woooow. I hadn't thought about moving the light at all. That's a neat idea. ^_^
But... when I tried calculating it that way, I ended up with 6 and 2/3 feet. :/ I think it's because I used the 3 foot shadow as the base of the similar triangle. How do you know to add up the shadows? And if you add them, why don't you add up the post heights?
I came up with the light being about 5.7 feet above the floor. Though I may be wrong. I had to look up some Trig functions. ^_^" It's been too long since I had used them regularly.
...I like math puzzles.
But, I don't think I like them much in games.