Front light that "pulses"
Pretty much all front and rear lights, except very cheap and simple ones, have a flashing or pulsing mode. Some have a harsh, strobe-like flashing, some have a softer pulsing effect. 

Running a front light in flashing mode is good for daytime use where you need to be visible.

Flashing mode is horrible if you need to see where you are going at night. If you want to run a flasher at night, get a small additional light in addition to a main light that has a decent main beam.