Most LED strips are either 12v or 24v. This means that when using them on a mains supply you will need a convertor to step the voltage down from 230v to 12v or 24v. The reason you would use 24v rather than 12 is because you can run a longer continuous length of strip due to a low current usual. In 12v format you should never run more than 5m in any on length. In 24v you can run up to 10m before needing a new power source.