Patent Description:
Almost all aircraft are equipped with exterior aircraft lights. In particular, large passenger air planes have a wide variety of exterior aircraft lights. Examples of such exterior aircraft lights include aircraft headlights such as take-off lights, landing lights, taxi lights, and/or runway turn-off lights.

Low ambient temperatures may result in ice forming on the exterior surfaces of such exterior aircraft lights. Ice forming on a light emission surface of an exterior aircraft light may cause a deterioration of the light output provided by the exterior aircraft light. This may result in unsafe conditions due to an insufficient illumination of areas in front of and/or next to the aircraft.

It therefore would be beneficial to provide an exterior aircraft light which allows for removing ice, which potentially deteriorates the light output of the exterior aircraft light, in a fast and reliable manner.

<CIT> discloses a lighting device with a housing comprising a cover plate, a light source and a reflector being accommodated in the housing, so that light can be generated by the light source. radiates into the reflector and, after reflection on its front side, passes through the cover plate and leaves the housing, and in the housing there is a device for defrosting and / or de-icing the cover plate is provided. The device comprises at least one infrared radiation source which is arranged on the back of the reflector and the reflector is designed to be at least partially transparent to infrared radiation which can be emitted by the infrared radiation source.

<CIT> discloses a lamp of a vehicle with a cover plate, the lamp having a lamp for generating light, the lamp having means for shifting the wavelength of at least part of the light generated by the lamp visible, short-wave range, into radiation in the long-wave wavelength range. The means is arranged in the lamp in such a way that the long-wave radiation generated by the means is directed towards the cover plate.

<CIT> discloses a headlight having a unit formed by an incandescent lamp as a temperature radiator for defrosting a lens cover. A light module with a light emitting diode light source is gripped in a headlight housing, where the lens cover is provided in the headlight housing. The incandescent lamp is arranged in a reflector body, where the light beam emitted from the incandescent lamp is directed by the reflector body on an area of the lens cover. The light beam of the light emitting diode light source is irradiated at the lens cover.

<CIT> discloses A multi-mode visible and infrared lighthead for use as a landing light or searchlight. The multi-mode lighthead incorporates a modular design wherein at least one visible light source and at least one infrared diode are mounted into the rear sector of a housing.

According to <CIT>, a headlight has an infrared emitter, and an incandescent filament arranged as a radiation source in an internal area of a lamp vessel. The filament has a filter body with a coated part having a filter layer, and an uncoated part. The parts are designed such that all of the radiation through the uncoated part essentially strikes a different area of a reflector than the infrared radiation that is transmitted through the layer.

<CIT> describes a method for protecting surfaces of the aircraft air intake from icing. The method inlcudes heating with infrared laser emitters. A spot of laser radiation is moved along heated surfaces.

Exemplary embodiments of the invention include an aircraft headlight comprises at least one visible light source for emitting a headlight light output; a light transmissive cover, which at least partially covers the at least one visible light source; and at least one infrared emitter for emitting infrared radiation for removing ice from the light transmissive cover. According to an exemplary embodiment of the invention, at least <NUM> % of the radiation energy, which is comprised in the infrared radiation emitted by the at least infrared emitter, is emitted by infrared radiation within a predefined wavelength range, and the light transmissive cover allows at least <NUM> %, in particular at least <NUM> %, more particularly at least <NUM> %, of the radiation energy, which is emitted within the predefined wavelength range, to pass through the light transmissive cover. The predefined wavelength range is from <NUM> to <NUM> and the light transmissive cover comprises quartz and/or silica.

Exemplary embodiments of the invention also include aircraft comprising at least one aircraft headlight according to an exemplary embodiment of the invention. Such aircraft may include air planes and helicopters.

The at least one infrared emitter allows for removing ice, formed on the light transmissive cover, fast and efficiently by heating and melting the ice with infrared radiation emitted by the at least one infrared emitter. As the light transmissive cover allows at least <NUM> %, in particular at least <NUM> %, more particularly at least <NUM> %, of the radiation energy, which is emitted by the at least one infrared emitter, to pass through the light transmissive cover, the infrared emitter is very efficient in melting the ice. Instead of heating the light transmissive cover, a large portion of the the infrared radiation may heat the ice directly, thus contributing to a highly efficient and fast melting of the ice.

As a result, ice formed on the light transmissive cover, which may deteriorate the emission of the visible aircraft headlight output, may be removed within a short period of time, after the at least one infrared emitter has been activated. In consequence, the full light output of the aircraft headlight, which allows for a safe operation of the aircraft even in dark environments, may be restored / achieved within a short period of time.

In an embodiment, at least <NUM> % of the headlight light output, generated by the at least one visible light source, is visible light. A visible light source producing / contributing to a headlight light output comprising at least <NUM> % of visible light does not produce a large a mount of waste heat and therefore may be operated very efficiently.

In an embodiment, the visible light source is an LED or comprises one or more LEDs. LEDs are very efficient in generating visible light without producing a large amount of waste heat.

