To choose well a physical contradiction

Following the former article about the definitions of different types of contradictions, it is proposed to further study the red eyes' problem.
As already said, the physical contradiction proposed for this problem was not well chosen. Why ? Because :
* it does not bring something new with regard to the pair of technical contradictions : it is a plain re-formulation of the TCs
* it does not go into the physical mechanisms responsible for the problem

For the sake of simplification, let us say that the red eyes' appearance on a photograph is caused by dilated pupils. Dilated pupils are caused by the relative darkness, which in turn necessitates the use of a flash.

Consequently, another physical contradiction can be expressed :
PC : The pupils must be dilated because there is a relative darkness, and the pupils must be non dilated to avoid the red eyes' phenomenon

Now the physical contradiction is rightly chosen. Actually it expresses opposite states (dilated / non dilated) of a part of the system (pupils) which is at the root cause of the initial problem.

In a coming article, it will be shown how to ultimately solve this physical contradiction