EP0930600B1 - Optical element comprising LED and two lenses for the generation of pointlike light sources for traffic signs and display panels - Google Patents

Abstract

The optical element has an LED (1), at least one converging lens (2) and a diverging lens (3). The LED and the lenses are arranged in a common housing (4) coaxial to the geometric axis of the element and at an angle of inclination to the geometric axis. The light emitted from the LED (1) is essentially all collected by the converging lens (2) and directed in a bundle to the diverging lens (3) which is a known distance away. It is then deflected to provide a predetermined light distribution in the observation direction. The diverging lens (3) is arranged such that all light beams leaving it are at an angle less than the angle of inclination. The housing (4) is formed as a complete cylindrical tube around the LED and the lenses. It is provided on its inside with a light absorbing color and/or structure.

Description

The invention relates to an optical element for traffic signs, in particular Variable message signs, scoreboards or the like, the at least one Condenser lens, one arranged in front of the convergent lens light source and one behind the Concentrating lens arranged dispersing lens, wherein convergent lens and diffuser lens the same have optical axis, on which the light source is arranged, and wherein Conveying lens, scattering lens and light source surrounded by a common housing are.

Such a display panel is disclosed in DE 42 25 139 A1. The said Document deals with the problem, at one above the viewer mounted display panel to direct their light emission as possible downward without the To tilt the table itself. The solution to this problem is provided by a corresponding optics, which consists of two elements, namely one of the light source close lying condenser lens and a scattering disc called element, close to the Lens is arranged and forms the front end of the optical element. However, the latter element is used to the exiting light down radiate.

In US 5 504 350 A a lens arrangement is associated with a Laser diode disclosed. The lens arrangements described herein are collectively and dispersing lens are not arranged at a distance from each other, but rather it is the collecting lens glued to a unit with a cover glass and the scattering lens. Moreover, in the context of these lens arrangements, a cup-shaped housing in which only the condenser lens is arranged; the scattering lens is on the Cover glass glued outside of the housing.

So far, in variable message signs, the light of one or more lamps means Optical fibers on a variety of points of light, which symbols or Characters are arranged, split and the switching between the ads through Turning on and off the associated lamps causes.

Since then succeeded, light emitting diodes (LED) with high light bundling, light intensity and Lifespan in a variety of colors or in almost all specified signal colors It has been tried to compare the advantages of the light-emitting diodes with those of the conventional ones used incandescent lamps, such as radiation of a directed light beam, essential Higher life and very favorable energy ratio in colored light, in advertising and information signs and traffic signaling. especially is trying to technologically complex fiber optics in variable message signs to replace. But the use in graphics-capable displays is forced, because at corresponding wiring each LED can be controlled individually and therefore individually programmable representations and information allowed.

Light-emitting diodes differ from conventional light bulbs not only by the Light generation by means of semiconductor technology, which is a nearly monochromatic colored Generated light, but also by integrated optical measures for light guidance, which on the one hand improve the useful light component, on the other hand universal, cheap Generate light distribution characteristics in narrow and wide beam versions, so that the LED is used directly as a signal light without any further optical measures can be.

While for advertising and information signs no higher-level regulations exist in terms of their photometric properties, such exist in the field of Traffic engineering for a long time, whereby in particular light color, Brightness, light distribution, uniformity and above all a low phantom light (pretense of a switched on Signal light from incident sunlight) are. The commercial designs correspond These requirements only partially, but still used as long as customer-specific versions of the LED completely uneconomical and from some manufacturers too for technological reasons currently are impracticable.

Be in traffic technology, the LED directly without additional used optical measures, light color, Brightness and uniformity mostly the specifications, The required light distribution is often only by pre-circuit reachable with additional lenses, the main problem is that high phantom light. The lentil of the usually crystal clear transparent LED body bundles incident sunlight directly on the highly reflective internals in the Inside the LED, such as reflector and reflector edge, Terminal lugs and contact points from where it is thrown back. Because of the crystal clear LED body is also the phantom light is relatively whitish and unfiltered and often appears brighter than the sun in unfavorable position actual signal light.

In traffic engineering, the requirement prevails that for phantom light assessment a sun reading of 10 degrees vertically above the optical axis of the signal (mostly the Direction of maximum light emission) is assumed. At such angles, anyway, additional measures be taken to the effect described above limit.

