> Err, my spectrophotometer has to illuminate the surface to be measured

Ah ok - I see where the confusion is now between us.  You are assuming that 
the OP wanted to reproduce the reflective surface that those xyY values were 
measured from, whereas I was just reproducing those exact xyY colours on the 
monitor.  FWIW my colour meter just measures the incoming spectrum, it has 
no light source, in fact we usually use it in a totally dark room.

> Thanks for the link but I'm already quite familiar with such things, they 
> are part of my per day pay-job.

Mine too, but mine is mainly dealing with emitted light, not reflective, I 
suspect that's where the confusion has arisen between us.

> Your main misconception seems to me that you are assuming xyY values are
> some given values already there by definition,

Yes, sorry, the link that was posted here was just a list of xyY values, I 
assumed you just wanted to reproduce those xyY values on an sRGB monitor (in 
the dark), not the colour of some reflective surface that the xyY data was 
originally generated from when viewed under sRGB standard conditions.

> Very true. And it just happens that CIE L*a*b is just another mathematical 
> representation of the CIE xyz color space where the same *need* for 
> reference white exists.

That's not strictly true.  When dealing with reflective surfaces, you need 
to specify the *illuminant* used, but with CIELAB you need to additionally 
specify a reference white - these do not necessarily need to be the same 
thing.  If you are using XYZ (or xyY, Yuv, Yu'v' etc) then you only need 
specify the illuminant.

That is why in our specs for emissive displays, if the customer wants XYZ 
values they just get XYZ values, but if they want CIELAB then the reference 
white needs to be specified for it to make sense.

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