Between the two of these I had more than enough ppfd. I mounted them so the spacing was even splitting the tent into thirds. Towards the end of the grow I noticed the outside edges didn't have as high of a ppfd reading. I changed them to about 22 inches apart now and its much more even of a rating. At 24" I get a reading above 900 ppfd at 100% power. I love these lights. I moved the drivers outside the tent and was able to keep the temperatures controlled with the exhaust fan.