EP2425418B1 - Illuminated sign for displaying a command and/or notice for taxiing aircraft traffic at an airport - Google Patents

Description

The invention relates to an illuminated sign for displaying a command and / or reference for the rolling air traffic at an airport according to the preamble of claim 1.

Such luminescent signs are arranged on taxiways and in the apron area at airports and have to comply in terms of their size, their photometric values, their protection and the like international standards, such as in Appendix 14, Volume 1, Chapter 5.4 and Appendix 4 of the ICAO (short for: International Civil Aviation Organization ) is given. Basically, a distinction between mandatory signs and signs. Mandatory signs are used to identify a site that, if exceeded, requires authorization from the tower. The respective mandatory signs are displayed in white on a red background. Examples include taxiway stop line signs, runway stop signs, Cat I, II and III runway category signs, runway designation signs and "NO ENTRY" signs. All other signs are informational signs. Signposts indicate destination labels with directional arrows, with black information signs on a yellow background. Location signs indicate the taxiway currently in use, with the signs in yellow on black Background are shown. Special signs show the so-called runway markers whose signs are shown in white on a black background.

For indoor illuminated signs are different light sources in use. From the product publication "PVO: Internally Illuminated Guidance Signs with Fluorescent Lamps (A.04.251e)", published by ADB - A Siemens Company under the order no. E10001-T95-A51-V2-7600, the use of a fluorescent lamp as a light source is known. This is characterized by a high light output of up to 100 lm / W, making it one of the most effective sources of light for indoor lighting. However, its lifetime is typically limited to less than 10,000 hours. In addition, the bias resistor of the light source may cause high frequency distortion in the constant current network. These distortions may hinder, for example, communication signals superimposed on the current signal. Another disadvantage of fluorescent lamps is their divergent switching times, which increases the time from power up to the full operation of the shield. Full operation is typically only achieved after about a minute of warm-up. Another disadvantage is the high reactive load of the ballast on the primary circuit, which limits the total number of signs in a circuit. Finally, there is a disadvantage in the reduced functionality at low temperatures, which is noticeable in both the switching times and in the light yield.

By contrast, the product specification "PVH: Internally Illuminated Guidance Signs with halogen lamps (A.04.255e)", published by ADB-A Siemens Company under the order no. E10001-T95-A96-V1-7600, the Use of halogen lamps known as light source. In particular, tungsten halogen lamps are used in low temperature environments. However, halogen lamps suffer from a significantly low lifetime, typically 1,500 hours, and low light output of approximately 25 lm / W or even less. Although these light sources have instantaneous switching times, but to achieve their full function in terms of light intensity and color location, they require a considerable period of time, for example 1.5 minutes or more. This precludes the use of such light sources for applications where fast response time is required, such as with alternating signs.

For some airfield applications, a brightness control of the light source is required to fill the important international standards. A dimming of fluorescent lamps is hardly possible, certainly not at low temperatures. Dimming halogen lamps, on the other hand, is easily possible, even at low temperatures. For halogen lamps have the disadvantage that at low currents a significant shift of the color locus to yellow is observed, resulting in a deterioration of the color contrast. For example, with mandatory characters representing white characters on a red background, the letters appear yellow while the red turns orange.

On the other hand, the product publication "PVO-LED: Interior illuminated taxiway signs, reference location mark" published 10/07 by Siemens Bacon Wien, discloses the use of light-emitting diodes or light-emitting diodes, hereinafter also referred to as LED, as the light source. The light emitting diodes are arranged in the housing of the illuminated sign and backlight the display panel by direct irradiation. In case of failure of individual LEDs of Light source suffers this illuminated sign with the disadvantage that this is accompanied by a visible destruction of the illumination homogeneity. In the worst case, the uniformity of lighting required by international standards can no longer be met. The number of light-emitting diodes used in the known illuminated sign is defined by the size of the display panel, by the distance between the light-emitting diodes and the display panel and by the radiation pattern of the light-emitting diodes. As a result, the number of LEDs used can not be reduced arbitrarily, such as through the use of light emitting diodes with a high light intensity or of light emitting diodes with a better light output.

