Introduce them slowly to natural sun. 3 week old plants under Florescent Light may be a little weak. You may want to put them out for awhile and see if the leaves go limp or curl up.
After a couple of days they should be strong enough to go out alone.
You can add a more gradual incline to the introduction to sunlight by having them in a sunny window for a day or two, and then moving them into full sinlight.
This might take away a small element of shock to the plant.