Luminous flux
It is the amount of light emitted by a light source (lamp), in the time of one second; The unit for measuring luminous flux is lumen.
Lumen
It is the measure of the total amount of visible light at a given angle, emitted by a lamp. Its symbol is lm.
Lighting
It is the luminous flux that covers an area in square meters; Its unit of measurement is lux.
Lux is equivalent to one lumen/m² and its symbol is lx.
Luminous intensity
It is the amount of luminous flux emitted by a lamp per unit angle; Its unit of measurement is the candela (CD).
Candle
It is the luminous intensity in a given direction of a lamp, which emits a monochromatic radiation of frequency 540×1012 hertz and of which the intensity radiated in that direction is 1/683 watts per stereoradian.
To clarify this concept, look at the following example: a light source (lamp) emitting 1 candela in all directions (360°) will provide a luminous flux of 4π = 12.57 lumens.
Luminance or brightness
It is the luminous intensity that a surface produces on the human eye, having two sources of luminosity. It is measured in candles.
Colour Rendering (CRI)
The Colour Rendering Index is an international measurement system designed to indicate the ability of a light source to faithfully reproduce colours by comparing it to a natural light source. The colour rendering index takes natural lighting as a reference.