Wattage... err.. "Watts" is a measurement of Power aka Energy which is produced.
It is not a 'rating' or 'capacity'... it means, when your headlight bulb is powered by 12V it will produce 55 Watts of Power. (or whatever the Wattage rating is)
Now, the more 'Energy/Power' the bulb is producing, the hotter it will be and then... run into the melting issues.
Did I mention I have a degree in EE?
...that is doing me no good in my current career I might add. So much for a investing in a college degree, I'm now a web administrator
