Why does the camera screen dim when using the hot shoe light?

This is because the photometric system of the camera will be affected when the hot shoe lamp is used, which makes it difficult for the camera to accurately measure the brightness of the environment, and thus it is impossible to automatically adjust the brightness of the camera screen. In addition, the hot shoe lamp usually emits strong light, which will distort the image displayed by the camera when the brightness of the camera screen remains unchanged.