In an embodiment, the predefined wavelength range is a range from <NUM> to <NUM>.

Ice has a large absorption coefficient for electromagnetic radiation having wavelengths in the range of <NUM> to <NUM>, in particular for electromagnetic radiation having wavelengths in the range from <NUM> to <NUM>. A large absorption coefficient means that a large percentage of the energy of electromagnetic radiation, having wavelengths in the range of <NUM> to <NUM>, is absorbed by ice. In consequence, electromagnetic radiation having wavelengths in this range is very efficient in melting ice.

In an embodiment, the light transmissive cover is made from a material comprising at least one of N-B270 glass, N-BK7 glass, pure silica glass, IR-Quartz glass and fused silica glass.

Quartz, silica, N-B270 glass, N-BK7 glass, pure silica glass, IR-Quartz glass and fused silica glass all have low absorption coefficients for infrared radiation, in particular for infrared radiation having wavelengths in the range of <NUM> to <NUM>, more particularly for infrared radiation having wavelengths in the range from <NUM> to <NUM>.

A low absorption coefficient means that a light transmissive cover made from these materials is highly transmissive for infrared radiation having wavelengths in the above mentioned ranges. As a result, a large portion of infrared radiation, having wavelengths in the above mentioned ranges, passes the light transmissive cover and reaches the ice, where it is absorbed for melting the ice, as it has been described before. Thus, forming the light transmissive cover from materials including quartz, silica, N-B270 glass, N-BK7 glass, pure silica glass, IR-Quartz glass and/or fused silica glass may contribute to efficiently melting any ice formed on the light transmissive cover by operating the at least one infrared emitter.

In an embodiment, the at least one infrared emitter is or includes at least one carbon infrared light emitter. Carbon infrared emitters are very efficient in producing infrared radiation having wavelengths in the above mentioned ranges, which are highly efficient for melting ice. Carbon infrared emitters further have short start-up times reaching their maximum power output within only a few seconds after being activated, for example within only <NUM> seconds, in particular within <NUM> to <NUM> seconds, after being activated.

In an embodiment, the at least one infrared emitter has a power capacity in the range of <NUM> W to <NUM> W. Infrared emitters having a power capacity in this range are very efficient in melting ice formed on the light transmissive cover within a short period of time.

In an embodiment, the at least one infrared emitter has a longitudinal dimension or length in the range of <NUM> to <NUM>, in particular a longitudinal dimension in the range of <NUM> to <NUM>, more particularly a longitudinal dimension in the range of <NUM> to <NUM>, for example <NUM>. Infrared emitters having these dimensions are well suited for being installed within an aircraft headlight.

In an embodiment, the aircraft headlight is an aircraft landing light and the at least one visible light source is at least one landing light source. An aircraft landing light is typically activated only a comparably short time before the aircraft lands, and it ideally provides a desired landing light output within a short period of time after being activated. Implementing an aircraft landing light as an aircraft headlight according to an embodiment of the invention may allow for removing the ice, which may have formed on the light transmissive cover of the aircraft landing light, within a short period of time, so that the aircraft landing light is able to provide the desired landing light output within said short period of time. Providing the desired landing light output within said short period of time, even when ice has formed on the aircraft landing light, enhances the safety of the aircraft, in particular the safety of the landing procedure of the aircraft.

Aircraft headlights according to exemplary embodiments of the invention may also be implemented as take-off lights, taxi lights or runway turn-off lights. The features described herein may also provide reliable operability of these aircraft lights, even at cold ambient temperatures, shortly after these lights have been activated.

In an embodiment, the at least one infrared emitter is configured for irradiating the emitted infrared radiation onto at least one selected portion of the light transmissive cover. The at least one selected portion may cover only a portion of the complete light transmissive area of the light transmissive cover. The at least one selected portion of the light transmissive cover may in particular include at least those portions of the light transmissive cover which are passed by at least <NUM> % of the headlight light output.

Such a configuration may allow for concentrating the infrared radiation, emitted by the infrared emitter, onto those areas of the light transmissive cover, which are passed by most of, in particular by at lest <NUM> % of the headlight light output. As a result, ice may be removed first from these areas, which are the most important areas for providing the desired headlight light output. Thus, in such a configuration, the infrared radiation, emitted by the at least one infrared emitter, may be used very efficiently for allowing the aircraft headlight to provide the desired headlight light output within a short period of time.

In an embodiment, the at least one infrared emitter is configured for irradiating the at least one selected portion of the light transmissive cover with an energy density of at least <NUM> W/cm<NUM> (<NUM> W/inch<NUM>), in particular with an energy density of at least <NUM> W/cm<NUM> (<NUM> W/inch<NUM>). Such energy densities have been found as very efficient for deicing the light transmissive cover within a short period of time, without overloading the electric power supply system of the aircraft.

