Patent Publication Number: US-2023141741-A1

Title: Interior aircraft lighting device, aircraft comprising an interior aircraft lighting device and method of starting an interior aircraft lighting device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to European Patent Application No. 21207607.9 filed Nov. 10, 2021, the entire contents of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention is in the field of aircraft equipment. The present invention is in particular in the field of aircraft disinfection, more particularly in the field of aircraft disinfection using ultraviolet light. In the following, ultraviolet light will be referred to as “UV light”. 
     BACKGROUND 
     For reducing the risk of distributing infectious diseases in an aircraft, it is desirable to regularly disinfect surfaces within the aircraft, which are routinely contacted by passengers and/or aircraft personnel. UV light may be used as a germicidal illumination for disinfecting the surfaces within an aircraft by irradiation. UV light sources, which may be employed for generating UV light, include gas discharge lamps. Gas discharge lamps comprise at least one excitable gas, which may generate electromagnetic radiation, in particular electromagnetic radiation including UV light, upon electric excitation. Usually, high electric voltages of several thousand volts are necessary for triggering a gas discharge reaction. In consequence, high voltage electric power supplies are needed for providing the high electric voltage needed for starting and operating gas discharge lamps, leading to high complexity, high cost, and high efforts for safety/electric isolation purposes. 
     It would be beneficial to provide an interior aircraft lighting device that is effective for disinfecting and that is easy to handle, in particular an interior aircraft lighting device that may have reduced electric voltages needed for generating the UV light employed for disinfection in an aircraft. 
     SUMMARY 
     Exemplary embodiments of the invention include an interior aircraft lighting device comprises at least two discharge light modules. The at least two discharge light modules include at least one first discharge light module and at least one second discharge light module. Each discharge light module contains at least one excitable gas. The at least one excitable gas emits electromagnetic radiation, in particular UV light, pursuant to electric excitation. In particular, the excitable gas may emit electromagnetic radiation, when suitably triggered and when an electric field, suitable for maintaining a gas discharge reaction, is continuously applied. The at least one excitable gas may be a single gas or a mixture of two or more gases. 
     The interior aircraft lighting device further comprises a plurality of electrodes, including at least two pairs of electrodes. 
     At least one pair of electrodes is assigned to each discharge light module for applying an electric field, extending between the two electrodes, to the at least one gas within the respective discharge light module. The electrodes may in particular be arranged outside the discharge light modules. The electrodes may further in particular be arranged outside the discharge light modules, but apply an electric field to the at least one gas contained within the respective discharge light modules. 
     Each pair of electrodes comprises two electrodes, which are spaced apart from each other along a longitudinal direction of the respective discharge light module. In consequence, the electric field, which is generated by applying an electric voltage to the two electrodes of a pair of electrodes, extends through the at least one gas, which is present between the two electrodes of the respective pair of electrodes. 
     The at least two pairs of electrodes include at least one first pair of electrodes, which is assigned to the at least one first discharge light module, and at least one second pair of electrodes, which is assigned to the at least one second discharge light module. In an interior aircraft lighting device according to exemplary embodiments of the invention, the distance between the two electrodes of the at least one first pair of electrodes, which is assigned to the at least one first discharge light module, is smaller than the distance between the two electrodes of the at least one second pair of electrodes, which is assigned to the at least one second discharge light module. 
     Since the distance between the two electrodes of the at least one first pair of electrodes is smaller than the distance between the two electrodes of the at least one second pair of electrodes, the minimum electric voltage for starting a gas discharge reaction between the two electrodes of the at least one first pair of electrodes is lower than the minimum electric voltage for starting a gas discharge reaction between the two electrodes of the at least one second pair of electrodes. 
     In consequence, a gas discharge reaction generating electromagnetic radiation, which in particular includes UV light, may be started between the two electrodes of the at least one first pair of electrodes by applying an electric voltage which is lower than the electric voltage which would be necessary for starting a gas discharge reaction between the two electrodes of the at least one second pair of electrodes, in which the distance between the two electrodes is larger than in the first pair of electrodes. This is because the electric field, which ultimately triggers the gas discharge reaction, is a function of the electric voltage between the electrodes and the distance between the electrodes, with a smaller distance between the electrodes resulting in a larger electric field for a given electric voltage. 
     After a first gas discharge reaction has been started between the two electrodes of the at least one first pair of electrodes, the electromagnetic radiation generated by said first gas discharge reaction, in particular the UV light portion of the electromagnetic radiation generated by said first gar discharge reaction, may excite the at least one gas between other electrodes, in particular the at least one gas which is present between the two electrodes of the at least one second pair of electrodes, which are assigned to the at least one second discharge light module. 
     Exciting the at least one gas with electromagnetic radiation reduces the strength of the electric field, which is required for starting a gas discharge reaction in said at least one gas. In other words, the electric voltage, which needs to be applied to the at least one second pair of electrodes for starting a gas discharge reaction between the two electrodes of said at least one second pair of electrodes, is reduced by exciting the at least one gas with electromagnetic radiation, in particular with electromagnetic radiation generated by the first gas discharge reaction. 
     In consequence, when the at least one gas between the two electrodes of the second discharge light module is excited by electromagnetic radiation, a second gas discharge reaction in the second discharge light module may be started by applying a lower voltage to the electrodes of the second pair of electrodes than in absence of electromagnetic radiation. The second gas discharge reaction in the second discharge light module may in particular be triggered by applying the same electric voltage, which has been applied to the two electrodes of the at least one first pair of electrodes for starting the first gas discharge reaction, to the at least one second pair of electrodes, although the second pair of electrodes has a larger distance therebetween than the first pair of electrodes. 