Since light-emitting diodes are to be regarded as punctiform light sources, objects in the light path between the light source and the display panel produce sharp shadows on the display panel. Such sharp shadows can lead to misinterpretations of the bid or hint displayed on the display panel. Another disadvantage with the use of light emitting diodes for direct lighting arises when these are retrofitted into a light sign, which was originally designed for the use of a fluorescent lamp as a light source. Thus, for example, the transmission of the blue portion of the light spectrum emitted by an LED can be visible through a yellow or red display panel. Thereby one sees the LED light source through the display panel in a different color, e.g. Violet in the case of a red display panel. Incidentally, the transmission coefficient for the LED spectrum is too small for display panels designed for fluorescent lamps or halogen lamps as the light source.

CA 2260583 describes a light-emitting sign for displaying an indication, comprising a frame which supports a transparent front wall and an opaque rear wall, and a light source with light-emitting diodes arranged between the front wall and the rear wall.

DE 94 12944 U1 describes a traffic sign, in particular as a destination and location sign or as a mandatory sign on aerodromes serving rolling traffic signs with a housing that is coated inside white matt, the one or double-sided on the side surfaces or a caption disk and equipped with the side surfaces of the inside lighting lamps is. The lamps are connected via a over the entire length of the housing extending arranged and their light heads receiving light carrier tube. The light carrier tube has a light exit slot extending over the entire length and facing the white coated side surface.

WO 02/089101 describes a luminous sign comprising light emitting diodes as illumination means, which are arranged within a body. The body includes a light-diffusing inner surface and a light-transmitting screen, which are disposed opposite to each other. The light emitting diodes are arranged such that emitting light is directed substantially to the light scattering inner surface of the body prior to transmission through the light transmitting screen.

The invention is based on the object to provide a luminous sign of the type mentioned, which overcomes the mentioned disadvantages while maintaining the advantageous use of light emitting diodes as a light source.

The object is achieved by a generic illuminated sign with the features specified in the characterizing part of claim 1. The illuminated sign has a diffusion panel, which is designed for scattering and / or backscattering incident light, wherein the light-emitting diodes is aligned on the diffusion panel, that the display panel is illuminated by stray light of the diffusion panel. An essential feature of the illuminated sign according to the invention thus consists in the indirect backlighting of the display panel by one or more light emitting diodes, which emitted by their orientation light initially falls mainly on the diffusion panel and scattered by this and / or backscattered to illuminate the display panel inside the housing. Due to the spacing between the diffusion and display panel, the latter is illuminated by a significantly larger virtual light source. Indirect lightening reduces or even eliminates sharp shadows cast on the display panel by objects placed in the light path between the diffusion panel and the display panel. Only partial and intrinsic shadows are visible, causing only soft brightness variations on the display panel. Thus, when retrofitting existing signs with existing indirect light sources according to the invention existing objects can be left in the housing, which significantly reduces the downtime by retrofitting. The indirect spreading lighting promotes considerably a uniform Color on the display panel. Indirect distribution lighting also achieves a consistent color location over the entire display panel, which prevents irritation in color perception. A particular advantage of indirect lighting is the maintenance of the efficiency of the illuminated sign in the event of failure of individual or even several light-emitting diodes, since the contrast to the background light is smaller than in direct lighting. Thus, the standard requirements can continue to be met even if individual LEDs fail. Similarly, in indirect spread lighting, hot spots due to a local high power density on the LED semiconductor chip are not visible on or through the display panel. Finally, in the case of indirect scattered illumination, it is possible to dispense with additional optical elements, such as eg light guides or beam splitters.

In a preferred embodiment of the illuminated sign according to the invention, the diffusion panel are formed as a rear wall and the display panel as a front wall of the housing, wherein the diffusion panel is provided with a scattering layer for the backscattering of incident light. The diffusion panel is here opaque, but inside provided with a litter layer, which scatters incident light back. The application of a diffusive coating on the back wall virtually increases the surface of the LEDs. The backscatter is also essential for the homogeneity of the illumination of the display panel, for soft shadow contours as well as for a consistent color location and a uniform color. Preferably, the housing has two side walls, a top wall and a bottom wall, which are either also provided with a litter layer or formed inside highly reflective with advantage are. In the latter variant polished metal can be used or a highly reflective coating with low scattering properties. As a result, the brightness is increased, in particular at the edge of the display panel.

