Light that we see is a group of a few wavelength electromagnetic radiations.

With photometry we can define work instruments,magnitudes and graphics, with which we can make lighting calculations.

Luminous Flux: emitted power in the form of luminous radiation to which the human eye is sensitive.

How much does each bulb shine? -->Its unit is the lumen(lm)

Luminous Intensity: luminous flux emitted in a particular direction:Its unit is the candel(cd)

Illuminance:the luminous flux received by a surface.Its unit is the lux(lx)

Luminance: relates luminous intensity with the visible surface seen by the human eye in a particular direction. The light that reaches the eye. Its unit is candels per square meter cd/m2.