you can grow mushrooms in the dark, you can grow lettuce with a florescent light. here are some of my lettuce grown with no sum and a florescent shop light with plant bulbs. these use very little power. you can only light low plants with them because you need to keep the bulb very close to the leaves.

Here is a link that might be useful: pics of my lettuce

Hi, is your low light caused by overhead trees? Or, are you trying to grow near a window? I had good luck growing several types of hot peppers and also lettuce in the shade of a large oak tree. The plants got direct sunlight only about 1 hour a day. If you are growing outside, you might be surprised at how well your plants might grow. You might be able to do a test by purchasing a few plants and placeing them in the area you are planning to set up your system. It might be the only way to really answer your question. You can use the link below to see the lettuce that is ready for harvest. chuck

Here is a link that might be useful: lettuce in the shade (most of the time)