Luminous efficiency refers to the ratio of the total luminous flux radiated by any source to the total radiant flux from that source commonly expressed in lumens per watt. The higher the lumen efficiency, the better ability the light sources have to convert electrical energy into light, which means that in the same brightness, lighting sources with higher lumen efficiency tend to be more energy saving. The figure below show the luminous efficiency of various light sources in different times.
A practical example:
A common 100 Watt incandescent lamp has a luminous flux of 1,350 lumens, its luminous efficiency will be 13.50 lumens per Watt (LPW).
A compact fluorescent lamp of 20 Watts has a luminous flux of 1,100 lumens, its luminous efficiency will be of 55 lumens per Watt (55lm/W).
By means of the example we notice that the two lamps have a similar luminous flux, that is to say they illuminate almost the same thing, nevertheless the saving lamp gives us four times more light for each watt consumed, that is to say it is more efficient, therefore it is known to him like ” Saving “. For this reason too, the energy saving lamp “burns much less” than the incandescent lamp, which generates a lot of heat, ie a lamp will be efficient when 100% of the energy delivered to light, most of it will transform In LUZ and a minor part in HEAT. The perception of HEAT will always be relative, since it is very likely that many lamps will “burn to the touch” except for many LED lamps that are more efficient than any other technology lamp and therefore “burn much less”.