Abstract:
The invention relates to a luminaire with at least one LED and a method for operating the luminaire. The luminaire has a sensor for detecting at least a part of the light emitted by the LED and also a control unit for evaluating the sensor signals and for influencing the LED in a manner dependent on the sensor signals. After the luminaire has been switched on, a specific LED current flows and the light intensity of the LED is checked. In the case of a light intensity below a reference value, the LED current is raised by a defined value.

Description:
BACKGROUND OF THE INVENTION 
   1. Technical Field 
   The invention relates to a luminaire with at least one LED as luminous means and a method for operating the luminaire. 
   2. Prior Art 
   The light intensity of luminaires with LEDs is subject to fluctuations depending on the age and on the temperature of the LEDs. The ageing process has a particularly serious effect. A reduction of the light intensity to just 50% or less is possible. The light intensity changes only slowly and the alteration can hardly be perceived from the vicinity of operators. 
   A reduction of the light intensity is particularly critical in connection with applications for which specific luminous ranges are legally prescribed. A main area of application of the invention is navigation luminaires on ships. Luminaires of this type are also referred to as position lanterns and must have a luminous range of two nautical miles in the USA, for example. Other countries have in part different regulations. 
   When the light intensity of the LED decreases, the actual luminous range may fall below the legally prescribed value, so that the envisaged function is no longer fulfilled. Even without the presence of legal provisions, maintaining a specific light intensity for a luminaire is advantageous and desirable, for instance for illuminating traffic areas or properties or in connection with other types of signal and position luminaires. 
   BRIEF SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a luminaire which enables a minimum light intensity to be complied with. In particular, the intention is to comply with a defined or even Constant light intensity. 
   The luminaire according to the invention is characterized by the following features:
         a) a sensor for detecting at least a part of the light emitted by the LED,   b) a control unit for evaluating the sensor signals and for influencing the LED in a manner dependent on the sensor signals.       

   In the simplest case, the control unit switches off the LED after a limit value of the light intensity has been undershot. The luminaire or LED can then be identified as defective and can be exchanged. Preferably, precisely one LED is provided as luminous means. 
   According to a further concept of the invention, it is provided that the control unit regulates the electric current of the LED (LED current) in a manner dependent on the sensor signals such that the light intensity of the LED remains above a reference value. After the luminaire has been switched on, the light intensity of the LED is detected by means of the sensor and adapted by regulating the LED current until a desired value is reached. 
   According to a further concept of the invention, a reference value for a desired light intensity of the LED is defined by the control unit as follows:
         a) after the luminaire has been switched on for the first time, a desired value of the light intensity is determined as reference value in a manner dependent on the sensor signals then present.   b) the reference value is stored by the control unit.       

