One of the distinctive characteristics of the vampires in Forever Knight is their ability to see in the dark. No episode clarified the mechanism by which this happens—whether their retinas are able to detect body heat using infra-red light; or whether, like many nocturnal animals, their eyes are modified to trap light to increase sensitivity. The special effects used to demonstrate to viewers that Nick Knight is employing night vision suggest the former; but the glowing contact lenses used in the second and third seasons suggest the latter.
Creating the "night vision" effectEdit
The ability of vampires to see in the dark was introduced in the series premiere, Dark Knight. However, the producers went further than merely demonstrating the consequences of this visual sensitivity. Special effects allowed viewers to see the world from Nick's perspective when he was using night vision.In Season One, when Nick was using his night vision, the scene was not only filmed from a camera angle that would show his point of view. An oval in the center of the screen was filmed in such a way as to turn all dark areas red. Outside this oval, the picture was out of focus. The in-focus oval implies that, as a predator, Nick's focus while hunting is limited to the central visual field.
In Season Two, the night vision effect was altered; and thereafter the red portion of Nick's vision occupied only the outer areas of the screen. An irregular band across the centre retained normal coloration. The advantage of the new effect was the relative lack of visual distortion in the central area of the screen—meaning that, when Nick spotted something, the viewer would be able to see it clearly.
Interpreting the "night vision" effectEdit
From the red colouring in both versions of the night vision effect, it has been inferred that vampires employ infra-red vision, or something similar, that allows them to perceive people by a heat signature. A close examination of the way the effect is produced indicates that, though this inference may well have been intended, in fact the effect does not support it.
In the first season, the red coloration affected all dark areas inside the central oval, whether part of a living being (or other heat source) or not. In subsequent seasons, the red coloration affected the peripheral areas of the visual field, with normal coloration in the areas where Nick focused his eyes—meaning that the people he was looking at were not turned red, and hence not affected by the night vision effect at all.
If viewers were actually seeing infra-red vision, then living bodies and other heat sources would be noticeably brighter (or "infra-redder") than their surroundings.
Having said this, the use of red in both versions of the night vision effect almost certainly was intended to suggest to viewers that Nick was indeed seeing in infra-red—though the association of "red" and "infra-red" is more linguistics than physics. If Nick were really seeing into the infra-red portion of the electro-magnetic spectrum, it would probably be interpreted by the visual centres of his brain as a colour completely different from anything on the spectrum visible to human beings.
Glowing eyes in the darkEdit
In the second and third seasons of the show, contact lenses which reflected light shone on them were used to provide the vampires with glowing eyes. Although most commonly employed to give orange eyes to vampires who were angry or lustful, they were also used to give the vampires glow-in-the-dark eyes. A red light mounted on the camera was shone into the actors' eyes, and the contact lenses reflected it back. Careful positioning made it possible for the eyes to glow even when the actor's face and figure remained dark.
Vampires' eyes are probably intended to glow in the same manner as the eyes of many other animals with excellent night vision. This is caused by a mirror-like layer of cells called the tapetum lucidum (which means "bright carpet" in Latin) which lies behind the retina. These cells reflect light back through the retina, so providing the photosensitive receptor cells with more stimulation. The brain therefore receives more information from the eyes which it can translate into images with more detail.
The reflected light, having passed through the retina, continues out of the eye through the pupil. Although the strength of this "eyeshine" is weak, it is sufficient to be seen by someone looking at the animal in the dark. The colour of eyeshine varies from species to species. While yellow eyeshine is probably more familiar (being seen in cats and dogs), red eyeshine occurs in rodents and birds. Human beings do not have a tapetum lucidum layer of cells in their eyes. Their night vision is poor; and their eyes do not glow in the dark.
When a flash photograph is taken of a human being (or any other animal that lacks a tapetum lucidum), light reflects off the interior surface of the back of the eye. The reddish pigmentation of this surface means that the reflected light is also red—with the result that human eyes appear to have red pupils in close-up photographs. However, although the "red eye effect" may be the same colour as glowing vampire eyes, the cause is quite different.