     As a result, gas discharge reactions in all discharge light modules of an interior aircraft lighting device according to exemplary embodiments of the invention may be triggered by applying a comparably low electric voltage, which is sufficient for triggering a gas discharge reaction between the at least one first pair of electrodes, assigned to the first discharge light module. In consequence, a power supply, which is capable of providing such a comparably low electric voltage, may be sufficient for operating the interior aircraft lighting device, and the complexity, costs, and/or isolation requirements of the power supply may be reduced. 
     In an embodiment, the discharge light modules may have a tubular shape extending in the longitudinal direction. The discharge light modules may have a circular or oval cross-section. Other shapes of the discharge light modules are possible as well. 
     In an embodiment, the at least two discharge light modules are supported by a common support, in particular by a common support plate. The common support plate may be a printed circuit board, in particular a printed circuit board comprising electric conductors for electrically coupling the electrodes with the electric power supply. 
     In an embodiment, the at least two discharge light modules are supported by separate supports, in particular by separate support plates, for example separate printed circuit boards. Using a plurality of separate supports for supporting the different discharge light modules may allow for a flexible arrangement of the discharge light modules in space. In such a configuration, the at least two discharge light modules may in particular be arranged independently of each other. 
     In an embodiment, the interior aircraft lighting device comprises a plurality, i.e. at least two, first discharge light modules; and/or the interior aircraft lighting device comprises a plurality, i.e. at least two, second discharge light modules. 
     Each of the first discharge light modules may comprise at least one first pair of electrodes, and each of the second discharge light modules may comprise at least one second pair of electrodes. 
     The distances between the two electrodes of the at least one first pair of electrodes are smaller than the distances between the two electrodes of the at least one second pair of electrodes. In other words, the first pairs of electrodes and the second pairs of electrodes may be defined by the distance between the electrodes of each of said pairs. In the context of the present application, the first pairs of electrodes may be defined as pairs of electrodes in which the distance between the two electrodes of each pair is smaller than a predefined distance, and the second pairs of electrodes may be defined as pairs of electrodes in which the distance between the two electrodes of each pair is larger than the predefined distance. 
     In an embodiment, the distances between the electrodes may be identical in all first pairs of electrodes, and the distances between the electrodes may be identical in all second pairs of electrodes, respectively. 
     In another embodiment, the distances between the two electrodes of all first pairs of electrodes are not identical, and/or the distances between the two electrodes of all second pairs of electrodes are not identical. The distances between the two electrodes of every first pair of electrodes, however, may be smaller than the predefined distance, and the distances between the two electrodes of every second pair of electrodes may be larger than the predefined distance, so that the distances between the two electrodes of all first pairs of electrodes are smaller than the distances between the two electrodes of all second pairs of electrodes. 
     In the context of the present application, a first discharge light module may be defined as a discharge light module to which at least one first pair of electrodes is assigned. Aa second discharge light module may be defined as a discharge light module to which no first pair of electrodes is assigned. 
     A plurality of second pairs of electrodes may be assigned to a second discharge light module. A plurality of pairs of electrodes including at least one first pair of electrodes may be assigned to a first discharge light module. In other words, any combination of first and second pairs of electrodes, including at least one first pair of electrodes, may be assigned to a first discharge light module. 
     In an embodiment, an odd number of electrodes may be assigned to a discharge light module. In such an embodiment, the electrodes assigned to a discharge light module may include a central electrode, which may be arranged between two outer electrodes along the longitudinal direction. In such a configuration, the central electrode may form one pair of electrodes with one of the outer electrodes and the central electrode may further form another pair of electrodes with the other one of the outer electrodes. 
     The distances between the central electrode and the two outer electrodes may be identical, so that the three electrodes form two similar pairs of electrodes, in which the distances between adjacent electrodes are substantially the same. Alternatively, the distance between the central electrode and a first one of the outer electrodes may differ from the distance between the central electrode and a second one of the outer electrodes. In such a configuration, the three electrodes form two different pairs of electrodes, in which the distances between the electrodes of each pair of electrodes are different. 
     The interior aircraft lighting device may comprise two, three, four, five, six, seven, eight, nine, ten or more first and/or second discharge light modules, respectively. Increasing the number of first and/or second discharge light modules may result in an increase of the total amount of electromagnetic radiation emitted by the interior aircraft lighting device. 
     In an embodiment, each discharge light module has a power capacity between 0.5 W an 2.0 W, in particular a power capacity between 1.0 W and 1.5 W. 
     In an embodiment, the at least two discharge light modules are arranged next to each other in a side-by-side arrangement such that electromagnetic radiation emitted by any of the at least two discharge light modules excites the at least one excitable gas in at least one other discharge light module, in particular the at least one excitable gas in at least one adjacent discharge light module. 
     In such a configuration, the electromagnetic radiation emitted by at least one discharge light module, in which a gas discharge reaction has been started, supports starting a gas discharge reaction in at least one other discharge light module. I.e., after a gas discharge reaction has been started between at least one first pair of electrodes of a first discharge light module, the electromagnetic radiation generated by said gas discharge reaction may excite the at least one gas between the electrodes of at least one other pair of electrodes, which may be arranged in a larger distance from each other than the first pair of electrodes, so that the at least one gas between said electrodes may be ignited by applying the same, relatively low voltage, which has been applied to the first pair of electrodes. 
     Said at least one other pair of electrodes may by arranged at the same discharge light module as the first pair of electrodes. I.e. a discharge light module may comprise at least two pairs of electrodes including a first pair of electrodes, which are arranged in a small first distance from each other, and at least one further pair of electrodes, comprising electrodes which are arranged in the first distance or in a larger second distance from each other. The further pair of electrodes may also be a second pair of electrodes, which is arranged at a different discharge light module, in particular at a second discharge light module. 