   The luminaire is switched on for the first time preferably in the absence of ambient light in order that the sensor exclusively receives light from the LED. 
   In an advantageous manner, the control unit prescribes a defined LED current when the luminaire is switched on for the first time. Said current can be stored in the control unit and is adapted to the structural and electrical data of the LED. The aim is a light intensity that suffices for the envisaged luminous range at the beginning of the service life of the LED. An increase in the LED current is intended to be necessary only with incipient ageing. 
   According to a further concept of the invention, the control unit permanently or cyclically compares the sensor signals with the reference value. In the event of the reference value being undershot, the control unit raises the LED current by a defined step from a present current value to a new current value. The new current value is then stored as present current value. 
   In an advantageous manner, when the luminaire is switched on again, the control unit prescribes the present current value that was stored last as LED current. 
   According to a further concept of the invention, the control unit raises the current value only up to a defined maximum value. It is thereby possible to avoid damage due to an excess of electrical power, for instance excessively great heating. 
   In an advantageous manner, the control unit concomitantly counts the operating hours of the LED after the current value has reached the maximum value. 
   The operating hours incurred after the maximum value has been reached are stored. Preferably, the control unit no longer switches on the LED if a defined number of operating hours has been reached. The defined number of operating hours is referred to as waiting time. Only after the waiting time has elapsed is it assumed that the luminaire no longer fulfills the intended purpose of use. The luminaire is then defined as defective. However, the luminaire is preferably not switched off during operation in progress. The control unit only prevents the luminaire from being switched on again as soon as the waiting time has been exhausted. This is particularly important and expedient for applications in which the luminaire is regularly switched on from time to time and, at the same time, an automatic switch-off during operation might have fatal consequences. Thus, by way of example, navigation luminaires on ships are not permitted to be automatically switched off suddenly at night. 
   An LED switch-off effected by the control unit means that a later attempt to switch on the luminaire does not lead to the LED lighting up. 
   According to a further concept of the invention, a light deflection device for the concentration or at least deflection of the light emitted by the LED is provided, at least a part of the light being deflected in the direction of the sensor by the light deflection device. The light deflection device may be a lens, a prism or a mirror, or else a combination thereof, e.g. a lens with partly mirroring or prismatic areas. A navigation luminaire with LED and essentially prismatic light deflection device is described in our European Patent Application EP 1 470 999 A2. Reference is expressly made to the disclosure of this application. 
   In an advantageous manner, the light deflection device deflects the light such that one part of the light is emitted by the luminaire and another part, in particular a smaller part, of the light is deflected in the direction of the sensor. 
   In an advantageous manner, the light deflection device has an in particular rod-type extension that extends in the direction of the sensor. In this respect, the extension acts as an optical waveguide with a light exit area facing the sensor. 
   According to a further concept of the invention, the LED defines an installation plane, a main emission direction of the light pointing away from the installation plane, and the sensor being arranged on the opposite side of the installation plane with respect to the main emission direction of the light. The sensor can be positioned in a manner protected by this arrangement, even with regard to the evolution of heat by the LED and the light emitted overall by the LED. The main emission direction preferably extends perpendicular to the installation plane. 
   According to a further concept of the invention, the extension extends (counter to the main emission direction) to behind the installation plane. As a result, the light separated off for the sensor is reliably conducted as far as the sensor. It is also possible to shade the sensor with respect to the light emitted overall. In an advantageous manner, the extension extends as far as the sensor. Light losses are thereby minimized. 
   According to a further concept of the invention, the light deflection device is arranged in front of a wall, the extension extending through a cutout in the wall. The wall is opaque to the light and shades the sensor from the light emitted overall by the LED. The wall may be part of a housing of the luminaire. 
   The method according to the invention for operating the luminaire is characterized by the following features:
         a) after the luminaire has been switched on, a specific LED current flows,   b) the light intensity of the LED is checked,   c) in the case of a light intensity below a reference value, the LED current is raised by a defined value,   d) steps b) and c) are repeated until the light intensity lies above the reference value.       

   The steps are carried out in the control unit. The latter is provided with a corresponding logic. 
   According to a further concept of the invention, the following method steps are provided:
         a) each time the LED current is raised, a check is made to ascertain whether an upper limit value of the LED current is reached,   b) if the upper limit value has been reached, the LED current is not raised any further, not even when the light intensity decreases.       

   The aim is to avoid additional damage within the luminaire or at the connected current source. 
   According to a further concept of the invention, the following method steps are provided:
         a) after the upper limit value has been reached, the operating hours (switch-on time) of the luminaire are counted,   b) after a defined number of operating hours has been reached, the switch-on function of the luminaire is blocked.       

