the voltage across the capacitor also changes with time as shown in Equation (3) V(t) = V + (Vsource - Vo)(1-e-t/charging), (3) where Vo = V (t) = Voe-t/discharging Qo/C is the initial voltage across the capacitor. (5) Capacitor Voltage (V) 4.0- 5 2.0- 1.5 Vow 0 5 10 charging discharging 15 Im 20 one cycle 25 Time (s) Figure 2: Voltage vs time for charging and discharging capacitor. The curve clearly shows the periodic charging (LED on) and discharging (LED off) process of a capacitor in an LED box; in addition, the filiping voltages high and Vow are also shown. Please note that in each LED on-off cycle, the on time ton is always greater than the off time toff. As evident in the figure, Vlow is the initial voltage for the charging process, while it is the initial voltage for the discharging process.