[LAU] OT: Guitar level- Mic or Line?

[Simon Williams]

Hello.

I often run the PA system for my CU at uni. So far we've been using 
jack-jack leads to connect guitars to the desk. However, my Dad has 
recently started using jack-XLR leads at my home church and says that 
it's much better.

After a very long conversation and lots of googling (which incidentally 
provides no info at all on the subject), I'm now completely confused.

Are guitars mic or line or what?

The rationale for using jack-XLR leads and connecting to the mic input 
on the desk is that guitars have mics in them so they are mic level. 
Apparently the battery unit in the guitar doesn't make it line level, 
but I'm not convinced.

The other thing I don't understand is that if that is the case, why do 
people use DI boxes? A DI box takes a high impedance (line level - I 
think) input and converts it to low impedance output (mic level). If the 
guitar is mic level already then what's the point?

Please, could someone shed some light on this because I'm now very confused.

Thanks in advance.
Simon