Anne, if you still have the packaging, return it to the store and tell them they told you wrong! Get your money back and find the 8.0. I know stores like Petsmart will take ANYthing back even if it has been opened, even food! Hopefully the store in question has the 8.0 or 10.0. Desert reptiles need the highest UVB there is. It seems like the 5.0 is usually used in conjunction with the 2.0 for iguanas?? Seems like I saw that somewhere. I am definitely not an iguana expert though