When most people think of the word gothic, they imagine people dressed in solid black with black lipstick, and figernail polish. Therefore, naturally whenever a lot of people that have not studied it might think of "Gothic" architecture to be a dark style of architecture with very little lighting. I would have to say that many of the Gothic era arhcitects would strongly disagree if one asked them. In the Gothic era, many of the cathedrals were very vertical in their design.
Since they had an extreme disadvantage in technology when compared to today, they had to use the best of their resources. This involved using larger windows to let more light into the cathedrals. The tall structures, meant that to illumiate the interior they had to use very large windows. Some people might have suggested the use of fire or candles. There were a little being used, this, however, also posed a threat for obvious reasons. Also, since these building were so tall, the architects needed more than one row of windows. These multiple windows, would also amplify the viewers attention to the height of the structure. It also to some had a symbolic means as the light God. Nevertheless, the cathedrals were not ever intended to be a "Dark" style like the word "Gothic" means in todays society when talking about an American style. It just simply was a era of art and architecture, and in my opinion the best era of art and architecture.