EP1554521A1

EP1554521A1 - Led projector for asymmetrical illumination

Info

Publication number: EP1554521A1
Application number: EP03758006A
Authority: EP
Inventors: Manfred Griesinger; Markus Hartlieb; Wilhelm Kincses; Hans-Georg Leis; Siegfried Rothe
Original assignee: DaimlerChrysler AG
Current assignee: Mercedes Benz Group AG
Priority date: 2002-10-24
Filing date: 2003-10-17
Publication date: 2005-07-20
Anticipated expiration: 2023-10-17
Also published as: WO2004038285A1; JP2006504249A; DE50304161D1; EP1554521B1; US20060098447A1

Abstract

The invention relates to a novel projector which has an asymmetrical illumination characteristic, and a clear light-dark limit, and uses almost the entire radiation power outputted from the semiconductor light source. To this end, the projector consists of a field of individual semiconductor light sources which are provided with optical elements having a novel form. Said optical elements have as flat a form as possible, such that the light admission inlet of the optical element has an elongated, essentially rectangular form. Furthermore, the optical elements comprise a central region, perpendicular to the light admission surface (F), the projection of said central region into a two-dimensional plane corresponding to a cylindrical two-dimensional cartesian oval. According to the invention, in order to better use the light emitted from the semiconductor light source, the light emergence surface (G) of the optical element, in the form of a cartesian oval, is combined with a parabolic reflector (A, B).

Description

LED headlights for asymmetrical illumination

The invention relates to an LED headlight, which has an asymmetrical illumination characteristic, and a method for operating such a headlight in accordance with the preamble of claims 1 and 10.

Controlling a vehicle in traffic is a demanding, highly dynamic task. It places considerable demands on visual perception, cognitive processing and motor coordination of the driver. There is a general consensus in the literature that around 90 percent of the information relevant to road traffic is absorbed by the sense of sight. It is therefore important to have good lighting in the traffic area at dusk and in the dark and in weather situations in which natural light is insufficient. The currently valid ECE regulations for the asymmetrical low beam on European roads represent a compromise between good visibility and the least possible impairment of other road users. A vehicle headlight must be designed in such a way that it forms the light it emits in such a way that the result the superimposition of the emerging light creates a light distribution prescribed for vehicle headlights; in particular, the formation of a clear cut-off line and an asymmetrical characteristic of the illumination are necessary to avoid the glare of oncoming traffic. The lighting system described in US Pat. No. 6,144,158 A generates an illumination characteristic by using a field of semiconductor lasers or alternatively a deflection device for the light beam of an individual semiconductor laser, which has the clear light-dark limit required in road traffic and an asymmetrical characteristic. However, the use of a laser light source which is necessary for the bundling of light but is not very robust and expensive in terms of vibrations has a disadvantage in relation to the possibilities of an economically sensible implementation.

A headlamp realized on the basis of inexpensive LED light sources is known from the document DE 100 05 795 AI. In doing so, its lighting characteristics become more variable

Headlights, realized by a field of single emitters with at least one optics arranged in front of each single emitter. Each of these optics can be shifted in relation to the individual elements in all three spatial directions in order to influence the respective light beam emitted by the individual light element. In this way, variable control of the beam emitted by the headlight can be achieved. Due to the rotation-symmetrical light distribution typical of the related LED optics, which has a large opening angle, no light distribution corresponding to the regulations of road traffic and having a clear light-dark limit can be created.

It is therefore the task of the invention to find a lighting device that can be manufactured inexpensively and that has an asymmetrical lighting characteristic, which at the same time has a clear light-dark limit and thereby utilizes as much as possible the total radiation power emitted by the semiconductor light source. The object is achieved by a lighting device and a method suitable for operating such a device with the features of claims 1 and 10. Advantageous refinements and developments of the invention are shown by the subordinate claims. The invention is explained in detail below using exemplary embodiments and figures.

