I do think it's lack of light. The others look quite spindly as well. For me, it's really tough to get enough light from a window, unless it's something like a south facing bay window that gets loads of sunlight. (I guess southfacing in America is the same as southfacing in Ireland, but it's hurting my brain too much to think about it.) Do you have a florescent tube light you can hang over them? You might also try putting them outside. Anything over about 10C should be warm enough, or even a little cooler if you cover them with clear plastic. (I'd bring them in at night). You could either transplant them or just sit the trays of seedlings outside. This may not apply to you, because it sounds like it's hazy where you are, but if they're going to be exposed to bright, direct sunlight, make sure the first day you take them outside is a cloudy one, so the leaves don't burn.

Thanks Jessica!

I'll give the seedlings some time outside and hope things improve. We are south facing but don't get great light indoors.

The thing about putting them outside too early is that they are very weak right now. Too much wind, or temperatures that are too cold will hurt them.

True, true. I've had good luck covering them (maybe an upside down clear storage bin, or glass cake pan, or something). (But if it starts to get warm, take it off!! I formed a nice tarp-table seedling oven last spring) I'll be watching your blog to see how you get along :-)

If you can make it to home depot you can buy a good fluorescent light set up for under $20.

Lithonia Lighting 2 Bulb, 40 Watt Fluorescent Shop Light Model 1233 $9.98 - this comes with a little bit of chain but you you might want to buy extra chain and extra S hooks in case you want to install the light some where at eye level.

The bulbs are sold separately but Home Depot has them for a reasonable price. We bought a 2 pack of Philips 40 watt T12 bulbs for $7 but they also have the T8 32 watt which I'm considering (lower wattage for same light output) for $6 for the 2 pack.