The "leds.mspct"
object contains "source_spct"
objects
with spectral irradiance data. As the exact distance from LED to cosine
diffuser and/or the the driving current vary among spectra, they have been
all normalized to the wavelength of maximum spectral energy irradiance.
When the details of the measurement conditions are know, these are stored
as metadata attributes. In any case, it needs to be taken into account than even
in these cases measurements have not been done in an optical bench, so
values of spectral irradiance are subject to errors due to possible
misalignment. The shape of the spectra, in contrast can be relied upon as
measurements were done with well calibrated instruments.
The output of LEDs at a given current decreases as their temperature
increases. The wavelength at the peak of emission can depend on the
temperature and current, but shifts tend to be only a couple of nanometres.
In LED arrays with heterogeneous LED chips or white LEDs based on secondary
emission from phosphor the shave of the spectrum can slightly change
depending on the drive current and temperature.
There is variation among LEDs of the same type, specially with respect
wavelength and light output. The data included are for individual LEDs and
can be expected to differ to some extent from the typical values in the
manufacturers specifications. Some of the LEDs for which data are included
are only of historical interest as their production has been discontinued,
usually replaced by new types with enhanced performance. When known, the
approximate "vintage" is provided in the metadata.
The spectral data are not expressed at constant wavelength intervals. Not
only the intervals vary in the raw data from the array spectrometer, but in
addition function thin_wl
has been applied to
reduce the storage space needed. In brief the wavelength interval has been
increased as much as possible in those regions of the spectrum that lack
detailed features (such as linear slopes and wavelength regions with zero
light emission).