that might be your problem (well I almost know forsure thats the problem)
heatlamps are not good light for these guys, I'm sure they could work but you wont get a healthy looking plant, they get too hot, they dry out soil, they dont peak very high in green or blue light
you want a fluorescent bulb, you can get one from walmart or lowes that will fit into that same lamp fixture in replacement of the reptile bulb and it cost about 5$ for 2 bulbs
they are called compact fluorescent bulbs with color temperature of around 6400k aka "cool white"
the higher the watts the better, but be sure not to confuse "watts" with "volts"
your not really lookin at the volts when buying a light, just want high wattage
the highest I found at walmart was 25watts and I kept them as close as you do with your light
this was my plant when I had it under the walmart bulb
http://i42.tinypic.com/11c4ks1.jpg
thats what your plant will look like with fluorescent lighting, seeing as how you seem to have everything else right the new light should bring that plant into full grow
and if your confused about the bulb specifics you can just write "compact fluorescent bulbs color temp around 6400k or 'cool white' " on a piece of paper and show it to the worker and hell help you
just remember you want the highest watts possible in the bulb which should be around 25-28 watts if you are buying from walmart or lowes
im talkin in circles now,
anyway hope this helps
gl!
/edit
I would probably just take that light off them and just give them indirect sunlight until you can get the new bulb
if you turn that light off and move em up to that window thats next to them they should be fine
aslong as no direct light blares through that window