In an embodiment, the at least one infrared emitter is configured for irradiating the at least one selected portion of the light transmissive cover with an energy density of at most <NUM> W/cm<NUM> (<NUM> W/inch<NUM>).

In an embodiment, the at least one infrared emitter is arranged closer to the light transmissive cover than to the at least one visible light source. In other words, the minimum distance between the at least one infrared emitter and the light transmissive cover is smaller than the minimum distance between the at least one infrared emitter and the visible light source.

In an embodiment, the distance between the at least one infrared emitter and the light transmissive cover is in the range of <NUM> to <NUM>.

In an embodiment, the distance between the at least one infrared emitter and the at least one landing light source is in the range of <NUM> to <NUM>.

Such a configuration may allow for reducing the amount of infrared radiation absorbed by the visible light source and/or by structural parts supporting the visible light source. In consequence, an undesirable heating of the visible light source by means of infrared radiation emitted from the at least one infrared emitter may be reduced.

In an embodiment, the aircraft headlight is configured such that the headlight light output, which is emitted by the at least one visible light source, passes the light transmissive cover in a first direction, and the at least one infrared emitter is arranged such that the at least one infrared emitter irradiates infrared light onto the light transmissive cover in a second direction, wherein the second direction is in-dined with respect to the first direction. The terms in a first direction and in a second direction are not intended to mean that the headlight light output and the infrared light are concentrated in a geometric direction. Rather, the terminology used is intended to mean that the headlight light output is provided around a first geometric direction and the infrared light is provided around a second geometric direction, with the first and second geometric directions being inclined with respect to each other.

In an embodiment, the angle between the first and second directions is larger than <NUM>°, the angle between the first and second directions may in particular be larger than <NUM>°, the angle between the first and second directions may more particularly be in a range of between <NUM>° and <NUM>°.

Such a configuration, in which the visible light output and the infrared radiation are emitted non-parallel but at an angle α > <NUM>° with respect to each other towards the light transmissive cover, may allow for a flexible arrangement of the infrared emitter with respect to the visible light source. The infrared emitter may in particular be arranged in a position and orientation which allow for efficiently irradiating those portions of the light transmissive cover with infrared light which are most important for generating the desired headlight light output, i.e. those portions of the light transmissive cover which are passed by most of the headlight light output.

In an embodiment, the light transmissive cover has an outer light output surface, an opposing inner light input surface and at least one lateral surface extending between the outer light output surface and the inner light input surface. In this embodiment, the at least one visible light source is arranged opposite to the inner light input surface so that the headlight light output, emitted from the at least one visible light source, enters into the light transmissive cover through the inner light input surface, passes the light transmissive cover, and exits from the light transmissive cover through the outer light output surface. The at least one infrared emitter is arranged at the at least one lateral surface of the light transmissive cover so that the infrared radiation emitted from the at least one infrared emitter enters through the lateral surface into the light transmissive cover.

Such an arrangement of the at least one infrared emitter with respect to the light transmissive cover may allow for very compact configuration of the aircraft headlight and for a very efficient use of the at least one infrared emitter.

In an embodiment, the at least one visible light source and the at least one infrared emitter are switchable independently of each other, i.e. the at least one visible light source and the at least one infrared emitter may be activated and deactivated independently of each other. This may allow for activating the at least one infrared emitter only if necessary, i.e. only if the ambient temperatures are below the freezing point. It further may allow for deactivating the at least one infrared emitter, after the ice on the light transmissive cover has been removed. As a result, it is possible to avoid a waste of energy by unnecessarily operating the at least one infrared emitter, and the lifetime of the at least one infrared emitter may be extended, as unnecessary operation of the at least one infrared emitter may be avoided.

In an embodiment, the aircraft headlight further comprises at least one temperature sensor and a controller. The controller may be configured for activating and deactivating the at least one infrared emitter based on temperatures detected by the at least one temperature sensor.

In such a configuration, the at least one infrared emitter may be activated if the temperature detected by the at least one temperature sensor is below a predefined threshold, for example a threshold of <NUM> or a threshold in the range of between <NUM> and +<NUM>.

Further, the controller may be configured for activating the at least one infrared emitter only for a predefined period of time, which is sufficient for melting the ice formed on the light transmissive cover.

Additionally or alternatively, the at least one infrared emitter may by activated and/ or deactivated by a manual switch provided in the cockpit of the aircraft.

In an embodiment, the controller may be configured for activating the at least one infrared emitter not simultaneously with the at least one visible light source, but a predefined period of time after the at least one visible light source has been activated. In other words, there may be a delay between activating the at least one infrared emitter and activating the at least one visible light source.

The delay / predefined period of time may be in the range of between <NUM> and <NUM>, in particular in the range of between <NUM> and <NUM>.

By activating the visible light source and the infrared emitter not simultaneously, but sequentially one after the other, a peak in power consumption, which may be caused by activating the light sources, may be flattened. In consequence, the risk of overloading the power supply system of the aircaft, which might occur if the light sources are activated simultaneously, may be reduced.

