I have a 50W LED driver and a programmable load. Please suggest a way to measure 120Hz ripple current! I have an oscilloscope and multi-meters.
"Ripple current <2% at 120Hz" means the power supply has decent regulation with input line induced load ripple from line bridge input to DC-DC converter that would not be visible. No need to measure it unless you need to verify the spec.
If you used any reverse biased photo diode (PD) the voltage into a load R will show 2% FS ripple on the current with all other light sources turned off driven by 60Hz or blocked radiance to PD.
If you don't have a PD, use any clear LED.