Glowing Mechanical Eyes

Robotic or Cyborg characters will frequently have obviously artificial eyes. Presumably these are some sort of video camera, which makes sense for an artifical creation. Unlike normal cameras, however, these will usually glow with an inner light. While this makes very little sense from a mechanical design perspective, it makes excellent sense from a character design perspective. Eyes convey a lot of information about a person; light-up eyes help make up for a robot face's lack of expressiveness.

By varying the intensity, shape, and color of the light, a robotic character can convey much of the emotion that would otherwise be lost. A brief flash of intense light can indicate surprise or anger. The light going out can show that the character is unconscious, blind, or dead; conversely, the light coming back on is a form of Eye Awaken. If the light is red, you might want to watch out (especially if its usually a different color, but suddenly turns red). If the eye glow can change shape, then it becomes nearly as expressive as normal eyes; the glow widen or narrow, the expressiveness of eyebrows can be simulated by eliminating strategic parts of the glow (a >:| face is popular with this technique), etc.

Glowing robotic eyes can also be used to indicate anything that glowing eyes can mean on organic characters as well, from impending doom to inner power. Glowing Mechanical Eyes are a prerequisite for Eye Lights Out. A Cyber Cyclops is a specific variant. If things that are supposed to glow are also able to see it's a case of Screens Are Cameras.

Film

 * Red glowing eyes are one of the most distinctive features of Terminators. In the original, after his bio eye was damaged, the Terminator was forced to wear sunglasses to hide his glowing robot eye.
 * The eyes of the characters in Robots glow, even forming torch-like beams in the dust in the air in pitch-black locations.
 * The Iron Giant has glowing irises and glowing pupils.
 * Star Wars gives almost all of its droids glowing eyes.
 * A notable scene in The Empire Strikes Back has Chewie trying to repair C-3PO; his eyes go out when Chewie fiddles with something, suggesting that C-3PO has been deactivated—but in a Subversion, he continues speaking, only complaining about how now he can't see.
 * In the Godzilla films, Kiryu's eyes glow red whenever he reverts back to his old instincts as the original Godzilla and goes on a rampage.
 * In Treasure Planet, Ben has LED eyes that illuminate in the dark in one scene.
 * The Autobots and Decepticons in Transformers.
 * That one car seen in Paris in Cars 2, unlike everyone else whose eyes are located on their windshields.
 * The Leviathan from Atlantis the Lost Empire has large mechanical optics, revealing the fact that it is actually a machine.
 * Most cartoon cars are often depicted this way, although Disney's Cars averts this (see above).

Live Action TV

 * In Battlestar Galactica, the Cylon's eye glows.
 * Animal Zords in Power Rangers have glowing eyes, as do the Megazords.

Toys

 * Most characters in Bionicle. On the toys, this is usually represented by transparent pieces, but in the animated media the eyes are given a definite glow.

Video Games

 * In Portal, the machine gun turrets, the personality cores, and GLaDOS all have glowing eyes.
 * Mass Effect uses glowing eyes for both the geth and generic security robots. Useful for lighting up when the unit activates. More subtly, the Illusive Man has glowing, blue cybernetic eyes. Also, as a result of his/her rebirth, Shepard can get glowing red eyes, but only with a high Renegade score.
 * In Kingdom of Loathing, a MagiTechMechaMech's eye will even continue to glow when severed.
 * Robots in Stealth Bastard have these.