The lighting optics are formed by a field (array) of individual optics. In this case, the individual optics are made as flat as possible in accordance with the invention, so that the light entry opening of the optics has an elongated, essentially rectangular shape. Each individual lens has a central area perpendicular to the light entry surface, the projection of which into a two-dimensional plane corresponds to a cylindrical 2-dimensional carto oval. A Kartoval is a geometric surface that, as the boundary surface of a refractive medium, collects the light from a focal point in a second focal point, even for large opening angles. In order to make better use of the light emanating from the semiconductor light source, the light exit surface of the optics shaped in the form of a carto oval is combined with a parabolic reflector within the scope of the invention.

In the following, the advantageous embodiments of the invention are discussed in detail using figures and the mathematical derivation of the geometry of the optics according to the invention. Here, based on an advantageous use of the optics within the headlights, only the case is considered that the second focal point, in which the light rays emanating from the light source meet, is infinite, ie the beam is converted into a parallel beam. In this way, the thematic treatment of the system greatly simplified. Further figures serve to explain in detail the advantageous refinements and developments of the invention.

FIG. 1 shows the beam geometry on which the refraction at the light exit surface of the optics is based. FIG. 2 shows the contour line of a carto oval resulting from the calculation.

Figure 3 represents that originating from a point source

Beam path and shows the critical angle of reflection resulting from the geometry of the optics.

FIG. 4 shows a 3-dimensional view of an optical system according to the invention.

Figure 4a forms the optics shown in Figure 4 as

3-dimensional edge image in four different views.

FIG. 5 shows a cross section through the optics according to the invention with the necessary adaptation of the parabolic contour of the reflector.

FIG. 6 shows the energy distribution of the light emerging from the optics according to the invention.

FIG. 7 shows schematically the part of an alternative embodiment of the optics based on a “composite parabolic reflector”.

FIG. 8 schematically shows a further alternative embodiment of the optics (with a view of the light inputs step surface), by means of which the light cone emanating from the optics can be specifically curved.

FIG. 9 shows the energy distribution of an alternative optic corresponding to FIG. 8.

FIG. 10 describes the positioning of semiconductor light sources on the optics according to the invention

The mathematical derivation of its contour curve is shown below to illustrate the shape of a carto oval. FIG. 1 shows the radiation geometry on which the calculation is based. Starting from a light source 60, two light beams 20 and 21 are shown schematically. Light beam 20 is intended to represent that light which emerges vertically from light source 60 without refraction from wall 10 of the optics from its light exit surface. Light beam 21, however, occurs under one

Angle φ from the semiconductor light source and strikes the inside of the wall 10 at an angle dφ against the normal. For this reason, the light beam 21 is refracted and emerges from the optics at an angle a at its light exit surface. Since the covering 10 has the contour of a carto oval in an inventive manner, the light beam 21 is deflected in such a way that it emerges parallel to the unbroken light beam 20 after exiting the optics. From this geometry of the beam path shown in FIG. 1 follows the relationship a - ß - φ (1.1) φ is the polar coordinate angle, a the exit angle from the refractive medium and ß the angle of incidence in the medium. According to the Refraction Act: s α. , = n (1.2) sin?

First, the required angle of incidence β is calculated as a function of φ in order to allow the light to exit the element in a parallel direction. From (1.1) and (1.2) it follows:

and the function you are looking for is calculated from this:

/? = arcta - (1 .4) n - cosφ

This function specifies the angle of incidence ß as a function of the polar coordinate angle φ. In the next step, the contour is then calculated. From Figure 1 follows dr _,

- = r-tan /? (1.5) dφ

With Eq. (1. 4) follows from this the differential equation dr sinφ,

- = ^τ - dφ (1. 6) rn - cos φ

This equation can be solved in an analytical form by substitution: n - cos φ _Q

(1.7) r ₀ n -cos φ This is the equation in polar coordinates of the contour line 11 of the carto oval shown in FIG. 2. r ₀ is the radius assigned to the angle ^ ", which is used to determine the absolute dimension of the contour.

