In the original Terminator film, the eponymous villain procures a pair of dark glasses in order to hide his damaged eye socket and red eye.
In T2: Judgement Day, the T-800 makes a great show of stealing a pair of glasses from the biker bar owner, despite having no eye damage to cover.
So why did he take the guy's glasses?
The Terminator wears sunglasses to create a parallel when Sarah wears them later:
James Cameron (writer / director / producer): We wanted T-800 to change, and we wanted Sarah to change; she starts out one way, becomes fixated on that, ends up becoming more of a machine that he does. We wanted the two of them to change characters as the film went on: she becomes the Terminator while he becomes a human being. And it's partly through the Terminator's transformation that she understands what humanity really is.
Mali Finn (casting director): Jim Cameron's movie (T2 ) does have all of those special effects but still is a character driven piece and has wonderful characters. We've got to have good actors as they're playing against all the special effects. That’s what distinguishes his action movies from other people’s action movies.
Mario Kassar (executive producer): He's a great storyteller who can always take a plot to much higher levels. As the movie progresses, Sarah becomes the Terminator. The sunglasses and use of red dot for targeting accent the transition visually.
As Cameron himself explains, there are two transitions occurring: over the course of the film, Sarah becomes the Terminator and the T-800 becomes a human being — both of which are symbolized by the sunglasses (or lack thereof).
The sunglasses are an important story device in The Terminator and T2. In the first movie they meant to dehumanize T-800 more and more as the movie progresses and as he takes on more damage, becoming less and less human-like in appearance. In T2...the sunglasses have an even deeper meaning and message. The sunglasses symbolize his gradual transformation — he wears the sunglasses in the beginning when he is nothing more than a killer with a blank mind and loses them when he's starting his journey to become more human...
(Source: James Cameron Online, "T2 Complexity")
This is answered in the Randall Frakes novelisation for the third Terminator film; T3: Rise of the Machines. In short, the T-800 has been supplied with extensive information (and detailed imagery) by John in order to help him look as much like the original Terminator as possible so that his earlier self will recognise the Terminator from the description supplied to him by Sarah and his own recollections.
Since we know that John had access to this info in the future, there seems no good reason that he wouldn't have also given the same information and instructions to the T-800 seen in T2: Judgement Day.
He [Terminator] headed directly for it, but caught his reflection in the window of a car. He stopped and looked at his image, bringing up one of the memories that John Connor had supplied of what T-800 had looked like twelve years ago. He took off the stripper's star-shaped sunglasses and tossed them aside. He did the same with the cap and red bandanna. His current image now nearly matched the previous overlay.
In a quote on the JamesCameronOnline site, Jim Cameron confirms that the goal was to make the Terminator as recognisable as possible for his former self and in keeping with his own memories of the timeline. This obviously opens up a massive can of worms as far as causality is concerned.
Connor specifically looked for that model to send because he remembered him as such and wanted to make sure that he's doing what he was suppose to do - send the T-800 that he remembers back in time to 1995 so he can protect him from the T-1000. He knew that for things to go the way they are suppose to, he has to find the terminator that looks like the one that he remembers.
The quotes are pretty impressive. However, when watching the film, the scene made total sense to me without those theories.
The T800 arrived naked and unclothed and then went to equip himself with a ride, outfit and weapon in proximity. The sunglasses were a perfect complement to the outfit.
The Terminator's "preference for a particular style of sunglasses." ...It is not about his choice. Like in the biker bar, he scans a woman and her clothes matched him in size, but his programming listed it as "inappropriate". Walking around dressed as a woman would not help him blend in. Therefore, the style of sunglasses he constantly chooses are deemed "appropriate" or acceptable for his appearance as a human male to human society.
It is beacuse the Terminators have infrared vision, so any kind of light (natural or artificial) would interfere with the quality of the images their perceive. That's why they need to darken ther field of view as much as possible to basically see in better quality (without being blurred with lights).
My thought when watching it was that it was an initial sign of the Terminator's incipient humanity — he's vain and thinks it looks cool. By the end of the film, it is strongly implied that his personality has developed more positive emotions too.
my thoughts are that due to the future being much darker because the sun was blocked out by ash and soot in the atmosphere so skynet created the terminators with that in mind, letting as much light as posable so when in the brighter past he uses sunglasses to let in less light so he can see better.
Because he's a Terminator. Terminators are machines and machines don't have the need to blink their eyes.
And Schwarzenegger is a human and as a human has the need now and them to blink his eyes. Which he obviously can't control. So they give him sun glasses so we don't get to see him blink his eyes.
