EP0402740B1 - Reflector for a lamp and method to determine the shape of a reflector - Google Patents

Description

The invention relates to a reflector for a lamp and a method for determining the shape of such a reflector.

The luminaires in question are intended in particular to illuminate a room, to illuminate an object or to couple light into a light guide.

In the prior art, conic intersection curves are known as reflector shapes, namely ellipse, parabola, hyperbola, circle and straight lines (the latter as so-called singular conic sections). As is known, these reflector intersection curves are created in flat sectional figures, which contain the optical axis of the lamp.

• a) Ellipse:
  • Die Ellipse ist definiert durch zwei Parameter, nämlich die große Halbachse a und die kleine Halbachse b. Von einem Brennpunkt der Ellipse ausgehende Strahlung wird vom Ellipsoid-Reflektor so reflektiert, daß sie im anderen Brennpunkt gebündelt wird, wonach sich die Strahlung mit einem relativ großen Winkel ausbreitet.
• b) Parabel:
  • Die Parabel ist durch einen Parameter (zumeist "p" genannt) definiert. Vom Brennpunkt des Paraboloids abgestrahlte Strahlung wird durch den Reflektor so reflektiert, daß sie zur optischen Achse parallel verläuft.
• c) Hyperbel:
  • Die Hyperbel ist durch zwei Parameter bestimmt, die reelle Halbachse a und die imaginäre Halbachse b. Vom Brennpunkt abgestrahlte Strahlung wird so reflektiert, daß sie sich von der optischen Achse entfernt. Die Aufspreizung der Strahlung ist dabei eine Funktion des Abstandes von der optischen Achse; je näher die Strahlung an der optischen Achse verläuft, um so spitzer ist der Winkel zu optischen Achse.
• d) Kreis:
  • Der Kreis ist definiert durch einen Parameter, nämlich den Radius r. Vom Mittelpunkt des Kreises abgestrahlte Strahlung wird so reflektiert, daß sie sich wieder im Mittelpunkt bündelt.
• e) Gerade:
  • Die Gerade ist definiert durch den sogenannten Richtungsfaktor m. Die optischen Eigenschaften eines geradlinigen Reflektors sind trivial.

The well-known reflector intersection curves ellipse, parabola, hyperbola, circle and straight line each have the following parameters and reflection properties:

• a) Ellipse:
  • The ellipse is defined by two parameters, namely the large semi-axis a and the small semi-axis b. Radiation emanating from one focal point of the ellipse is reflected by the ellipsoid reflector in such a way that it is concentrated in the other focal point, after which the radiation propagates at a relatively large angle.
• b) Parabola:
  • The parabola is defined by a parameter (usually called "p"). Radiation emitted from the focal point of the paraboloid is reflected by the reflector in such a way that it runs parallel to the optical axis.
• c) Hyperbole:
  • The hyperbola is determined by two parameters, the real semi-axis a and the imaginary semi-axis b. Radiation emitted from the focus is reflected so that it moves away from the optical axis. The spreading of the radiation is a function of the distance from the optical axis; the closer the radiation is to the optical axis, the more acute the angle to the optical axis.
• d) Circle:
  • The circle is defined by a parameter, namely the radius r. Radiation emitted from the center of the circle is reflected in such a way that it is concentrated again in the center.
• e) Straight:
  • The straight line is defined by the so-called direction factor m. The optical properties of a rectilinear reflector are trivial.

The above-described reflection properties of the conical reflectors cannot be changed in principle even by varying the parameters mentioned.

In general, the designer of a certain reflector is given boundary conditions according to which the luminaire is to be constructed, for example the light exit diameter and the length of the luminaire can be predetermined on account of the structural conditions and also the desired light distribution at a certain distance from the luminaire.

Conventional reflectors with conical sectional figures force the designer to make considerable compromises if the constraints are tight. Given given boundary conditions, reflectors with conical sectional shapes rarely allow the luminaire to be optimally designed with regard to the desired light distribution. In the case of curve types with two parameters, such as ellipse and hyperbola, only the focal point can be varied, although there are restrictions due to the light source used.

If the boundary conditions (parameters) and the focal point are fixed, the shape of the reflector curve is also determined.

