Hi Laurie, congrats! And way to plan ahead
First, here is an excellent "sticky" with lots of info on starting with and caring for ducklings (I'd read through the whole thing):
https://www.backyardchickens.com/t/750869/raising-and-caring-for-ducklings#post_10611711
I think the general rule of thumb is to keep young ducklings around 85 or 90 degrees farhenheit. After they are one week old, you lower the temperature by five degrees... and continue lowering the temperature by five degrees each week after that.
I started out with an incandescent 60 watt bulb and kept the thermostat in our house up to maintain a warm temperature. Then I switched to a clear infrared heat lamp (which shines white) after about a week. Some people say that white light makes ducklings pick each other and fight, so they recommend a red or blue light. This has not been my experience.
Whatever light you use, make sure the ducklings have enough space to get away from the heat if they get too hot (shine the light on one side of the brooder). Then place their food and water at the other end so they are not forced to stay under the heat to eat and drink. You can tell if their brooder is at the right temperature by observing their behavior:
Too cold = they are piled up on one another and tightly packed together to keep warm
Too hot = they are scattered about away from the lamp (I guess sometimes they pant, too)
Perfect = they are loosely grouped together and move about freely
