TE Connectivity BF series Photocontrol - OFF/ON Ratio

When looking at BF Series Photocontrol from TE Connectivity, you may notice an OFF/ ON Ratio parameter, 4:1.
What does OFF/ ON Ratio mean?

Please note that the standard turn-on light level, as specified by ANSI C136.10, is 1.5 footcandles (Fc).

A footcandle is a measurement of light intensity and is defined as the illuminance on a one-square foot surface from a uniform source of light. With an OFF:ON ratio of 4:1, it means the luminaire (street light) will turn OFF at a light level of 6 footcandles .

Applicable Part Numbers