The lumen (symbol: lm) is the SI derived unit of luminous flux, a measure of the total "amount" of visible light emitted by a source. Luminous flux differs
When you're shopping for light bulbs, compare lumens and use the Lighting Facts label to be sure you're getting the amount of light

Lumens are the measurement units of "luminous flux." This is the total number of packets of light that is created by a source of light.
A lux is the unit of illumination. One lux equals 1 lumen per square meter.
A lux accounts for the area in which the lumens are spread. If 2,000 lumens are spread over 1 square meter, it lights that area up with an illumination of 2,000 lux. from the lumen.