Should I be worried with yellow and brown tipped l...

Once burnt, they will not recover and become un-burnt. It was not caused by the lights. It was caused by over feeding with nitrogen (usually), but it will not affect yield or potency. Watering to run off is vital, it helps to prevent nutrient salts from building up to toxic levels in the substrate and burning your plants. If growing in soil, you should aim for a schedule of plain water/plain water/feed/plain water/plain water/feed so that your plants are getting nutrients every 7-10 days. This is ample feed and will ensure what is added is used up by the plant before the next lot of fertilizer is given and will stop any burning, as long as a sensible feeding program is used. Hope this helps, Organoman.