   In this case, the LED remains dark despite the luminaire being switched on. However, the LED is preferably not switched off during operation in progress after the defined number of operating hours has been reached. 
   Further features of the invention emerge from the claims and from the rest of the description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Advantageous exemplary embodiments of the invention are explained in more detail below with reference to drawings, in which: 
       FIG. 1  shows a flowchart for illustrating the control of a luminaire with LED, 
       FIG. 2  shows an exploded illustration of a luminaire with LED according to the invention, namely a stern luminaire as navigation luminaire on ships, 
       FIG. 3  shows a housing part with LED on a small circuit board in a perspective illustration, 
       FIG. 4  shows a rearward (relative to the direction of travel of the ship) plan view of the stern luminaire, 
       FIG. 5  shows a section through the stern luminaire along the line V-V in  FIG. 4 , 
       FIG. 6  shows a section through the stern luminaire in accordance with  FIG. 4  along the line VI-VI, 
       FIG. 7  shows a plan view of the stern luminaire, 
       FIG. 8  shows a plan view of a rear side of the stern luminaire without a rear wall (front side or front wall as seen in the main direction of travel of the ship), 
       FIG. 9  shows a perspective illustration of the internals of the stern luminaire, namely a housing part with connecting link for receiving an LED and for bearing a lens, 
       FIG. 10  shows a plan view of the components corresponding to  FIG. 9 , but without a lens, 
       FIG. 11  shows an exploded illustration of the constituent parts of a navigation luminaire according to the invention for the starboard side of a ship analogously to the stern luminaire corresponding to  FIG. 2 , 
       FIG. 12  shows a view of the starboard luminaire analogously to  FIG. 10 , but from a somewhat different viewing angle, 
       FIG. 13  shows a view of the rear side of the starboard luminaire in accordance with  FIG. 10  and analogously to  FIG. 8 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A stern luminaire as navigation luminaire of a ship has the following parts in accordance with  FIG. 2 : 
   A rear wall  20 , a circuit board  21  with electrical and electronic components and circuits for driving an LED  22 , a housing part  23  preferably made of aluminum, a small circuit board  24  with the LED  22  held centrally, a lens  25 , a light-transmissive covering  26 , a housing covering  27  and suitable fixing means, here a screw  28  with head covering  29 , nut  30  and spreading sleeve  31 . 
   The luminaire according to the invention constitutes a further development of the luminaires shown in EP 1 470 999 A2. There is correspondence with regard to the configuration of the lens  25  as far as the deflection of the externally visible emitted light is concerned. Significant deviations according to the invention in the construction of the lens  25  in relation to the representation in the aforementioned European patent application are explained in more detail further below. The light is emitted through the lens, in accordance with the legal regulations, essentially only via a laterally delimited sector of a horizontal plane. 
   The LED  22  is arranged fixedly on the small circuit board  24 . The latter has contacts  32  for the connection of electrical lines (not shown). 
   The housing part  23  essentially comprises a central housing wall  33 , on which is formed a connecting link  34  for receiving the small circuit board  24 . Furthermore, the housing wall  33  is provided with a peripheral side wall  35 . The latter has on the exterior a shoulder  36  for bearing a corresponding area (not shown) of the housing covering  27 . 
   The small circuit board  24  has a peripheral edge with cutouts  37  into which corresponding projections  38  of the connecting link  34  enter. Moreover, the cutouts  37  and projections  38  are arranged and designed such that the small circuit board  24  can be inserted into the connecting link  34  only in a defined position. 
