Optical: systems and elements – Holographic system or element – Using a hologram as an optical element
Patent
1994-06-08
1996-02-06
Sikes, William L.
Optical: systems and elements
Holographic system or element
Using a hologram as an optical element
359 84, 359 85, 359 49, G02F 1137, G02F 1135
Patent
active
054900050
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The present invention relates to a light sensor for regulating the brightness of an illumination device for a display device.
BACKGROUND OF THE INVENTION
In known illumination devices, by way of example, a transflexive or transmissive liquid crystal display is surface-illuminated via a light guide to provide the illumination. In this case, a phototransistor is used to control the brightness of the display disposed in the light flux and regulates the illumination device as a function of the light flux. In European Published Patent Application No. 0 115 575 A3 a light guide is proposed which is constructed with two mutually opposite end faces and detects both the light incident through the windscreen of a motor vehicle and the light from the observation space in front of the dashboard. The total light which falls onto a milky white plastic body of the light guide is detected on laterally arranged sensors. With its relatively large dimensions, the light guide is arranged behind the windscreen in the region of the dashboard cover of a motor vehicle. Said light guide requires a relatively large amount of space, which is needed in this region for other electrical devices. Furthermore, the arrangement of the light guide behind the windscreen must be taken into consideration even when designing the passenger compartment, so that certain impediments to design freedom are imposed on the designer.
SUMMARY OF THE INVENTION
The light sensor according to the present invention, has, in contrast to the prior art, the advantage that the light sensor is constructed as a compact unit with the display device. An additional space in the region of the dashboard is not required, since the light guide has a light-collecting film, which is relatively thin and, as a result, hardly alters the construction of the display device. It is particularly advantageous that no readjustment is required, since the complete display device can be preassembled at the factory.
The use of a light-collecting film is particularly favorable for the reason that, on account of its structure, it deflects a part of the light onto the side surfaces, which are not illuminated by the incident light. If a sensor is now arranged at one of the side surfaces, then it receives the deflected lateral light, without its arrangement disturbing the transmitted light behavior of the collecting film. Such light-collecting foils are, in addition, economically available on the market. It is also advantageous that the light-collecting film performs the function of light filtering if the display is intended to appear in a specified color.
It is particularly advantageous that the light-collecting film is a plastic film, since it does not splinter in the event of an accident and, as a result, is not hazardous.
A very simple refinement of the arrangement in accordance with the present invention is in particular obtained by the use of a photoresistor, of a photodiode or of a phototransistor element, since such devices can directly convert the received light into a corresponding electrical signal.
If the light guide is, for example, arranged directly in front of an LCD display in the viewing direction, then the light falling onto the display device shines through it. In this case, the display brightness can be regulated to a desired value as an area integral over the entire area of the display device.
The light emerging into the sensor is advantageously intensified by mirror-coating the free lateral surfaces.
It is particularly advantageous that, as a result of the formation of a correction factor for the illumination regulation, the display device appears uniformly bright irrespective of the number of driven elements.
A further advantage can also be seen in that the brightness of the display can be predetermined by means of a setting element. As a result of this, the brightness of the display can individually be matched to the wishes of the driver.
In the case of an arrangement of the light guide behind the display device, but in front of an illuminatio
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patent: 4915479 (1990-04-01), Clarke
patent: 4920257 (1990-04-01), Fuerthbauer et al.
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Bayer Chemie, "FLAD Fluorescence-Activated Display, LISA-Plastics", Praxisinformation, Jul. 1982, pp. 1-6.
Abraham Fetsum
Robert & Bosch GmbH
Sikes William L.
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