Actually, of all the exotic reptiles out there, green iguanas are among of the most difficult to care for.  They have very complex heating, lighting, housing, and dietary requirements.

 

Heating.  Green iguanas are reptiles.  This means, among other things, they depend on their surrounding enviroment to regulate their body temperature.  If it is cold outside, a green iguana will be cold inside it's body as well.  This differs greatly from the thermoregulation of a pet dog.  Dogs are mammals and use a lot of energy to maintain their inner body heat.  Even if it is cool outside, a dog's core body temperature remains warm enough to carry out normal body functions.  One of the most important body functions is digestion.

 

An iguana's body temperature must be raised to about 90 degrees fahrenheit in order to digest it's food.  Since it cannot regulate it's internal temperature, it needs a basking area of at least 90 degrees fahrenheit to warm it's body enough to digest it's food.  As the caregiver of a captive iguana, providing that area is your responsibility.  It's also your responsibility to ensure that it stays warm enough without getting to warm.  Yes, iguanas like the heat, but they'll also die if they are kept too hot for too long.

 

That's why it's important to have a temperature gradient in your enclosure.  When your iguana gets too hot, it cannot sweat to cool itself down.  Instead, it moves to a cooler place.  Your temperature gradient should start at about 75 degrees fahrenheit in the coolest spot, have a midlevel of about 85 degrees, and top off at 90-95 degrees in the basking spot.  This is achieved with heat lamps strategically placed in certain spots in the iguana cage and a good digital thermometer with a probe to test your gradient and make sure the temperatures are correct.

 

At night, your iguana still needs to keep warm.  If your house drops below 75 degrees at night, you'll need an alternate source of heat so that your iguana can get a good night's sleep without a light.