Light vs. Dark is a very polarizing binary in today's society. One can see it in everything from interior design to comic book characters. In society, black usually represents bad, dark, evil while white represents good, light, and purity.
This photo is representative of the stereotype that men are generally more aggressive and evil (hence being on the dark side of the photo) than women. You can see a woman on the light left side of the photo representing light, goodness and purity.
The above picture is an example of our cultures view of black and white cats. Black cats are seen to be bad luck and evil; they should be avoided. White cats however, don't have this ugly superstition to carry around with them.
Above is a yin-yang. This is a Chinese symbol created in the Confusion religion to represent how good (white) and evil (black) interact. It's symbolism represents how all evil has a little good in it and all good has a little evil in it.
This is another yin-yang from the same website. On the dark side of the yin-yang negative words are displayed while on the light side positivity can be seen. This is just another affirmation that light and dark really do represent good and evil in our culture.
On the left side of this photo one can see a dark demonic figure representing evil. On the right side, you one see a woman figure surrounded by light. They two don't intermingle reenforcing the binary of light and dark.
In this photo the Grim Reaper is wearing all black and holding a weapon. This is a negative figure in today's culture. The Grim Reaper represents death and darkness. The other figure looks to be an angel glowing with light. There's a much more tranquil look to it.
This image depicts two castles. One has a dark cryptic feel and of course is black to follow suit. The other is a beautiful white castle surrounded by white fluffy clouds instead if an overcast sky as seen behind the dark castle.
This last photo is almost the epitome of the light and dark binary. On the right is an angel cloaked in white trying to lead a demon covered with black and horns to the light side she is on. Almost as if to say that good always prevails over evil.
As one can see, In every one of the pictures light/white represents good, whereas dark/black represents evil. The culture we live in today has made this so because their ancestors where taught the same. This idea on a light and dark binary has been around nearly forever and I doubt it will fade out anytime soon/