Luminous flux is known as the power of light perceived by the eye. The SI unit of luminous flux is known as lumen where one lumen is the amount of luminous flux emitted from a directional unit point source through a unit solid angle.
Since the human eye can see only the visible spectrum of light which is perceived in the form of luminous flux and thus lumen.
Lumen may be defined as the S.I. unit of the luminous flux and denoted by the ln. The human eye can only see the wavelength of the lights lies in the visible spectrum.
The power of light perceived by the eye is known as Luminous flux . One lumen may be defined as the amount of luminous flux emitted from a directional unit point source through the unit solid angle.
Im not sure but if you think of it, the one that you didn't put any salt is a independent variable because it doesn't really rely on anything it doesn't have salt. The Dependent variable would be the 2nd and the 3rd cup because it doesn't have much salt but the 4th cup has lots of salt so its basically controlled. Hope it helps !
