1. In this circuit design, use 10K ohm resistor and 500uF capacitor, then 5T (time to reach 90% capacity) = 5 x RC = 25ms
2. select AC power source at 40Hz 240V, then current can reach 24mA (over 20mA for LED), and power cycle is 25ms
3. simulation speed: 5 ms/s (i.e. 1s in reality = 5ms in simulation; here 40Hz or 25ms/cycle, then 5s in real per cycle)
4. without capacitor, sharp drop and up back and forth between 6 to 2V every direction switching from + to -, and obvious on and off can be seen; with capacitor, only smooth up and down between 5.94 to 5.86V drop, almost flat, and then only dimmer observed
