You are blocking the light. What should I do? (longish)

I just moved to an office next to the window, with a door and venetian blinds on both sides. I like to keep the blinds on the aisle side, where the cubicles are, shut all the time because a lot of people walk around and distract me and I do enjoy privacy, since it means I can check out the boards without someone looking at me surfing the internet and such. Anyway, I moved on friday and shut the blinds, with the firm intention of keeping it that way permanently. Then co-worker from the cubicle comes in and starts complaining that the blinds being closed block the light and that I am a horrible person for not considering the people outside, and that the fact that I have an office doesn’t mean I can disregard them, etc. He was really upset by the whole thing, and apparently took an assertiveness training class or something, because I could see it was uncofortable for him to confront me with this, so I felt sorry for him. Although I was a little pissed at first, since the whole point of having an office is to be able to have privacy, else there wouldn’t be any point to it, the blinds and the window are inside my office and the amount of light that seeps through from the window is negligible compared the electrical lighting, but, being the extremely nice person that I am, I conceded and opened two of the blinds. The point is Who is right here? Who has a right to choose? Does he have a right to light, however small an amount that might be?

I am not the best liked person on my floor anyway, because of the promotion and my age in comparison to co-workers, but I do like my privacy. What should I do?