In LCD/LED displays, does the back light strobe or remain on?
Generally the backlight will remain steady all the time. 

There is such a thing as color sequential LCDs that strobe backlight, but they are not common. 

Here is a modern LCD backlight driver chip. The ripple voltage at the output is only a few tens of mV which will result in very little ripple current. 

Don't be confused by the PWM mentions in that datasheet, that refers to an input into the driver chip that is used to program the output current as an alternative to I2C.