-free Fresnel structure having varying angle inclinations relative to the imminent collimated light. The collimated light is collected by these effective flanks and is scattered by the respectively adjacent effective flank.

Description

Arrangement for uniform or predeterminable lighting of large areas

The invention relates to an arrangement for the uniform or predefinable illumination of large areas with a light source, with the aim of achieving a largely constant illuminance distribution over the respective area. With the solution according to the invention, for example, large-area lighting can be achieved outdoors, but also in closed rooms, so that it is suitable, for example, for illuminating traffic or office spaces. However, it can also be a desired predetermined illumination of certain surface areas of a surface to be illuminated, such as in particular external ones

Edge areas of such an area can be reached.

When illuminating areas with large aperture angles where the edge radiation is emitted at angles of approx. 120 °, the edges of

surface areas to be illuminated to a considerable drop in the illuminance levels achievable there.

Taking into account the photometric distance law and the inclined projection of the emitted light onto the respective surface to be illuminated, illuminance drops occur with a factor cos (w) ³ , based on the center of the illuminated surface (at 60 °: 0.125). For example, there is a reduction in illuminance at the edges in relation to the center of the respective area to 1/8 in conventional solutions.

For many applications, however, a uniform illuminance distribution over the entire area to be illuminated is desirable.

For this purpose, in the case of known solutions, especially aspherically shaped and free-form reflectors are used, which place high demands on the calculation and manufacture of such aspheres and reflectors with free-form surfaces. Such reflectors usually also have to be calculated and manufactured separately for the respective application.

In another alternative, it is also state of the art to use separately calculated optical elements with Fresnel structures for such illumination, which allow the illuminance distribution to be varied over relatively wide ranges.

In conventional Fresnel optics, however, the so-called active and interference edges are used alternately, whereby the interference edges tend to be one have a negative influence on the lighting and often have to accept light losses.

It is therefore an object of the invention to propose possibilities with which uniform or predetermined illumination of large areas can be achieved in a cost-effective, variable form and a relatively small size of at least one reflecting element to be used can be maintained.

According to the invention, this object is achieved with an arrangement which has the features of claim 1. Advantageous refinements and developments of the invention can be achieved with the features specified in the subordinate claims.

The arrangement according to the invention for uniform or predetermined illumination of large areas, the respective large areas always being to be evaluated in relation to the size of the respective light source or the light radiation emitted by a light source, uses at least one reflective element on which a Fresnel structure is formed and collimated light of the light source is reflected on the surface provided with the Fresnel structure. A slight divergence can be tolerated in the light directed onto this surface and, if necessary, can also be compensated for by suitable measures on the reflecting element.

In this case, a Fresnel structure that is at least partially free of flanks is formed on the at least one reflecting element. This Fresnel structure is formed from alternating active edges, each with respect to the incident col- limited light have changing angular inclinations. As a result, collimated light incident with an active flank aligned at an angular inclination is collected, and the incident collimated light is scattered with the active flank that is adjacent to such an active flank and is oriented at a different angle inclination.

In a preferred form, such an interference-free Fresnel structure should be formed at least in the radially outer region of such a reflective element with respect to the optical axis of the entire system or the collimated light. Of course, however, there is also the possibility of providing the entire surface area of a reflective element according to the invention used for reflection with a Fresnel structure free of interference flanks.

It is also advantageous to form a Fresnel structure on its rear side on reflective elements to be used according to the invention, so that the collimated light strikes the respective active edges of the Fresnel structure according to the invention via the surface of the reflecting element facing the respective light source Dependence of the respective angle of inclination of the active surfaces is reflected and, after a refraction at the interface, which is arranged opposite the interference-free Fresnel structure on the surface of the reflecting element, is additionally broken, so that such a refraction again makes the beam guidance advantageous for the desired uniform large area Illumination can be used. In this case, the reflective element to be used according to the invention should be formed from a material transparent to the respective light with a known refractive index, and the outer surfaces of the interference-free Fresnel structure should be coated with a coating reflecting the respective light. Thus, the actual reflective elements can consist of a suitable plastic that can be processed, for example, by injection molding or conventional hot stamping.

However, the collimated light is reflected directly on the surface of an interference-free Fresnel structure without the respective one

If light impinges in advance through the material of a reflecting element on the respective active flanks, the Fresnel structure according to the invention which is free of interference flanks can also be formed exclusively from a corresponding reflective material or, as already mentioned, such a reflective coating has been formed on a corresponding Fresnel structure without interference flanks.

In an arrangement according to the invention, however, it is also possible to use more than one reflecting element with a Fresnel structure free from interference flanks. It is thus possible to arrange several such reflecting elements next to one another in the form of a so-called “array”, which can also be connected to one another in a fixed or releasable manner. In this form, as in a modular system, different dimensions and the respective ones can be used Install arrangements according to the invention that take the application into account. Both one and several reflecting elements, on which Fresnel structures free of rafters are formed, should be arranged as far as possible in a common plane, which is also aligned as parallel as possible or at an inclined angle to the respective surface to be illuminated.