For example, it is possible to form a small light spot with a parabolic reflector. The size of the light spot can then only be changed by changing the size of the reflector overall.

Elliptical reflectors are often used to illuminate a relatively large area. However, the light distribution within the beam angle is very inhomogeneous and drops sharply with increasing distance from the optical axis to the outside.

It is known to prepare the microstructure of the reflection surface, for example by roughening, hammering or sandblasting, so that the radiation becomes more homogeneous, i.e. the light intensity is reduced in the middle and increased at the edge. However, this method has disadvantages insofar as the width of the scattered light cannot be adjusted mathematically in the construction of the lamp, but rather depends on empirical values and tests. Another disadvantage of this method is that the scattered light also occurs far outside the radiation angle and thus makes the delimitation of the light spot unclear. In the known methods of homogenizing the light distribution, the efficiency of the lamp is relatively low, i.e. In order to achieve a certain predetermined brightness, a relatively large amount of energy must be accepted. The results regarding the uniformity of the light distribution within the beam angle can also be improved.

From US-PS 3 390 262 a reflector is known in which only a reflector close to the edge cut corresponds to a conic section, while an inner reflector section is constructed differently. The transition between the two mentioned reflector sections is discontinuous. The latter has disadvantages in the manufacture of reflectors with regard to the tool. At the point of discontinuity, the reflector cannot be shaped exactly according to the tool and stray light is usually generated. You have to expect an energy loss. Even with this known solution, the homogenization of the light distribution cannot be achieved to the desired extent.

From DE-OS 35 07 143 a lamp is known, the reflector consists of segments which are arranged so that each segment reflects radiation emanating from another area of the light source, so that points on a surface to be irradiated each receive radiation that is reflected by several different segments.

Document US-A-3 398 272 describes a reflector cut curve that is not conical. This reflector intersection curve is generated in such a way that two constants are defined (specific angles). By specifying these constant angles, the reflector is completely defined and is calculated using a mathematical equation.

The invention has for its object to provide a way to construct reflector shapes with which desired light distributions can be generated with great efficiency as required. It should not be necessary to prepare the microstructure of the reflection surface (as explained above) and the reflector should also not have any seams connecting different curves.

The inventive solution to this problem is described with its configurations in the claims.

The two curves between which the reflector according to the invention runs can in particular be two different ellipses (ie ellipses with at least one different parameter), two different parabolas (ie parabolas with different parameters) or an ellipse and a parabola.

The reflector shape according to the invention is thus characterized in the latter example in that it is neither a pure ellipse nor a pure parabola, but rather continuously, i.e. over their entire extent, an "in-between" between such conventional known reflector shapes. The reflector shape according to the invention does not correspond to a conic section.

The reflection properties of reflectors constructed in accordance with the invention are fundamentally different from the reflection properties of conical reflectors and generally do not correspond to simple “mean values” from the reflection properties of reflectors corresponding to the enveloping curves. In other words, the light distributions achieved according to the invention are not always an “intermediate thing” between the properties of the two enveloping curves used. This is especially true if the two enveloping curves are different types of conic sections, such as a parabola and an ellipse.

The invention not only proposes certain reflector shapes, but also gives the luminaire designer a method in which he can generally construct an optimal reflector shape depending on the given boundary conditions for the luminaire and the desired light distribution, the desired light distribution largely without the use of additional optical aids such as lenses, etc. can be achieved.

According to the teaching according to the invention, reflector shapes can be constructed with which radiation from a light source can be optimally coupled into a radiation conductor. Conventional, purely ellipsoidal reflectors generate relatively large angles of incidence between the radiation to be coupled in and the light guide. A reflector according to the invention, on the other hand, enables a relatively small angle of incidence between the radiation to be coupled in and the light guide, as a result of which the radiation is guided through the radiation guide, e.g. Fiber, is improved.

According to the teaching of the invention, it is also possible to create a reflector that can be used for a given distance, e.g. one meter, which can concentrate radiation with high efficiency at a certain point. The bundling is better than with a paraboloid-shaped reflector.

In comparison with ellipsoidal reflectors provided for large beam angles in the prior art, a reflector constructed according to the invention enables a relatively uniform light distribution.

Exemplary embodiments of the invention are explained in more detail below with reference to the drawing.