• Das Diffusionspaneel ist lichtundurchlässig, aber von beiden Seiten zurückstreuend ausgebildet. Vorder- und Rückwand sind als Anzeigepaneel ausgebildet, wobei auf beiden Seiten des Diffusionspaneels Lichtquellen angeordnet sind, die getrennt voreinander ansteuerbar sind. So kann das Leuchtschild zur wechselnden Anzeige auf Vorder- und Rückseite verwendet werden.
• Das Diffusionspaneel ist lichtdurchlässig oder halblichtdurchlässig ausgebildet, wobei Vorder- und Rückwand als Anzeigepaneele ausgebildet sind. Die Lichtquelle kann nur auf einer oder zu beiden Seiten des Diffusionspaneels angeordnet sein, so dass die Anzeigepaneele durch reflektiertes und/oder hindurchtretendes Streulicht beleuchtet werden.

In an advantageous embodiment of the illuminated sign according to the invention, the diffusion panel is arranged in the housing between a front wall and a rear wall of the housing and the rear wall and the front wall are formed as display panels. The at least one light-emitting diode is arranged between the rear wall and the diffusion panel. Here are several variants possible:

• The diffusion panel is opaque but backscattered from both sides. Front and rear wall are formed as a display panel, wherein on both sides of the diffusion panel light sources are arranged, which are separately controllable. Thus, the illuminated sign can be used for changing the display on the front and back.
• The diffusion panel is translucent or semitransparent formed, the front and rear walls are designed as display panels. The light source can be arranged only on one or both sides of the diffusion panel, so that the display panels are illuminated by reflected and / or transmitted stray light.

The diffusion panel of the illuminated sign according to the invention preferably has color pigments whose distribution determines a color location of the display panel.

In an advantageous embodiment of the illuminated sign according to the invention, the display panel has a disc and attached thereto a film, which according to the displayed bid and / or Information sign is colored. The disc consists of a 5 mm thick special Plexiglas, such as translucent polycarbonate, while the inside or outside glued foil is a color layer with Lambert radiator properties. Alternatively, the display panel may be given its color design by a layer of paint applied to the pane or by coloring the pane.

In a preferred embodiment of the illuminated sign according to the invention, the at least one light-emitting diode is designed as a high-power light-emitting diode. The high-performance LED is charged with a rated current of at least 100 mA and has a luminous intensity of at least 20 lm. The light output may also increase up to 100 lm / W, which allows the restriction to a smaller number of LEDs in order to achieve the standard brightness levels required. Compared to conventional light sources, such as fluorescent and incandescent lamps, the light-emitting diodes have significantly longer lifetimes of more than 30,000 hours or more than 50,000 hours or even over 100,000 hours. Luminescence diodes are also at low temperatures below 0 ° C, preferably below -40 ° C, functional, by having very short switching times and the light output and the setting of the color place done instantaneously. In addition, light-emitting diodes are adjustable in their brightness, without the color location shifts. High-performance light-emitting diodes have a low thermal resistance of, for example, 10 K / W, which makes it very easy to achieve the dissipation of heat, for example by enabling small base-point solutions for the heat sink. Reduced heat sink heatsinks reduce self-shading on the display panel, which improves the light output of the light emitting diodes. About that In addition, the low thermal resistance of the LEDs contributes to the extension of their life, which depends directly on the base temperature and the applied flow stream. Compared to conventional light sources, such as a fluorescent lamp, consumes a bid sign, which is operated with high-power LEDs, only 2/3 of the current. The low heat losses heat the illuminated sign only moderately, which not only increases the life of the LEDs, but also the color film on the display panel. Incidentally, the low voltages with which light-emitting diodes are operated considerably reduce the human accident risk. As an alternative to high-performance light-emitting diodes, it is also possible to use ultra-bright light-emitting diodes which emit a light intensity of, for example, 10 Im at a power consumption of 200 mW. Ultrabright light emitting diodes can be arranged close together to achieve comparable brightness characteristics to high performance light emitting diodes.

