That 6V wire can't provide the necessary amperage for these bigger lights, which is why Biktrix developed this lighting assembly...
By taking typical 6V headlight outputs from various Bafang/etc head units, and using it to switch higher (main) voltage to operate the more powerful headlight, you end up with a lighting assembly which can be installed to many different ebikes, which is awesome, because it means you can switch the headlight from the main button pad, or even trigger it by photo-sensor (on display models like Bafang DPC-18, on the Ultra bikes). That photo-sensor is also adjustable in settings for trigger sensitivity...
Additionally, there's always the option of adding integrated running lights/tail light into this config, all on the same lighting circuit, taking care to use lights which can run at the higher voltage (higher voltage lights are ideal, since they don't need thick wires to deliver power). That would be DIY custom job, but perhaps (I'd figure, pretty likely), future bikes might come with complete lighting solution all pre-integrated.
I know a few people have cooked up this sort of solution before, I was going to myself actually and still plan to this spring, I'm really glad Biktrix developed and tested a solid and cost-effective solution I can build from. The light itself is well suited to the task, I took it for some testing! Compares well against higher end lighting, I run an Outbound light on my daily ($200 USD and lacks battery/bike integration, unfortunately). Good lighting quality is a fine feature, but in my opinion, integration and running off the main battery are more valuable for the cyclists experience.
