DC Wire Gauge (size) requirements?

I'm an electrician, but I deal with mostly AC circuits from 120v-480v... I do some lower voltage stuff like Fire Alarm (24v). It's my understanding that DC systems need larger wire, is there a conversion chart or Allowable Ampacities of Conductors chart for DC systems?
If I have 4 100 Watt lights on 12 volts DC it comes to 33.4 Amps, 12 and maybe 14 gauge wire would be okay if it was an AC circuit, but what about for DC?
I pretty much want to find out if I can replace 2 of my 55w lamps with 100 watt lamps without running new wire

 

It depends on the length of the wire, but 14 should be ok.

Look at this.

 

Thanks! Exactly what I needed

 

I use 12-14 for all my lightsz on my truck