   When the small circuit board  24  has been inserted into the connecting link  34 , this and the LED  22  bear as closely as possible on the housing wall  33 . The heat that arises is thus effectively dissipated or distributed over the housing part  23  altogether. 
   The essentially annular connecting link  34  is at the same time provided with cutouts  39  on the inside, corresponding projections  40  of the lens  25  being held in said cutouts. Further parts of the lens  25  rest on the exterior of the connecting link  34  (apart from an exception mentioned further below). Consequently, the lens  25  also has a precisely defined relative position with respect to the connecting link  34  and thus with respect to the housing part  23 . 
   The circuit board  21  is arranged in a manner resting on the rear side  41  of the housing wall  33 , said rear side being remote from the connecting link  34 , and may be held there for example by means of an adhesive-bonding connection. An internal space  42  is formed between the rear side  41  and the rear wall  20  and serves for receiving the components arranged on the circuit board  21 . The rear wall  20  has two cutouts  43 , namely for insertion of the spreading sleeve  31  and for the passage of electrical connecting lines  44 . 
   An essential special feature is a pin-type extension  45  on the lens  25 , to be precise essentially parallel to the projections  40 . The extension  45  is arranged at the edge, in particular at the corner, on the lens  25  and extends counter to a main emission direction—arrow  46 —of the LED  22 . 
   The housing wall  33  has a cutout or hole for the extension  45 , to be precise outside the connecting link  34 . As a result, the light from the LED  22  does not pass directly to the extension  45 . However, the extension  45  receives light only via its contact with the rest of the lens  25  or else part of the lens  25 . On account of the length of the extension  45 , a light exit area  48  at the end thereof lies in the region of the rear side  41  of the housing wall  33 . 
   The circuit board  21  is provided with a light-sensitive sensor  49 , which is arranged in direct proximity to the light exit area  48  and can be used to measure the light intensity of the LED  22  indirectly, namely via the lens  25  and the extension  45 . Furthermore, the circuit board  21  has a programmable control unit (not specifically shown) formed from electronic components which serves for driving the LED. 
   The housing covering  27  has a window  50 , into which the light-transmissive covering  26  is inserted from the inside. Directly beside the window  50 , the housing covering  27  has a cutout, namely a hole  51  for passage of the screw  28 . The light-transmissive covering  26  lies over a partly cylindrically curved outer light exit area  52  of the lens  25 , to be precise at a small distance in the region of a vertex  53  and at larger distances laterally alongside the latter, see  FIG. 6  in particular. 
   The starboard luminaire in accordance with  FIGS. 11 ,  12 ,  13  and also the port luminaire are constructed in an analogous manner. Angular connecting links  54  are provided in order to represent an obliquely lateral light emission. Moreover, the housing coverings  27  are provided with laterally offset windows  56 . 
   In the embodiment shown here, the luminaire has precisely one LED. The latter receives an LED current of approximately 200 mA at the beginning of its service life. The LED is maximally loaded with 350 mA. 
   For the stern luminaire, use is made of a light-intense white LED, in particular an LED from the manufacturer LUMILEDS Lighting LLC, San Jose, Calif., USA, preferably of the type LXHL-PD01 luxeon emitter (hemispherical dome). Of course, it is also possible to use LEDs from other manufacturers with similar specifications. The current values mentioned relate to the white LED. A green LED is used in the starboard luminaire and a red LED in the port luminaire. The colored LEDs have in some instances a higher luminous efficiency than white LEDs. The electrical values must be adapted correspondingly. 
   The operation of the luminaire and the function of the circuit are explained with reference to the flowchart in  FIG. 1 . A distinction is to be made between
         the first time that the luminaire is switched on,   normal operation,   the waiting mode,   the defect mode.
 