For the desired homogeneous illumination of the respective relatively large area, minimum distances on an arrangement according to the invention should preferably be observed in order to be able to achieve the desired effects. Thus, the distance A of the one or more reflective element (s) from the surface to be illuminated should be at least five times, preferably at least ten times as large as the diameter or the surface diagonal of the cross section of the respective collimated light, which is directed to the respective o - Which is directed towards the correspondingly arranged reflective element (s).

As a result, the effects achievable with the invention can be exploited even better. It can be taken into account here that one of the two active flanks of a pair of oppositely oriented active flanks arranged adjacent to one another performs the function of a concave reflex (concave mirror) and the other active flank performs the function of a convex mirror (arched mirror). The active flank performing the function of a convex mirror scatters the light in the direction of the outer edge of the surface to be illuminated and the active surface performing the function of a concave mirror collects the light in the direction of the focal point, but since the distances of the surface to be illuminated are kept relatively large, too the light reflected with such an active edge is actually scattered. The images obtained on the respective differently oriented active surfaces by reflection on the surface to be illuminated overlap on the surface to be illuminated in each case and the illuminance is homogenized over the entire surface to be illuminated. The light distribution is independent of the respective geometry of the light source or the beam geometry of the light radiation emitted by it, so that one can speak of illumination in the so-called "far field". The photometric limit distance of the photometric distance law should be taken into account.

The invention will be explained in more detail below by way of example.

Show:

Figure 1 in schematic form an example of an arrangement for illuminating large areas;

FIG. 2 shows a partial representation of a reflective element with a conventional Fresnel structure, as can be used in an arrangement according to FIG. 1;

FIG. 3 shows in schematic form the reflection behavior of a conventional Fresnel structure on the active and interference flanks;

4 shows the reflection behavior on a conventional Fresnel structure with multiple reflections on the interference flank; FIG. 5 shows, in schematic form, the basic reflection behavior on an interference-free Fresnel structure to be used according to the invention and

Figure 6 in three-dimensional form a calculated illuminance distribution over an area that can be achieved with an arrangement according to the invention.

In Figure 1, an arrangement for illuminating large areas 5 is shown in schematic form. In this case, collimated light 1 ′ from a light source 1 is directed onto a reflecting element 2 provided with a Fresnel structure and is reflected back by the latter in the direction of the surface 5 to be illuminated with a correspondingly large aperture.

FIGS. 2 and 3 show partial representations in which conventional reflective elements provided with a Fresnel structure are shown with their respective beam guidance.

Thus, FIG. 2 indicates how the collimated light of the light source 1 strikes the active flanks of a conventional Fresnel structure through the material of a reflecting element, is reflected at a radially outward angle according to the angle of incidence on the respective active flanks and on the outer surface , is accordingly broken again as the interface of the reflecting element.

3 is intended to illustrate how part of the incident collimated light 1 'does not only appear on an active flank 6 of a conventional Fresnel structure, but is also reflected on an interference flank 7, so that this part, which reflects both on active and interference flanks, leads to greater illumination, with a correspondingly increased illuminance of the central, central region of the respective area to be illuminated ,

As can be clearly seen from FIG. 4, part of the collimated light 1 ′ strikes an interference flank directly, is reflected by the latter on an active edge and from the active edge again on the interference edge and is then reflected by the reflecting element 2 for illuminating a surface , The proportion of the light reflected by the reflecting element 2 emerges almost parallel to it, so that an undesirable increase in the illuminance occurs in the central region of the surface to be illuminated.

In the case of the reflecting elements 2 shown in FIGS. 3 and 4, such an undesired light guidance, which occurs in particular as a result of the reflections on the interference flanks, could be avoided if an interference flank angle of 0 ° has been observed, this angle being considered in relation to the optical axis shall be. In one embodiment according to Figure 3 then, a light beam after reflection on a vertical Störflanke with the same angular would kel rightward emerge from the reflective member 2, so it on the other side with the gle ^'cozy distance of at surface to be illuminated - would hit. An analog behavior would show a light beam on the opposite side of the reflecting element 2, so that then no increase in the illuminance in the central len central area of the surface to be illuminated would be recorded. However, such Fresnel structures are unsuitable because of the usual shaping manufacturing processes, since they make non-destructive demolding impossible.

However, FIG. 5 is intended to illustrate the advantageous reflection behavior of a Fresnel structure free of interference edges on a reflective element 2 that can be used in the invention in a schematic form.

