I would genuinely like to know how VW etc get approval for their oem units?
VWs LED headlights are designed as sealed units (non-replaceable LEDs) with lenses/reflectors that work solely with LEDs. LEDs emit light in a different way to incandescent bulbs - far more linear with bright light projecting forward rather than 360 degrees like incandescent bulbs.
VW OE LED units aren’t open units that they simply ram an LED ‘bulb’ into.
This means VW can design the unit (reflector and lens) especially for LED light emission patterns and ensure they meet the legal requirements in terms of light spill, beam pattern, beam length, perceived brightness and ensure the units self-level (and have the ability to wash?) in order to prevent dazzling.
As I understand it THQ V3 units - which take replaceable bulbs, are designed around that (replaceable bulb) standard - in this case H7.
Aftermarket LEDs fitted into units designed for replaceable incandescent bulbs can dazzle (due to the aforementioned light emission/levelling issues) and, therefore, are not legal.
Designing a light unit that can take either light source and remain bright enough to allow the driver to see but not so bright as to dazzle other road users is not easy although projector style light units, rather that reflector, do allow you to get close. Having said that the vehicle would generally still need some self levelling and potentially headlight washing capabilities to prevent dazzle due to light scatter.
I believe THQ do manufacture a sealed LED unit - their ‘Audi style’ light, that comes with built in LEDs (that cannot be replaced like bulbs). These would be (I assume) road legal as they were designed and manufactured solely with LEDs in mind. They’d be a great option if you can afford them.
As Sasquatch points out lights must fit certain criteria determined by the relevant local authorities. The UK is dropping a bit behind it seems as in a few European countries you can now fit certain aftermarket LED bulbs (Philips Ultinon 6200 are approved I believe). This is possible because Philips have spent a lot of time and money on design, testing and manufacturing to ensure a very precise/controlled light output (and a lot of money lobbying relevant bodies for approval). So it is possible in theory with the right circumstances.