Credit: Brand X Pictures/Gardening/Sandra Ivany
There may be several reasons for leggy seedlings.
1. Air temperature is too high. Warm temperatures are ideal for germination, but to sustain top growth, 68 F (20°C) or so would be excessive. Trying dropping the room temperature a few degrees after the seeds sprout.
2. Poor light quality. On dull days or when the only light source is a window, consider supplemental light, but make sure the bulbs are suitable for plant use. Grow lights offer a broader light spectrum and less heat than traditional light bulbs.
3. Improper watering and feeding. Water and fertilize seedlings according to their particular needs. Avoid extreme conditions, such as excessive feeding under poor light.