Switching on for the First Time
       

   The luminaire (lantern) is switched on for the first time in dark surroundings, so that the sensor  49  does not receive any light, preferably in the factory after production of the luminaire. 
   The luminaire is switched on. The LED remains off, however. Firstly, the sensor checks the presence of light. If light is detected, the LED continues to remain off. If the sensor  49  signals surroundings without light, the LED is switched on after a pause of 5 seconds. After a further 5 seconds, the light intensity measured by the sensor  49  is assumed as initial value and a light intensity that is up to 10% less than that is stored as desired value. The stored desired value is preferably 97% of the light intensity detected by the sensor. The desired value is also designated as reference value. Afterward, the LED automatically goes out or the luminaire is switched off manually. 
   Normal Operation 
   After the luminaire has been switched on in normal operation (middle branch of the flowchart in  FIG. 1 ), the light intensity of the LED is measured. If the desired value (reference value) is undershot, the initial LED current is increased by a defined magnitude. The resultant LED current is stored as present current value. After a waiting time of 5 seconds, the light intensity is measured again by the sensor  49  and, if appropriate, the LED current is increased. 
   The light intensity of the LED decreases due to ageing. It is possible to maintain the light intensity by adapting the current value. In this case, the current value in the present example increases from initially 200 mA to a maximum of 350 mA. The increase is effected in discrete steps, preferably in 256 approximately identical steps. 
   Waiting Mode 
   After the maximum current value has been reached, a further increase in the current intensity is not recommendable. The thermal, mechanical and/or electrical safety of the luminaire might be jeopardized. Moreover, the luminaire is only operated for a specific time duration (waiting time) and can no longer be switched on after this has elapsed. The first time the desired light intensity is undershot with the maximum current value being present simultaneously, the waiting time begins; a waiting time flag is set. Starting from this point in time, the operating duration, in particular the operating hours of the LED, is counted and stored. After 200 hours have elapsed, the waiting time has elapsed and the LED is deemed to be defective. 
   Luminaires are usually switched on and off again dependent on daylight, so that a daily cycle is established with a cycle duration that is significantly shorter than the waiting time. As a result, enough time remains for the maintenance personnel to implement measures for exchanging the luminaire or just the LED. 
   In order to facilitate such measures, when the luminaire is switched on, firstly a check is made to ascertain whether the waiting time flag is set. If this is the case, the LED briefly flashes a number of times, in particular three times, upon switch-on and then lights up without any further interruption. The flashing LED makes the maintenance personnel aware of the imminent failure of the LED. 
   Defect Mode 
   After the waiting time has elapsed, the LED is deemed to be defective, although generally only light with a reduced light intensity is emitted. In the defect mode, the LED is no longer switched on. Correspondingly, when the luminaire is switched on, a check is made to ascertain whether the waiting time has elapsed. If so, the LED remains dark. In order to avoid a failure of the luminaire in darkness, the LED is not automatically switched off during operation in progress. It is only prevented from being switched on again after the waiting time has elapsed. 
   The signaling of a specific operating state of the LED depending on the light intensity and/or the LED current may be effected when the luminaire is switched on or off, in particular by means of a brief flashing mode of the LED. 
   The functions described for operation of the luminaire are realized in suitable electronic circuits (control unit) with corresponding software on the circuit board  21 . With knowledge of the functions described, the construction of such a circuit is possible for a person skilled in the art of electronics, even without effecting an inventive step in this case. 
   List of Reference Symbols: 
   
     
       
             
             
           
         
             
                 
             
           
           
             
               20 
               Rear wall 
             
             
               21 
               Circuit board 
             
             
               22 
               LED 
             
             
               23 
               Housing part 
             
             
               24 
               Small circuit board 
             
             
               25 
               Lens 
             
             
               26 
               Light-transmissive Covering 
             
             
               27 
               Housing covering 
             
             
               28 
               Screw 
             
             
               29 
               Head covering 
             
             
               30 
               Nut 
             
             
               31 
               Spreading sleeve 
             
             
               32 
               Contacts 
             
             
               33 
               Housing wall 
             
             
               34 
               Connecting link 
             
             
               35 
               Peripheral side wall 
             
             
               36 
               Shoulder 
             
             
               37 
               Cutouts 
             
             
               38 
               Projections 
             
             
               39 
               Cutouts 
             
             
               40 
               Projections 
             
             
               41 
               Rear side 
             
             
               42 
               Internal space 
             
             
               43 
               Cutouts 
             
             
               44 
               Lines 
             
             
               45 
               Extension 
             
             
               46 
               Arrow 
             
             
               47 
               Cutout 
             
             
               48 
               Light exit area 
             
             
               49 
               Sensor 
             
             
               50 
               Window 
             
             
               51 
               Hole 
             
             
               52 
               Light exit area 
             
             
               53 
               Vertex 
             
             
               54 
               Connecting link 
             
             
               56 
               Window