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Old December 23rd, 2017, 09:31 AM
Doug Kerr Doug Kerr is offline
Senior Member
Join Date: May 2006
Location: Alamogordo, New Mexico, USA
Posts: 8,401

Hi, Asher,

Keeping in mind that I have not yet had breakfast, the matter of the units of the CIE SPD's for the various standard illuminants proves elusive. I do not have the definitive CIE document, and I don't plan to buy it (it is quite expensive - CHF 88, I think)).

I do have what seem to be authentic transcriptions of the CIE definitions of a couple of those SPDs (which are in terms of a value for each 5 nm of wavelength). I might have thought that to normalize these SPDs the vertical scale would have been chosen to make the area under the curve (and thus the implied total power) constant, but that does not at all prove out for the examples I have.

For example, if we consider the vertical axis unit to be the foobar, then for Standard Illuminant A the total area under the curve is about 48121 foobar-nm, while for Standard Illuminant D65 the total area under the curve is about 40972 foobar-nm.

But those are in the same neighborhood, so perhaps there is only some subtlety of which I am yet unaware.

I shall press on.

Best regards,

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