It seems to be a common form of words in fiction to talk about people's eyes being ‘alight’, or ‘blazing’, or occasionally ‘flashing’, or having suddenly ‘lit up’ at some particular moment.

I've always vaguely wondered about this. Obviously they don't literally mean that people's eyes emit self-generated light under the influence of particular emotions. (Well, perhaps they do in some SF or fantasy, but the use of this descriptive form is by no means restricted to technologically or magically enhanced characters.)

A reasonably plausible fallback option might be that when eyes open or move in a particular way it alters their reflective properties; but I honestly can't say I've ever seen anything in the real world which could remotely be attributed to a phenomenon of this type. On the other hand, I don't tend to watch people's eyes all that much – I couldn't tell you my own eye colour or that of people I've gone out with, let alone that of anyone else – so perhaps it does happen and I just fail to notice.

It's been brought particularly to my attention in the last week because I felt an expression on my own face which I somehow subconsciously associated with one of the above phrases. It felt somehow right to me that if I'd been writing fiction involving that expression, I would have been forced to describe it as ‘his eyes lit up’ or something similar; and yet I've never seen anyone's eyes actually do that, and have no particular evidence to suggest that mine did at that moment. I just felt that in an ideal world they ought to have done.

This question has been faintly bothering me for years and years, but as a result of the above it's finally made it to the top of my list of things to be curious about. So, a straw poll for my readers: has anybody ever seen someone's eyes genuinely do, in real life, anything that could be described by any of the luminous metaphors listed above?

While we're at it, I've also never been entirely convinced by descriptions like ‘his face didn't move, but his eyes clearly showed his gratitude’. Has anyone seen that in real life, or is it a commonplace exaggeration appearing only in written fiction?