     The electromagnetic radiation emitted by the gas discharge reaction, which has been started between said other pair of electrodes, may excite at least one gas in at least one further discharge light module. The electromagnetic radiation emitted by the gas discharge reaction, which has been started in said at least one further discharge light module may excite at least one gas in yet another discharge light module and so on. 
     In consequence, gas discharge reactions in all discharge light modules may by activated in a cascade or chain reaction, wherein the start of the first gas discharge reaction is facilitated by a small distance between the electrodes and each gas discharge reaction, except for the first gas discharge reaction, is supported by electromagnetic radiation generated by at least one previously started gas discharge reaction. 
     In an embodiment, the discharge light modules are arranged in a parallel arrangement, i.e. in an arrangement, in which the longitudinal directions of the discharge light modules are oriented basically parallel to each other. The discharge light modules may be spaced apart from each other in a lateral direction, which is oriented laterally, in particular basically orthogonally, to the longitudinal direction. 
     Such a parallel arrangement of the discharge light modules may allow for a spatially compact arrangement, in which the discharge light modules occupy only a relatively small area of space, but which may allow for generating an emission of electromagnetic radiation having a high energy density. Such a parallel arrangement may further allow for efficiently exciting the gas in at least one discharge light module with electromagnetic radiation generated by a gas discharge reaction, which was started in at least one other discharge light module. 
     In an embodiment, the discharge light modules may have a length in the longitudinal direction of between 20 mm and 100 mm, in particular a length of between 40 mm and 80 mm, more particularly a length of between 50 mm and 70 mm. 
     In an embodiment, the discharge light modules may have a diameter in a transverse direction, which extends transversely, in particular orthogonally, to the longitudinal direction, of between 2 mm and 8 mm, in particular a diameter of between 3 mm and 7 mm, more particularly a diameter of between 4 mm and 6 mm. 
     In an embodiment, the first distance between the two electrodes of a first pair of electrodes is between 2 mm and 7 mm, in particular between 4 mm and 6 mm, more particularly about 5 mm. 
     In an embodiment, the second distance between the two electrodes of a second pair of electrodes is between 4 mm and 20 mm, in particular between 8 mm and 12 mm, more particularly about 10 mm. The second distance may in particular be at least 20% larger than the first distance, further in particular at least 50% larger than the first distance, yet further in particular at least twice as large as the first distance. 
     The above mentioned dimensions of the discharge light modules and the above mentioned distances between the electrodes of the pairs of electrodes have been found suitable for generating an effective emission of electromagnetic radiation, in particular UV light, which is well suited for disinfection. 
     In an embodiment, the electromagnetic radiation, which is emitted by the at least one gas, after a gas discharge reaction has been started, includes electromagnetic radiation in the range of UV light, in particular electromagnetic radiation in the range from 210 nm to 230 nm, more particularly electromagnetic radiation in the range from 215 nm to 225 nm, and even more particularly electromagnetic radiation in the range from 221 nm to 223 nm. Electromagnetic radiation/UV light in the above mentioned ranges is very well suited for disinfecting surfaces and other components by irradiating said surfaces and/or components with said electromagnetic radiation. 
     In an embodiment, the at least one gas in the discharge light modules includes or is a gas mixture comprising at least two gases, in particular xenon and crypto-chloride. Such a gas mixture has been found as very efficient for generating UV radiation, which is very well suited for disinfecting surfaces and other components, by starting a gas discharge reaction is said gas mixture. 
     In an embodiment, the interior aircraft lighting device further comprises an electric power supply for applying an electric voltage to each pair of electrodes. The electric power supply may be configured for applying an electric voltage between 1000 V and 5000 V. 
     The electric power supply may be a variable electric power supply, which may allow for varying the electric voltage applied to the electrodes. In particular, the electric power supply may be configured to supply a trigger voltage in start operation and a lower voltage in a steady state operation. The voltage for the steady state operation may be significantly below the trigger voltage, in particular less than 90%, further in particular less than 80% of the trigger voltage. 
     In an interior aircraft lighting device according to exemplary embodiments of the present invention, a reduced electric voltage may be sufficient for starting the gas discharge reactions between the electrodes. In consequence, an electric power supply providing an electric voltage in the above mentioned ranges may be sufficient for starting and maintaining the gas discharge reactions. As compared to previous approaches, the electric voltage for starting the gas discharge reactions may be reduced by 20% or 30% or 40% or 50% or even more. In other words, as compared to previous approaches, the electric voltage for starting the gas discharge reactions may be less than 80%, in particular less than 70%, further in particular less than 60%, yet further in particular less than 50% of the starting voltages of previous approaches. 
     In an embodiment, the method may include gradually increasing the electric voltage applied to the pairs of electrodes until a gas discharge reaction is started. This may allow for determining the minimum electric voltage, which is necessary for starting a gas discharge reaction of the at least one excitable gas, which is present between the electrodes. Such a method may prevent the gas discharge light modules from being started with an electric voltage which is higher than necessary. 
     Exemplary embodiments of the invention also include an aircraft, in particular a passenger aircraft, comprising at least one interior aircraft lighting device according to an exemplary embodiment of the invention. 
     Exemplary embodiments of the invention further include a method of disinfecting at least one component and/or surface within an aircraft, in particular within a passenger aircraft, wherein the method includes: starting a gas discharge reaction in at least two discharge light modules of an interior aircraft lighting device according to an exemplary embodiment of the invention by applying an electric voltage to every pair of electrodes of the at least two discharge light modules and irradiating the at least one component or surface with electromagnetic radiation emitted by the at least two discharge light modules of the interior aircraft lighting device. The electric voltage, which is applied to the pairs of electrodes may in particular be an electric voltage between 1000 V and 5000 V. 
