Light is an electromagnetic wave that spreads in space and time.
Visible light is within a narrow segment of the electromagnetic
radiation spectrum like radio waves, radars, microwaves,
infrared, ultraviolet and X-rays.
Light can be defined as any radiation generating immediately
a visual sensation. The light wave is characterized by
its amplitude and wavelength (see Fig.1)
It is as well emitted by the sun as by an artificial source of lighting (bulb, light fixture).
It is formed by the “association” of a set of radiations, a mixture of colours.
The light perceived as white can be synthesized by adding the three primary colours to which the human eye is sensitive: red, blue and green.
We speak here of so-called additive synthesis by trichromy.
THE LUMINOUS FLUX describes the amount of light emitted by a light source.
The unit of measure is the lumen (lm).
ILLUMINANCE describes the density of luminous flux at a point on a surface. It decreases with the square of the distance.
The unit of measurement is lux (lx) or lm / m². 1lx = 1 lm / m².
Describes the amount of light emitted in a given direction.
It is largely determined by flux guide elements, reflectors for example
and is represented by the photometric curve.
The unit of measure is Candela (cd).
The only photometric quantity perceived by the eye.
It determines the luminosity of a surface and strongly depends on the reflection index (color and surface). The unit of measurement is cd/m².
This is the ratio of the luminous flux by the quantity of electrical energy consumed (lm/W). It indicates how much light you get for the power you use.
Unit of measure is lumen per Watt (lm/W).
Correlated Colour Temperature (K), simplified by language abuse as Color Temperature,
characterizes the apparent color of the light emitted by the source.
It allows to define warm (2500 K) to cold (<5000 – 5300 K) light ambiances.
