Why are Some Finishes Labeled "Photochemically Reactive"?

The term "photochemically reactive" appears to relate to a formula's potential to form ozone and contribute to smog, not any risk that the finish will change color in sunlight. October 19, 2014

We are thinking of switching to Becker Acroma as our go-to system for white pigmented CV and clear CV. Here is the thing though - we were using Gemini strictly for a few years and the label reads that it is not photo-chemically reactive, as I expected seeing that as a rule I always thought CV would not change color. Why is it though that the Becker Acroma white CV says it is in fact photo-chemically reactive? Does that mean once our new white CV doors hit the sun coming through the kitchen they will turn yellow?

Forum Responses
(Finishing Forum)
From Contributor B:
From what I've been able to find, it can mean that a photo chemically reactive coating may change color, or it may mean that it is creating ozone or smog, depending upon where you look. It's odd though that Beckers says it is photo-chemically reactive. It would seem unlikely that they mean that it yellows, but then it could be a nitrocellulose modified system, then it would change color.

From Contributor N:
I'm lucky that one of my main cabinet maker clients also happens to have a PHD in chemistry, so I posed this question to him and this what I made of his answer (paraphrased and simplified, so hopefully I got it right). To be considered photo-chemically reactive the material needs to be a certain percentage of known photo-chemically reactive chemicals either in aggregate or individually with the percentage being different dependent on what chemicals are in what percent. Put more simply; if CV brand X is 19% photo-chemically reactive chemicals it may slip below the criteria but Brand Y is 20% so it's labeled as being photo-chemically reactive. If you really want to know how the material you're using stacks up you would have to know what's in it, what chemicals are considered photo reactive and in what percent they are present. MSDS, PDS, EDS would be good places to start.

From the original questioner:
This one really has me scratching my head. The only thing I can think of after reading your responses is either it does in fact have some nitrocellulose in it and/or it is creating some fog as it gases off?

From Contributor W:
If a product is photo-chemically reactive it has nothing to do with the finish changing color or reacting somehow with sunlight. Here is the actually definition: Photochemical reactivity is a measure of how much a compound reacts in the atmosphere and contributes to the formation of ozone. Often the term is shortened to just "reactivity." It is a measure of the unique characteristics of a compound relative to its ability to form ozone. Reactivity is also affected by the characteristics of the atmosphere in which it reacts, so it is not just a function of the chemical itself. Other chemicals that may be present in the air, and the intensity of the sunlight, can affect the reactivity of a chemical. Reactivity is often used rather loosely to refer to the rate of ozone formation, the amount of ozone formed, or both.