“In close-up photography, any out-of-focus spots of light appearing inside the viewfinder will record on digital media or film in the shape of the aperture in use. Additionally, the distance between the main subject and the background lights determines just how large and diffused the out-of-focus spots will be. The spots are called specular highlights.” — Bryan Peterson, from Understanding Exposure.
Aperture priority, 50mm at ISO 100. Exposed for 1/350 sec at f2.8.