2012-05-12 18:41:29 UTC
in Wikipedia and many other places the efficiency of artificial light
sources, e.g. incandescent bulbs, is stated in per cent, and thus
treated as energy conversion efficiency. Here, the typical values for an
incandescent lamp (non-halogen, with a filament temperature of about
2700 K) are around 5% with 95% being wasted as "heat".
I am familiar with the definitions of luminous efficacy and efficiency,
both being well explained at . However, according to this a light
bulb has a luminous efficacy about 12-15 lumens per watt, corresponding
to a luminous efficiency of about 2% (lumens per watt devided by the
theoretical maximum of 683 lm/W for monochromatic light near 550
nanometres). The value of five per cent does never occur. This would
correspond to a 100 per cent efficiency between 240 and 300 lm/W. The
maximum for a truncated Planck spectrum (i.e. clipped to the 400-700 nm
range) lies in this range , but it is never clearly cited as such.
Furthermore, this truncated Planck figure is ambigous since it strongly
depends on the truncation wavelengths and the reference wavelength (the
refecence paper uses 5800 Kelvins and 400-700 nm).
So, is there any "official" definition (maybe ISO) of the energy
conversion efficiency of a light source, and if so, how is it related to