How do these 3-way bulbs work? They have two filaments. The first switch activates the 40 watt filament; the second turns that off and turns on the 60 watt filament; the final switch turns them both on for a combined 100 watt output. (Of course a 3-way bulb could provide different wattage levels; this is just one common version.)
Early in the move to LED light bulbs, 3-way LEDs weren't readily available. They have become so, though they're still not as common as LEDs with a single level of light output. Nor are they as inexpensive. But when you're looking for flexibility, they make for an easy solution.
Typical of our stance to carry brand name bulbs to give you the best lighting experience possible, we carry this Philips 3-way LED bulb that replaces a 40 / 60 / 100 watt 3-way incandescent bulb.