Depends on the site
Lhr is most effective on dark, thick, actively growing hair-rarely more than 20% in any area.
Most hairs are in "rest" phase -- fairly immune to all wavelengths and energies. You have to superheat the stem cells in the bulb and bulge of the growing hair follicle
in order to kill it - not just make it a smaller, lighter (poorer) target. It takes 5 to 8 sessions over 2 years to get 70+% kill rate.