     In an embodiment, the aircraft comprises a lavatory and/or a galley, and the at least one interior aircraft lighting device is installed within the lavatory and/or within the galley of the aircraft for disinfecting components and/or surfaces within the lavatory and/or galley by irradiating said components and/or surfaces with electromagnetic radiation/UV light emitted by the at least one interior aircraft lighting device. 
     In an embodiment, the aircraft comprises at least one passenger seat. At least one interior aircraft lighting device according to an exemplary embodiment of the invention may be arranged within or next to the at least one passenger seat for irradiating at least a portion of the at least one passenger seat with electromagnetic radiation, in particular UV light, which is emitted by the at least one interior aircraft lighting device. Such a configuration may allow for disinfecting at least a portion of the at least one passenger seat with electromagnetic radiation emitted by the at least one interior aircraft lighting device. 
     In an embodiment, the aircraft comprises at least one passenger service unit arranged above the at least one passenger seat. At least one interior aircraft lighting device according to an exemplary embodiment of the invention may be arranged within or next to the at least one passenger service unit for irradiating at least a portion of the at least one passenger service unit with electromagnetic radiation, in particular UV light, which is emitted by the at least one interior aircraft lighting device. Such a configuration may allow for disinfecting at least a portion of the at least one passenger service unit with electromagnetic radiation emitted by the at least one interior aircraft lighting device. 
     Exemplary embodiments of the invention also include using an interior aircraft lighting device according to an exemplary embodiment of the invention for disinfecting at least one component and/or surface within an aircraft by irradiating the at least one component and/or surface with electromagnetic radiation, which is emitted by the at least two discharge light modules of the interior aircraft lighting device. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Further exemplary embodiments of the invention are described below with respect to the accompanying drawings, wherein: 
         FIG.  1    depicts an aircraft, in particular an air plane, in accordance with an exemplary embodiment of the invention in a schematic side view. 
         FIG.  2    depicts a schematic view of an overhead passenger service unit (PSU). 
         FIG.  3    depicts a schematic cut-open view of an aircraft in accordance with an exemplary embodiment of the invention, showing a passenger cabin of the aircraft. 
         FIG.  4    depicts a schematic view of an interior aircraft lighting device according to an exemplary embodiment of the invention. 
         FIG.  5    depicts a schematic view of an interior aircraft lighting device according to a further exemplary embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    depicts an aircraft  100 , in particular an air plane, in accordance with an exemplary embodiment of the invention in a schematic side view. In the exemplary embodiment shown in  FIG.  1   , the aircraft  100  is a large passenger air plane, comprising a cockpit  103  and a passenger cabin  104  housing a plurality of passenger seats  106 . The aircraft  100  may be a commercial passenger air plane, a private air plane, or a military aircraft. It is also possible that the interior aircraft lighting device and the method according to exemplary embodiments of the invention are implemented in a rotorcraft, such as a helicopter. 
     Passenger service units (PSU)  102  are arranged above the passenger seats  106 . 
     In an exemplary configuration, in which the aircraft  100  comprises six passenger seats  106  per row (cf.  FIG.  3   , which will be discusses in more detail further below), each row of passenger seats  106  may have two passenger service units  102  associated therewith, one passenger service unit  102  assigned to the passenger seats  106  on the left side of a center aisle  114  and one passenger service unit  102  assigned to the passenger seats  106  on the right side of the center aisle  114 . 
       FIG.  2    depicts a schematic view of an overhead passenger service unit (PSU)  102 , which is arranged above the passengers of a single passenger row, as it is seen from the side of a passenger sitting on a passenger seat  106  below the overhead passenger service unit  102 . 
     On the side, which is shown to the left in  FIG.  2   , the overhead passenger service unit  102  comprises a row of three adjustable reading lights  26   a - 26   c , which are arranged next to each other. 
     Six electrical switches  27   a - 27   c ,  28   a - 28   c  are provided to the right side of the reading lights  26   a - 26   c , a respective pair of two switches  27   a - 27   c ,  28   a - 28   c  next to each of the reading lights  26   a - 26   c . One of the switches  27   a - 27   c  of each pair is configured for switching the adjacent reading light  26   a - 26   c , and the second switch  28   a - 28   c  of each pair is configured for triggering a signal for calling cabin service personnel. 
     A row of three adjacent gaspers  29   a - 29   c  is provided next to the switches  27   a - 27   c ,  28   a - 28   c.    
     Adjacent to the gaspers  29   a - 29   c  is a removable cover  40 , which covers a cavity housing at least three oxygen masks (not shown). In the event of a pressure loss within the cabin, the removable cover  40  will open, the oxygen masks will drop out of the cavity, and each of the passengers, sitting below the overhead passenger service unit  102 , may grasp one of the oxygen masks. The oxygen masks will be supplied with oxygen allowing the passengers to continue to breathe normally. 
     On the side opposite to the gaspers  29   a - 29   c , a grid  42  is formed within the overhead passenger service unit  102 . A loudspeaker (not shown), which may be used for delivering acoustic announcements to the passengers, is arranged behind said grid  42 . 
     Next to the grid  42 , there is a display panel  44 , which may be configured for selectively showing a plurality of visual signs (not shown), such as “non smoking” or “fasten you seat belt”. The display panel  44  may be illuminated from behind, in order to deliver visual information to the passengers sitting below the overhead passenger service unit  102 . 
       FIG.  3    depicts a schematic cut-open view of an aircraft  100  in accordance with an exemplary embodiment of the invention, depicting a passenger cabin  104  of the aircraft  100 , also referred to as aircraft passenger cabin  104  herein. 
