In-game I have the ‘Very light sensitive’ mutation. When I am outside there seem to be two things going wrong. Either I get no debuff at all (even though it’s during the day-time and I’m in the middle of a field), or under the @-screen it shows a debuff (In the sunlight iirc) but even though it colors my stats red, it does not detract anything from them.
tl;dr: Very light sensitive (and maybe also light sensitive) does not work. The debuff is not applied, even though it does sometimes give the message that it is.