Irradiation is an optical phenomenon interfering in the visibility of a text. It results from the simultaneous contrast which takes place between the colour of the text and its background. It modifies, according to the lighting and the scale, the aspect of the typeface, through over-exposure or underexposure. This phenomenon, similar in the case of excessive reduction or distance, can be artificially simulated.
On the left, a simulation of irradiation phenomenon, through under-exposure and over-exposure with the Berthold Bodoni, Clarendon Linotype, and Bell Centennial, and Minuscule Quatre, in the same size. and we can notice that : the thinner parts disappear, angles are rounded off, the close zones merge together.
This optical tests teached me a lot about the structure that should be given to Minuscule. The weight should be not too light nor too bold, with a reduced contrast, big spacing, big xheight and very opened shapes.