Filter Design for AMLCD Full-Color Displays Compatible with Night Vision Devices

摘要

Active Matrix Liquid Crystal Displays (AMLCD) require a properly chosen light source and built-in pixel color filters to produce a full-color display. The red end of the full-color spectrum from the display conflicts with the response of night vision devices, and therefore both must be filtered to be mutually compatible. The design of such filters is straightforward once the appropriate data has been gathered and the engineering trade-offs have been made. Although the limitations of interference filter design must be properly considered, the filter design process is heavily dependant upon choosing the proper lamp, pixel filters, and system design scheme. Two filter system approaches are considered here. One, which is in common use, is to use a short wave pass edge filter at the display to limit the output light to wavelengths less than ～650 nm, and to have a long wave pass filter at the night vision device which transmits only wavelengths longer than ～650 nm. The second approach is to use a filter to pass a narrow band of red light which may be at wavelengths even longer than 650 nm, and then to use a complementary narrow band blocking notch filter at the night vision device to prevent the entrance of conflicting light. Some trade-off examples and efficiencies are shown.