To produce the illusion that the vampire's eyes were glowing, a flashlight was shone onto the actor's eyes through a narrow rectangle cut into a piece of cardboard. If the actor's face were well lit, the additional brightness to the eyes could be quite effective. However, scenes with vampires tended to be set at night, and the actor's face was often in relative darkness. As a result, the artifice generally failed to produce a successful illusion of glowing eyes. It simply looked like a bar of light across the top of the face.