     The aircraft passenger cabin  104  is equipped with a plurality of passenger seats  106 . The passenger seats  106  are arranged next to each other forming a plurality of passenger seat rows. Each passenger seat row comprises two groups of passenger seats  106 , respectively including three passenger seats  106 . The two groups of passenger seats  106  are separated from each other by a center aisle  114 , extending along a longitudinal axis A of the aircraft  1 . 
     The aircraft passenger cabin  104  is further equipped with four lavatories  108   a - 108   d . In the exemplary configuration depicted in  FIG.  3   , lavatories  108   a - 108   d  are provided at four locations within the aircraft passenger cabin  104 . A first lavatory  108   a  is located at the front portside end of the aircraft passenger cabin  104 , a second lavatory  108   b  is located at the front starboard end of the aircraft passenger cabin  104 , a third lavatory  108   c  is located at the rear portside end of the aircraft passenger cabin  104 , and a fourth lavatory  108   d  is located at the rear starboard end of the aircraft passenger cabin  104 . Additionally or alternatively, lavatories  108   a - 108   d  may be provided at other locations of the aircraft passenger cabin  104  as well. 
     The aircraft passenger cabin  104  is further equipped with a galley  110 , in order to allow for preparing meals and drinks for the passengers. 
     At least one of the lavatories  108   a - 108   d  and the galley  110  is provided with an interior aircraft lighting device  2  according to an exemplary embodiment of the invention. 
     In the exemplary embodiment depicted in  FIG.  3   , each lavatory  108   a - 108   d  and the galley  110  are provided with an interior aircraft lighting device  2  for generating UV radiation, respectively. However, exemplary embodiments of the invention also include aircraft  100  in which only one or any subset of the lavatories  108   a - 108   d  and the galley  110  are provided with an interior aircraft lighting device  2  generating UV radiation. 
     Although not explicitly depicted in  FIG.  3   , interior aircraft lighting devices  2  for generating UV radiation according to exemplary embodiments of the invention may also be provided next to the passenger service units  102  (cf.  FIGS.  1  and  2   ) for disinfecting said passenger service units  102  by irradiating the passenger service units  102  with UV light. 
     Interior aircraft lighting devices  2  according to exemplary embodiments of the invention may also be provided within the passenger cabin  104  for irradiating and disinfecting the passenger seats  106  located under the passenger service units  102 . The interior aircraft lighting devices  2  may, for example, be integrated into the passenger service units  102  or arranged next to the passenger service units  102 . 
     Interior aircraft lighting devices  2  according to exemplary embodiments of the invention may also be provided within the cockpit  103  of the aircraft  100  for disinfecting surfaces touched by the pilots. 
     As UV light may be harmful to humans, in particular to the human eye, the interior aircraft lighting devices  2  according to exemplary embodiments of the invention, provided within the passenger cabin  104  and/or within the cockpit  103  of the aircraft  100 , may be activated only after the passengers and crew have disembarked after the flight, so that no humans are present within the aircraft  100 . 
     Interior aircraft lighting devices  2  according to exemplary embodiments of the invention, located in the lavatories  108   a - 108   d , however, may also be activated during flight, when the lavatories  108   a - 108   d  are not occupied and the doors of the lavatories  108   a - 108   d  are closed, so that no or only very small amounts of UV light can exit the lavatories  108   a - 108   d . Interior aircraft lighting devices  2  located within the lavatories  108   a - 108   d  may, for example, be activated in regular time intervals or after a predefined number of passengers have used the respective lavatory  108   a - 108   d , in order to ensure hygienic conditions within the lavatories during the flight. 
       FIG.  4    depicts a schematic view of an interior aircraft lighting device  2  according to an exemplary embodiment of the invention. 
     The interior aircraft lighting device  2  comprises at least two discharge light modules  3 ,  4 , in particular four discharge light modules  3 ,  4 , which are arranged in a side-by-side arrangement next to each other. The number of discharge light modules  3 ,  4  depicted in  FIG.  4    is only exemplary. The skilled person understands that an interior aircraft lighting device  2  according to an exemplary embodiment of the invention may comprise only two discharge light modules  3 ,  4  or any number of discharge light modules  3 ,  4 , which is larger than two. 
     In the embodiment depicted in  FIG.  4   , each of the four discharge light modules  3 ,  4  has a tubular shape. Each of the four discharge light modules  3 ,  4  has a length L in a longitudinal direction A of between 20 mm and 100 mm, in particular a length L of between 40 mm and 80 mm, more particularly a length L of between 50 mm and 70 mm. Each of the four discharge light modules  3 ,  4  has a diameter D of between 2 mm and 8 mm, in particular a diameter D of between 3 mm and 7 mm, more particularly a diameter D of between 4 mm and 6 mm. 
     The distances d between the discharge light modules  3 ,  4  in a lateral direction B, which is oriented orthogonally to the longitudinal direction A, are between 4 mm and 10 mm, in particular between 5 mm and 9 mm, more particularly between 6 mm and 8 mm. 
     The discharge light modules  3 ,  4  are made of glass or a similar material which is light transmissive and gas tight. Each discharge light module  3 ,  4  contains at least one excitable gas, in particular a mixture of at least two gases, which emits electromagnetic radiation  14  when an electric field having a sufficient strength is applied to the respective discharge light module  3 ,  4 , so that the electric field passes through the at least one excitable gas. 
     In order to allow for applying such an electric field to the at least one excitable gas within the discharge light modules  3 ,  4 , the interior aircraft lighting device  2  comprises a plurality of electrodes  5   a ,  5   b ,  6   a ,  6   b . A pair of electrodes  5   a ,  5   b ,  6   a ,  6   b  is assigned to and arranged next to each discharge light module  3 ,  4 , respectively. The electrodes  5   a ,  5   b ,  6   a ,  6   b  are located outside the respective discharge light modules  3 ,  4 . 
