# Reducing the Power Consumption of VR Displays with a Field Sequential Color LCD
## 5 Discussions  
Through eliminating color filters, both spatial resolution and optical efficiency can be tripled, but the shorter capacitor charging time needs to be considered as well. Because of the reduced turn-on time (\(\sim\)0.3 ms), LED backlights should be optimized to generate the required peak brightness. A multistring LED backlight driving system [35] was proposed to alleviate the requirement for a higher peak power and reduce power consumption. On the other hand, the shorter capacitor charging time will slightly lower the transmittance, but the \(\sim\)3\(\times\) optical gain may compensate for the decreased transmittance. Furthermore, using multiple ICs to scan the gate lines simultaneously can restore it to an original charge time without FSC. The increased cost will still be much cheaper than micro-OLEDs using a whole silicon wafer. Another strategy is to employ TFTs with a higher mobility and thereby reduce the time constant of the capacitor.  
As for contrast ratio, the mini-LEDs can be employed to increase the contrast ratio of the LCD [36; 37]. With the help of mini-LEDs, the vertical alignment (VA) mode will not outperform the FFS mode in terms of contrast ratio. Furthermore, it is challenging to obtain such a fast response time using VA mode. For a fair comparison, we used a high-performance negative dielectric anisotropic LC mixture [38] in simulations. The LC mixture features a high birefringence (\(\Delta n\) = 0.191 at \(\lambda\) = 550 nm), and low viscosity (\(\gamma_{1}/K_{33}\) = 6.7 ms/\(\upmu\)m\({}^{2}\) at 50 \({}^{\circ}\)C). Other simulation conditions are as follows: cell gap is 2 \(\upmu\)m, on-state voltage is 5.2 Vrms, and operating temperature is 50 \({}^{\circ}\)C. The simulated results are listed in Table 2. The average GTG response time is 3.8 ms, which is much slower than that of FFS LCDs at the same temperature. To further decrease the response time of VA mode, a slightly thinner cell gap of 1.8 \(\upmu\)m and a higher on-state voltage of 6 Vrms are employed. The average GTG response time is decreased to 3.1 ms, which is still slower than that of FFS LCDs.  
In a conventional VA cell, a negative dielectric anisotropy (\(\Delta\epsilon\)) LC is usually used and the electric field is in the longitudinal direction. However, if a lateral field is applied to activate the VA cell, then a positive \(\Delta\epsilon\) LC can also be considered, as reported in [39], where an additional longitudinal field is applied to accelerate the LC director's restoring time. As a result, both fast turn-on and turn-off processes can be achieved, even at a low temperature [39]. Bidirectional field switching (BFS) has also been demonstrated to achieve fast response time [40]. Here, a BFS controller is used to switch between the vertical field and the twisted-planar field. Both approaches can achieve fast response time, but the driving circuits are complicated, and the optical transmittance is reduced.  
Besides response time, viewing angle is another concern for VA mode. Negative c-plate compensation films may be introduced to widen the viewing cone of VA mode. On the positive side, the VA mode with incident circularly-polarized light can exhibit a much higher transmittance than the FFS mode using zero rubbing angle. Micro-OLED is another type of light engine that exhibits ultrahigh contrast ratio and small form factor. However, when the cavity effect of a micro-OLED panel is weak, the broad angular distribution will cause more stray light in the pancake system, which in turn degrades the system contrast ratio. Overall, the FFS FSC-LCD using a locally dimmable mini-LED backlight is a strong contender for VR displays.