Of course, equation 1.7 described in polar coordinates can be also transfer to the Cartesian coordinate system, which gives the following equation (1.8): b + if (1.8) An optic that has an exit surface in the form of a surface according to equation 1.8. Kartovals described, can only parallelize the light of a point source in a limited angular range. This angular range is specified by the limit range of total reflection. FIG. 3 shows the beam path of the light beams 21a-d for a point source 60 and the resulting critical angle ^. The contour of the light exit surface of the optics in the form of a carto oval ensures that all exit from the light source 60 within twice the critical angle (U _g)

Light rays 21a-d and 22 emerge from the optics in parallel. The limit angle> _g is given by the law of refraction

(1.2), where the exit angle α = 90 °. So that will

sin? = - and the critical angle φ „= 9Q ° -ß. For n = l, 5 results thus n ^s a critical angle of 48.2 °. Radiation that lies outside this opening angle cannot be used sensibly with this element. Because semiconductor light sources in the

With such elements, a large part of the light is usually lost in a much larger angular range. Therefore, in order to circumvent this problem within the scope of the invention, the lighting optics, which essentially have the shape of a two-dimensional carto oval, are combined with a parabolic reflector , This reflector should also have the property of converting light from the focal point into a parallel bundle. This leads to the element shown in FIG. 4, with the side surfaces A, B and E and the light entry surface F. As can be seen from FIG. 4, the inventive optics are quite flat, the light entry opening F having an essentially rectangular cross section, one dimension of the cross-section being significantly smaller than the other; as explained below with reference to FIG. 10 the rectangular cross section is advantageously made so narrow that just one semiconductor light source 60 can just be attached to the entire surface of the optics. For better clarification of the 3-dimensional configuration of the inventive optics shown in FIG. 4, a 3-dimensional edge image of this optics is shown in four different views in FIG. 4a. The illustrations there emphasize the edges of the optics, as do the hatched areas A, B and 10 (light exit opening).

In a particularly advantageous manner, it is conceivable to either mirror the outer surfaces A and B of the parabolic reflector or to design them to be totally reflective. In this way, the best possible light yield of the semiconductor light source is achieved, since almost all of the light emanating from the light source is converted into a common parallel beam.

FIG. 5 shows the projection of the side surface E of the optics according to the invention, the contour of the cardio-shaped central region and the parabolic reflector adjoining it on the outside clearly appear. The reflector is now ideally designed in such a way that refraction takes place in the regions 40a and 40b of the contour corresponding to the surfaces C and D when the beam 23a emerges so that the beams 23a and 21 emerging from the optics run in parallel. The course of the light beam 23a should in this case be turned by rotating the parabola contour 41a corresponding to the outer surfaces A and B of the optics

Direction towards 41b can be influenced. For this purpose, the parabolic contour 41 must be turned inwards by the necessary angle in order to avoid that a light beam 23x is removed from the optics. occurs, which does not run parallel to the other parallel beam.

In the inventive design of the optics of the lighting system, the deflection and alignment of the light takes place predominantly in the vertical plane, that is to say the light is bundled into a horizontally running strip. As a result of a calculation, FIG. 6 shows the energy distribution of the light emerging from the optics according to the invention. In the upper part of the figure, the intensity profile of the light emanating from a horizontally arranged optic is shown in a false color representation. Next to and below, the intensity distribution in the x-direction and y-direction is shown in curve form. This makes it clear that the light beam emerging from the optics is strongly bundled in the y direction. The light intensity emanating from the optics is also clearly localized in the x direction. In the simulation on which FIG. 6 is based, it was assumed that the light source was centered with respect to the light entry surface F is attached to the optics, as will be explained in detail later, however, it is also conceivable to install the light source at a different position on the light entry surface F in order to thereby specifically influence the illumination characteristics of the optics.

