A light bulb is actually a lot better than a fuse as it will start to take the excessive power, using it to light the bulb and creating more resistance in the circuit. I think there are two advantages over a fuse. One, a fuse will just pass all the power until it's rating has been somewhat exceeded and it finally blows, sending all that power to the tweeter before hand, where as a light bulb takes most of the excess power and then uses it to light the bulb and creat more resistance which than lowers the power going to the tweeter. Number two, the light bulb can be used over and over again since it doesn't blow and leave you tweeter-less until it's replaced like a fuse does.I have a set of ARC Audio ACS-265 (Rainbow) crossovers and
they use a 12v 20w light bulb to fuse the tweeter rather than a fuse.
Why do they do this?
The previous owner blew one of them. They must have been running
a lot of wattage because the cases are slightly melted near the bulbs
If someone burnt out the light bulb and burned the crossover case, they were getting real stupid with that set of speakers.