When I got mine I tested to see how far I could push them before needing to power inject, hooked them up at 100% intensity and powered up 1 string. It was nice and bright all the way along the string. Next I added another string of 50, these were ever so slightly duller than the first string. Then I added a 3rd sting and these were substantially duller. So if you were only injecting at one end then you would have to inject every 50, if you are injecting between strings then you could inject every 100 because the voltage travels both ways. Ie, it will power the 50 before and 50 after the injection point.