What is the name of the polished lamp before photography?

Cell phone size? Exposure meter, right? . . Hehe, it's not polishing. Does it sometimes have a white cover on it, half the size of a ping-pong ball? If so, it is an exposure meter, in order to measure the shutter speed and aperture size required under different intensity of light. By measuring, we can get the camera speed and aperture size when shooting.

Very close because a portrait photographer's face color is slightly different, which will cause different reflection effects. Although the light intensity is the same, the result is not necessarily.