Thus, the collimated light 1 'emitted by the light source 1, not shown here, at least almost orthogonally strikes a planar flat interface of an otherwise transparent reflecting element 2, the respective active edges 3 and 4, which are parallel to the collision with respect to the optical axis - aligned light is aligned, are inclined at an opposite angle, and the angle of incidence is reflected on these, here reflective coated active edges 3 and 4, taking into account the respective angles of incidence. The respective reflected light is then refracted accordingly on the opposite surface of the reflecting element 2. FIG. 5 clearly shows that the collimated light 1 ′ incident from the active surfaces 3 and 4 oriented at different angular inclinations is reflected in opposite directions and is additionally refracted.

Depending on the position / distance of the active edges 3 and 4 in relation to the optical axis of the incident collimated light 1 ', the light reflected in each case on the active edges 3 and 4 and possibly additionally refracted is opened once in the direction deflected the radially outer edge of the surface 5 to be illuminated and the other of the active surfaces 3 or 4 in each case directs light in focused form to a corresponding focal point and with a correspondingly large distance between the reflecting element 2 and the surface 5 to be illuminated above the focal point which is in the optical Axis is arranged in the radially outer direction further outwards, so that the desired effect according to the invention of a uniform illuminance, which is to be achieved over the entire surface 5 to be illuminated, can be achieved.

In a form that is not shown, based on the optical axis of an arrangement according to the invention, the respective angles of inclination of active flanks 3 and 4 of a Fresnel structure free of interference flanks can be adapted according to their distances in relation to the optical axis and correspondingly different angles of inclination of active surfaces 3 and 4 on the reflective element.

In one example, analogous to a reflective element 2, as shown in FIG. 5, the surface of a reflective element 2, into which the light enters and exits again, can also be concave and / or convexly curved at least in regions , As a result, a divergence of the collimated light 1 'directed at the corresponding surface of the reflecting element 2 can be compensated for and, on the other hand, the exit angle of the surface formed on such a surface in a curved manner can be improved for the desired homogeneous illumination of the respective surface 5 reflective elements 2 broken light can be exploited. FIG. 6 shows in three dimensions a calculated illuminance distribution over an illuminated surface 5, which can be achieved with an example of an arrangement according to the invention.

The surface 5 to be illuminated considered here had a circular shape with a diameter of 7100 mm, with a distance of the surface from the reflecting element 2 of 2500 mm.

The following further parameters of an example of an arrangement according to the invention were taken into account in the calculation:

A maximum edge ray inclination of 55 ° was assumed for light reflected on a reflecting element 2, which is directed onto a surface to be illuminated. This peripheral beam angle would correspond to the respective outer light rays, as can be seen in FIG. 1.

This resulted in a decrease in illuminance of cos ³ (55) = 0.189, which would correspond to approximately 19% in relation to the center of the area to be illuminated.

Through the calculation for a reflective element 2 according to the invention, a clear compensation could be demonstrated for this, so that a uniform illuminance distribution over the quite large area could be achieved.

The calculation was based on the well-known aspherical equation:

Z = (l / rxh ² ) / (l + _Λ / l + (l-cc) xh ² / r ² + A ₂ h ² + A ₄ h ⁴ + A ₆ h ⁶ + A ₈ h ⁸ ....) The radius used was r = 157.67 mm

a cone cutting parameter cc = -1

A ₂ = 0

A ₄ = -1.73625E-7

A ₆ = 1.23325E-11 and

A ₈ = -5.0425E-16 is displayed.

The respective distance from the optical axis was taken into account as h.

The reflective element was made of a transparent material with a refractive index of n = 1.49.

Claims

claims

1. Arrangement for uniform or predeterminable illumination of large areas with a light source, from which collimated light is directed onto at least one reflective element with a reflective surface designed in Fresnel structure, characterized in that at least in some areas a Fresnel structure with no flanks with alternating changes Effective flanks (3, 4) are formed, each with changing angular inclinations with respect to the incident collimated light and once with a light-collecting and once with a light-scattering effect for incident collimated light.

2. Arrangement according to claim 1, characterized in that a Fresnel structure with no flanks in relation to the optical axis is formed at least in the radially outer region of a reflecting element (2).

3. Arrangement according to claim 1 or 2, characterized in that the Fresnel structure without flanks is formed on the back of reflecting elements (2).

4. Arrangement according to one of the preceding claims, characterized in that a plurality of reflecting elements (2) in one plane, forming an array, are arranged side by side.

5. Arrangement according to one of the preceding claims, characterized in that the distance A of the reflecting element (s) (2) to the surface to be illuminated is at least five times corresponds to the diameter or the area diagonal of the cross section of the collimated light.

6. Arrangement according to one of the preceding claims, characterized in that the respective angle of inclination of the alternately arranged active flanks (3, 4) is changed radially outwards starting from the optical axis.

7. The arrangement as claimed in one of the preceding claims, characterized in that the surface of the reflecting element which is opposite the flank-free Fresnel structure is at least partially concave and / or convexly curved.