The lamp holder was tested with an electric pen, and the bulb was in good condition. Why doesn't it light up when it is installed?

First, you can test the aluminum skin of the down-pressed light bulb with an electric pen. If the electric pen is on, it means that you have connected the contact that should be connected to the zero line to the fire line, and there will be hidden dangers. Correct it quickly, and then unscrew the screw that fixes the lamp holder to see if there is any conductor such as iron in it that causes a short circuit.

When installing the light bulb, be sure to pay attention to the following points:

1, please check whether the lamp you bought is in good condition;

Please check whether the lamp holder is in good condition. You can unscrew the screw that fixes the lamp holder and see if there is a conductor such as iron inside to cause a short circuit.