I have not seen 100 watt halogen lamps in a while. The OEM headlight bulbs were 40/55 I think, or about that. So on low, you draw 40 watts per lamp. LED headlights draw what @Obo said, so the savings is not significant. If you put higher wattage H4's in, you will save the difference between them and the LED's 36 watts. Taillights, etc. will save you as Obo said. The main advantage of LED's is low maintenance and brighter, colder (more blue) light.