In an embodiment, the at least one visible light source and the at least one infrared emitter are operable with electric AC power having a voltage of between <NUM> V and <NUM> V, in particular a voltage of <NUM> V, and/or with electric DC power having a voltage of between <NUM> V and <NUM> V, in particular a voltage of <NUM> V. This may allow for installing and operating the aircraft headlight in different kinds of aircraft, in particular in aircraft having different types of electric power supply systems.

Exemplary embodiments of the invention further include a method of operating an aircraft headlight comprising at least one visible light source, a light transmissive cover, and at least one infrared emitter, wherein the method comprises: emitting a visible headlight light output through the light transmissive cover, and emitting infrared radiation onto the light transmissive cover. At least <NUM> % of radiation energy comprised in the infrared radiation is emitted by infrared radiation within a predefined wavelength range, and the light transmissive cover allows at least <NUM> %, in particular at least <NUM> %, more particularly at least <NUM> %, of the radiation energy, which is emitted within the predefined wavelength range, to pass through the light transmissive cover.

In an embodiment, the method includes activating the at least one infrared emitter and the at least one landing light source, and the method further includes deactivating the at least one infrared emitter some time after the at least one infrared emitter and the at least one landing light source have been activated.

Alternatively or additionally, the method may include detecting a temperature within the aircraft headlight, in particular a temperature at the light transmissive cover, and deactivating the at least one infrared emitter after a predetermined temperature has been reached.

Such a method may allow for a very efficient operation of the at least one infrared emitter. It may in particular avoid unnecessarily operating the at least one infrared emitter, after the ice has been melted and removed from the light transmissive cover.

In an embodiment, the method includes activating the at least one infrared emitter not simultaneously with the at least one visible light source, but a predefined period of time after the at least one landing light source has been activated. The predefined period of time may by in the range of between <NUM> and <NUM>, in particular in the range of between <NUM> and <NUM>.

By activating the visible light source and the infrared emitter not simultaneously, but sequentially one after the other, a peak in power consumption, which may be caused by activating the light sources, may be flattened. In consequence, the risk of overloading the aircraft's power supply, which might occur if the light sources are activated simultaneously, may be reduced.

Further exemplary embodiments of the invention are described below with respect to the accompanying drawings, wherein:.

The aircraft <NUM> has a fuselage <NUM> and two wings 104a, 104b, extending laterally from the right and left sides of the fuselage <NUM>. Each of the wings 104a, 104b supports an engine 106a, 106b. In further exemplary embodiments, which are not depicted in the figures, each of the wings 104a, 104b may support more than one engine 106a, 106b, each of the wings 104a, 104b may in particular support two engines 106a, 106b, respectively. In further embodiments, one or more engines 106a, 106b may be mounted to the fuselage <NUM> as well.

A vertical stabilizer <NUM> and two horizontal stabilizers 110a, 110b are mounted to a tail portion of the fuselage <NUM>.

The aircraft <NUM> further comprises a landing gear configuration, including two main gears 111a, 111b, which are arranged under the wings 104a, 104b, and a front gear <NUM>, which is located under a front portion of the fuselage <NUM>. Other landing gear configurations, in particular landing gear configurations comprising more than two main gears 111a, 111b, are possible as well.

An aircraft headlight <NUM> is mounted to the front gear <NUM>. Additional aircraft headlights <NUM> are provided at the roots 114a, 114b of the wings 104a, 104b next to the fuselage <NUM>.

Each of the aircraft headlights <NUM> may be an aircraft take-off light, an aircraft landing light, an aircraft taxi light, a runway turn-off light, or a multi-functional light combining at least two functionalities of an aircraft take-off light, an aircraft landing light an aircraft taxi light, and a runway turn-off light.

The aircraft headlight configuration, depicted in <FIG>, is only exemplary and not limiting. In other words, other aircraft headlight configurations comprising at least one aircraft headlight <NUM> are possible as well. Aircraft headlights <NUM> may also be mounted to other components of the aircraft <NUM>.

The aircraft <NUM> shown in <FIG> is an air plane <NUM>, in particular a large commercial passenger or cargo air plane <NUM>. It is pointed out that other types of aircraft, such as smaller air planes <NUM>, may be equipped with aircraft headlights <NUM> in accordance with exemplary embodiments of the invention as well. Aircraft headlights <NUM> according to exemplary embodiments of the invention may in particular be mounted to helicopters, too.

<FIG> shows a schematic cross-sectional view of an aircraft headlight <NUM> according to an exemplary embodiment of the invention. The depicted cross-section view may also be considered a cross-sectional side view, i.e. a cross-sectional view onto a vertical cross-sectional plane, when the aircraft headlight <NUM> is in its normal operating position.

The aircraft headlight <NUM> comprises a housing <NUM>, which may be mounted to landing gear 111a, 111b, <NUM>, to a wing 104a, 104b, or to the fuselage <NUM> of an aircraft <NUM>, as it is depicted in <FIG>.

