The symptoms: A frankly disturbing yellowish hazy appearance. Progressively dimming headlight output no matter how new the actual light bulb is. Complete loss of hope and total emotional breakdown. Okay probably not that last one, but your headlights are still dim.
The causes of this condition are simple. Take a little UV exposure. Mix in a couple hundred thousand miles of highway and off-road driving. And top it off with a lifetime of simple neglect.
The solution is equally easy. Spend $100-$300 on replacement housings and bulbs. While this is obviously the best way to go for ideal light output, it's not in everyone's budget (including my own). For the rest of us looking for an improvement that won't break the bank, I found the solution in a $2.00 bottle of polish at the local Wal-Mart.