Phoenix,
Unfortunately, light intensity comes in gradations from very low to direct with lots of stops along the way.
Low light usually refers to the minimal light that is enough to keep a few selected species alive. Indirect light usually refers to natural light that is bright enough to read fine print by throughout the day. Bright indirect light is what you get all day long on a north windowsill.
Your Fittonia needs the latter to do well. It is not really a low light
plant, although it cannot tolerate direct sun.
Caladiums and Coleus are also not low light
plants. In fact, both require at least a few hours of direct sun each day.
BTW, light coming through a window is much less intense than light outside. Thus,
plants that do well in light shade outside will need direct sun inside. That accounts for some of the confusion that experienced outdoor gardeners have with indoor
plants.