I'm not sure if yours is the upgraded version. But they told me the u2 is brighter
difference brightness seem to be around 7% between the two emitters, which has been discussed on another forum. It also depends on the comparison is made between high, mid or low end of each emitter.
if its a low end U2 compared with a high end t6, the output would be closer.
and I believe the tint of the light also make a difference.