| 摘要 |
<p>A spectacle lens (12a, 12b) comprises a liquid crystal layer (22) and electrode assembly (26, 28) sandwiched between a pair of identically curved glass plates (18, 20) and layers of polarization material (30, 32) on the outer surfaces of the plate. The optical density of the lens is controlled by appling across the electrodes variable duty cycle voltage pulses having a magnitude greater than a threshold voltage of the liquid crystal layer and a frequency at least as great as the critical flicker fusion frequency of the eye. The duty cycle of the pulses is controlled in response to ambient light intensity measured by a photocell (16). In order to reduce response time and increase operating lifetime of the liquid crystal layer, tri-level (+V, O, -V) rather than bilevel (+V, O) pulses may be applied to the liquid crystal electrodes. </p> |