     The discharge light modules  3 ,  4  and the electrodes  5   a ,  5   b ,  6   a ,  6   b  may be arranged on a common support  7 , in particular a common support plate  7 , such as a printed circuit board  7 . 
     In alternative configurations, the discharge light modules  3 ,  4  and the electrodes  5   a ,  5   b ,  6   a ,  6   b  may be supported by different supports  7 , in particular by multiple support plates or circuit boards  7 . Such a configuration may allow for a more flexible arrangement of the discharge light modules  3 ,  4 . 
     For supplying electric power to the electrodes  5   a ,  5   b ,  6   a ,  6   b , the electrodes  5   a ,  5   b ,  6   a ,  6   b  are electrically coupled to an electric power supply  10  via electrical lines  8 . Electric conducting paths  9   a ,  9   b  may be formed on and/or within the support  7  for electrically coupling the electrodes  5   a ,  5   b ,  6   a ,  6   b  to the electric power supply  10 . 
     Each pair of electrodes  5   a ,  5   b ,  6   a ,  6   b  comprises a first electrode  5   a ,  6   a  and a second electrode  5   b ,  6   b , respectively. The first electrodes  5   a ,  6   a  of all pairs of electrodes  5   a ,  5   b ,  6   a ,  6   b  are coupled to a first pole  11   a  of the electric power supply  10 , and the second electrodes  5   b ,  6   b  of each pair of electrodes  5   a ,  5   b ,  6   a ,  6   b  are coupled to a second pole  11  b of the electric power supply  10 . In other words, the pairs of electrodes  5   a ,  5   b ,  6   a ,  6   b  are coupled in parallel to the electric power supply  10 . In consequence, the electric power supply  10  applies the same voltage U to all pairs of electrodes  5   a ,  5   b ,  6   a ,  6   b.    
     The electric power supply  10  is a high voltage power supply  10 , which is capable of and configured for applying an electrical voltage of between 1000 V and 5000 V to the electrodes. The electric power supply  10  may be a variable electric power supply  10 , which allows for varying the electric voltage U applied to the electrodes  5   a ,  5   b ,  6   a ,  6   b.    
     In the embodiment depicted in  FIG.  4   , each electrode  5   a ,  5   b ,  6   a ,  6   b  has a longitudinal extension b, i.e. an extension in the longitudinal direction A, of between 2 mm and 5 mm, in particular a longitudinal extension b of between 3 mm and 4 mm. 
     The discharge light modules  3 ,  4  include a first discharge light module  3 , and a plurality, in particular three, second discharge light modules  4 . A first pair of electrodes  5   a ,  5   b  is assigned to the first discharge light modules  3 . A second pair of electrodes  6   a ,  6   b  is assigned to each of the second discharge light modules  4 , respectively. 
     The two electrodes  5   a ,  5   b ,  6   a ,  6   b  of each pair of electrodes  5   a ,  5   b ,  6   a ,  6   b  are arranged in a distance a 1 , a 2  from each other along the longitudinal direction A. The distances a 1 , a 2  between the two electrodes  5   a ,  5   b ,  6   a ,  6   b  of each pair are measured between the centers C of the electrodes  5   a ,  5   b ,  6   a ,  6   b  along the longitudinal direction. 
     A first distance al between the electrodes  5   a ,  5   b  of the first pair of electrodes  5   a ,  5   b , which are assigned to the first discharge light module  3 , is smaller than a second distance a 2  between the electrodes  6   a ,  6   b  of the second pairs of electrodes  6   a ,  6   b , which are assigned to the second discharge light modules  4 . 
     The first distance al between the electrodes  5   a ,  5   b  of the first pair of electrodes  5   a ,  5   b  may be between 3 mm and 7 mm, in particular between 4 mm and 6 mm, more particularly between 4.5 mm and 5.5 mm. The second distance a 2  between the electrodes  6   a ,  6   b  of the second pairs of electrodes  6   a ,  6   b  may be between 6 mm and 14 mm, in particular between 8 mm and 12 mm, more particularly between 9.5 mm and 10 mm. 
     An electric voltage U, which exceeds a minimum ignition voltage Uign, may be applied to the two electrodes  5   a ,  5   b ,  6   a ,  6   b  of a pair of electrodes  5   a ,  5   b ,  6   a ,  6   b  for starting a gas discharge reaction, generating a light bow  12  within the at least one gas contained in the associated discharge light module  3 ,  4 . The ignition voltage Uign is defined by the properties of the at least one gas within the discharge light modules  3 ,  4 , and by the distance a 1 , a 2  between the two electrodes  5   a ,  5   b ,  6   a ,  6   b.    
     In a lighting device  2  according to an exemplary embodiment of the invention, as it is schematically depicted in  FIG.  4   , the distance al between the electrodes  5   a ,  5   b  of the first pair of electrodes  5   a ,  5   b  is smaller than the distances a 2  between the electrodes  6   a ,  6   b  of the second pairs of electrodes  6   a ,  6   b . In consequence, a first minimum ignition voltage Uign1, which is necessary for starting a gas discharge reaction generating a light bow  12  emitting electromagnetic radiation  14 , in particular electromagnetic radiation  14  in the range of UV light, between the first electrodes  5   a ,  5   b , which are assigned to the first discharge light module  3 , is lower than a second minimum ignition voltage Uign2, which is necessary for starting a gas discharge reaction between the second electrodes  6   a ,  6   b , which are assigned to the second discharge light modules  4 . 