In a preferred embodiment of the illuminated sign according to the invention, the at least one light-emitting diode is designed to emit white light in the form of a Lambert radiator. White light-emitting diodes now achieve a comparable light output to the fluorescent lamps. The generation of white light is known to be based, for example, on phosphorus-based conversion from blue to white light. White light emitting diodes are commercially available with different lenses or without an external lens. Can be used both inorganic and organic light-emitting diodes, but also so-called potential well-emitting diodes. Particularly suitable for indirect lighting is the lambert radiation characteristic. Their maximum light output is perpendicular to the PCB, wherein beam directions deviating from this main direction are attenuated with the cosine of the deviation angle. Alternatively, laterally radiating surface radiators or radiators with a Batwing characteristic in the form of bat wings can also be used.

In a preferred embodiment of the illuminated sign according to the invention, the at least one light-emitting diode is covered by a transparent protective layer. The protective layer is highly transparent, so that the transmission losses are low. It can for example consist of polycarbonate or PMMA and serves to protect the LEDs from dust and dirt, which could significantly affect the light intensity of the LEDs.

In an advantageous embodiment of the illuminated sign according to the invention, the light source in the form of a matrix arranged on light-emitting diodes. The matrix is, for example, a planar arrangement which is aligned parallel to the rear wall or to the display panel. Alternatively, the matrix can be arranged laterally on the side, top or bottom wall or also on a combination thereof. Preferably, the light-emitting diodes are arranged spaced apart in equidistant units, for example in a row and column pattern. The matrix arrangement favors a highly homogeneous lighting of the display area in order to meet the requirements of international standards. According to the invention, a uniformity factor between adjacent measuring points, which may not exceed 1.5, is changed. Due to the arrangement in matrix form, the light source can be easily adapted to the type and size of the respective illuminated sign, of which there are over 70 different in the airfield area. Likewise, the density of the light emitting diode array can be easily changed, in which the distance unit is adjusted. Signs, for example, require a lower LED density than mandatory signs. Thus, a simple adaptation to future developments in the LED technology in terms of light intensity and luminous efficiency of the LEDs is given. As a result, different variants for bidding, information and in particular location signs can be provided, which helps to save electricity costs, because. Signs, for example, require 20% less energy than mandatory signs.

Preferably, at least part of the light-emitting diodes of a luminous shield according to the invention has an optical element for beam shaping. As a result, the brightness level of the light source can be improved approximately at the edge of the display panel.

It is likewise preferred if the light-emitting diodes of a light shield according to the invention have a higher light intensity at the matrix edge than the light-emitting diodes in the matrix interior. Thus, expensive high-performance LEDs can be used at the edge, while in the middle of the matrix cheaper light emitting diodes can be installed. This also allows brightness changes to be reduced by setting adjacent measurement points more uniformly.

Alternatively, at least one light-emitting diode in the matrix center has a greater light intensity than the light-emitting diodes on the matrix edge. The texts for the mandatory signs (white letters on a red background) and the signs (yellow letters on a black background) are shown in the center of the display panel, and thus the brightness of the characters can be increased by using higher intensity light emitting diodes in the center of the display Luminous matrix can be increased.

In another preferred embodiment of the illuminated sign according to the invention, the matrix has a plurality of separately replaceable matrix modules with light-emitting diodes. On the one hand, this simplifies the compilation of differently sized light-emitting diode arrays and, on the other hand, the modular construction favors the retrofitting of existing signs but also the maintenance of illuminated signs constructed according to the invention.

Preferably, a matrix module of a luminous shield according to the invention has a printed circuit board equipped with the light-emitting diodes, which can be fixed to a holding device in the housing. A simple retrofitting of existing signs is ensured if both conventional light sources and the matrix modules inventive luminous signs can be fixed to the holding device.

Advantageously, the transparent protective layer extends over the matrix module to cover all the light-emitting diodes arranged thereon, for example as a cap or cover.

In another preferred embodiment of the illuminated sign according to the invention this comprises a heat sink, which is thermally conductively connected to the removal of heat with the one or more light-emitting diodes. About the heat sink is essentially the temperature management, which is essential in particular when using high-power LEDs.

