This article explains why the the 1002l / 1502L are not as bright when powered USB-C 5v

Both the 1002L and the 1502L offer the ability to power the device using the USB Type-C 5v input option. Using this method reduces the brightness to 60%, disables the internal speaker and will only support the right peripheral port (default). 

The user can change the active peripheral port to top or left via the On-Screen Display (OSD).