As someone who uses both dark mode and light mode, a major factor is if I'm in a darker area. When I read books on my phone, I prefer dark mode at night and li

As someone who uses both dark mode and light mode, a major factor is if I'm in a darker area. When I read books on my phone, I prefer dark mode at night and light mode during the day. To what extent are these studies testing these sub-optimal reading conditions? Are they just testing optimal conditions which could have different results?