Congratulations on deciding to get a leo; they're wonderful creatures!
The ideal temperature range for a leo is 31C - 32C (88F - 90F) at the hot end, down to about 24C (75F) at the cold end. The easiest way to attain these temperatures is often just using a heat mat (controlled by a thermostat), which covers between about a third and a half of the floor area of the viv. Heat mats are often used in preference to bulbs as they heat the substrate (as leos absorb heat through their bellies, it's the temperature of the substrate that's crucial).
Website for all things geckoey