     In other words, a gas discharge reaction, generating a light bow  12  emitting electromagnetic radiation  14 , can be started within the first discharge light module  3  by applying a first voltage U1≥Uign1 to the first pair of electrodes  5   a ,  5   a , wherein the first minimum ignition voltage Uign1 is lower than the second minimum ignition voltage Uign2, which would be necessary for starting a gas discharge reaction between each of the second pairs of electrodes  6   a ,  6   b , which are assigned to the second discharge light modules  4 . Thus, when a first voltage Uign1≤U1≤Uign2 is applied to all electrodes  5   a ,  5   b ,  6   a ,  6   b  of the interior aircraft lighting device  2 , a gas discharge reaction is started only between the first electrodes  5   a ,  5   b  assigned to the first discharge light module  3 , as the first voltage U1 is not sufficient for starting a gas discharge reaction between the second electrodes  6   a ,  6   b  assigned to the second discharge light module  6 . 
     However, when the at least one gas within a discharge light module  3 ,  4  is irradiated with electromagnetic radiation  14 , in particular with electromagnetic radiation  14  including UV light, the gas molecules of the at least one gas are excited. As a result, the minimum ignition voltage Uign, which needs to be applied to the electrodes  5   a ,  5   b ,  6   a ,  6   b  for starting a gas discharge reaction, generating a light bow  12  within the at least one gas, is reduced. 
     After a gas discharge reaction in the first discharge light module  3  has been started, as it has been described before, a portion of the electromagnetic radiation  14 , which is emitted by the light bow  12 , generated by said gas discharge reaction, irradiates and excites molecules of the at least one gas within at least one of the second discharge light modules  4 . The electromagnetic radiation  14  in particular irradiates and excites the gas molecules of the at least one gas with the second discharge light module  4 , which is arranged next to the first discharge light module  3 . This excitation of the gas molecules reduces the voltage Uign, which is necessary for starting a gas discharge reaction within said second discharge light module  4 . In consequence, a gas discharge reaction within at least one second discharge light module  4 , in particular within the second discharge light module  4 , which is arranged next to the first discharge light module  3 , may be started by applying the first voltage U1 to the second part of electrodes  6   a ,  6   b , which are assigned to said second discharge light module  4 , as well. 
     The electromagnetic radiation  14 , emitted by the light bow  12  generated by the gas discharge reaction within said at least one second discharge light module  4 , will excite the gas molecules in at least one further second discharge light modules  4 . This excitation may allow for starting an additional gas discharge reaction within at least one further second discharge light modules  4 , without increasing the voltage U applied to the electrodes  5   a ,  5   b ,  6   a ,  6   b  beyond the first voltage U1, which was applied to the first pair of electrodes  5   a ,  5   b.    
     Thus, after a first gas discharge reaction has been started in the first discharge light module  3  by applying the first voltage U1 to the first pair of electrodes  5   a ,  5   b , further gas discharge reactions in additional second discharge light modules  4  may be started by applying the same, relatively low, first voltage U1 to the electrodes  6   a ,  6   b , assigned to said second discharge light modules  4 , in a cascade or chain reaction, in which the gas molecules within at least one additional discharge light module  4  are excited by the electromagnetic radiation  14  emitted by the previously started discharge light modules  3 ,  4 . 
     This cascade or chain reaction may allow for starting gas discharge reactions in all discharge light modules  4  by applying the first voltage U1 to all pairs of electrodes  5   a ,  5   b ,  6   a ,  6   b . The first voltage U1 is lower than the second ignition voltage Uign2, which would be necessary for starting gas discharge reactions in the second discharge light modules  4  having electrodes  6   a ,  6   b , which are spaced apart at the larger distance a 2  from each other, if the gas molecules within the second discharge light modules  4  would not be excited by electromagnetic radiation  14 . 
     As a result, the gas discharge reactions within all discharge light modules  3 ,  4  may be ignited by applying the lower first voltage U1 to the electrodes  5   a ,  5   b ,  6   a ,  6   b . Thus, there is no need for applying a higher second voltage U2≥Uign2 to any of the pairs electrodes  5   a ,  5   b ,  6   a ,  6   b  for starting the gas discharge reactions. In consequence, an interior aircraft lighting device  2  according to an exemplary embodiment of the invention, as it is depicted in  FIG.  4   , may be ignited completely by applying the first voltage U1 which is lower than the second ignition voltage Uign2. 
     After all discharge light modules  3 ,  4  have been ignited, the power supply  10  may lower its output voltage to a voltage level sufficient for maintaining the emission of electromagnetic radiation from the discharge light modules  3 ,  4 . In other words, the power supply  10  may lower its output voltage from a trigger voltage level, as described above, to a steady state operation voltage level. The voltage level for steady state operation may be below Uign1. 
       FIG.  5    depicts a schematic view of an interior aircraft lighting device  2  according to another exemplary embodiment of the invention. 
     The components of the interior aircraft lighting device  2  depicted in  FIG.  5   , which are analogous to the components of the interior aircraft lighting device  2  depicted in  FIG.  4   , are denoted with the same reference signs, and the analogous features will not be discussed in detail again. Reference is made to their description above. 
     The interior aircraft lighting device  2 , schematically depicted in  FIG.  5   , differs from the interior aircraft lighting device  2 , which is schematically depicted in  FIG.  4   , in that in the embodiment shown in  FIG.  5   , two pairs of electrodes  51   a ,  51   b ,  52   a ,  52   b , in particular two first pairs of electrodes  51   a ,  51   b ,  52   a ,  52   b , are assigned to the first discharge light module  3 . In each of the two first pairs of electrodes  51   a ,  51   b ,  52   a ,  52   b , the electrodes  51   a ,  51   b ,  52   a ,  52   b  are spaced apart from each other in a distance a 11 , a 12 , respectively, which is smaller then the second distance a 2  between the two electrodes  6   a ,  6   b , assigned to the second discharge light modules  4 . 
