I have all my plants under one light fixture. I started all of them form seeds no earlier than 6 weeks ago. The fixture is a 5 lamp T5 light. The lamp is about 2' above the table on which it sits.
Some plants I started only 3 - 4 weeks ago. And some others I just started about 12 days ago, and a couple are already 10" tall.
My tomatoes and pepper plants are GIGANTIC for being about 6 weeks old. Meanwhile, I have lots of other plants that can still use being under the lamp for 2 more weeks - which is when I generally plant everything, about May 15th.
I can't raise the fixture because it would be too high for the shorter plants. Some of these tomato plants are getting close to 2' tall, while some plants are only a few inches tall. I have been putting the bigger plants outside for several hours a day when the weather is nice. I plan to start hardening off the rest of the plants this weekend.
The tomato plants seem to be wanting even more light, as do some of my peppers.
I am contemplating planting them, covering them in almost a mini greenhouse - home made PVC boxes with the UV film. Sound like a good idea? Heck I just looked and 2 of the pepper plants are already flowering, and I think I see the beginnings of flowers on some of the tomato plants.