For a light bulb? How do you know which side is negative and which side is positive?

Are you doing a physics experiment? Incandescent light bulbs are generally used in physics experiments in middle schools, regardless of positive and negative poles, and the filament inside is tungsten wire. Semiconductor light source-LED (Light Emitting Diode) has positive and negative polarities, which can be measured by multimeter. If the lamp body is transparent or translucent, the internal structure can be seen, and the positive and negative poles can generally be judged by naked eyes. Is there a problem?