>>1928767My phone mount, which allows me to use it as a cycling computer/gps hooks to the left. So it mounts on the right to be centered. I typically mount my light underneath on the 3 prong GoPro fingers, but if that's being occupied by an actual GoPro or I just want an additional light I mount it on the left then. I tend to follow this convention of "light on left" even on my around town bike which doesn't the carry my phone on its bars.
Left hand is front brakes - there's a reason it controls front shifting, you want it on available on standby more than right which is occupied with more frequent rear shifting. Lights require no interaction once activated - in contrast your right hand can multi-task a bit and use bells/horns or some other more interaction dependent handlebar device.
