Methods of color change (ie /greenired) in the dot-matrix LC Head UP Display, using the Double-Layered Super Twisted Nematic (D-STN) LCD. are discussed.
Since LCD is a non-emissive device, the display color depends not only on the transmission spectrum of LCD but also on the backlight color.
To achieve a color change by altering the transmission spectrum of an LCD, an additional LC cell, such as an ECB(Electrically Controlled Birefringence) cell or a TN cell with a color polarizer, can be stacked on the D-STN cell. In the case of the ECB cell, display color can be controlled electrically, but disadvantage of this technique are that the color purity for red is poor and the birefringence of the cell is temperature dependant. Therefore, a temperature compensation technique for the operating voltage is required. On the other hand the TN cell can also give color switching between two colors, but the operation is much easier than that of the ECB. However the color purity and ON-transmission of a TN color switch are lower than backlighting color change technique.
Another method available for creating color change involves using a backlight technique. A change in color is achieved by using two kinds of fluorescent lamps which have different luminous substances (green & red). The color can be changed between the two colors arbitrarily, using a dimming technique.
