Leopard gecko eggs hatch anywhere from 45 days to 65 days, and like Drewlowe said it depends on the temperature as to how long it takes. The lower the temp(females-79-81 dgrs) the longer it takes and the higher the temp(males88-90 dgrs) the less it takes.
For an incubator you can use a 10 gallon aquarium, a large pickle jar(eat the pickles first
) a submersible heater, and a styrofoam lid to cover the 10 gallon snug. Fill the pickle jar with water, stick in the heater, plug in the heater, place the jar and heater into the aquarium on one side, and put the syrofoam lid on top. Voila! Instant incubator!
For the eggs I use individual deli cups for each pair laid. Punch 5 holes around the top of each container(not the lid). I fill them 1/3 full of vermiculite, add 3 tbsp warm water and mix it thoroughly. Then you can place ready made delis into the incubator and add eggs as your females lay them. No fuss no muss! Be sure to place a thermometer in the incubator too, measuring the temp inside the incubator not inside the delis. This method has not failed me yet!
They don't need light but it isn't harmful either. But it would be best to keep the incubator away from sunny parts of your house to prevent overheating!