It's fine for the way your phrased your question. If a 55g is 21" tall, minus substrate of 2 to 3", you're at about 18" from light to substrate... you'll get about 25 to 28 PAR. This puts you in the upper part of low light. Perfect for low tech and no co2. If you want to get to medium light and above, you can go with a finnex but you should dose a lot of liquid carbon or inject co2. I like the Sat+ because I can run dim settings all day in my "non-photoperiod" times without the risk of getting algae. Finnex is great too, I have owned 4 finnex fixtures at one point. IMO, I like the "full spectrum" output of the Sat+. Colors just pop more in my fish and having the ability to change the color and intensity is great. But if you want to hit medium light and grow more plants, then I'd get the Planted+ but be prepared to dose a good amount of Excel or get co2.