Luminance is the amount of visible light leaving a point on a surface in a given direction. The unit of luminance is candela per square meter (symbol cd/m²)
Luminous intensity or Candlepower is the total luminous flux emmitted by a source per unt solid angle. The SI unit of the quantity is candela (symbol cd).
Luminous flux is energy per unit time that is radiated from a source over visible wavelengths. It is a a weighted average of the radiant flux in the visible spectrum from about 330 nm to 780 nm. The SI unit of luminous flux is lumen (symbol lm). It is the luminous flux emitted into unit solid angle (1 steradian) by an isotropic point source having a luminous intensity of 1 candela.
Illuminance is the luminous flux incident on an element of the surface, divided by the area of that element. It is used in photometry as a measure of the intensity of incident light, with wavelengths weighted according to the luminosity function, a standardized model of human brightness perception. The SI unit of illuminance is lux (symbol lx). It is expressed as one lumen of luminous flux incident on one square meter of area.