The aircraft headlight <NUM> further comprises a light source support <NUM>, for example a printed circuit board, which is arranged within the housing <NUM> and supports at least one visible light source <NUM>. In the exemplary embodiment depicted in <FIG>, the light source support <NUM> supports three visible light sources <NUM>. In alternative configurations, which are not explicitly shown in the figures, the light source support <NUM> may support more or less than three visible light sources <NUM>.

The at least one visible light source <NUM> is configured for emitting a visible light output, i.e. a light output comprising predominantly visible light, typically white light, for providing a visible aircraft headlight light output. The at least one visible light source <NUM> may in particular be configured for providing a light output comprising at least <NUM> % of visible light.

The at least one visible light source <NUM> may be an LED or comprise at least one LED. LEDs are very efficient in outputting visible light and produce only a small amount of waste heat.

For forming the light, emitted by the at least one visible light source <NUM>, into the desired aircraft headlight light output, at least one optical component <NUM>, <NUM>, such as a reflector <NUM> and/or a lens <NUM>, is associated with each visible light source <NUM>, respectively.

The aircraft headlight <NUM> further comprises a light transmissive cover <NUM>, which is arranged at a light output side <NUM> of the aircraft headlight <NUM>, for protecting the at least one visible light source <NUM> and the associated optical components <NUM>, <NUM> from adverse environmental influences, such as water, dirt and/or mechanical impact.

The light transmissive cover <NUM> comprises an inner light input surface 14a, facing the at least one visible light source <NUM> and the associated optical components <NUM>, <NUM>, and an opposite outer light output surface 14b, facing the light output side <NUM> of the aircraft headlight <NUM>. The light transmissive cover <NUM> further comprises at least one lateral surface 14c, extending between the inner light input surface 14a and the outer light output surface 14b, in particular along the circumferences of the inner light input surface 14a and the outer light output surface 14b.

Light emitted by the at least one visible light source <NUM> enters into the light transmissive cover <NUM> through the inner light input surface 14a, passes the light transmissive cover <NUM>, and exits the light transmissive cover <NUM> through the opposite outer light output surface 14b.

The aircraft headlight <NUM> further comprises power supply lines <NUM> for electrically connecting the aircraft headlight <NUM> to an electric power supply system <NUM> of the aircraft <NUM>.

Depending on the type of aircraft <NUM>, in which the aircraft headlight <NUM> is to be installed, the aircraft headlight <NUM> may be configured for operating with electric AC power having a voltage of between <NUM> V and <NUM> V, in particular a voltage of <NUM> V. Additionally or alternatively, the aircraft headlight <NUM> may be configured for operating with electric DC power having a voltage of between <NUM> V and <NUM> V, in particular a voltage of <NUM> V.

In case of low ambient temperatures, in particular in case of ambient temperatures below <NUM>, ice <NUM> may form on the outer light output surface 14b of the light transmissive cover <NUM>. Ice <NUM> forming on the outer light output surface 14b of the light transmissive cover <NUM> may deteriorate the optical properties of the light transmissive cover <NUM> and, in consequence, may also deteriorate the headlight output emitted by the aircraft headlight <NUM>.

Therefore, it is desirable to remove the ice <NUM> formed on the outer light output surface 14b of the light transmissive cover <NUM> as fast as possible, when the aircraft headlight <NUM> is activated.

According to exemplary embodiments of the invention, ice <NUM> formed on the outside of the light transmissive cover <NUM> is removed by melting the ice <NUM> using infrared radiation <NUM>.

In order to melt the ice <NUM> very quickly, after the aircraft headlight <NUM> has been activated, an aircraft headlight <NUM> according to an exemplary embodiment of the invention comprises at least one infrared emitter <NUM>, which is configured for emitting infrared radiation <NUM> towards the light transmissive cover <NUM>.

In the exemplary embodiment depicted in <FIG>, at least one infrared emitter <NUM> is provided at the outer circumference of the light transmissive cover <NUM>. The at least one infrared emitter <NUM> is configured for emitting infrared radiation <NUM> into the light transmissive cover <NUM> through the at least one lateral surface 14c of the light transmissive cover <NUM>.

The infrared emitter <NUM> may be a circumferential, for example a circular, infrared emitter <NUM> extending circumferentially around the outer circumference of the light transmissive cover <NUM>. Alternatively, the aircraft headlight <NUM> may comprise one or more infrared emitters <NUM> which are arranged at one or more lateral surface(s) 14c of the light transmissive cover <NUM>.

The aircraft headlight <NUM> may further comprise at least one infrared reflector <NUM>, which is associated with the at least one infrared emitter <NUM> and configured for directing and optionally focusing the infrared radiation <NUM>, emitted by the at least one infrared emitter <NUM>, towards the light transmissive cover <NUM>. Employing at least one infrared reflector <NUM> may enhance the efficiency of the at least one infrared emitter <NUM>.

