Here's why:
* Light intensity decreases with distance: As light travels further away from its source (the lamp), it spreads out over a larger area. This means the amount of light hitting a specific point, like your book, becomes weaker.
* The inverse square law: This law states that the intensity of light is inversely proportional to the square of the distance from the source. In simpler terms, if you double the distance from the lamp, the light intensity decreases by a factor of four.
* Less light on the book: With less light hitting the pages, the contrast between the words and the background becomes less pronounced. This makes the words harder to distinguish, leading to eye strain and fatigue.
Therefore, the further you are from the lamp, the dimmer the book becomes, making it harder to read.