I would go with the last guy, you probably have too much stuff on the circuit. I'm not an electrician but learning the amps-watts-voltage conversion is pretty important. The fuse blows because you have too much stuff drawing power on that fuse. My system is on a circuit breaker and I had misjudged a circuit and overloaded it, but like a dummy kept resetting the breaker and actually probably could have started a fire. I didn't realize a certain high amp item was sharing a breaker and I actually had some wire melt through a plastic junction box. Luckily all of this wiring was in exposed studs so I didn't burn the place down and I could see where the damage was to replace the wire.
The fuse blows because more juice than is supposed to be loaded on the wires is being put through to prevent fires. To try and keep from over complicating, say for example 14 gauge wire would melt at like 200 degrees, the fuse on that run should blow at like 150 degrees, to make sure the line doesn't overheat and cause a fire.
Most electrical items have a wattage or amperage or should anyway if you look at the labeling. Grow bulbs are usually easy because you buy them in specific wattage.
A standard house circuit is 15 amps and 110 volts in the USA and uses 14 gauge wire. You may have to do a little algebra, but the key is to not put more than like 70% load on any circle. The 30% is to account for any kind of surges. I think there is probably some exact proportion reccomended by electrical code you can follow, but I approximate around there keeping in mind higher amp items like HIDs and A/Cs fluctuate more than things like a small fan.
watts/volts = amps
or
amps x volts = watts
in any case, a standard 15 amp watt circuit should blow at about 1650 watts on a 110 circuit. So you only want to run up to 1200 watts or so of lighting on a 15 amp circuit. When a device like a fan or dehum provides an exact amperage pull, its much easier to know what you can have on a circuit. For example I have a fan that pulls like 2 amps, and an AC that pulls like 10 amps. If I put those 2 on the same circuit I have to make sure not to plug anything else on there. Most higher amp items like that will even have a warning in the manual to put them on their own circuit.
But learn from my mistake, make sure you don't over load the circuit and keep blowing it. Just because the breaker or fuse blows as a safety precaution, the line still overheats to cause this to happen and could still irreparably damage the wiring if done over and over. The electrical aspect is what burns people's homes down, so make sure you get it right. I got lucky with my stupid mistake, and now I am super paranoid every time before I plug anything substantial into an outlet.