1. Field of Invention
The invention relates to a light module for a motor vehicle headlamp.
2. Description of Related Art
A light module as depicted in published German Patent DE 10 2009 053 581 B3 is known in the art which exhibits an optical fiber configuration having at least one first optical fiber branch and a second optical fiber branch. Each of the two branches exhibit a light entry surface and a light exit surface, wherein in each case the light exit surface is bordered by two narrow sides and two long sides. The two branches are disposed such that a narrow side of the first branch is disposed parallel and directly adjacent to a narrow side of the light exit surface of the second branch. The narrow sides of the light exit surfaces of the two branches are of the same length, while the long sides of the light exit surface of the second branch are longer than the long sides of the light exit surface of the second branch. Each branch has two transport surfaces, which border an optical fiber volume extending between the light entry surface and the light exit surface of each branch, on which light propagated in the optical fiber experiences a total internal reflection, and which are bordered by the long sides of the light exit surface of the branch.
The branches, together with numerous other branches, are a component of a primary lens. Each light entry surface has an LED, the light of which is coupled in the branch, and decoupled by the light exit surface. The light exit surfaces are disposed in a matrix, such that the sum of the light exit surfaces forms a surface emitting light in the manner of combined pixels, the shape of which can be varied by switching LEDs on and off. The light emitting surface is located in the interior of the headlamp, in the form of an inner light distribution, at a spacing of a focal length of a secondary lens thereof, and is projected therefrom in the form of an external light distribution in the region in front of the headlamp. This known light module will also be referred to as a matrix light module.
When the light module is used in a motor vehicle headlamp, the external light distribution on the driving surface occurs as an image of the inner light distribution, present in the interior of the headlamp in the form of combined pixels, which is formed on the light exit surface of the primary lens. By switching individual LEDs on and off (and thus, individual pixels), the images of the pixels in the external light distribution also appear as either light or dark. The switching off or dimming of individual LEDs (or groups of LEDs) thus enables, for example, a targeted limiting of the illumination in regions in which oncoming traffic could be blinded.
As known in the art, light modules may also generate light distributions having stripe-shaped individual light distributions lying adjacent to one another. Each stripe is generated by one optical fiber branch and one light source. In comparison with the matrix light module, each optical fiber branch replaces a column of optical fiber branches of the matrix in this case. The intended horizontal angular resolution of a light module of this type (which generates stripe-shaped light distributions) lies, for example, between 1.0° and 1.5° in the horizontal plane, wherein this directional condition is related to the designated use of the headlamp in a motor vehicle. This limitation is obtained in connection with the light sources normally available for use in motor vehicle headlamps, which have fixed dimensions in terms of their geometry and emit only limited luminous flux. This requirement further limits the variability of the lens system.
The high-power LEDs that are preferred and known in the art have a rectangular luminous (and thus active) light emitting surface, and a size of approximately 0.5 mm2. The active surface is constant, independent of the luminous flux delivered. The LED emission pattern (for example, the angular distribution of the emitted light) is likewise constant. Normally, this concerns a so-called Lambert characteristic. The so-called warm luminous flux in continuous operation of LEDs is, for example, approximately 80 lumen at a maximum acceptable electrical operating current. It is to be expected, however, that the warm luminous flux may increase to a certain degree over time. However, with respect to the present invention, the available luminous flux should be regarded as being limited.
For financial reasons, and due to reliability concerns, it is generally intended that the number of light sources in a light module be kept as low as possible. Light modules that generate stripe-shaped light distributions (in the following, also referred to as striped-light modules), are therefore preferred over light modules that generate light distributions created in a matrix. In order to project a sufficient luminous flux onto the driving surface, using a striped-light module (and thus, the fewest possible LEDs) in order to thus generate light distributions having predefined high maximal values for the luminosity and a predefined change to the luminosity along a vertical angular scale, a high degree of efficiency regarding light transference is also necessary. For this, the degree of efficiency regarding light transference is understood to mean, for example, the luminous flux exiting a secondary lens after its standardization to the luminous flux entering the primary lens.
Thus, the objective of the present invention is to provide a light module which enables a generation of vertical, stripe-shaped light distributions with a small number of light sources. The stripe-shaped light distribution should exhibit a first narrow side having a pronounced maximum luminosity. Starting from there, and running to the opposite second narrow side of the stripe-shaped light distribution, the luminosity should diminish. The maximum gradient of the illumination or luminosity facing the first narrow side of the light distribution should be much steeper than the maximum gradient facing the second narrow side. As a result, it should be possible to create an illuminated stripe having a sharply focused light/dark border at the first narrow side, an adjoining region of maximum luminosity, and a softly focused and continuously diminishing luminosity, thus a luminosity diminishing continuously over the length of the stripe as the distance to the sharply focused light/dark border and the luminosity maximum increases. The luminosity should decrease disproportionately in relation to the increase in distance as the distance to the maximum increases, and accordingly, in the opposite direction, the luminosity should increase disproportionately starting from the second narrow side toward the maximum luminosity, in relation to the distance from the second narrow side.