The heat sink of a luminous shield according to the invention preferably has a metal core arranged in the printed circuit board. The metal core printed circuit board, or MCPCB (Metal Core Printed Circuit Board), is narrow, preferably approximately as wide as the smallest width of the LED housing. The metal core acts as a heat sink and distributor, the narrow version leads to only a slight intrinsic shadow on the display panel when the module is mounted in the light path of the light-emitting diodes.

Further preferably, the heat sink of a luminous shield according to the invention has a ribbed metal profile against the printed circuit board. The heat transfer properties are improved when an additional heat sink in the form of a ribbed metal profile is mounted to the metal core of the circuit board. This improves the life of the light-emitting diodes, especially at high currents. In particular, light-emitting diodes with a greatly reduced base point can be mounted on thin metal-core printed circuit board strips, which improves the heat distribution. Additional heatsinks can thus be made smaller, which in turn improves the heat distribution. The additional heat sink can be increased in the direction perpendicular to the circuit board without causing photometric losses on the display panel.

In another particularly advantageous embodiment of the illuminated sign according to the invention, this comprises a control device for controlling the brightness of the at least one light-emitting diode. Through the use of light-emitting diodes as the light source, stepless dimming is possible, for example, by pulse width modulation of the LED flow, without shifting the color locus.

In yet another advantageous embodiment of the illuminated sign according to the invention, this comprises a monitoring device for monitoring the function of the light source. As a result, the time-consuming and costly personal inspection by maintenance personnel can be saved, which minimizes the maintenance and downtime and thus the downtime of the airfield facility.

Preferably, the monitoring device of an illuminated sign according to the invention has at least one photodiode for detecting the light emitted by the at least one light-emitting diode. By attaching a photodiode on the LED strip of printed circuit board, a continuous deterioration of the light intensity of the LEDs can be detected, which is usually a very slow decay process.

Advantageously, the monitoring device of an illuminated sign according to the invention has measuring means for determining the current and / or voltage of the at least one light-emitting diode. An instantaneous LED failure of one or more matrix modules may result in the loss of uniform brightness distribution on the display panel. The electronic monitoring circuit detects such catastrophic failures so that they can be corrected immediately.

In yet another preferred embodiment of the illuminated sign according to the invention, the housing is divided by at least one partition into at least a first and a second housing part, wherein the first housing part, a first light source and a first display panel and the second housing part have a second light source and a second display panel, and wherein the first and second light sources are separately controllable in such a way that the illuminated sign is designed to alternately display a first or second bid and / or reference by the first or second display panel. Such change signs can be used very advantageously, especially at night.

• FIG 1 ein erfindungsgemäßes Leuchtschild mit Teilausschnitt,
• FIG 2 ein Matrixmodul eines erfindungsgemäßen Leuchtschildes,
• FIG 3 ein Transmissionsspektrum eines Anzeigepaneels,
• FIG 4 der Leuchtdichteverlauf einer Lumineszenzdiode auf dem Anzeigepaneel
  schematisch veranschaulicht ist.

An embodiment of the invention will be explained in more detail below with reference to the drawings, in which

• FIG. 1 an illuminated sign according to the invention with partial detail,
• FIG. 2 a matrix module of a luminous sign according to the invention,
• FIG. 3 a transmission spectrum of a display panel,
• FIG. 4 the luminance profile of a light-emitting diode on the display panel
  is illustrated schematically.

According to FIG. 1 a luminous shield 10 according to the invention comprises a box-shaped housing 20 having a front, translucent display panel 21, with a rear wall 22 arranged opposite thereto, with two opposite side walls 23, with a removable top wall 24 and with a bottom wall 25 arranged opposite thereto. Apart from the display panel 21 the housing 20 is made of metal because of its advantageous thermal resistance between a light source arranged in the housing 20 and the outer ambient air. Alternatively, the housing 20 may also be made of organic material, for example of glass fiber reinforced plastic. The display panel 21 comprises a front screen, which is formed for example of 5 mm thick acrylic glass or translucent polycarbonate, and an inside-mounted film, which is designed in accordance with the displayed bid or sign Z color. The color foil can be glued on and has Lambert radiator properties. For backlighting of the display panel 21, the light source with a plurality of light emitting diodes 32 is disposed within the housing 20. The housing 20 of the illuminated sign 10 is placed on two support legs 40 with breakaway coupling.