While with signalers those with a variety of LEDs in a fixed arrangement equipped signal unit in their entirety regarding phantom behavior and can be improved are with variable message signs preferably consider the individual light point optics, so that these in any number and arrangement too Symbols or characters can be combined.

A known measure is to have a convergent lens in a suitable distance in front of a relatively wide-beam LED to set (Fig. 8). The obliquely incident sunlight is at sufficient distance of the LED to the convergent lens for Completely outside the LED passed and on housing surfaces absorbed. However, this arrangement has the disadvantage of large space requirement and is therefore not suitable for universal application.

Another measure is the preassignment of horizontal slats (Figure 9 above) or pipe sections (Fig.9 Middle) to shield the sunlight, too small, long sun visors or barges (Fig.9 below), especially used with multiple LED spots, such as which is also common with signalers in principle. Here is especially disadvantage that these attachment elements either Protected by a windshield from weather and dirt or need to be cleaned frequently. You will be in front all used for LED arrangements in the rectangular grid.

Another measure is the use of in the Signal color colored lenses or LED bodies (tinting). The sunlight must pass through the colored component twice, especially the foreign color components of the light be filtered out, the LED light only once, with the Coloring for the actual signal color as permeable as possible is. This makes the sunlight essential weakened, the useful light decreases in much less Dimensions. The disadvantage is not only the lower useful light intensity, resulting from a higher number of points of light must be compensated, but also the phantom light in Signal color, which is opposite to white phantom light in many applications are considered particularly critical.

Another disadvantage is the usually circularly symmetrical Light emission of the LEDs, which leads that a large amount of light is emitted unused into irrelevant areas, if not also optical measures are taken against it.

Furthermore, commercially available light-emitting diodes emission characteristics, which are usually do not agree well with the required light distribution of the light spots. hereby Without additional optics, disproportionately more LEDs often need to be used just to turn in light-poor areas still have enough light. In many cases, the required light distribution can not be achieved at all without additional measures.

The object of the invention is to provide a universal LED optics for variable message signs develop, which can be used without windscreen and with a smooth outside and the benefits of the LED, such as low energy consumption, long life and Maintenance-free benefits, on the other hand, but has virtually no phantom light, which individually adaptable, in particular oval light distributions without substantial Loss of light allows to different LED designs, LED suppliers or Abstrahlcharakteristiken is adaptable and the smallest possible axial distance adjacent optics allowed.

This object is achieved according to the characterizing part of Claim 1 solved.

Further advantageous embodiments of the invention are in the subclaims characterized.

1 shows in section a non-inventive example, to facilitate the understanding of the invention.

The invention will now be described with reference to the drawings. FIGS. 2 to 7 show preferred embodiments in section, Fig. 8 and 9 previously common solutions compared.

Fig. 1 shows a vertical section through a non-inventive optics. The light source 1, Shown in all examples as LED with a broad emission characteristic, you send Light 6 on the immediately before coaxially arranged converging lens 2. This is on the one hand a better light bundling possible than by the use of a narrow beam LED, on the other hand, the light bundling can be affected. Within the LED 1 are installed 19 internals. They serve the power supply and the Positioning of the actual luminous semiconductor chip 20, but also form a Auxiliary reflector 21, the side-emitting light in the main emission reflect reflected and therefore have high-gloss surfaces. The LED works therefore for optics located in the immediate vicinity not as spotlights, they emits a mixture of direct and reflected light rays. The light can Therefore, only very poorly focused, which is why for the lens geometries too no physically accurate information can be given, but only qualitative Descriptions of their properties.

At each point of the surface of the converging lens 2 exit light beams 7, whose Divergence δ is due to the nature and size of all internals 19, 20 and 21 and for each position of the converging lens 2 must be determined separately. The geometry of the Conveying lens is therefore preferably determined in iterative calculations. Conveniently, the light beams 7 are deflected so that as many as possible Light rays fall through the scattering lens 3, which is coaxial at a certain distance is arranged to the converging lens. There, the light beams 7 are deflected so or scattered, that the desired light distribution 8 is achieved.

