How would you consider connecting two different types of LEDs, a white (6 V @ 150mA) and red (2 V @ 350mA) in a series-parallel combination? (W W R W W R W W) << parallel multiple strings of 8 series connected LEDs.
Similar LEDs will share more or less the same characteristics within a series / parallel circuit using a constant current and a small current balancing circuit (mirror or similar).
If I use a CC driver for the LEDs, it will divide the current to each parral string for instance 150mA per string. But now I have a couple of 350mA LEDs within each series string. This will either cause the efficacy to be next to zero or they will not even light up. Driving all the strings at 350mA will probably create a small electrical fire.