Lumens, also known as luminous flux, is the measure of the perceived power of light from a natural or artificial light source. In simple terms it is the measurement of how bright a bulb or tube is.
Whether you are 1 meter away or 100 meters away from a light source it is still emitting the same amount of lumens.
Lux is the measure of the apparent intensity of light hitting or passing through a surface at a given distance. A light source 1 meter away will have a far greater lux than if you were 10 meters away.
So in summary the difference between the units Lumen and Lux is that Lux takes into account the area over which the luminous flux is spread at a FIXED distance. Whereas Lumens is the amount of light coming from a light source irrespective of the distance.