The angle α gives the light incidence limit for stray light, especially the light of the low sun 12, which still does not produce phantom light, before. The regulations go from a sun's position of 10 degrees vertically above the Reference axis (mostly the direction of maximum useful light intensity) out. Because of unavoidable tolerances and the Size of the sun's diameter itself is recommended Fixing this inclination angle α to about 9 degrees, it But you can also choose any other angle become. The size of the angle Á certainly determines the entire geometry of optics.

The geometry of the scattering lens 3 is set so that the emerging light beams 8 with their inclinations β always remain below the inclination angle α. Hiedruch will ensured that in the opposite direction no Sunbeam 12, provided it is at an angle γ greater than or equal to the optics, the same way back either over the reflector 21 or directly to the Chip 20 of the LED 1 finds and so a lighting of the LED simulated. Nevertheless, light rays 22 to the LED 1 penetrate. They meet others, not immediately involved in the light emission surfaces 23, or often reflected several times on the glass body of the LED and broken and generate in this way also one certain phantom light. The length of the optics is therefore preferred set so that no sunbeam at all 12, the angle of incidence γ greater than / equal the inclination angle α, to the convergent lens 2 or LED 1 can penetrate. This is the case inside with a mat as possible, light-absorbing Surface structure, such as Circumferential grooves and preferred executed in black, so that it hits all the rays of light 12 can absorb as well as possible.

It is immediately obvious that sun rays 12 with an arbitrarily steeper angle of incidence γ in the housing 4 on absorbed in the front, so for all positions of the sun assumed the phantom freedom above the inclination angle α can be.

The housing 4 is completely closed on the circumference, on the one hand, to be able to absorb light at every point, on the other hand, to allow light exchange within the device prevent, but also to the pollution of the lenses too prevent.

The optic is mounted in a matrix plate 24. The Dimensions of the components are not significantly larger in Diameter than the LED itself, so is also one accordingly tight arrangement possible. At the purchase of certain Light losses, the diameter can be even further be reduced.

It is possible to achieve a smooth exterior Diffuser 3 with flat front surface run and the Completely install spreaders on the inside, It is even conceivable, the scattering lens 3 completely flat without Refraction to perform when the of the converging lens. 2 generated light distribution already corresponds. In this case could also be used instead of the scattered lenses 3 a common Windscreen can be arranged in front of the device.

Fig. 2 shows a construction which is generally a lesser Length as shown in Fig. 1. The divergent ones Beams of light 7 cross each other before striking on the scattering lens 3 and form there a focal spot. 9 For this purpose, the converging lens 2 requires a higher refraction of light as in the previous example. Depending on the desired light distribution 8 and the resulting refractive power of the scattering lens 3, there is also the possibility that all the sun's rays 12, which has an angle of incidence γ greater than or equal to Include angle of inclination α, absorbed on the housing wall become.

Through the focal spot 9 also creates a free space between Housing wall and Nutzlichtstrahlen which either by a constriction of the housing 4 at this point, better but by the installation of at least one aperture 10 the Phatomlichtverhalten can significantly improve.

3 shows an aperture 10 in the region of the focal spot 9, the opening 11 to the periphery of the light beam 7th is adapted. It holds sunbeams 12 from further penetration completely inside the housing.

The light absorption on a housing wall is done by an unavoidable surface gloss never completely, so that on the housing wall diffusely reflected light rays can reach the LED. Another improvement of Phantom light effect is possible if all penetrating Light rays 12 are caught at the aperture 10 can.

Fig. 4 shows such optics in plan and plan. The Spreading lens 3 has a focal point 14 in the region of Focal spot 9, where there is also a diaphragm 10. Of the Distance to the scattering lens 3 and the aperture size is so chosen that the focal point of sun rays 12, which parallel to the inclination of the inclination angle α, within the aperture 10 or just behind it. So no sunbeam can penetrate further into the interior.

Under certain circumstances, even low light losses, represented by the cut off useful light beam 13, be taken over. It is also shown that the Aperture 10 is not required here in the upper area of the optics is because no sunlight can get there.

The formation of the scattering lens with focal point 14 has to Result that the light distribution 8 according to the optical imaging laws an upside down image of the aperture 11 and the prevailing light distribution there and intensity. The definition of the light distribution must in this case by appropriate detailing of the Conveying lens 2 done by the light beams 7th be swiveled more or less. If necessary, join increased losses due to edge light rays 13 at the diaphragm 10, or no longer on the scattering lens 3 hitting Nutzlichtstrahlen on.

