It's possible that the lighting change is coming into play, but I think it's likely coincidence. If the low temp is up at 30, then I'd guess that's more at fault. It's tough to make adjustments with the ambient temps being a bit higher, but maybe try to increase airflow with a fan nearby and see if that helps a little. Hopefully the heat will break soon and the cool side temps will go back to the low-mid 20s. I'd leave the new basking bulb as it is for now and see how it goes after the room temps drop again.