The horizontal width of the light spot can be influenced in a particularly advantageous manner by inclining the side surfaces E of the optics in such a way that the optics tapers from the light exit surface G to the light entry surface F. A corresponding geometry is shown in FIG. 7, which shows a side view from the direction of the side surfaces A and B. It is clear that in this profitable embodiment of the invention the height expansion Fj of the light entry surface F of the optics is smaller than the height expansion Gj whose light exit surface is 10. Such elements, in particular also with parabolic side surfaces, are known from solar technology (CPC, compound parabolic concentrator). The following relationship applies: sinαl _ K, _{(1> 8)} sinα2 F _t where al and a2 describe the respective angular range within which the light beams (25, 26) are received by the optics, or under which they then emerge from the optics. Equation (1.8) shows that increasing the exit area reduces the angular range in which the light is emitted. In a particularly profitable manner, it is possible to create the largest possible acceptance angle in the beam direction in order to avoid optical losses. This can be achieved either by mirroring or by appropriately shaping the curvature of the side surfaces E, so that total reflection occurs there. FIG. 7 shows, by way of example, with a dashed line, the curvature profile of the side surface E for a parabolic curvature. In accordance with the procedure described above and also shown in FIG. 5, a suitable parabolically shaped reflector can be adapted according to the invention to a cartoval central region shaped in this way, in order to optimally utilize the light emitted by the light source.

In a further advantageous embodiment of the optics according to the invention, the cross section of the light entry surface F of the latter, deviating from the generally rectangular shape, has a trapezoidal shape, as shown in FIG. The side surfaces of this trapezoidal shape are inclined by the angles α and β relative to the horizontal. It is conceivable that the two angles of inclination and ß are the same in their amount or else to choose different from each other. According to the illustrations in FIG. 6, FIG. 9 shows the result of a calculation of the energy distribution of the light emerging from the advantageous optics with inclined side surfaces. The angle of inclination and β were chosen to be 5 ° and 7 °, respectively. In the upper part of the figure, the intensity profile of the light emanating from an essentially vertically arranged optic is again shown in false color. In addition and below, the intensity distribution at certain positions in the x-direction and y-direction is shown in curve form. As can be clearly seen from the figure, the radiation characteristic of the optics in the far field, contrary to the case shown in FIG. 6, has a clear curvature perpendicular to the radiation direction. On the other hand, this radiation characteristic also shows a clear light / dark transition. In this simulation, too, it was assumed that the light source was centered with respect to the light entry surface F of the optics is attached.

FIG. 10 shows the projection of the light entry surface F of the optics according to the invention, in this case with a rectangular cross section, with a semiconductor light source 60 adjoining it in the center. In general, the semiconductor light source 60 is applied centrally on the light entry surface as shown in FIG. 110. In this case, the thickness dimension of the optics is selected in a profitable manner so that it exceeds the dimensions of the semiconductor light source 60 as little as possible. In this way, optics are created with an optimally small space requirement, which makes it possible to accommodate a large number of optics within an illumination source according to the invention in the smallest space and thus to achieve maximum light output. By moving the semiconductor light source 60 along the connecting line between the points P1 and P2 it is achieved that the light emerges asymmetrically from the optics. It is conceivable either to position the semiconductor light source 60 fixedly at any point along this connecting line in order to achieve the desired asymmetrical radiation characteristic, or to arrange the optics displaceably above the semiconductor light source 60 so that the desired asymmetry of the light emission is achieved by suitable displacement the optics compared to the semiconductor light source 60 can be achieved. Alternatively, it is also conceivable to arrange a plurality of semiconductor light sources at the light entry surface F of the individual optics along the connecting line between P1 and P2 instead of a displaceable optics. In this way, the light characteristic of the light emerging from the optics can be changed in an advantageous manner without mechanical adjustment, simply by targeted electrical control and selection.

When arranging the optics for the lighting device according to the invention, it is advantageously conceivable to individually arrange the individual semiconductor light sources 60 for the respective optics arranged in a field in such a way that the lighting device has an asymmetrical radiation characteristic. In addition or as an alternative, however, it is also conceivable to achieve the asymmetrical radiation characteristic by arranging individually shaped optics adapted to the desired light emission, in which case it is conceivable for some of the optics with a rectangular light entry surface F (corresponding to FIG. 10) and another part of the optics with trapezoidal light entry surfaces F (corresponding to FIG. 8). The optics can also at least partially correspond in a profitable manner. chend be executed in the embodiment shown in Figure 7.