According to the invention, the display panel 21 of the light-emitting diodes 32 is not directly, but indirectly, by backscattering their emitted light, illuminated by the diffusion panel 22 formed as a rear wall. The rear wall 22 is provided for this purpose with a litter layer, which scatters incident light back. This diffusive layer is preferably in the form of a polyester powder coating with a silk-matt surface finish, eg with a gloss level of 60%. The degree of gloss influences the tendency of adhesion to be minimized by protection, which is particularly important in the case of the indirect illumination provided according to the invention. The side walls 23 and bottom and top walls 25, 24, however, consist of polished metal or have a highly reflective coating with low scattering properties in order to increase the brightness at the edge of the display panel 21.

The light source preferably has high-power light-emitting diodes which are arranged in the form of a matrix. The matrix comprises a plurality of vertically aligned matrix modules 30 arranged side by side in the housing 20 and each fixed to a holding device 33. The matrix modules 30 can be plugged in and can be exchanged separately. In this way, the light-emitting diodes 32 are arranged on a plane in equidistant units, which is aligned in parallel between the display panel 21 and the rear wall 22.

According to the invention, the light-emitting diodes 32 are aligned with the rear wall 22 in such a way that light emitted by them is at least partially reflected by the rear wall 22 and illuminates the display panel 21. As a result, the display panel 21 is indirectly illuminated by a virtual light source, which is shown on the rear wall 22, and which is significantly larger than the real light source. Due to the indirect backscatter on the rear wall 22, the failure of individual light emitting diodes 32 on the display panel 21 is not or at least less than visible in direct lighting. The same applies to shadows cast by objects which are arranged in the light path between the rear wall 22 and the display panel 21, of which in the application according to the invention only partial shadows or intrinsic shadows and thus only soft brightness variations are visible. The inventive indirect backscattering also causes a high consistency of the color locus over the entire display panel 21, which prevents irritation in Färbwahrnehmung. The litter layer itself also increases the surface area of the virtual light source projected onto the rear wall 22. Overall, a very high uniformity of the luminance over the entire display panel 21 is achieved according to the invention.

This is also on FIG. 4 which shows the profile 60 of the luminance L of a light-emitting diode 32 as a function of the vertical position y on the display panel 21. The dashed line 61 shows the profile of the luminance L in direct illumination of the display panel 21 through a light emitting diode 32, while the solid line 62 shows the course of indirect illumination. The maxima of both curves coincide at the vertical position of the considered light-emitting diode 32, but are of different heights. At a sufficient distance from the position of the light emitting diode 32, both curves 61 and 62 fall to the value of the backlight 63, which consists of housing-internal reflections and scattering. According to the invention, the lower luminance difference between the maximum for indirect illumination 62 and the backlight 63, which is significantly smaller than the brightness contrast between the maximum in direct illumination 61 and the background 63, is exploited. The failure of such a light-emitting diode 32 is therefore essential for indirect illumination less important as with direct lighting. The functionality of the illuminated sign according to the invention and thus the availability of the associated taxiway are thus higher than in the prior art.

The modular structure of the matrix-shaped light source offers great advantages. The area density of the light-emitting diodes 32 can be adjusted both by the spacing of the light-emitting diodes 32 on a matrix module 30 and by the distance of the individual matrix modules 30 from one another. This also allows a simple adaptation of the light source to different sizes of illuminated signs according to the invention, of which there are for example over 70 different in the airfield area. The mandatory signs require, for example, a higher luminance than signs. However, both require highly homogeneous illumination of the display panel 21 to meet the requirements of international airport standards. The uniformity factor between adjacent measuring points must not exceed 1.5.

Advantageously, the light-emitting diodes 32 at the edge of the matrix have a greater light intensity than the light-emitting diodes 32 in the matrix center. As a result, the luminance at the edge of the display panel 21 can be improved.

