What is the difference between candela, lumens, and lux, and how do they each measure the brightness or intensity of light?

Candela measures the intensity of light emitted in a specific direction, lumens measure the total amount of light emitted by a source, and lux measures the amount of light that falls on a surface. Candela is used for directional light sources like flashlights, lumens for overall brightness of a light source, and lux for the brightness of light on a surface.