View Single Post
Old December 23rd, 2017, 10:56 AM
Doug Kerr Doug Kerr is offline
Senior Member
Join Date: May 2006
Location: Alamogordo, New Mexico, USA
Posts: 8,604

Hi, Asher,


The vertical values of the SPD are indeed "relative", and are normalized so that the value at 560 nm is 100 units!

So, the dimensionality of the vertical axis is power per unit wavelength, but the actual unit is chosen for each SPD so the value at 560 nm is 100 units.

And I didn't even have breakfast yet (but it looms).

I found this in a nice (and concise) discussion of standard illuminants provided by Image Engineering:

But I had guessed it the first time I saw the PSD's for three of the standard illuminants plotted on the same chart!

But it takes we dotards a while to catch on! Especially when yet unfueled.

Best regards,

Reply With Quote