There are many dimming methods for desk lamps. From the practical application, there are three main methods: SCR voltage regulation (including unidirectional and bidirectional SCR), series capacitor voltage reduction, series inductor voltage reduction, series diode voltage reduction and so on. These methods can save electricity while changing the brightness of white woven lamps, and the darker the brightness, the more energy-saving it is. The lower the brightness, the longer the life of the bulb. And the power consumption on the buck element is very small. The method of changing the brightness of light bulb with series adjustable resistor or custom resistor, which is learned in junior high school textbooks, also has great power loss. The greater the voltage drop across the resistor, the greater the power loss across the resistor. Through calculation, we can know that it can also save electricity to a certain extent, but the effect of saving electricity is very small, that is to say, it basically does not save electricity. So in real life, we can't see a desk lamp with a series resistor to adjust the light.