Hi Mike-- there’s not been much information on why some consumers respond to treatment better than others. Some of it may be practitioner skill and treatment parameters used.
A published study by Liew suggests that even in dark-haired consumers, there is a correlation between eumelanin levels in hair and effectiveness. Even in brown- and black-haired consumers, there is fluctuation in eumelanin levels (some have more pheomelanin, which appears to be less affected by laser). The more eumelanin the better. unfortunately, it’s not something you can tell by lloking-- you have to get a hair analysis done.
This is just one of many factors, however. It’s likely that many other things affect laser and electrolysis results, most notably heredity and hormone levels.
If you’re light-skinned and dark-haired and have responded well to electrolysis (especially thermolysis), it’s likely that laser will reduce the size of dark hairs and lighten their colors. Although it may not eliminate all hairs, this usually gives a satisfactory cosmetic effect. In some consumers, this reduction is permanent.
So no guarantees, but you’re more likely than most to have a good result if you find a good practitioner.