If at least some of the individual optics within the lighting device are assigned a plurality of semiconductor light sources, a swiveling of the luminous cone emitted by the device or generally a change in the asymmetrical lighting properties of the lighting device can be effected in a simple manner by means of electronic control, in each case by one of the several semiconductor light sources assigned to an optical system is controlled. Such an alternate control of the light sources attached to an individual optic leads to the same beam swiveling as is the case from the prior art for displaceably arranged lens optics, without however having to resort to a fragile, less robust mechanism. Furthermore, this advantageous embodiment also offers the possibility of individually controlling the individual optics within a group of optics without effort, which is not economically feasible in a mechanically variable deflection device.

In a particularly profitable manner, the lighting device is designed such that the semiconductor light sources can be dimmed or activated or deactivated independently of the others, individually or in groups, in order to be able to illuminate the surroundings in a targeted and situation-appropriate manner.

In a particularly advantageous manner, the inventive lighting device is suitable for use as a headlight in a motor vehicle in order to asymmetrically illuminate the surroundings in front of the vehicle. In a profitable manner, when used in a motor vehicle, the individual optics assigned to the headlight are aligned with respect to the road surface in such a way that the x-axes of the optics run essentially parallel to it; ie the individual optics should be arranged essentially vertically (corresponding to, for example, FIG. 4).

Claims

DaimlerChrysler AG Finkele patent claims

1. Lighting device, in particular for use in a motor vehicle, which is formed by a field of individual optics, each of which is assigned at least one semiconductor light source, in particular a luminescent diode, characterized in that the light entry opening of the optics has an elongated, essentially rectangular shape that the optics have a central area perpendicular to the light entry surface, the projection of which into a two-dimensional plane corresponds to a cylindrical 2-dimensional carto oval, and that this central area is combined with a parabolic reflector.

2. Lighting device according to claim 1, so that the outer surfaces A and B of the reflector are rotated in the direction of the central region of the optics in such a way that all steels emerging from the optics are essentially parallel.

3. Lighting device according to one of claims 1 or 2, characterized in that the outer surfaces A and B of the reflector are mirrored or designed to be totally reflective.

4. Lighting device according to one of the preceding claims, that the side surfaces E of the optics are inclined in such a way that the optics tapers from the light exit surface G to the light entry surface F.

5. Lighting device according to claim 4, so that the side surfaces, in particular by mirroring or curvature, are formed in such a way that a large acceptance angle arises in the beam direction.

6. Lighting device according to one of the preceding claims, that the cross-section of the light entry surface of the individual optics, deviating from the rectangular shape, has a trapezoidal shape, the side faces of which are offset by the angles a and ß

Normals of the base are inclined.

7. Illumination device according to one of the preceding claims, that a plurality of semiconductor light sources are assigned to at least one of the individual optics.

8. Beieuchtungs device according to one of the preceding claims, characterized in that the individual semiconductor light sources can be switched individually.

9. Lighting device according to one of the preceding claims, that the optics and the semiconductor light sources are arranged displaceably relative to one another.

10. A method for controlling a lighting device according to one of the preceding claims, that the semiconductor light sources can be controlled individually as a function of the desired radiation characteristic, with the semiconductor sources being able to be activated in whole or in part.

11. The method as claimed in claim 10, so that in the event that a plurality of semiconductor light sources are assigned to a single optical system, these are controlled as a function of the desired radiation characteristic.

12. The method according to any one of claims 10 or 11, so that the lenses and the semiconductor light sources are shifted against one another in order to change the radiation characteristic of the lighting device.

13. Use of the lighting device according to one of the preceding claims as a motor vehicle headlight for asymmetrical illumination of the surroundings in front of a motor vehicle.