Like everything American - I supersized

Luminous flux is often used as an objective measure of the useful power emitted by a light source. Energy conscious consumers (Use LED's) commonly compare the luminous flux of different light bulbs, since it provides an estimate of the apparent amount of light the bulb will produce, and is useful even when comparing different technologies.
It is wrong or at least imprecise to refer to luminous flux as a measure of "brightness" since, for example, a nearby source of light may appear much brighter than a faraway source with much higher luminous flux. This is because not all of the emitted flux is received by your eye, and you receive less flux from sources that are farther away. In general, brightness has no unambiguous scientific meaning, and should be used only for nonquantitative references to physiological sensations and perceptions of light. luminous flux is the measure of the perceived power of light. It differs from radiant flux, which is the measure of the total power of light emitted, in that luminous flux is adjusted to represent the sensitivity of the human eye.
Brightness may be ambiguous scientifically but luminous flux thankfully is not. [Power of light /surface are] means I can run and bike faster. oh oh oh

Borrowed and adapted from http://en.wikipedia.org/wiki/Luminous_flux