Just checked my seedlings and am really happy with the germination so far. There is definitely a difference between older and newer seeds - the former having a lower germination rate. However I am hoping I will get at least one from each variety, as I can save my own seed at the end of the season.
My setup has been a little experimentation and I am quite happy with the result. My setup is done on a budget. Essentially I made a box out of scrap plasterboard to contain things.
At the bottom is an incandescent light bulb. It came from a homemade incubator and is set up to keep the contains at 21°C, the ideal temperature for hatching chicken eggs. It also happens to be a great temperature for tomatoes. I placed a support around this to hold the tray above the light safely.
On top of the tray, I have my seed trays. They were soaked from the bottom to wet the seed mix, and I spray the tops with a misting spray to keep it moist.
On top I place my light. They are multicoloured waterproof led lights. They have a stick on backing and are USB powered. I stuck them on a plastic board and aimed them at the centre of each small tray to make sure the light was spread evenly. I used a 2 metre length. I put another plasterboard piece on top to keep the heat in.
I plugged everything into a timer that turns on at 7am and off at 7pm to imitate a natural cycle.
If I was doing this again I would use more light. I will be doing another set up without the heat for plants that are able to germinate at lower temperatures.