Normally white mode

The intensities J(A) in the on- and off-states are averaged with the function of the sensitivity of the human eye t/(A) and the energy distribution of the illumination source H X) over the visible spectrum (380-780 nm). The electrooptic effect in the twist cell placed between parallel and crossed po-laroids is called, in [98], the normally black and normally white mode, in accordance with the appearance of the twist cell in the off state. Contrast ratios in the white mode are considerably higher than in the black mode, as the luminance in the on state for a normally white mode could be very small and limited only by the quality of polaroids and orientation. 

FIGURE 4.17. Isocontrast curves for the normally white mode [98] (twist cell between crossed polarizers in white light). The first polarizer is (a) perpendicular and (b) parallel to the director on the input substrate. 

Electrooptical effect, Twist (normally white mode)... 

In the case that the transmissive axes of the upper and lower polarizers are placed parallel, the OFF state of the display is black and this configuration is called normally black mode. Since the normally black mode gives some light leakage in the black state, the normally white mode is adopted in aTFT-LCD. 

The optical properties of aTN cell were calculated using Jones matrices by Gooch and Tarry [12]. The normalized transmittance Ttn in the OFF state in the normally white mode is given by... 

Fig. 4.2.2 Transmittance of monochromatic light through a TN cell in the normally white mode. The transmittance value normalized to that of the incident light was lOOVo. A TN cell requires two polarizers and this reduces their OFF-state transmittance by half. Thus, the maximum value of the transmittance is 50%.

Figure 1. Configuration and off- and on-state of a normally white mode operated twisted nematic (TN) cell.

Figure 5. Influence of different azimuthal angles 6 and polar angles

Contrast Ratio of the Normally Black and Normally White Mode... 

To obtain a comparable viewing angle with VA and IPS, OCB requires more sophisticated optical compensation based on a discotic material [58]. Figure 8.31 shows the compensation schemes for a normally white OCB mode. The fundamental idea is similar to that for TN. The retardation matching between the cell and the optical compensation film is especially important for the OCB mode, partially because the black state of the normally white OCB cell has a finite residual retardation value that must be compensated by an optical film. For example, any retardation fluctuation of the cell or the film is easily noticeable. The OCB system requires a high level of uniformity. And the cell parameters, as well as the film parameters, should be optimized in order to maximize the optical performance. 

So, one has to make a compromise between contrast and operating voltage. The light is significantly elliptically polarized in normal White-Taylor mode LCDs, as p is kept moderately large (much more than A/Wg) in order to reduce the operating voltage and memory. 

Figure 4 DynDom [67] analysis of the first two normal modes of human lysozyme. Dark grey and white indicate the two dynamic domains, separated by the black hinge bending region. The vertical line represents a hinge axis that produces a closure motion in the first normal mode. The horizontal line represents a hinge axis that produces a twisting motion in the second normal mode. (Adapted from Ref. 68.) The DynDom program is available from the Internet at http //md. chem.rug.nl/ steve/dyndom.html.

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