How cool? If you are on a self-build then you can enclose the trays and lights sufficiently to keep them warm. A 2x40W shoplight produces quite a bit of heat. I start cactus and succulent seedlings in a propagator heating solely by the lights inside it. If its really cold, get some polystyrene sheets for insulation. One tip: run the lights at night for warmth and off when the basement is warmest during the day/evening.

Think about heating cables for a little bottom heat during germination, but almost anything will grow on nice and compact at 60F or so.

Thank you for your reply!
Running the lights at night should have been obvious, but I didn't even think of that! Thanks for the tip.
This is our first month in this home, so I am not sure what basement temps are like on average, but my guess is they won't go below 60 in daytime.
Thanks again for the tips!

i'm in a similar situation to the original poster - seed-starting area confined to a room in a cool basement. on average the daytime temperature down there is about 52 degrees F. i have a heat mat to aid in germination; however, i'm wondering if i need extra heat for normal growing conditions. i've read a few suggestions for draping mylar blankets around the seed starting shelf unit. will this really help keep things warm or just brighter? and if i were to set up mylar and/or plastic sheeting as insulation would i need to provide a little fan for air circulation as another poster suggested?

You don't want to make it very warm once the plants germinate. Too much warmth will tell them to grow, grow, grow!!! This will cause them to become spindly and weak under the florescent lights, which cannot give them what natural sunlight does. It's best to let the growing conditions be bright, but slightly on the cool side to encourage compact growth.

I use some aluminum foil tented around the lights to add brightness until I get around to buying the Mylar. When I used the foil around the lights plus the germination mat the trapped heat pretty much cooked and killed a bunch of my seedlings with temps approaching 100 degrees. The fan I tried using to dissipate some of the heat couldn't move enough air through the tent. Even if the fan did move enough air, then the added heat plus moving air would spell extra drying conditions, which means unless you were checking the moisture 3+ times a day you'd lose plants to dehydration. I would NOT use the mylar with the germination mat. The mylar plus lights should keep quite toasty enough for a basement that's already at about 52 degrees ambient.

You could also install a nearby space heater on a thermostat, if the above measures don't quite give you enough heat. You probably won't need it for longer than another month or so anyway.

Humidity domes on seed trays trap a bit of the heat produced by fluorescent lights (as well as humidity) and seem to speed germination. Remove them for an hour each day to air out the seed flats. For seeds that like slightly cooler germination temperatures, I drill half a dozen 1/8" (3 mm) holes in the top of the dome.

Here is a link that might be useful: Seed-starting supplies