Reading a book for two hours is more of a strain on the eyes than watching TV (20 feet away) for two hours because of several reasons:
Distance: When watching TV, the screen is usually located at a distance of about 6-10 feet away from the viewer, whereas when reading a book, the eyes are usually focused on a much closer distance, which can be more strenuous for the eyes.
Lighting: The lighting conditions while reading a book can also be more strenuous for the eyes than while watching TV. While reading a book, the lighting conditions may not be optimal, which can lead to eye strain, while watching TV, the lighting is usually better controlled, and the screen emits its own light, which reduces eye strain.
Contrast: Books have a high contrast between the text and the paper, which can cause the eyes to work harder to adjust to the different lighting levels. TV screens, on the other hand, tend to have a lower contrast, which can be easier on the eyes.
Eye movements: Reading involves frequent eye movements, such as focusing on individual letters and moving the eyes from one line to another, which can cause eye strain over time. Watching TV, on the other hand, requires less frequent eye movements, and the eyes can rest on the screen for longer periods without straining.
Overall, reading a book for two hours can be more strenuous on the eyes than watching TV (20 feet away) for two hours due to the closer distance, less controlled lighting conditions, higher contrast, and frequent eye movements required while reading.