# Reducing the Power Consumption of VR Displays with a Field Sequential Color LCD
## 4 Power Consumption  
Power consumption is an important performance metric for VR displays. To evaluate the power consumption of the FSC LCD, both optical and electrical parts must be considered. In the optical part, the power consumption of the LCD originates from the backlight which can be estimated by the following equations:  
\[P_{\text{optical}}=L_{\text{backlight}}/\eta_{\text{LED}} \tag{4}\]  
\[L_{\text{display}}=L_{\text{backlight}}\times\eta_{mixing}\times DC\times AR \times T_{LC} \tag{5}\]  
where \(L_{\text{backlight}}\) is the brightness of the backlight, \(\eta_{\text{LED}}\) is the efficiency of LEDs with the unit of nits/W, \(L_{\text{display}}\) is the required brightness of FSC LCD, \(\eta_{\text{mixing}}\) is the efficiency of mixing light in the backlight, \(DC\) is the duty cycle of backlight emission, \(AR\) is the aperture ratio of the 1T1C pixel circuit, and \(T_{\text{LC}}\) is the LC transmittance after passing through two polarizers. For \(\eta_{\text{LED}}\), different efficiencies of RGB LEDs need to be considered. In the electrical part, the power consumption can be divided into dynamic and static parts. The dynamic power consumption of the 1T1C pixel circuit is described as follows:  
\[P_{\text{dynamic}}=N\times f\times C_{p}\times V_{\text{SCAN}}{}^{2}+N\times f \times(C_{S}+C_{L}+C_{P})\times V_{\text{DATA}}{}^{2} \tag{6}\]  
where \(N\) is the total number of pixels, \(f\) is the refresh rate of the FSC display, \(V_{\text{SCAN}}\) is the voltage difference of the scan line, \(V_{\text{DATA}}\) is the voltage difference of the data line, \(C_{P}\) is the parasitic capacitor of the TFT, \(C_{S}\) is the storage capacitor, and \(C_{L}\) is liquid crystal capacitor in a pixel circuit. The parasitic capacitors include the gate-to-source capacitor and the gate-to-drain capacitor of the TFT in the pixel. The origins of dynamic power consumption for a pixel are explained as follows. When the scan signal turns the TFT on or off, the parasitic capacitors of the TFT are charged or discharged. Moreover, the storage, liquid crystal, and parasitic capacitors are charged or discharged to the data voltage as the TFT in a pixel is turned on. In the electrical part, the static power consumption is also shown in the following equation:  
\[P_{\text{static}}=N\times\Delta V\times l_{\text{leakage}} \tag{7}\]  
Figure 9: Simulated color shift versus viewing angles for RGB wavelengths at horizontal (dashed lines) and vertical directions (solid line), respectively, for (**a**) FSC LCD with RGB LEDs, and (**b**) LCD with QDs and color filters. where \(\Delta V\) and \(I_{\text{leakage}}\) represent the voltage difference of the capacitor and the leakage currents of the TFT in a pixel, respectively. When the TFT in a pixel is turned off, the leakage current of the TFT changes the voltage stored in the capacitors, thus causing static power consumption. Finally, the electrical power consumption can be calculated by summing the dynamic and static power consumptions. Based on the above model, the power consumption of the FSC LCD and conventional color filter-based LCD can be thoroughly compared. For the electrical power consumption, they are almost the same if the capacitance and operating voltage are assumed to be the same. Although the frame rate for FSC LCD is tripled, the number of pixels is reduced by 3\(\times\), leading to the same value for the product of \(N\) and \(f\). On the other hand, the major difference of optical power consumption depends on the absorption of color filters, the aperture ratio (\(AR\)), and the efficiency of LEDs (\(\eta_{\text{LED}}\)). For the color filter-based LCD, the absorption of color filters can reduce the luminance by approximately 3\(\times\), but the optical power consumption can be partially mitigated by white LEDs because of their higher efficiencies than RGB LEDs. For this reason, the aperture ratio plays a key role in comparing their power consumptions.