• Fig. 1 schematisch einen Schnitt durch ein erstes Ausführungsbeispiel eines Reflektors;
• Fig. 2 einen Schnitt durch ein zweites Ausführungsbeispiel eines erfindungsgemäßen Reflektors;
• Fig. 3 eine Lichtstärkeverteilung einer Leuchte mit einem herkömmlichen EIlipsoid-Reflektor und
• Fig. 4 eine Lichtstärkeverteilung einer Leuchte mit einem erfindungsgemäßen Reflektor gemäß Fig. 2.

It shows:

• Figure 1 shows schematically a section through a first embodiment of a reflector.
• 2 shows a section through a second exemplary embodiment of a reflector according to the invention;
• Fig. 3 shows a light intensity distribution of a lamp with a conventional ellipsoid reflector and
• Fig. 4 shows a light intensity distribution of a lamp with an inventive ß reflector according to FIG. 2nd

In the exemplary embodiment shown in FIG. 1, the optical axis is provided with the reference symbol 1. The reflector cut curve R according to the invention is shown with a solid line. The entire reflector is created either by rotation of the curve R about the optical axis 1 or by translational displacement of the curve R if a channel-shaped reflector is to be created.

The shape of the reflector cut curve R is formed such that it lies between two narrowing (envelope) curves in the manner described in more detail below, which are an outer ellipse Ei and an inner ellipse E2 in the exemplary embodiment shown in FIG. 1. The ellipses Ei and E2 differ with respect to at least one parameter (a and / or b).

The use of two ellipses according to FIG. 1 as an envelope for the reflector cut curve R enables a reflector shape with which, in particular, radiation can be optimally coupled into a light guide, that is to say the coupled radiation has a relatively small angle of incidence. For this purpose, the two ellipses Ei, E2 and the reflector intersection curve R have a common optical axis 1. Two focal points F ₁ , F ₂ coincide. A fixed point O also lies at the location of the focal points F,, F ₂ . The fixed point O defines a polar angle and a distance ratio described in more detail below.

The reflector formed in this way is not an ellipsoid.

As can be seen in FIG. 1, the reflector intersection curve R runs much closer to the inner ellipse E2 in the vicinity of the apex than with increasing approach to the edge R _{a of} the reflector. This is explained in more detail below using the "distance ratio".

The exemplary embodiment shown in FIG. 1 can be modified in such a way that instead of the two ellipses, two parabolas are placed next to one another as enveloping curves for the reflector cut curve R. In order to be able to achieve strong focusing of the radiation at a given distance from the luminaire with a reflector constructed in this way, it is provided (conversely as in the exemplary embodiment according to FIG. 1 described above) that the reflector shape is close to the apex (ie on the optical axis). is closer to the outer parabola (not shown) than to the inner parabola (not shown). With increasing approach to the edge of the lamp, the reflector cut curve R approaches the inner parabola. The reflector is not a paraboloid.

With the above-described reflector shape with two parabolas as envelopes, a luminaire is generated whose radiation is not aligned exactly parallel to the optical axis, but rather is reflected somewhat inwards. A light spot whose diameter is smaller than the opening diameter of the lamp can thus be generated at a given distance from the lamp without using a lens.

In the embodiment shown in FIG. 1, the course of the reflector cut curve R between its two enveloping ellipses Ei, E2 is generated by means of a beam 2 originating from a fixed point O, which coincides with the focal points F1, F _{2 of} the ellipses, and the beam 2 generated by this beam Polar angle a described. The beam 2 intersects the ellipses E _i , E2 and the reflector intersection curve R. The intersection points are provided with the reference symbols A, B and C, respectively. 1 shows two positions of the traveling beam 2, 2 ', the corresponding reference numerals being provided with a line in the second position.

wobei a der Abstand zwischen den Punkten A und O, b der Abstand zwischen den Punkten B und O und c der Abstand zwischen den Punkten C und O sind.A distance ratio k can now be defined as follows:

where a is the distance between points A and O, b is the distance between points B and O and c is the distance between points C and O.

In the exemplary embodiment according to FIG. 1, the distance ratio k is relatively small in the region of the vertices S ₁ , S ₂ and S _{R of} the curves Ei, E2 and R, ie the vertex S _{R of} the reflector R is closer to the vertex S _{2 of} the inner envelope Ellipse E2 as at the vertex S _{1 of} the outer envelope ellipse Ei.