In the configuration depicted in <FIG>, infrared radiation <NUM> emitted by the at least one infrared emitter <NUM> enters into the light transmissive cover <NUM> via at least one lateral surface 14c of the light transmissive cover <NUM>. After having entered into the light transmissive cover <NUM>, the infrared radiation <NUM> is reflected by the inner light input surface 14a and the outer light output surface 14b of the light transmissive cover <NUM> until it reaches a portion of the outer light output surface 14b which is covered by ice <NUM>. The infrared radiation <NUM> is absorbed by said ice <NUM>, thereby heating and melting the ice <NUM>.

The aircraft headlight <NUM> may comprise at least one temperature sensor <NUM> and a controller <NUM>. The at least one temperature sensor <NUM> may be configured for detecting a temperature within the aircraft headlight <NUM> and providing an associated temperature sensor signal to the controller <NUM>.

The controller <NUM> may be configured for controlling the operation of the aircraft headlight <NUM>, in particular for controlling the operation of the at least one infrared emitter <NUM> based on the temperatures detected by the at least one temperature sensor <NUM>. The controller <NUM> may, for example, activate the at least one infrared emitter <NUM> for a predefined amount of time, after the aircraft headlight <NUM> has been activated, if the temperature detected by the least one temperature sensor <NUM> is below a predetermined threshold. The predetermined threshold may, for example, be <NUM>, or a temperature in the range of between <NUM> and +<NUM>, in particular a temperature in the range of between <NUM> and +<NUM>.

<FIG> shows a schematic, partially cross-sectional side view of an aircraft headlight <NUM> according to another exemplary embodiment of the invention. <FIG> in particular shows an exemplary embodiment of an aircraft headlight <NUM> located at a root 114a of a wing 104a of an aircraft <NUM> (cf.

Similar to the embodiment depicted in <FIG>, the aircraft headlight <NUM> depicted in <FIG> comprises a plurality of visible light sources <NUM> in combination with associated optical elements, in particular reflectors <NUM>, for emitting a visible aircraft headlight light output.

The aircraft headlight <NUM> depicted in <FIG> also comprises a light transmissive cover <NUM> and an infrared emitter <NUM> for emitting infrared radiation <NUM> towards the light transmissive cover <NUM>.

Different from the embodiment depicted in <FIG>, the infrared emitter <NUM> depicted in <FIG> is not configured for emitting infrared radiation <NUM> through a lateral surface 14c of the light transmissive cover <NUM>. Instead, the infrared emitter <NUM> is configured for emitting infrared radiation <NUM> onto the inner light input surface 14a of the light transmissive cover <NUM>, facing the visible light sources <NUM> and the infrared emitter <NUM>.

In the exemplary embodiment of an aircraft headlight <NUM> depicted in <FIG>, the infrared radiation <NUM>, emitted by the infrared emitter <NUM>, passes the light transmissive cover <NUM> for heating ice <NUM>, formed on the outer light output surface 14b of the light transmissive cover <NUM>. A portion of the infrared radiation <NUM> which does not pass the light transmissive cover <NUM>, as it is absorbed by the light transmissive cover <NUM>, heats the light transmissive cover <NUM>. Heating the light transmissive cover <NUM> also contributes to melting ice <NUM> formed on the outer light output surface 14b of the light transmissive cover <NUM>. Heating the light transmissive cover <NUM>, however, is less efficient than heating the ice <NUM> directly by infrared radiation <NUM> absorbed by the ice <NUM>.

For melting ice <NUM> formed on the outer light output surface 14b of the light transmissive cover <NUM> efficiently and in order reduce an undesirable heating of the visible light sources <NUM> by the infrared radiation <NUM> emitted by the infrared emitter <NUM>, the distance d<NUM> between the infrared emitter <NUM> and the light transmissive cover <NUM> may be smaller than the distance d<NUM> between the infrared emitter <NUM> and the visible light sources <NUM>.

The distance d<NUM> between the infrared emitter <NUM> and the light transmissive cover <NUM> may, for example, be in the range of <NUM> to <NUM>.

The distance d<NUM> between between the infrared emitter <NUM> and the visible light sources <NUM> may, for example, be in the range of <NUM> to <NUM>.

Alternatively or additionally, the aircraft headlight <NUM> may be configured such that the amount of infrared radiation <NUM> emitted by infrared emitter <NUM>, which reaches the visible light sources <NUM>, is reduced. The aircraft headlight <NUM> may, for example, comprise a shield <NUM>, which prevents infrared radiation <NUM> emitted by the infrared emitter <NUM> from reaching the visible light sources <NUM>.

The aircraft headlight <NUM> may be configured such that a considerable portion, for example at least <NUM> % or at least <NUM> %, of the visible headlight light output passes through limited portions of the light transmissive cover <NUM>. Said limited portions may in particular cover only a portion of the total area of the light transmissive cover <NUM>. In such a configuration, it may be beneficial to concentrate the infrared radiation <NUM>, emitted by the infrared emitter <NUM>, onto said limited potions, in order to use the infrared radiation <NUM> emitted by the infrared emitter <NUM> highly efficiently.

