Illumination for Transflective Liquid Crystal Displays with Improved Efficiency
Original Publication Date: 1995-Mar-01
Included in the Prior Art Database: 2005-Mar-30
Disclosed is a method of illuminating transreflective Liquid Crystal (LC) Displays for improved performance over existing products in either reflective or transmissive modes.
Illumination for Transflective Liquid Crystal Displays
a method of illuminating transreflective Liquid
Crystal (LC) Displays for improved performance over existing products
in either reflective or transmissive modes.
Liquid Crystal Displays are flat panel displays
which can be operated in either reflective or transmissive mode.
They are designed to utilise either ambient lighting or if this is
insufficient a built in backlight. They are conventionally a
compromise in performance between a true reflective or true
transmissive panel. The transmission of the system in each mode is
less than optimum because of the requirement to allow for the other
mode of operation. The use of such displays in power restricted
systems (e.g., laptop PCs, Notebook PCs) means that power efficiency
in the backlit mode has to be sacrificed in order to have the
reflective option. A display which was selectable and thus optimised
in each mode would be a significant improvement on the current
displays used. The construction of these displays usually has a
semireflective mirror (surface) immediately behind the LC cell.
Behind this is the backlight unit. The reflected light is attenuated
by the coefficient of reflectivity of the semireflective
(semisilvered) surface. The transmitted light (when the backlight is
on) is attenuated by the coefficient of transmission of the
semireflective (semisilvered) assembly. The sum of these two
coefficients must be less than 1. Thus using this configuration it
is not possible to improve one mode without a degradation of the
efficiency in the other.
solution permits the display to be electrically
switched from being either a reflective cell or a transmissive cell
under user control. The display would be used as a conventional
reflective display (with the benefits of low power consumption) in
high ambient light environments. When the backlight is switched on
the display would convert to a conventional backlit configuration
with similar overall efficiency to a normal backlit display,
permitting low light operation. The principal of operation is to
separate the mirror 1 with reference to the Figure, from the LC cell