Apparent brightness

The apparent brightness of a radiation is defined by the relationship between its luminous Flow and its radiant Energy flux.

More exactly, if one calls $\backslash \; Phi\; \backslash ,$ the radiant energy flux of a radiation and $F\; \backslash ,$ luminous flow corresponding, the apparent brightness K is given by the relation:

The unit of luminous flow being the lumen and the radiant unit of energy flux being the Watt, the apparent brightness will be expressed in lumen by Watt.

The value of the apparent brightness is always a number ranging between 0 and 683 lumens per Watt.

0 lumen per Watt is the apparent brightness of a radiation not including/understanding any frequency in the visible beach.

683 lumens per Watt is the apparent brightness of a monochromatic radiation of frequency 540×10¹² Hertz, i.e. corresponding to the maximum of sensitivity of the human eye.

As example, the apparent brightness of the solar radiation is approximately 250 lumens by Watt.

Notice

The apparent brightness is a concept very frequently used wrongly by certain professional environments (manufacturers of lamps for example) to indicate the relationship between the luminous flow emitted by an apparatus and its consumed power. One speaks then about apparent brightness of a system to indicate what one must normally call luminous Rendement of a lamp.

See too

• the wikilivre of photography and more especially the chapter dedicated to the apparent brightness.