When light rays coming from a bright source(s) of light (such as the sun or artificial light) directly reach the front element of a camera lens, they can reflect and bounce off different lens elements, diaphragm and even off the sensor, potentially degrading image quality and creating unwanted objects in images. Better known as lens “flare”, the effect can impact images in a number of ways: it can drastically reduce image contrast by introducing haze in different colors, it can add circular or semi-circular halos or “ghosts” and even odd-shaped semi-transparent objects of various color intensities. Flare is not always undesirable in photography though – sometimes in is used creatively to add artistic elements to images. In fact, lens flare is often deliberately added to movies and computer games to add a sense of realism and boost the visual experience of the viewer.

You are asking about flare and ghost images: The camera lens consists of numerous polished glass lenses. Each can act like a mirror in that they reflect away some of the light that otherwise might pass though. Moreover, some of this light hits other surfaces within the lens array. The result is ghost images and flare. The lens maker does his best to mitigate these unwanted reflections. Each lens surface is coated with a a transparent mineral coat. The thickness of the coat is adjusted so that reflections from the underling polished glass are alleviated. This coating scheme is not perfect, some residual reflections occur. Ghost images such as the image of lamp and spiral bulb are likely when a bright light source is within the view of the lens. You can moderate ghost image and flare by trying not to aim the camera in the direction of bright lights. A lens shade can help. Bottom line is, flare and ghost images keep popping up in our pictures. Sometimes they contribute an a arty atmosphere, sometimes they impede what we wish to accomplish.