Home Depot has these for around $8 each.
TCP Light Bulb Model 28927
(edited to only show pertinant info)
Light Output: 1,950 lumens
Energy Used: 27 watts
It says, "Replaces 100W incandescent bulb". So, do I need to get a 100W fixture for this? How many of these would be needed for a 20 gallon Drosera terrarium?