An example of such a configuration is depicted in <FIG>.

A large portion of the visible light output, in particular at least <NUM> % or <NUM> % of the visible headlight output emitted by the visible light sources <NUM>, passes through the light transmissive cover <NUM> in portions A and B, depicted in <FIG>. In such a configuration the other, non-marked portions of the light transmissive cover <NUM> are almost negligible. In order words, ice <NUM> formed on the light transmissive cover <NUM> outside areas A and B does not considerably deteriorate the headlight light output of the aircraft headlight <NUM>.

In order to use the infrared radiation <NUM> emitted by the infrared emitter <NUM> in a highly efficient manner, it may be beneficial to concentrate the infrared radiation <NUM>, emitted by the at least one infrared emitter <NUM>, onto said portions A and B, so that ice <NUM> formed on these portions A and B will be heated fast and melted first. Such a configuration results in a fast improvement of the visible headlight light output, provided by the aircraft headlight <NUM>, after the infrared emitter <NUM> has been activated.

Melting ice <NUM> formed on the light transmissive cover <NUM> by means of infrared radiation <NUM> is particularly efficient when a large percentage of the infrared radiation <NUM>, irradiated onto the ice <NUM>, is absorbed by the ice <NUM>, and only a small percentage of said infrared radiation <NUM> passes the ice <NUM> and/or is reflected by the ice <NUM> without being absorbed.

It is therefore beneficial to adjust the infrared radiation <NUM>, emitted by the infrared emitter <NUM>, to the absorption properties of ice <NUM>.

<FIG> shows a graph, in which the absorption coefficient α of ice <NUM> with respect to electromagnetic radiation is plotted on the vertical axis as a function of the wavelength λ of the electromagnetic radiation. The wavelength λ is plotted on a logarithmic scale extending along the horizontal axis of the graph.

<FIG> shows that the absorption coefficient α of ice <NUM> is relatively high for electromagnetic radiation in the range of between <NUM> and <NUM>, in particular in the range of infrared radiation <NUM> having wavelengths in the range of between <NUM> and <NUM>. In other words, a large percentage of infrared radiation <NUM> having wavelengths in this range is absorbed by ice <NUM>, so that infrared radiation <NUM> having wavelengths in this range is very efficient for melting ice <NUM>.

In consequence, it is beneficial to configure the at least one infrared emitter <NUM>, which is employed in an aircraft headlight <NUM> according to the embodiment of the invention, to predominantly emit infrared radiation <NUM> having wavelengths in the range of between <NUM> and <NUM>, in particular infrared radiation <NUM> having wavelengths in the range of between <NUM> and <NUM>. The at least one infrared emitter <NUM>, employed in an aircraft headlight <NUM> in accordance with exemplary embodiments of the invention, may in particular be configured such that at least <NUM> %, more particularly at least <NUM> %, of the energy emitted by the at least one infrared emitter <NUM> is emitted as infrared radiation <NUM> having wavelengths in the range of between <NUM> and <NUM>, in particular infrared radiation <NUM> having wavelengths in the range of between <NUM> and <NUM>. In order to cause a fast melting of ice <NUM> formed on the light transmissive cover <NUM>, the at least one infrared emitter <NUM> may be configured for irradiating the light transmissive cover <NUM>, or at least the relevant portions A, B of the light transmissive cover <NUM> (see <FIG>), with infrared radiation <NUM> having an energy density of at least <NUM> W/cm<NUM> (<NUM> W/inch<NUM>), in particular with infrared radiation <NUM> having an energy density of at least <NUM> W/cm<NUM> (<NUM> W/inch<NUM>), on the light transmissive cover. Also, the infrared irradiation <NUM> may have an energy density of at most <NUM> W/cm<NUM> (<NUM> W/inch<NUM>) on the light transmissive cover.

The at least one infrared emitter <NUM> may, for example, be a carbon infrared emitter <NUM>. Carbon infrared emitters <NUM> are very efficient in producing infrared radiation <NUM> having wavelengths A in the above mentioned preferable ranges, i.e. infrared radiation <NUM> which is very efficient in melting ice <NUM>. Carbon infrared emitters further have a small start-up time, reaching their maximum power output within only a few seconds after start-up, for example within only approximately <NUM> to <NUM> seconds after being activated.

The carbon emitters may have a total power capacity in the range of <NUM> W to <NUM> W. Such a power capacity may allow for a fast melting of the ice <NUM>, without overloading the electric power supply system <NUM> of the aircraft <NUM>.

Carbon infrared emitters <NUM> having a longitudinal dimension or length of <NUM> to <NUM>, in particular a longitudinal dimension of <NUM> to <NUM>, more particularly a longitudinal dimension of about <NUM>, have been found as well-suited for being installed within typical aircraft headlights <NUM>.

