SPECIFICATIONLiquid crystal cell arrangement for antiglare glassesThe invention relates to a liquid crystal cell arrangement for antiglare glasses.
It is known in the art to achieve a transparency control of a plurality of liquid crystal cells dependant on the ambient light conditions using a reference signal detected by means of a light sensor. This reference signal represents a measure for the transparency control or, in fact, the controlling quantity for the latter. Consequently, this would mean that, for example in accordance with G.D.R. Patent application No. A 61 F 24377 ill, for the embodiment of a transparency control for separately drivable liquid crystal cells being treated as a whole functional unit, it is essential to compare the value of the incident luminous intensity to a predetermined value of the luminous intensity considered to be the glaring value, for every liquid crystal cell or each group of such cells being compared with the light sensor.This comparison results in a signal representing the difference between the value of the incident intensity and the glaring value. Because this signal is not in itself sufficient for driving the liquid crystal cells it must be amplified afterwards. Furthermore, it is known that the level of luminous intensity causing glare depends on the ambient light conditions. For example. a light source can be perceived as a glare during night-time, when the human eye can only cope with small brightness differences, whereas the same light source does not appear as a glare in the day-time when the human eye can cope with larger brightness differences. The glaring value is, hence, not a constant but a variable quantity, which is dependant on the ambient brightness conditions.
It is an object of the invention to provide an arrangement for driving liquid crystal cells in antiglare glasses, wherein the transparency control of the liquid crystal cells adjusts to the varying ambient light conditions automatically.
It is a further object of the invention to provide an arrangement for driving liquid crystal cells in antiglare glasses, which relates the luminances possibly causing a glare, automaticallty to the ambient light conditions.
According to the present invention, there is provided a liquid crystal arrangement for antiglare glasses, comprising a plurality of first liquid crystal cells, which form an eye shield and which are electrically connected to first light sensors via firstdriving units, and an additional liquid crystal cell which is disposed in front of said first light sensorand which is arranged to act as a variable filter, saidadditional liquid crystal cell being connected, via asecond driving unit, to an additional light sensor which is adapted to respond to the ambient luminance. Advantageously, each driving unit includes acontrol member for setting the response thresholdof the arrangement and for aligning the transmissioncoefficient of the driving units.
Advantageously, the sensitivities of the first andadditional light sensors are equal and the transmission coefficients of the first and second driving units are equal, and the material of the liquid crystal cells forming the eye shield has a flatter electro-optical characteristic than that of the material of the liquid crystal cell acting as a variable filter.
Preferably, the sensitivities of the first light sensors which are electrically connected to the liquid crystal cells forming the eye shield are lower than that of the said additional light sensor for measuring the ambient luminance, the electro-optical character- istics of the liquid crystal cells being congruent and the transmission coefficients of the driving units being equal.
Advantageously, if the electro-optical characteristics of the liquid cells are congruent and the sensitivities of the light sensors are equal, the transmission coefficients of the driving units electric ally connected to the liquid crystal cells forming the eye shield, are lower than the transmission coefficient of that driving unit, which is electrically connected to the liquid crystal cell acting as a variable filter.
To relate a luminance which might cause a glare to the ambient average luminance, it is necessary for the transmittance of the liquid crystal cell which is disposed in front of the light sensors to vary as a function of the ambient brightness in the same mode as the luminance, which might cause a glare, varies as a function of the ambient luminance. Hence, it is an advantage to set a response threshold for the liquid crystal cells of the eye shield, with the exceeding of the threshold being equivalentto a glare effect and causing the liquid crystal cells to be obscured in dependence on the luminance.
It can occur that one and the same signal value, which causes the liquid crystal cells of the eye shield to be obscured, corresponds to different luminances, each causing a glare, in dependence on the ambient luminance.
Advantageously, the entire driving process is reduced to a comparison to a fixed value, which is the response threshold.
It is an advantage of the present arrangement that it can be achieved using simple electronics. There is no comparing of the measured parameters to state differences between them and, hence, no differential amplifier is necessary. These features permit, advantageously, the use of the portable arrangement under constantly varying light conditions. Adaption to the relevant light conditions is carried out automatically. Additionally, it is an advantage of the present arrangement that it permits the embodiments wherein the compensation of manufacturing tolerances can be achieved by the use of control members provided in the driving units.
Furthermore, the arrangement is particularly appropiate for both day and night usage of the antiglare glasses since the varying ambient light conditions are automatically taken into account.
The present invention will now be described further hereinafter, by way of example only, withreference to the accompanying drawings, in which:Figure 1 shows an arrangement in accordance with the present invention for driving a plurality ofliquid crystal cells in antiglare glasses;Figure 2 shows a diagrammatic representation of the transmittance T3 as a function of the ambient luminance bu, Figure 3 shows the relation between the ambient luminance bu and the luminance ~B being perceived as a glare dependant on the time t; andFigure 4 shows the transmittance T7 as a function of the luminance ~A in a restricted angle of vision range.