Alternatively, at least one light-emitting diode 32 in the center of the matrix has a greater light intensity than the light-emitting diodes 32 at the matrix edge.

The light-emitting diodes 32 are formed in the illustrated embodiment as high-performance light-emitting diodes. These are energized with a rated current of at least 100 mA and have a light intensity of at least 20 Im. There are also light levels of over 100 lm possible, reducing the number of required LEDs 32 can be reduced for the standard to be fulfilled luminance. In addition to the very high lifetimes, the LEDs 32 are characterized by their puncture even at very low temperatures. They have very short switching times and are instantaneously fully functional in terms of light output and color location. For example, the LED types K2 from Philips Lumileds or type XR-E from CREE are particularly suitable. The low thermal resistance of these light-emitting diodes simplifies the heat dissipation in illuminated signs 10 according to the invention; In addition, it contributes to an extended life of the LEDs 32. The low power consumption of high power LEDs 32 is another advantage.

The light-emitting diodes 32 are designed to emit white light in the form of a Lambert radiator. These today have a luminous efficacy comparable to that of a fluorescent lamp. The white light is generated, for example, by phosphor-based conversion of blue light. Advantageously, in the illustrated embodiment, an outer lens in front of the light emitting diode 32 is dispensed with.

However, the light-emitting diode 32 is covered by a transparent protective layer. This consists of a highly transparent material, such as polycarbonate or PMMA, to keep the transmission losses low. The protective layer keeps dust and dirt from the light emitting diodes 32, which could otherwise affect their light intensity.

FIG. 2 shows a matrix module 30 of the light source of a luminous sign 10 according to the invention. The module 30 comprises a strip-shaped printed circuit board 31, on which the high-performance light-emitting diodes 32 are arranged at equidistant intervals.

The printed circuit board 31 is designed as MCPCB, thus comprising a metal core as a heat sink, which in FIG. 2 is not explicitly shown. The width of the printed circuit board strip 31 is not dimensioned substantially larger than the LED housing itself. In this way, the matrix module 30 inserted into the housing 20 forms only a slight shadow. Due to the low self-shading on the display panel 21, the light output of the light source is improved.

The heat transfer properties of the printed circuit board 31 is further improved by an additional, designed as a ribbed metal profile 34 heat sink, which is thermally conductively connected to the circuit board 31. The rib profile extends in a direction perpendicular to the printed circuit board 31 and thus parallel to the main light path between the rear wall 22 and the display panel 21. This configuration of the metal profile 34 also keeps the self-shading of the matrix module 30 low.

The high-power light-emitting diodes 32 have a lambert radiation characteristic whose maximum light emission is perpendicular to the printed circuit board 31.

Advantageously, the protective layer extends over the matrix module to cover all the light-emitting diodes arranged thereon. This results in a smooth surface over the matrix module, which prevents the accumulation of dust and dirt and allows easy removal of dirt. The protective layer may be provided as a cap or cover for one or more matrix modules.

Not shown is a control device by means of which the light source is continuously dimmable. The control device regulates the brightness of the LEDs 32 for example by pulse width modulation of the LED current supply. Advantageously, the color location is not shifted.

Also not shown is a monitoring device for monitoring the function of the light source. This comprises on the one hand on the circuit board 31 arranged photodiodes to monitor the light emitted by the LEDs 32 light. If the light intensity of a light-emitting diode 32 decreases over time, a corresponding message is output to a maintenance center. The failure of individual light emitting diodes 32 or a complete matrix module 30 is also reported to the maintenance center in order to restore the normal functioning of a luminous shield 10 according to the invention as soon as possible.

Another advantage of the illuminated sign 10 according to the invention is still based on FIG. 3 explained. Here, the transmission spectrum 50 of a display panel 21 is applied with a red colored foil for a bid sign. The spectrum is normalized to the value 100, which is achieved at 51, namely the wavelength λ of 650 nm red color. Below the cut-off wavelength 52, which is at a wavelength λ of slightly less than 600 nm, light having lower wavelengths is substantially filtered out, which is equivalent to the effect of a low-pass filter. However, the transmission spectrum has a transmission peak 53 between 400 nm and 450 nm. The emission spectrum of the light-emitting diodes 32 used in accordance with the invention exhibits a maximum at about 450 nm, which would be visible in the transmission spectrum at least in the case of direct illumination of the display panel 21 due to the transmission peak 53. This problem of direct lighting occurs especially in use from high power LEDs that emit photons from a much smaller area than fluorescent lamps, for example. Thus, under direct illumination, the blue maximum of high power LEDs on the red display panel is perceived in a different color, such as purple.

