In aircrafts, light-emitting diodes (LEDs) are increasingly used as lighting means, because compared with traditional lighting means, relative to their mass, their power consumption and the generated waste heat, they radiate light at higher intensity. LEDs are offered with increasingly higher power, but their aperture angle compared with traditional lighting means is relatively small, and the angle of emission of the light beam from the LED can vary. The beam of a LED can be widened by means of a diffuser. Because of the narrow space conditions in an aircraft, the distance between the LED and the diffuser is relatively low.
The diffusers which are usually used in an aircraft for an aircraft light source comprise a transparent plastic material, into which a specified quantity of white scattering particles, e.g. titanium dioxide granules, is mixed. The diffusion, i.e. the random light mixing, is achieved by multiple reflection of the light as it passes through the diffuser. However, as with every reflection, part of the light energy is absorbed and reflected (back) in the wrong direction.
Therefore, because of the desired flat form of the aircraft light source, the result, as previously mentioned, is a relatively low distance between a light source and a diffuser. Therefore, either the proportion of scattering particles must be very great, and/or the thickness of the diffuser must be very great. Both measures result in considerable light losses, with the result that lighting means with an increased lighting power must be used, and/or the number of lighting means must be increased, which results in an additional space requirement, an increase of mass and an increased power consumption. Additionally, to illuminate the cabin a plurality of LEDs can be used, at least one LED emitting light at a wavelength which differs from the wavelength of the light which another LED emits. For instance, if red, yellow and blue light, each of which is generated by a LED which emits red, yellow and blue light respectively, are radiated onto the diffuser, light output which in total is white can be generated. By varying the portion of red light and/or blue light, the color temperature of the light which the aircraft light source emits can be varied. For instance, the portion of red light can be increased when the passengers want to relax. On the other hand, the portion of blue light can be increased if it is desirable to increase the attentiveness of the passengers. Further, a tint which the user wants in each application case can be given to the light which is emitted into the cabin. As previously mentioned, LEDs have a relatively small angle of radiation and are close to the diffuser. Consequently, for sufficiently good color mixing, a diffuser with a high density of scattering particles and/or a thick diffuser is required, resulting in high losses of intensity.
There is also a need for overhead or side panels in the form of lighting surfaces.
It is an object of the invention to create an improved aircraft light source.
SUMMARY
The object is achieved by an aircraft light source which comprises at least one LED and a diffuser. The diffuser has one body with a first index of refraction and a plurality of second bodies which are arranged in the first body and have a second index of refraction. In the case of this diffuser, the light is deflected at the transition from the first body to the second body and vice versa, because these have a different index of refraction. Because the light is essentially not absorbed or reflected, the light losses are comparatively small. A traditional diffuser, e.g. a diffuser which is based on a white dyed material, a surface which is structured on both sides, or titanium dioxide granules, has a degree of transmission τ of about 0.4 to about 0.5. The diffuser which is used with the aircraft light source according to the invention, with a first body which has a first index of refraction and multiple second bodies which are arranged in the first body and have a second index of refraction, has a degree of transmission τ of about 0.8 to 0.9. By varying the thickness of the diffuser, the number and/or size of the second bodies, a desired degree of diffusion can be set. For instance, the thickness of the diffuser is about 1 mm to about 3 mm, preferably about 2 mm. The size of the second bodies is for instance about 10 μm to about 70 μm, preferably about 40 μm.
The first body can comprise a flame-retardant material, and/or the second bodies can have a flame-retardant material. The materials which are used in an aircraft are subject to approval regulations. These provide that the materials which are used in an aircraft are essentially flame-retardant. The first body can have a plastic material, e.g. polycarbonate. The second body can have glass. Both polycarbonate and glass are flame-retardant materials, so that approval of them for use in aircraft is not critical. Flame-retardant in the context of the present invention can also be interpreted as flame-resistant.
Polycarbonate is also preferred as the material for the first body because it has a relatively good resistance against acids and alkaline fluids. The first body can be the carrier for the plurality of second bodies, and is, for instance, arranged on the outside of an overhead or side panel. Because polycarbonate is relatively resistant to acids and alkaline fluids, it can be well cleaned using normal cleaning materials.
The second bodies can be essentially spherical, resulting in specially high deflection and refraction of the light, and thus particularly good beam divergence and/or light mixing. The second bodies can be distributed in several planes of the first body, i.e. from the point of view of a passing-through light beam they are arranged in succession, resulting in a further improved beam divergence and light mixing.
In operation, the LED has a predefined light cone, and the diffuser has a predefined light emission area. The LED and the diffuser can be spaced at such a distance from each other that the area on the light entry side of the diffuser which is illuminated by the light cone of the LED is smaller than the radiating area, which the diffuser generates from the light cone, on the light emission area of the diffuser. The second bodies can refract the light which enters on the light entry side of the diffuser in such a way that it exits on the light emission side of the diffuser at a position which on the light entry side of the diffuser is not illuminated by a LED. The result is an aircraft light source with specially uniform light output.
The aircraft light source can comprise a plurality of LEDs, the plurality of LEDs and the diffuser being spaced at such a distance from each other that the light cones of the LEDs do not overlap. Because the second bodies, as described above, can deflect the light laterally, the result is an aircraft light source with a uniform light output, although the diffuser on the light entry side is not illuminated uniformly.
The aircraft light source can comprise a plurality of LEDs, at least one LED emitting light of a different wavelength than another LED, and the plurality of LEDs and the diffuser being spaced at such a distance from each other that the light cones of the LEDs do not overlap. As mentioned above, the second bodies can deflect the light which enters on the light entry side laterally and/or refract it, and thus mix it, so that on the light emission side of the diffuser the result is a uniform light output with respect to location and color. The aircraft light source can comprise a plurality of LEDs, at least one LED emitting light of a different wavelength than another LED, and the plurality of LEDs and the diffuser being spaced at such a distance from each other that the light cones of the LEDs at least partly overlap.
The aircraft light source can be aircraft cabin lighting. The aircraft light source can also be used as a position light or as a floodlight, for instance on a nose wheel or aerofoil.
The invention is now explained in more detail on the basis of FIG. 1, which shows a schematic cross-section through the aircraft light source according to the invention.