Re: "Colorimeter"

On 18/05/2025 20:43, Don Y wrote:

On 5/18/2025 5:37 AM, Martin Brown wrote:

On 18/05/2025 03:29, Don Y wrote:

On 5/17/2025 2:03 PM, Martin Brown wrote:

>

If you are serious about doing this right then a 2D CCD sensor and a prism hires grating combo at right angles will allow you to quantify the entire visible spectrum at ultra high resolution. Be careful though Perkin-Elmer (and others) have some very good lock out patents on this trick (may be about to expire).

>
Again, not looking to make an "instrument".  The phone idea may work
if the CCDs don't freak out with high intensity sources.

>
CCDs are almost indestructible unless you point them at the sun. Even then they handle it much better than a human eye. Webcams are probably a lot cheaper though. If you find one of the paint firm's colour matching apps and test chart it may already do what you want or close enough.

 The way it was described to me (how does the light falling on this body compare
to the light on some other body) suggests it was expected to receive radiant
light directly (not reflected light of of two bodies that have different
reflectance characteristics)
 But, I don't know how intense the light would be.

As ever the devil is always in the details. Identical colours but with different surface finishes can look incredibly different. Vantablack is very much like looking into the void it is quite literally blacker than black!
Any other "black" looks grey next to it.

I was asked because of my past experience with the colorimeter shining light
directly onto the detector, through filters.  (I've seen products that can
tell you what color an object is, etc., using reflectance)

You can trick almost any sensor. Human eye can be quite easily misled by didymium glass which is a narrowband Na-D blocking filter used to see into a bright yellow sodium flame when glassblowing.
Side effect is to produce cartoon like out of gamut colours when the brain tries to compute colours from the cones. Its apparent colour varies radically with the source of illumination.
The same property is shared with the natural gemstone Alexandrite.
https://en.wikipedia.org/wiki/Chrysoberyl
Such materials are rare and highly prized for their strange behaviour.
--
Martin Brown