With increasing polar angle a, the distance ratio changes in such a way that near the edge R _{a of} the reflector the reflector lies closer to its outer envelope ellipse Ei than to its inner envelope ellipse E2.

wobei a_max der größte Polarwinkel des wandernden Strahles 2 ist (also entsprechend etwa dem Strahl 2' in Fig. 1), d.h. der Winkel des den Rand R_a der Reflektorschnittkurve R streifenden Strahles. In den vorstehenden Gleichungen (I), (11) und (111) bedeutet y eine reelle Zahl, insbesondere 1 und auch U und V bedeuten jeweils reelle Zahlen.The variation of the distance ratio as a function of the polar angle a can be represented analytically, for example, by the following equations:

where a _{max is} the largest polar angle of the traveling beam 2 (corresponding approximately to the beam 2 'in FIG. 1), ie the angle of the beam grazing the edge R _{a of} the reflector section curve R. In the above equations (I), (11) and (111) y means a real number, in particular 1 and also U and V each mean real numbers.

The reflector should not have any discontinuities, i.e. the change in the distance ratio as a function of the polar angle a should follow a continuous function. The reflector preferably has a continuously differentiable shape. This also applies to the other exemplary embodiment of a reflector according to the invention shown in FIG. 2.

The construction of a reflector according to the invention is described above using polar coordinates. Polar coordinates have certain advantages here, but it is also possible to use Cartesian or other coordinates.

The reflector R shown in Fig. 2 is used to generate a uniform light distribution. An ellipse E and a parabola P are placed side by side so that the focal point F _{1 of} the parabola coincides with a focal point F _{2 of} the ellipse E. The fixed point O, which defines the beam 2 and the polar angle a, also lies in the two focal points on the optical axis 1.

In the exemplary embodiment shown in FIG. 2, the distance ratio k of the reflector R as defined above is constant between the enveloping curves E and P.

By changing the distance ratio k, the optical properties of the reflector R can be changed as required. The closer the distance ratio k is to 1.0, the more similar are the optical properties of the reflector R to those of a parabolic reflector.

The optical properties of the reflector R in the exemplary embodiment according to FIG. 2 are determined by the parameters a, b of the ellipse E, the parameter p of the parabola P, the distance between the apex S _E and Sp of the ellipse E and the parabola P on the optical one Axis 1 and the distance ratio k described above.

In a modification of the exemplary embodiment described in FIG. 2, the distance ratio k can also vary as a function of the polar angle a, in particular in accordance with the above functions (1), (2) and (3).

The exemplary embodiment according to FIG. 2 can also be modified such that the focal points of the parabola or ellipse do not coincide. The distance between the vertices S _E and Sp on the optical axis 1 can also be reduced; in extreme cases, the two vertices can coincide.

It is also possible, in a modification of the exemplary embodiment according to FIG. 2, to arrange the ellipse outside the parabola, that is to say to reverse the size ratio of the parabola and ellipse.

Furthermore, the exemplary embodiments shown in FIGS. 1 and 2 can be modified such that the optical axes of the enveloping curves E _i , E2, E, P do not coincide in each case. The optical axis of one envelope curve can be slightly inclined with respect to the optical axis of the other envelope curve.

beschrieben werden, wobei a, b, c, d, e und f jeweils Konstante und x und y Variable sind.The above-described exemplary embodiments of curves enveloping the reflector shape, such as Ei, E2, E, P, can be done using equations

are described, where a, b, c, d, e and f are constants and x and y are variables.

The light distribution of a reflector according to the invention can be determined both mathematically and empirically. A computational determination is particularly simple if an analytical expression for the distance ratio or the course of the curve R is given, so that the tangent can be calculated by differentiation. From the tangents at a large number of points, which are selected with constant angular distances from each other on the reflector cut curve R, the directions of the rays leaving the lamp result from the law of reflection ("angle of incidence equals angle of reflection") and this results in a given distance of the intensity distribution of the luminaire, ie the number of incoming light beams per unit area.

