Taken straight from the led gardener. The guy knows his shit
Wiring LEDs in Parallel Parallel wiring is most often used when working with constant voltage drivers. A lot of people are now using constant voltage drivers and wiring up their COBs in parallel, since the drivers are usually cheaper and people are more comfortable working with low voltages like 36V, as opposed to high-voltage series circuits that can be 200V+. One drawback is the fact that wiring COBs in parallel does make them vulnerable to thermal runaway. Thermal runaway refers to the process that occurs when a COB heats up, causing it to draw more current, which heats it up further, drawing even more current, and this loop continues until it destroys itself. Unless you implement something like a resistor to limit the maximum current, there’s nothing stopping the COBs from pulling as much current as the driver will provide if the COBs go into thermal runaway, or the voltage output of the driver rises. That being said, in my own testing, current levels have always stabilized at reasonable drive currents and I have only seen thermal runaway occur at very high currents that nobody is going to run at (3+ amps per COB!).