I think light mode is far better with respect to being able to comfortably read and use digital device for a long period of time and I think there are enough studies to back that up. There are indeed a bunch of studies to back this up. The consensus is that our eyes are roughly 26 percent worse at reading when it comes to dark mode. The biggest scientific factors for this, are focus, light scatter, and contrast. Let's use a camera lens to explain the first one. Focusing is largely affected by how much light is coming into our eyes and how we focus that light. If a lot of light is coming in like when using light modes, eye pupils contract allowing less light in, creating a wide depth of field, meaning everything is in focus. If this is inverted, less light coming in, that causes our pupils to dilate and that creates a shallower plain of focus, meaning our eyes have to put more efforts into focusing on individual objects. When it comes to reading, you want everything to be in focus. You need that light background for the pupil to work appropriately to minimize amount of light coming in. It also increases your depth of the focus, the eye just works better more comfortably.