Fig. 4 further shows that the focal point 14 only in vertical Direction is required. In the plan you can see that with the help of the vertical scattering optics 15 on the inside the scattering lens 3 a horizontal width spread of the radiated Light 8 is done, so that a total of any oval light distribution can be achieved.

Fig. 5 shows the deflection of the light distribution 8 by a Angle e, which by a horizontal lens structure 16 is effected. This will increase the visibility in those cases improved, in which the display device is not inclined can be tilted down. At the same angle ε the phantom light sensitivity also improves because also the sunbeams 12 downwards by this amount be directed against the aperture 10.

For all versions with non-circular symmetrical Light distributions, screens and optics are recommended Unround design of the optics, so that the correct installation is ensured by positive engagement.

Fig. 6 shows in addition to the round shape an oval design for optics with horizontal axis of symmetry, in particular Also oval radiating optics, as well as an egg-shaped design with only a single positioning possibility.

In a further embodiment of the invention, the housing 4 also run split, making the aperture light can be integrated. The subdivision allows in particular the construction of a modular system with different Light distributions and manufacturer-specific LED designs. Fig. 7 shows such a modular system optical, mechanical and electrical interfaces represents.

In the front housing 4, the scattering lens 3 and the aperture 10 housed, the rear housing contains the respective Condenser lens and the LED. While the front housing 4 together Aperture 10 is the same here, the rear housing varies depending according to LED type. Since each LED design has its own radiation characteristics has, must also the condenser lens be customized. If in the focal spot 9 each LED type has approximately the same light distribution can they are arbitrarily combined with different scattering lenses 3 become. These can have the same outer barrel, the different scattering structures are located on the Inside. Above a LED 1a is shown in SMD technology, which practically always soldered on a board is. So can all the LED 1a on a common board 17a, which also equal the interconnection and power supply includes, be attached. The board 17a becomes after soldering on extensions 18a of the associated housing 4a caught, so that the optics all together be supported and aligned. Even the mix with other types of LED is possible, if necessary, their housing 4b are recessed in the board 17a. Below is an LED 1b in standard design ø3 or ø5 mm. This can either also be soldered onto a board 17b, For this purpose extensions 18b are used for the exact positioning Housing 4 b attached. But you can also freely wired be, especially in small quantities and individually designed devices recommends.

Especially with free wiring, it is possible to Move housing parts against each other and so the look to adjust. For this purpose, at the contact points 25 Thread, Schnapprillen or the like may be appropriate. All Optics are mounted in a common matrix plate 24 and have the same look to the viewer. Of course, also different front housing 4 with different apertures 10 may be present. Furthermore, All illustrations can also be with colored lenses or Be carried out light sources, which through the lenses self-generated reflex phantom light reduced. Both condenser lens 2 as well as scattering lens 3 can also be used as a Fresnel lens be executed.

The representations of the LED or light sources are only exemplary. The rapid development in this field is constantly creating new designs and functional principles, which ongoing adaptations of housing 4 and converging lens 2 require. Of course, any other light sources are used.

Claims (4)

1. Optical element for traffic signs, in particular variable traffic signs, display panels or the like, which comprises at least a positive lens (2), a light source (1) arranged upstream of the positive lens (2), and a dispersing lens (3) arranged downstream of the positive lens (2), the positive lens (2) and dispersing lens (3) having the same optical axis on which the light source is also arranged, and the positive lens (2), dispersing lens (3) and light source (1) being surrounded by a common housing (4), characterized in that a focal spot (9), resulting from the arrangement of the light source (1) relative to the positive lens (2) and formed by the diverging light beam (7) emerging from the positive lens (2), is situated upstream of the dispersing lens (3).
2. Optical element according to Claim 1, characterized in that a constriction, in particular a stop (10), which is arranged in the region of the focal spot (9) is provided in the housing (4).
3. Optical element according to Claim 1 or 2, characterized in that the focal point (14) of the dispersing lens (3) is situated in the region of the focal spot (9).
4. Optical element according to one of Claims 1 to 3, characterized in that the housing (4) is provided on the inside with a black colour and/or a mat surface structure, for example circumferential grooves.

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