Well I can't decide between a single and double bright. It's for a 20gal tall so for 64$ I can get single bright that's 24-36inch or a 18-24inch double bright. Or I could save some money and get a 18-24inch single bright for 44$. What should I do? I want effective lighting.
If for freshwater, here is the rule of thumb: single bright for no plants, double bright for low to moderate plants and reef capable for other plants. I don't own one yet, but have been researching them. Read the customer reviews and you should get a feel for who is successful and happy with what.