In Figure 1 the schematic representation of an arrangement for driving a plurality of liquid crystal cells in antiglare glasses is shown. The antiglare glasses consist of eye shields mounted in a frame (not visible) with arms (not visible). The eye shields are formed from liquid crystal cells 7.1, 7.2, 7.3. Light sensors 1,4.1,4.2,4.3, oriented towards the optical viewing direction, as well as associated driving units 5.1, 5.2, 5.3, are mounted in the frame of the eye shields. A liquid crystal cell 3, acting as a variable filter, is disposed in front of the light sensors 4.1,4.2, 4.3, and, as a result, the incident light L impinges as a filtered attenuated light 10a on the light sensors 4.1, 4.2, 4.3.The light sensor 1 for measuring the ambient luminance is not covered by the liquid crystal cell 3, but, via signal lines 9a (input), 9b (output) and a driving unit 2, is directly electrically connected to it. The light sensors 4.1, 4.2, 4.3, in turn, are connected to the relevant sections of the liquid crystal cells 7.1,7.2,7.3 forming the eye shield for the human eye 6.In detail, this electrical connection is embodied as follows: the light sensors 4.1,4.2,4.3 are connected to the driving units 5.1, 5.2, 5.3 via the respective signal lines 10b, and the driving units 5.1, 5.2, 5.3, in turn, are connected to the liquid crystal cells 7.1,7.2,7.3 via the signal lines 10c. A power supply unit 8 is connected to the driving units 2 and 5.1,5.2,5.3 via signal lines 8a. The driving units 2, 5.1, 5.2, 5.3 each include a control member (not visible) for aligning the transmission coefficient of said driving units.
The representations in Figures 2 to 4 are used to illustrate the mode of operation of the abovedescribed arrangement.
The light sensors 4.1,4.2,4.3 and the appertaining driving units 5.1,5.2,5.3 are matched to the liquid crystal cells 7.1, 7.2,7.3 such that, when a preset threshold value of light intensity is exceeded, a signal is delivered by the relevant driving units 5.1, 5.2, 5.3, which effects a variation of the transmittance T7 of the affected sections of the liquid crystal cells 7.1, 7.2, 7.3. Above the threshold value of light intensity, the transmittance 77 is varied in depend ence on the luminance ~B of the glaring radiation.
The filtered light impinging onto the light sensors 4.1,4.2,4.3 is controlled in dependence on the ambient luminance bu by the light sensor 1, the driving unit 2 and the liquid crystal cell 3. Figure 2 shows a diagrammatic representation of the transmittance 73 as a function of the ambient luminance bu As is known, the luminance ~B being perceived as a glare depends on the ambient luminance bu, as it is represented in Figure 3 in dependence on the time t.This means that in a restricted angle of vision range and at a certain value of the ambient luminance ~u, the luminance ~A is only then perceived as glaring if it exceeds the value ~B. In the graph of Figure 4, the luminances ~A is subdivided into sections 4)A < < > B at a certain ambient luminance 4)u and #A > ~B at a certain ambient luminance ~u, the graph indicating the relation between ~A and 77.
Since the light sensors 4.1, 4.2, 4.3, changing the transmittance 7 of the liquid crystal cells 7.1,7.2,7.3, are optically coupled with the liquid crystal cell 3 acting as a filter, and the transmittance 73 of the liquid crystal cell 3 changes as a function of the ambient luminance 4u, it is achieved that the transmittance 77 changes in dependence on the luminance ~A, occuring in a restricted angle of vision range, and on the ambient luminance ~u provided that ~A > ~B for a certain Qj,.Hence, the arrangement is automatically adjusted to the specific light conditions L, and, for that purpose, the required dependent between the ambient luminance bu and the luminance ~B being perceived as a glare, is obtained by a simple optical coupling system.
Possibilities for obtaining the required dependence between ~A and ~B, which are predetermined by the transmittance of liquid crystal cell 3: 73r and the transmittance 77 Of the liquid crystal cells 7.1, 7.2, 7.3, dependent on ~u or ~A, respectively, are given in the form of the sensitivities of the light sensors 1, 4.1, 4.2, 4.3, the transmission coefficients of the driving units 2, 5.1,5.2, 5.3, and the behaviour of the electro-optical characteristic of the liquid crystal cells 7.1,7.2,7.3. The said required dependencies are obtained by adjusting the transmission coefficients.
This is carried out, first of all, by means of the control members (not visible) of the driving units 2, 5.1, 5.2, 5.3. At the same time, the response threshold of the liquid crystal cells 7.1, 7.2,7.3 is is set, with the exceeding of the response threshold effecting a variation of the transmittance 77. The transmittance 73 of the liquid crystal cell 3 has no response threshold, as is indicated in Figure 2.