Re: "Colorimeter"

On 5/18/2025 2:40 PM, Martin Brown wrote:

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.

Yeah, but reflecting light off a surface changes the problem.
I think they are interested in characterizing the *sources*.

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.

I am always entertained by the use of different colors to force the eye
to focus at different distances for adjacent areas.  We had a smiley face
painted on the inside of an elevator door, at school, that was red/blue
(more like orange blue).  It always left riders with borderline headaches.

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.