Color spectrometer: Can I use a RAL K7 color fan as reference?


I bought a used eye-one Pro spectrometer (without UV filter, calibration expired 2016) and wanted to check if it is working as intended.

eye-One Pro

I also happen to have a RAL K7 color fan. It seems like various web pages have conflicting (or under defined) information regarding LAB and XYZ values of these RAL colors, but there are offical reference cards with XYZ colors available.

There we can see that RAL3028 has X=28.2, Y=17.4 and Z=6.5 (DIN 5033: instrument geometry d/8°, standard illumination D65, standard observer 10°)

Now I place my eye-one Pro on the color RAL3028 of my RAL K7 color fan and take a measurement with spotread:

spotread -i D65 -w -Q 1964_10

Spot read needs a calibration before continuing

Place the instrument on its reflective white reference S/N 322202,
 and then hit any key to continue,
 or hit Esc or Q to abort:
Calibration complete

Place instrument on spot to be measured,
and hit (A-Z) to read white and setup FWA compensation (keyed to letter)
(a-z) to read and make FWA compensated reading from keyed reference
'r' to set reference, 's' to save spectrum,
'f' to report cal. refresh rate, 'F' to measure refresh rate
'h' to toggle high res., 'k' to do a calibration
Hit ESC or Q to exit, instrument switch or any other key to take a reading:

 Result is XYZ: 24.389055 13.839679 3.148777, D65 Lab: 44.002129 59.361484 41.763412

This appears to be a pretty big difference? I also tried to use FWA:

spotread -i D65 -w -Q 1964_10

Spot read needs a calibration before continuing

Place the instrument on its reflective white reference S/N 322202,
 and then hit any key to continue,
 or hit Esc or Q to abort:
Calibration complete

Place instrument on spot to be measured,
and hit (A-Z) to read white and setup FWA compensation (keyed to letter)
(a-z) to read and make FWA compensated reading from keyed reference
'r' to set reference, 's' to save spectrum,
'f' to report cal. refresh rate, 'F' to measure refresh rate
'h' to toggle high res., 'k' to do a calibration
Hit ESC or Q to exit, instrument switch or any other key to take a reading:

Measured media to setup FWA compensation slot 'A'
FWA content = 0.376687

Place instrument on spot to be measured,
and hit (A-Z) to read white and setup FWA compensation (keyed to letter)
(a-z) to read and make FWA compensated reading from keyed reference
'r' to set reference, 's' to save spectrum,
'f' to report cal. refresh rate, 'F' to measure refresh rate
'h' to toggle high res., 'k' to do a calibration
Hit ESC or Q to exit, instrument switch or any other key to take a reading:

 Result is XYZ: 24.301383 13.741372 3.127816, D65 Lab: 43.859720 59.593824 41.655072

Why is there this big difference? Is there a better (not super expensive way) to check the instrument?

I see three possible reasons that could introduce an error:

  • the measurement was flawed (e.g. wrong arguments for spotread)
  • the color reference is flawed (maybe the K7 color fan isn’t accurate enough)
  • the instrument is out of the calibration (at least it is still passing all self tests)