Imagine a candle flame centered within a sphere that is one foot in radius. That point source, of uniform intensity equal to one candela, produces an amount of light flowing through one square foot of the sphere's area that is defined as one lumen. The amount of light falling on that one square foot of the sphere is equal to one footcandle. Since the area of the sphere is equal to 4p, then the amount of light flowing through the sphere is 4p lumens, or about 12.57 lumens. In other words, a one candela source produces 12.57 lumens and an illuminance of one footcandle at a distance of one foot.
Luminous flux is the time rate of flow of light.
The unit of measure is the Lumen . If you graphed the light levels through the time of a day it would be a bell shaped curve. The lumen differs from the candela in that it is a measure of light flux irrespective of direction. The appropriate units of measure are Footcandle and Lux. One footcandle is the illumination produced by one lumen uniformly distributed over one square foot of a surface, or conversely this is the illumination at the point of a surface which is one foot from, and perpendicular to, a uniform point source of one candela.