     Each of the two first pairs of electrodes  51   a ,  51   b ,  52   a ,  52   b  comprises a first electrode  51   a ,  52   a , which is electrically coupled to the first pole  11   a  of the electric power supply  10 , and a second electrode  51   b ,  52   b , which is electrically coupled to the second pole  11   b  of the electric power supply  10 . 
     In consequence, gas discharge reactions, generating a light bow  12  between the two electrodes  51   a ,  51   b ,  52   a ,  52   b  of each first pair of electrodes  51   a ,  51   b ,  52   a ,  52   b , may be started by applying a first voltage U1≥Uign1 to the electrodes  51   a ,  51   b ,  52   a ,  52   b  of the first pairs of electrodes  51   a ,  51   b ,  52   a ,  52   b , respectively. 
     By starting two gas discharge reactions within the first discharge light module  3 , two light bows  12  are generated. The generation of an additional light bow  12  results in the emission of additional electromagnetic radiation  14  from the first discharge light module  3 . As a result, the amount of electromagnetic radiation  14 , in particular electromagnetic radiation  14  including UV light, emitted from the first discharge light module  3  and, in consequence, also the amount of electromagnetic radiation  14  emitted from the interior aircraft lighting device  2 , are increased. This results in an enhanced efficiency of the interior aircraft lighting device  2 . 
     Similar to the embodiment depicted in  FIG.  4   , the electromagnetic radiation  14 , emitted by the light bows  12  generated in the first discharge light module  3 , excites gas molecules of the at least one gas within at least one of the second discharge light modules  4 . This starts a cascade or chain reaction, which results in sequentially starting gas discharge reactions in all discharge light modules  3 ,  4 , as it has been described before with respect to the embodiment depicted in  FIG.  4   . 
     In the exemplary embodiment depicted in  FIG.  5   , the distances a 11 , a 12  between the two electrodes  51   a ,  51   b ,  52   a ,  52   b  of the two first pairs of electrodes  51   a ,  51   b ,  52   a ,  52   b  are identical. This, however, is only an exemplary configuration. 
     In an alternative configuration, which is not explicitly depicted in the figures, but which may also form an embodiment of the present invention, the first discharge light module  3  may be equipped with two pairs of electrodes  51   a ,  51   b ,  52   a ,  52   b , wherein the distances a 11 , a 12  between the electrodes  51   a ,  51   b ,  52   a ,  52   b  are different in each pair of electrodes  51   a ,  51   b ,  52   a ,  52   b  (a 11 ≠a 12 ). 
     In particular, the distance all of only one of the two pairs of electrodes  51   a ,  51   b ,  52   a ,  52   b  may be small enough for allowing a gas discharge reaction to be started by applying the relatively low voltage Uign1 to the electrodes  51   a ,  51   b  of said pair of electrodes  51   a ,  51   b . The electromagnetic radiation  14 , which is emitted by the light bow  12  generated by said gas discharge reaction, will support the starting of a further gas discharge reaction between the electrodes  52   a ,  52   b  of the other pair of electrodes  52   a ,  52   b , which are provided at the first discharge light module  3 , even if the distance a 12  between the electrodes  52   a ,  52   b  of said other pair of electrodes  52   a ,  52   b  is larger and would require a higher voltage U≥Uign1 to be applied to the electrodes  52   a ,  52   b  for starting a gas discharge reaction in the absence of electromagnetic radiation  14 . 
     Increasing the distance a 12  between the electrodes  51   a ,  51   b ,  52   a ,  52   b  of a pair of electrodes  51   a ,  51   b ,  52   a ,  52   b  increases the length of the light bow  12 , which is generated by the gas discharge reaction. In consequence, increasing the distance a 12  between the electrodes  51   a ,  51   b ,  52   a ,  52   b  increases the amount of electromagnetic radiation  14  emitted by the first discharge light module  3 . 
     It therefore might be beneficial to arrange only the electrodes  51   a ,  51   b  of a single first pair of electrodes  51   a ,  51   b  in a first (lower) distance from each other, in order to allow for starting a gas discharge reaction between these electrodes  51   a ,  51   b  by applying a first (lower) voltage U1≥Uign1 to these electrodes  51   a ,  51   b , and to arrange the electrodes  52   a ,  52   b ,  6   a ,  6   b  of all other pairs of electrodes  52   a ,  52   b ,  6   a ,  6   b  in a larger distance a 2 &gt;a 1  from each other, in order to increase the total amount of electromagnetic radiation  14 , which is emitted by the interior aircraft lighting device  2 . 
     In the exemplary embodiments depicted in  FIGS.  4  and  5   , the electrodes  6   a ,  6   b  of all second pairs of electrodes  6   a ,  6   b  are arranged in the same distance a 2  from each other. Although it is not explicitly shown in the figures, it is also possible that the distances a 2  between the electrodes  6   a ,  6   b  of the second pairs of electrodes  6   a ,  6   b  are not the same in all second pairs of electrodes  6   a ,  6   b . Instead, there may be at least one second pair of electrodes  6   a ,  6   b , in which the distance a 2  between the electrodes  6   a ,  6   b  is different. 
     In such a configuration, it is possible that the distances a 2  between the electrodes  6   a ,  6   b  of the second pairs of electrodes  6   a ,  6   b  vary between the different discharge light modules  4 . Alternatively or additionally, it is possible that two or more second pairs of electrodes  6   a ,  6   b  are assigned to at least some of the second discharge light modules  4 . In such a configuration, the distances a 2  between the electrodes  6   a ,  6   b  of said second pairs of electrodes  6   a ,  6   b , which are assigned to the same second discharge light module  4 , may be identical or different. 
     While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.