Video cameras sensitivity to light is expressed in terms of "Lux" (nanoampheres, 10-9 of signal current) or "Lumen" (microampheres, 10-6 of signal current). The lumen and lux are photometric units. The lumen describes the amount of light that falls upon a surface per second. The lumen may be related to the foot-candle as follows: One foot-candle is the intensity of illumination on a surface of one square foot when perpendicular rays of light flux totaling one lumen strike the surface. This occurs when the standard candle illuminates a one-foot-square white surface located one foot away. Below is a chart of approximate illuminations. I hope the chart below will clarify the definition.