Unlike CFL's and florescent lighting, LED's don't have mercury. So this would apply to the Finnex Fugeray and Ecoxotic. The Fugeray has a splash guard to protect the LED's from water too. IMO, with the criteria you mentioned (eg. Low light, low maintenance, etc.) the 30" FugeRay would fit your 20g-L perfectly without having to suspend the light or bother with co2. Just keep low to moderate light tolerant plants and you'll be good. Dose with Flourish Comprehensive and Excel as directed and you'll have a nice low tech planted tank.
Oh my, I just realized in that post I said I liked the Ecoxotic because it has mercury. LOL. I meant to say, because I don't
think it has mercury.