When people are describing someone they have a romantic interest in they tend to use phrases such as “radiant” or other descriptions that conjure up images or light. For some reason when I thought of this idea I had lots of examples in my head but now seem unable to find any actual examples other than my thoughts.
This could be due to the physiological change in a person’s eyes as when someone looks at someone they are attracted to their bodies will produce more dopamine which has the effect of dilating pupils. Pupil dilation would let more light into the viewers eyes and so they might perceive the person they are looking at to be brighter than normal.
However, this might instead be due to people using similar phrases they have heard before and are prevalent in society, but this still would not explain where these phrases come from. As most works of literature can be shown to borrow heavily from those which came before and so if a few ancient authors used similar imagery it would then create an image that seems to be right due to the authors familiarisation with the image. Thus the idea that these phrases have some physiological cause seems to be the most convincing.
There could be another explanation in the broader way in which goodness is associated with light. Examples of this are the large amount of comparisons between God and light in the Bible. The angles are always described as being cloaked in light as shows by the description of one in Daniel 10:5-6 in which he says that the angle was “like lightning, his eyes like flaming torches, his arms and legs like the gleam of burnished bronze”. This association of light with good is also present in more contemporary examples, such as Star Wars, the bad faction is the “dark side”.
This presumably stems from evolution as humans cannot see very well in the dark and so associate it with danger and thus evil, whereas light enables humans to see and removes the dangers of darkness and so is perceived to be good. This idea also associates light with power as one of the most powerful thing in early society would have been fire and so light would become associated with power.
I think it is probably a mixture of these two explanations which causes the type of phrase I am discussing as if someone is describing someone to be attractive they will most likely also want to depict them as powerful and good, but may be influence by the way attractive people seem better illuminated that all others due to pupil dilation.