Now using 5nm band size, 360-780 range and CIE 1931 standard observer
and D50 illuminant for the conversion. To specify what spectral data
means in relation to colorimetry we need to specify the wavelength
range, observer and illuminant expected.

When experimenting with HLC-Colour-Atlas-XL_SpectralData_v1-2.cxf the
inaccuracies of the spectal data resampler in coloritto have become
apparent, for now - using 5nm provides the best results for all input
data wavelengths - resampling with bandpass filtering and work to avoid
shifting the data is needed.

The 360-780 range is the range recommended by E308 and probably other
attempts at standardising spectral to tristimulus conversions.