The infrared radiation <NUM> emitted by the at least one infrared emitter <NUM> needs to pass the light transmissive cover <NUM> before it reaches the ice <NUM> formed on the outer light output surface 14b of the light transmissive cover <NUM>.

In order to use the infrared radiation <NUM>, emitted by the at least one infrared emitter <NUM>, very efficiently for melting ice <NUM> formed on the outer light output surface 14b of the light transmissive cover <NUM>, it is desirable that the percentage of infrared radiation <NUM>, which is absorbed by the light transmissive cover <NUM>, is small.

Conventionally, the light transmissive cover <NUM> is frequently made of acrylic glass.

Acrylic glass, however, has a relatively high absorption coefficient, which is equivalent to a relatively low transmission coefficient T, for electromagnetic radiation having wavelengths in the range of <NUM> to <NUM>, which is beneficial for melting ice, as it has been discussed before. More specifically, a typical average transmission coefficient T of acrylic glass in the desirable range of wavelengths, i.e. wavelengths in the range of between <NUM> and <NUM>, is less than <NUM> %.

In consequence, a considerably large portion of the infrared radiation <NUM>, emitted by the at least one infrared emitter <NUM>, would be absorbed by a light transmissive cover <NUM> made of acrylic glass. This would result in a low efficiency of melting ice <NUM>, formed on the light transmissive cover <NUM>, by means of infrared radiation <NUM>.

In order to enhance the efficiency of melting ice, formed on a light output surface of an aircraft headlight <NUM> according to the embodiments of the invention, other materials than acrylic glass, in particular materials having a larger transmission coefficient T for infrared radiation <NUM> in the range of between <NUM> and <NUM>, may be used for forming the light transmissive cover <NUM>.

<FIG> depicts the transmission coefficient T of a borosilicate glass having a thickness of <NUM>. The transmission coefficient T is plotted on the vertical axis, as a function of the wavelength λ of the infrared radiation <NUM>, which is plotted on the horizontal axis.

<FIG> shows that, over a wide range of wavelenghths λ, the transmission coefficient T of borosilicate glass is significantly larger than <NUM> %, which is a typical transmission coefficient T of acrylic glass.

Even better transmission properties of the light transmissive cover <NUM> is achieved by using specialized glasses, which comprise a high volume content of quartz / silica, such as glasses which are known as N-BK7 glass or as N-B270 glass, respectively.

In <FIG>, the transmission coefficients T of these glasses, having a thickness of <NUM>, are plotted as a function of the wavelength λ. The solid curve illustrates the transmission coefficient T of N-BK7 glass, and the dashed curve illustrates the transmission coefficient T of N-B270 glass.

In the relevant range of wavelengths A between <NUM> to <NUM>, the glasses show an average transmission coefficient T of more than <NUM> %. In consequence, forming the light transmissive cover <NUM> from these glasses may allow for considerably improving the efficiency of deicing the light output surface of an aircraft headlight <NUM> by infrared radiation <NUM>.

Similar or even more pronounced effects may be achieved by forming the light transmissive cover <NUM> from pure silica, which has been purified from OH content. Glasses of these type are known as "IR-quartz" and/or "fused silica".

In <FIG>, the transmission coefficients T of such glasses are plotted as a function of the wavelength λ. In <FIG>, the dashed line indicates the transmission coefficient T of a glass having a thickness of <NUM>, and the solid line indicates the transmission coefficient T of a glass having a thickness of <NUM>.

<FIG> shows that, in the favorable range of wavelengths λ between <NUM> to <NUM>, transmission coefficients T of up to almost <NUM> % may be reached, even for a "thick" glass having a thickness of <NUM>. Forming the light transmissive cover <NUM> from "IR-quartz" and/or "fused silica" may therefore allow for a very efficient deicing of the light transmissive cover <NUM> using infrared radiation <NUM>, which passes the light transmissive cover <NUM>, as it has been described before.

Claim 1:
Aircraft headlight (<NUM>), comprising:
at least one visible light source (<NUM>) for emitting a headlight light output;
a light transmissive cover (<NUM>), at least partially covering the at least one visible light source (<NUM>); and
at least one infrared emitter (<NUM>) for emitting infrared radiation (<NUM>) for removing ice from the light transmissive cover (<NUM>);
wherein at least <NUM> % of radiation energy, comprised in the infrared radiation (<NUM>) emitted by the at least infrared emitter (<NUM>), is emitted within a predefined wavelength range; and
wherein the light transmissive cover (<NUM>) allows at least <NUM> %, in particular at least <NUM> %, more particularly at least <NUM> %, of the radiation energy, which is emitted within the predefined wavelength range, to pass through the light transmissive cover (<NUM>);
characterised in that the predefined wavelength range is from <NUM> to <NUM> and the light transmissive cover (<NUM>) comprises quartz and/or silica.