The working principle of the adjustable table lamp is that the resistor R2, the potentiometer RP1, the capacitor C constitute a resistance-capacitance phase shifting circuit, and the RP1 can be adjusted to change the conduction angle of the triac V, thereby changing the brightness of the bulb EL. Resistor R1 is a current limiting resistor. The charging speed of C is also related to the parallel circuit. In the case where R1 and RP2 are fixed, the size of the shunt is determined by the resistance of the photoresistor RL. When the grid voltage rises, the brightness of the light increases, the resistance of RL becomes smaller, the shunt increases, the voltage across the capacitor C rises slowly, the conduction angle of the thyristor V decreases, the output voltage decreases, and the brightness of the light decreases. Conversely, when the grid When the voltage drops, the RL resistance increases, the shunt decreases, the thyristor conduction angle increases, the output voltage increases, and the brightness of the light increases. The brightness of the light is automatically stabilized at the set value.