Claims (15)

1. A light sign (10) for displaying an instruction and/or guidance for taxiing airplane traffic at an airport, comprising a casing (20) with a translucent display panel (21) for representing instruction and/or guidance symbols (Z), a diffusion panel (22) and a light source arranged inside the casing (20) and between the display panel and the diffusion panel with a plurality of luminescent diodes (32) for illuminating the display panel (21),
   characterized in that the diffusion panel is configured for scattering and/or back-scattering of incident light, wherein the luminescent diodes (32) are directed towards the diffusion panel (22) in such a way that the light emitted by the luminescent diodes falls essentially on the diffusion panel (22) and is scattered and/or back-scattered by the diffusion panel (22), so that the display panel (21) is not directly, but indirectly illuminated by a virtual light source placed on the diffusion panel and which is bigger that the real light source, wherein the illumination of the display panel (21) does not exceed a uniformity factor of 1.5 between neighbouring measurement points.
2. The light sign (10) according to claim 1, wherein the diffusion panel (22) is constituted as a back panel, and the display panel (21) is constituted as a front panel of the casing (20), and wherein the diffusion panel (22) is provided with a scattering coat for back-scattering incident light.
3. The light sign (10) according to claim 1, wherein the diffusion panel (22) is arranged inside the casing (20) between a front panel and a back panel of the casing (20) and is constituted to be semitranslucent or translucent, and wherein the back panel and the front panel are constituted as display panels (21), wherein the at least one luminescent diode (32) is arranged between the back panel and the diffusion panel (22) so that the front panel is illuminated by scattered light passing through.
4. The light sign (10) according to any of the claims 1 to 3, wherein the diffusion panel (22) comprises colour pigments, the distribution of which determines a colour location of the display panel (21).
5. The light sign (10) according to any of the claims 1 to 4, wherein the luminescent diodes (32) are constituted as high performance light emitting diodes.
6. The light sign (10) according to any of the claims 1 to 5, wherein the light source comprises luminescent diodes (32) arranged in the form of a matrix.
7. The light sign (10) according to claim 6, wherein the luminescent diodes (32) at the edge of the matrix have higher light intensity than the luminescent diodes (32) inside the matrix.
8. The light sign (10) according to claim 6, wherein at least one luminescent diode (32) in the middle of the matrix has a higher light intensity than the luminescent diodes (32) at the edge of the matrix.
9. The light sign (10) according to any of the claims 6 to 8, wherein the matrix comprises several separately interchangeable matrix modules (30) with luminescent diodes (32).
10. The light sign (10) according to claim 9, wherein a matrix module comprises a transparent protective coat covering the luminescent diodes of the matrix modules.
11. The light sign (10) according to claim 9 or 10, wherein a matrix module (30) comprises a printed circuit board (31) equipped with the luminescent diodes (32) which can be fastened to a holding device (33) inside the casing (20).
12. The light sign (10) according to any of the claims 1 to 11, with a heat sink, which is connected in a thermally conductive manner to the luminescent diodes (32) for dissipating heat.
13. The light sign (10) according to any of the claims 1 to 12, with a monitoring device for functional monitoring of the light source.
14. The light sign (10) according to claim 13, wherein the monitoring device comprises measuring means for determining the current and/or voltage of the luminescent diodes (32).
15. The light sign (10) according to any of the claims 1 to 14, wherein the casing (20) is divided by at least one partitioning wall into at least a first and a second casing part, wherein the first casing part comprises a first light source and a first display panel, and the second casing part comprises a second light source and a second display panel, and wherein the first and second light sources can be driven separately in such a way that the light sign (10) is configured for alternately displaying a first or second instruction and/or guidance via the first or second display panel.

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