It doesn't need to be directly under the lights. I have it in multiple tanks using the legs for Coralife and Satellite CF fixtures so the light is about 3-4 inches above the water and it does fine anywhere from directly under 2 x 65w bulbs to the edge of a 44 gallon pentagon with 1 65w bulb (meaning VERY indirect light). Sometimes it drifts around the tank so it gets variable light, other times it will get stuck near an edge long term and get indirect light, or the roots will get tangled in a plant and it ends up directly under a light. It tends to grow faster with more light, but it's fast growing anyway so that's not really a bonus. 
Is your tank open top or do you have a glass cover? The only time I've really had a problem with it is when I have a cover on the tank and insufficient air space between the water surface and glass. In those conditions it starts degrading and may die off if I don't lower the water or provide more air flow by cracking open the cover an inch or so. The leaves will get yellowish and may get a bit soft or slimy if it's not getting enough air circulation.
I've accidentally burnt a couple leaves when dosing with excel and they develop brown dry spots where they've been burnt. I'd expect something similar if it was getting burnt by lights but I'm not sure if that's the case.
Is your tank open top or do you have a glass cover? The only time I've really had a problem with it is when I have a cover on the tank and insufficient air space between the water surface and glass. In those conditions it starts degrading and may die off if I don't lower the water or provide more air flow by cracking open the cover an inch or so. The leaves will get yellowish and may get a bit soft or slimy if it's not getting enough air circulation.
I've accidentally burnt a couple leaves when dosing with excel and they develop brown dry spots where they've been burnt. I'd expect something similar if it was getting burnt by lights but I'm not sure if that's the case.
