if its on your 20 h 2 wpg would be considered low-medium depending on what kind of lighting you have if you had 2 regular flouresent lighting it would be low, but if you had 2 wpg with power compacts i would consider that medium.
Normal Output Flourescent. This is the standard florescent tube. Tubes also come in Ho (high output) and VHO , very high output. Each requires their own ballast, based on their wattage, not tube length. ALso you might here about ODNO, over driven normal output. This is done by using a ballast to run 2,3 or 4 tubes of a specific wattage and wiring it in such a way as to powewr 1 tube, of hte same wattage, multipal times. This does not double the light output each time. Generally you can assume maybe a 30-40% increase in light output. This, ofcourse, makes the bulbs life shorter. Hope that helped
wow.. thanxs for the info. And also: would 65watts, 36 watts, or 28 watts over a 20 gallon be the most reasonable and let me use the broadest spectrum of plants? Becasue Im planning on getting a new fixture as my current one i found out is kinda meesed up (it doesnt turn on sometimes) and I want to know which i should get
Well, since it is PC lighting, 36 watts would grow all the maderate to moderate high platns. I would only go for 36watts if youare not going to use CO2. Since you want to grow lots of differnet species of plant, go for the 65watts and use CO2 injection. Make sure youresearch it though a bit first. I don't know your green thumb level so please don't take offense to that The best thing you can do to learn this stuff is to read read read the posts, then ask questions, adns tart setting it up. The biggest thing to learn is fertalization basics and what equipment, test kits, etc you will need. If you go with the 65watts then llok and see if 1x65 bulb or 2x36 watt bulbs would be better for you. Even ligh coverave is important, especialy if you want forground plants like glosso.. 2x36 might be a better way to go although that is even more light. Actually, you should considera 55watts PC light. Good wattage and a wide range of bulb K rating to choose from.
Sorry to ramble but hope that helps. Check out a very old post by tsunami. He had 55watts over a 20 long. It will help give yousome starting ideas atleast. Just do a search for his name. Must be around christmas time for a reference