You should be aware that there is a huge difference in calibrating a sensor for measuring the color of light and measuring the color of a surface (reflected color, apparent color).
I guess that you all know that when mixing light, you mix red, blue and green, as with good old CRT color tv's, LCD screens and RGB LED's.
While when you mix colors as in printing, and in reality also in paint, are mixing Cyan, Magenta, Yellow and "K" (black) (CMYK).
When using sunlight for any type of color reference the rule of thumb is to use a slight cloudy day. High, bright sunshine is only useful for testing max output af a solar cell system.
Bright sun light will give you too much blue and UV and sun light is NOT intensity linear over the visible spectrum.
So if you need to measure the exact radiometric intensity of one color (wave length) against another sun light is NOT the right reference :-/
Would be convenient though :-)
When you calibrate your LCD/LED monitor you are calibrating for a specific type of task - graphic work that ends as a printed brochure or photographic work that ends on hi-gloss paper or
calibration when the work is for movie and video production or photographic work for projected shows.
Philips did a color calibrator, mainly for CRT's - maaaaany years ago ;-). It was developed in DK (that is why I know) and it was pretty expensive and often used for "mega-screen" setups for concerts.
I can't remember how many sensing head they had on the largest system, but many and automatic calibration of the CRT's. It only took a few hours to sync the colors of a 10 by 20 CRT wall and not days.