What is the voltage before the light bulb glows?

When the bulb is illuminated normally, the voltage at both ends of the small bulb is equal to the rated voltage.

The normal light emission of the bulb means that when the voltage of the bulb reaches the rated value, the bulb will emit light normally. For example, if the nameplate of a light bulb is "2W, 12V", then when the voltage of the light bulb is 12V, the light bulb and the light bulb will emit light normally, otherwise it is not called normal light emission.

A small, normal light bulb means that the light bulb works at rated voltage. When the light bulb works at rated voltage, it must play its rated power.

Rated voltage is the best voltage for long-term operation of electrical appliances. If it is high, it is easy to burn out; if it is low, it will not work normally (the light bulb will not glow normally, and the motor will not work normally). At this time, all components in the electrical appliance are working in the best condition. Only when they work in the best state, the performance of electrical appliances is relatively stable, so that the life of electrical appliances can be extended.