MAXIMUM POSSIBLE LUMINOUS EFFICACY OF LIGHT SOURCES

Abstract

The question of white light sources creation with maximum possible luminous efficacy is always timely. With the appearance of semiconductor light sources, it become possible to revolutionary changes in this regard. There are a lot of publications which appeared in last years about light emitting diodes creation with 276 lm/W luminous efficacy. Whilst luminous efficacy of real light sources is not exceeding 80-100 lm/W. Just only in such values of luminous efficacy we can talk about significant increasing of average duration of glow of series light emitting diodes. This is because in light emitting diodes luminous flux is proportional to the current. With increasing of current, loss in p-n transition increasing in the square. This leads to a decreasing of luminous flux and average duration of glow. For effective dissipation of each surplus Watt of heat, it is necessary from 80 to 100 grams’ weight of radiator and low thermal resistances contact places. This leads to increasing size and weight of light emitting diodes products. That is why, the decrease of luminous flux during transitional process from the moment of switching on to transition into steady-state regime of lighting products should not exceed 10%. Adherence of this requirement, limits the maximum value of light emitting diodes light sources luminous efficacy, close to the spectrum and intensity of Sun radiation and acceptable average duration of glow – 172 lm/W. As part of finished lighting products, luminous efficacy may be even lower - from 0.32 to 0.74 from the above values, namely: 38-8 lm / W for ideal white light emitting diodes from 55-127 lm / W for light emitting diodes with a low color rendering index. It is also obtained analytical expressions for determination luminous efficacy of white light sources for day and night vision. This makes it possible to determine visual efficiency of light sources to the value of S/P-factor