Available on LIFX Original, LIFX White 800, White 900 and LIFX Color 1000 running the latest firmware.
Not supported by current LIFX and LIFX + (gen 3) bulb firmware. There is not currently a default restore option for these bulbs.
Return your lights to white via wall switch:
Flick the wall switch off
Flick the wall switch back on for about 1-2 seconds
Flick the switch off again
Flick the switch back on
A double flick will set them back to 100% brightness on 3500K white.