Difference between a lumen and lux?

As far as i know, lux is the unit used to measure illuminance and lumen is used to describe how much light is contained in a certain area after its been reflected. Let me know if am wrong... but if this is right then why do people request say that bulbs should display lumen instead of watts. Shouldn't it be lux really since that's the measurement for illumiance. Because you want to know the power the flash light gives for example, and not what it reflects since all objects reflect light differently.