LCD SHUTTER CONTRAST IMPROVEMENT USING WAVE-LENGTH SHIFT
Original Publication Date: 1988-Jun-30
Included in the Prior Art Database: 2004-Apr-04
Xerox Disclosure Journal
The Liquid Crystal Shutter imaging systems currently experience xerographic latitude problems because of lack of contrast between the on and off states of the shutter. A method of increasing xerographic latitude without changing the contrast is disclosed, whereby the wavelength of the residual light reaching the photoconductor is changed to a value that is on the less sensitive portion of the photoconductor response curve. As an example, consider an LCD Shutter system with a 550 nM fluorescent light source. In the shutter open state, the light reaching the photoconductor is also distributed around this value. The residual light reaching the photoconductor is approximately 1/10 the power of that of the open state and is distributed around the same mean value (550 nM). By using the LCD molecules to filter out the wavelengths about 400 nM in the off state, a 25:l contrast is achieved, as far as the photoconductor is concerned, even though the light intensity is still 1O:l. This wavelength conversion is done independently as each pixel in the array switches to the off state.