Characteristics and relative emissions of the five light sources.

The Tab. 1 can be read in different ways. For instance, if a constant radiative emission is required independent of lamp-type, then two LED lamps are needed to supply the VIS emissions by one HPS lamp. However, if the human perception is considered, one can easily recognize that LED lamp emits about 27% more than HPS lamp. In this case only 4 LED lamps are necessary to produce the luminous energy equivalent to 5 HPS lamps. Note that all these evaluations were made for direct emissions of the lamps considered and not for a diffuse radiation of a night-sky that can be detected at the ground as a diffuse irradiance .