Green iguanas need a warm enclosure with a hotter basking zone and cooler areas so they can regulate their own body temperature.
How hot should the basking area be?
Adult green iguanas are commonly provided a basking area around 95°F, while the rest of the enclosure remains cooler. Juveniles may use somewhat warmer basking conditions. Measure the basking area directly instead of judging heat by touch.
What about the rest of the enclosure?
Create a gradient rather than heating the entire enclosure to one temperature. Large iguana habitats should include warm areas as well as places where the animal can move away from the heat.
What happens at night?
A nighttime temperature drop is normal. If supplemental night heat is necessary, use an appropriate lightless heat source with suitable temperature control rather than leaving bright basking lights on overnight.
If you use a ceramic heat emitter, read What Fixture Do I Need for a Ceramic Heat Emitter?. You can also browse Iguana Supplies.