Patent ID: 6501443
Filing Date: 2002-12-31
Classification: G02C,G02F

Abstract:
A device comprising:a liquid crystal lens having an optical density which can vary in response to a voltage of a drive signal applied thereto, wherein when the voltage of the drive signal applied thereto is less than a first threshold value said liquid crystal lens exhibits a substantially uniform minimum optical density, and when the voltage of the drive signal applied thereto is greater than a second threshold value said liquid crystal lens exhibits a substantially uniform maximum optical density, and wherein when the voltage of the drive signal applied to said liquid crystal lens is between said first and second threshold values said liquid crystal lens operates in a transition region and exhibits an optical density between said minimum and maximum optical densities; and an electrical circuit including: means for detecting an ambient light level; and means for controllably varying the optical density of said liquid crystal lens dependent on the ambient light level, including means for changing a duty cycle of the drive signal driving said liquid crystal lens, wherein an amplitude of the voltage of the drive signal remains substantially constant between said first and second threshold values as the duty cycle changes, so as to cause said liquid crystal lens to operate in the transition region, between said minimum and maximum optical densities.