What you talk about here is dominant wavelength, when the light is weak only that peak is detected.
I'd also point out my first comment(earlier post), about measuring nonsense. These are Toms sequence readings for one point, according to his settings 0 white.
Dominant wavelength effect, maybe, but appears to blue region, but then look at the scatter and eractic readings seen as linear lines. This is noise. Which is correct??? Hard to tell. The noise is possibly also the display, also hard to tell.
The fact is, in the field without lab grade equipment or lab environment you ain't going to measure 0.001 cd/m^2 accurately or easily. Detection and accuracy are two completely different things.