You could try the very basic of low light plants, but even then 20w on a 40g might not do much IMO
and 2800K is at the low end of the spectrum for plants.
I'd suggest looking at this light which would get you in a good low to med/low light plant selection IMO
. You could do a combo of 6700K, 10kK or a 10kK/Actinic combo which I just did on my 29g and it looks/works great. The blue bulb does little for plants, but it does look good
T5-ho 3ft / 2LAMP Aquarium lighting
PlantGeek.net - Your Aquatic Plant Resource
is a great site to find out about plants.