dimensional displays is the use of lenticular arrays14,15 to create a fixed number of viewing zones (usually about seven to nine) in which the left and right images are coherent although with reduced resolution (see Figure 10.1). At present, the acceptance of the latter approach has been limited by restriction of the positions from which the display can be observed; image quality suffers significantly if an improper position is used.
Another trend for LCDs is in providing greater color fidelity than is currently possible. That is related to another recent trend: the replacement of fluorescent tubes with LEDs in the display backlight. The most common backlight now consists of white LEDs, which themselves consist of blue emitters passing through a color-converting phosphor, typically cerium-doped yttrium aluminum garnet (Ce:YAG).
A problem with such white LEDs in an LCD backlight application is that the color filters are not perfect. The light from the green and the red filters overlaps with yellow wavelengths passed by both filters. That results in colors that are less true, so, for example, a completely green image appears more yellow-green than true green.
It has been suggested that the color-filter deficiencies might be addressed by substituting LEDs that emit only in relatively narrow wavelength bands of RGB. Although that might be done with RGB rather than white LEDs, another possibility is that quantum dots (QDs) would substitute for phosphor (see Figure 10.2). QDs would have the advantage of providing much more precise and narrow-wavelength color conversion so that emission of the white LED with QD color conversion would not need to emit at all in the yellow band where the green and red filters overlap. The result would be more pure colors and a broader color gamut.
Of the several kinds of touch technologies, three are most prevalent: resistive, in which a touching object presses down and causes two separated layers to connect to each other at that point; optical, in which a touching object appears as a shadow, and cameras can locate and measure the size of the object; and capacitive, in which an electrically conducting finger touching a screen results in a distortion of the screen’s electrostatic field and a change in capacitance. Resistive touch technology was the first to be used, most commonly in bank automated teller machines and cash registers. It has low cost but low resolution. Optical touch technology was invented and commercialized (for example, the HP 150 PC in 1984) with much
14 Johnson, R.B., and G.A. Jacobsen. 2005. Advances in lenticular lens arrays for visual display. Proceedings of SPIE—The International Society for Optical Engineering. Volume 5874.
15 Kim, H., and J. Hahn. 2010. Optimal design of lens array for wide-viewing angle multi-view lenticular 3D displays. Proceedings of the International Meeting on Information Display and International Display Manufacturing Conference and Asia Display, October 11-15, 2010, Seoul, Republic of Korea.