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Institut Jozef Stefan

Dusan Ponikvar

Janez Pirs

Bojan Marin

Silvija Pirs

Matej Bazec

Bernarda Urankar

Sivija Pirs

A new concept of the LCD light-switching optical filter allowing for very high, electrically controlled, continuously variable light attenuation (up to &#x2267;100,000) optimized/symmetrized for the light incidence along the normal to the LCD plane is proposed. The new LCD light-switching optical filter also exhibits very low light attenuation dependence for the oblique incidence of light within a limited cone of angles off the normal incidence direction in compliance with the international safety and quality regulation EN 379 for personal protection equipment. According to the invention the problem is solved by specific, novel modification of the general principle of highly twisted nematic LCDs, allowing for the adaptation of the light transmission/driving voltage characteristics to specific requirements of the driving electronics as well as 'symmetrizing' the overall optical birefringent properties, which in turn results in a high degree of their angular compensation.

Variable contrast, wide viewing angle LCD light-switching filter

The invention relates to the problem of the driving of the LCD electrooptic-switching element () with alternating, square-wave electric signals, the amplitude of witch can vary between different voltage levels in correspondence with the actual functioning state of the LCD electrooptic-switching element. The polarity changes of the electric driving signals is controlled by the integrator (), integrating the difference of the electric potentials on the driving electrodes () of the LCD electrooptic-switching element, in such a way that the value of time integral of the driving electric field is always kept within a selected interval. Besides this the time dependence of the electric driving signals can be optionally modified so that with every change of the polarity of the electric driving signals, the potentials on both driving electrodes get the same value for a time, which is significantly shorter than the switching time of the LCD electrooptic switching element.

Driving scheme and electronic circuitry for the LCD electrooptical switching element

Growing community of inventors

Ljubljana, Slovenia

Dusan Ponikvar