Without changing the power supply voltage, please design a circuit diagram to change the brightness of the bulb

Take the simplest circuit
Power supply + switch + sliding rheostat + small bulb are all connected in series
When the sliding rheostat slides, the brightness of the small bulb changes

How to understand the acceleration effect of resistor and capacitor in series circuit with LED lamp after a resistor and a capacitor are connected in parallel

If there is no capacitor in this circuit, the LED will light up after power on. There is a process from dark to bright, which takes a long time. If the capacitor is connected in parallel with the resistor, the voltage of the capacitor will not change suddenly, so at the beginning of power on, All the voltage is applied to the LED, and the brightness of the LED is very high in a very short time. Then, as the charging current of the capacitor is getting smaller and smaller, the work of the LED is carried by the resistance. The work is over! Do you understand

81 3.3V 20mA LEDs in series, what kind of resistance and capacitance should be used in the resistance capacitance circuit
Should 0.3uf resistor be used for capacitor?

If 81, it is not suitable to use 220 V power supply. Although it can light up, it only lights up at the peak point of alternating current, which will cause insufficient brightness and stroboscopic
It is recommended to divide it into two sections, 40 or 41 in each section, so that it can work normally under 220 v. at this time, 0.27 UF capacitor + full bridge rectifier + 10 UF electrolytic capacitor filter is selected, the capacitor voltage is 400 V, and two 1m resistors are connected in parallel at both ends of the two capacitors

Without changing the power supply voltage, please design a circuit diagram to change the brightness of the bulb