I can only speak from personal experience but, they do make me feel more awake. I have never come across or used a UV emitting one so it isn’t the vitamin D aspect. Definitely take that as a supplement. I think it works for the same reason you aren’t supposed to have bright or bluish lights at night. Instinctive trigger to be more awake. https://www.thenational.scot/news/24849810.sad-lamps-work-buy-use/