I've done exactly what you're attempting before, controlling a COB LED (Bridgelux Vero series), with an Arduino.
The easiest way to do simple on/off switching with these lights is to use a driver than can dim to 0, Meanwell LDH series for example. All MW drivers with the 3-in-1 dimming function interface easily to Arduino and using the TimerOne library to generate a 10KHz PWM means you get smooth, efficient dimming functionality if you require it. Using a 10k pulldown on the dimming line ensures the COB gets turned off if anything goes wrong on the control-side.
I've run sets of lights controlled this way with timing provided by a DS3231 safely for ~14 months.