In order to produce a single homogeneously illuminated light spot on a wall remote from the lamp with a reflector R according to FIG. 2 without the use of aids (caps or the like), it is provided that the light beam S reaching the opening edge _{Ra of} the reflector R with the optical axis 1 includes an angle β which is equal to the angle β 'which the beam S' reflected at the edge forms with the optical axis. In this case, the direct radiation from the light source at location O and the reflected radiation form the same light cone.

The light source does not necessarily have to be arranged in the focal points F1, F ₂ or at location O.

FIGS. 3 and 4 show a comparison of the light intensity distributions in a conventional lamp with an ellipsoidal reflector and a lamp according to the invention according to Fig. 2. In Fig. 3, the light intensity distribution 1 ₁ is a lamp with a conventional ellipsoidal reflector as a function of emission angle in applied in the usual way. The curve 1 ₁ it can be seen that the brightness decreases starting from a maximum at 0 to the side strong.

In contrast, in a reflector according to the invention, the light intensity distribution 1 ₂ according to FIG. 4 is much more uniform and remains almost constant within a certain angle. The the 4 is constructed as described above with two conic section curves, namely a parabola with p = 39.0, an ellipse with a = 90.2 and b = 56.0 and a distance ratio k of 0.22 (constant ).

It is possible to provide a reflector surface according to the invention with facets in order to avoid an aesthetically disruptive appearance of light and dark rings in the light spot in certain light sources which have a wound spiral wire.

In the case of a channel-shaped reflector in particular, the shape need not necessarily be symmetrical with respect to the central longitudinal plane of the reflector. Rather, the lower part of the reflector can differ from the upper part in order to achieve an optimal adaptation to the required lighting.

Claims (10)

1. A reflector for a lamp having a cutting line (R) which is not of the shape of a conic section in a plane including the optical axis (1) of the lamp, characterized in that the points of the reflector cutting line (R) lie between two conic sections (E₁, E₂; P, E) enveloping the reflector cutting line between them, the distances of points (B, B') on the, reflector cutting line from points of intersection (A, C) of straight lines (2, 2') with the enveloping conic sections (E₁ , E₂; P, E) corresponding to a given distance ratio (k).

2. The reflector as claimed in claim 1, characterized in that the straight lines (2, 2') forming the points of intersection (A, C) with the enveloping conic sections (E₁, E₂; P, E) start from an origin (O) as polar coordinates.

3. The reflector as claimed in claim 1 or 2, characterized in that the enveloping curves (E, , E₂) are of the same type of conic and the distance ratio (k) of the reflector cutting line (R) varies in response to the distance of the reflector cuting line from its apex (S_R).

4. The reflector as claimed in any one of the preceding claims, characterized in that the enveloping curves (P, E) are of different types of conics and the distance ratio (k) of the reflector cutting line (R) is constant or varies in response to the distance of the reflector cutting line from its apex (S_R).

5. The reflector as claimed in any one of the preceding claims, characterized in that the foci of the two enveloping conic sections coincide.

6. The reflector as claimed in any one of the preceding claims, characterized in that the foci of the two enveloping conic sections lie on top of each other on the optical axis (1).

7. The reflector as claimed in any one of claims 1 to 5, characterized in that the apices (Si , S₂, S_R; Sp, S_E, S_R) of the two enveloping curves are spaced from one other on the optical axis (1) of the lamp.

8. The reflector as claimed in any one of the preceding claims, characterized in that the base angles of a triangle formed of a light beam reflecting at the reflector edge and of the optical axis (1) are the same.

9. The reflector as claimed in any one of the preceding claims, characterized in that the reflector cutting line (R) is steady, especially steadily differentiable.

10. A method of generating a reflector shape whose cutting line (R) is not of the shape of a conic section in a plane including the optical axis (1) of the lamp, characterized in that the points of the reflector cutting line (R) are determined such as to each lie on straight lines (2, 2') starting from an origin (O) that is fixed with reference to the reflector and to form a different angle (a, a') with the optical axis (1) for each point (B, B') on the reflector cuting line (R), and in that the locus of the point (B, B') on the straight line (2, 2') between two conic sections (E1, E₂; P, E) enveloping the reflector cutting line (R) between them is determined such that the distances of the point (B, B') from the points of intersection (A, C) of the straight line (2, 2') with the enveloping conic sections (E₁, E₂; P, E) are determined by a given distance ratio (k).

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