If you itch to start growing things weeks before it's time to start most of your seedlings, use the space under lights (or your sunniest south-facing window) to grow quick crops of lettuce.
There is a happy symmetry to the fact that translucent clamshell boxes used to package gourmet salad greens also make ideal containers for growing lettuce indoors. To get the boxes ready for duty, use the tip of a stout knife to make 8 or 9 gashes in the bottom of each one. Then add 2 inches of moist potting soil before planting a pinch (about 25) lettuce seeds, barely covering them with soil. After generously spritzing the surface with water from a pump-spray bottle, pop on the tops and slip the boxes under your grow light, or in any warm, bright spot.
Five days later, when the seeds are up and growing, remove the tops and place them under the boxes, so they become watering trays. The soil usually stays nicely moist if you fill the trays with water every day. By the way, don't try to remove the labels from the lids. Hot water will warp them, especially if they're made from cornstarch.
You can let your boxes of lettuce bask in the sun from a south-facing window on bright days, but they will be happy to spend most of their time under the light. Keep the lights on for about 12 hours a day, like from 7 in the morning until 7 at night.
The first cutting is ready in 3 to 4 weeks. By holding the boxes sideways, you can clip the leaves right into a colander while keeping the growing crowns intact. The plants will be ready to cut again in about 2 weeks.
If you want to use the clamshell boxes to start another crop, you can lift out the mat of seedlings and transplant it to a larger container. As days get warmer in the spring, you can start lettuce and other salad greens in clamshell boxes and transplant the mats into a cold frame or plastic-covered tunnel.