I think Anthony is the one who is best suited to give you the best advise on how to handle this scenario, considering your seasonal weather averages and all. Given your moderate climate, I'm sort of puzzeled why you you would need to go through the extra work of adding lights; but it it certainly won't hurt and of course, it will help produce bigger baby bulbs. The question will become, how long are you going to extend the growing? I'd say if you have two true leaves you would be ok just letting them go dormant as they are.
I had a late group here last Fall. I brought them inside and grew them out an additional 3 months before I began to force dormancy. Refer to my posts in the 'Starting Lilies From Seed' thread: Nov 4th, Nov 29th, Jan 1st, Jan 27th, for a little background on what I did. I used the same light setup that I use for starting my seedlings: a Hydrofarm 'Jumpstart' unit that has a single T5 type 48' AgriGro 6500k, 5000 lumin, 54 watt bulb. The bulb height was adjust to about 12 to 15 inches above the plants and run for 16 hours on, 8 hours off. This single bulb setup will accomodate 12 six inch 1 gallon pots when they are in 2 rows of six and probably is all you would need. But since I had extra setup (units) from seeding, I eventually added two more in my theory of packing in as much growth as I could in the shortest possible time frame. It worked great. Although--I do think I was providing way more light than necessary with the extra units-?- For smaller applications, there is a 24 inch type T5, 26 watt model available which gives off the same light wavelengths as the larger one. I prefer the AgriGro T5 lights because they are cool and seem to give off the right spectrum of light that lilies like. There are other bulb types out there too, like T8 setups one can do, with a variety of k and lumin values and with a variety of wavelenght/spectrum profiles but this is the one I settled down with for lilies I'll edit in some photos when I pull out a box.
Edit in Photos added:
In the last photo, those are 1 gallon, 6 and 1/2 inch diameter pots of clones that I just pulled from the the cold room (rooting), but it illustrates how many pots will fit with a 48' setup. The light itself is easily adjusted up or down for height.
