One of the more obvious differences is that paper is very close to a Lambertian reflector while LCD pixels are more directed. Hence the LCD viewing angle problem, though that gap is closing.
Apart from that, I think it mostly comes down to the fact that an LCD pixel doesn't actually change it's reflected colour when it starts emitting light of a different colour. This means that incident light falling upon the pixel and being reflected will necessarily become noise -- it won't contribute to the image. For instance, if the colour of the LCD surface is some kind of grey and the LCD is emitting green, the resulting colour will be
incident * r_reflected + emitted
Where `incident` is the incident light from the environment, `r_reflected` is some factor (< 1) representing the amount of grey component reflected from the incident light and `emitted` is the emitted green light. The result is some kind of mix of grey + green.
On the other hand, if you had a green coloured paper, then there is no emitted component so it becomes just
incident * r_reflected
Where `r_reflected` now represents the proportion of green light that is reflected. The end result is a more pure green.
Ok, that makes sense. But does any of that have any bearing on eye strain? Because it sounds mainly like a color reproduction issue, which seems pretty orthogonal to the whole 'black text on white background vs white text on black background' debate.
Apart from that, I think it mostly comes down to the fact that an LCD pixel doesn't actually change it's reflected colour when it starts emitting light of a different colour. This means that incident light falling upon the pixel and being reflected will necessarily become noise -- it won't contribute to the image. For instance, if the colour of the LCD surface is some kind of grey and the LCD is emitting green, the resulting colour will be
Where `incident` is the incident light from the environment, `r_reflected` is some factor (< 1) representing the amount of grey component reflected from the incident light and `emitted` is the emitted green light. The result is some kind of mix of grey + green.On the other hand, if you had a green coloured paper, then there is no emitted component so it becomes just
Where `r_reflected` now represents the proportion of green light that is reflected. The end result is a more pure green.