예레미야애가 2:11의 Halakhah

To preserve your sense of sight, take the following precautions: Do not come suddenly, all at once, from a dark place to a well-lit one. If you need to enter from a dark place to a lighted one, open the door a bit and look at that small amount of light for a few moments, then open it more and again look at that light for a few moments, and then open it completely. Do the same when going from a lighted area to a dark one. This is because the shift from light to darkness, or from darkness to light, without any transition, damages the sense of sight. For this reason G-d, blessed be His name, in His great mercy created the world in such a way that the sun shines upon the earth little by little, not all at once, and likewise sets little by little. For this we bless Him as “the One who illuminates the earth and those who dwell upon it, with mercy,” meaning that He mercifully makes the sun shine little by little, and not suddenly, all at once. Reflected light from the sun—meaning that the sun shines on something and from there the light is reflected—is a light that is damaging to the eyes. Therefore you should take care not to dwell in a house where all the windows are on the north side, because the sun does not come to the north, so that all the light that comes from that side is only reflected light. Similarly, even if the windows are on the eastern, southern or western sides, if you cannot see the sky through the windows—for example, if there are high walls opposite them—then the light that comes through them is also only reflected light. You should take care not to be occupied with writing, reading a book, or any sort of detailed work by twilight, or in the middle of the day, when the sun’s light is at full strength. You should also not do too much writing, reading of books with fine print, or any other sort of detailed work by candlelight at night. Too much staring at the color white also damages the eyes; that is why the sky appears blue, not white, so it should not damage the eyes. Likewise, staring excessively at a bright red color, or at fire, is also damaging. Smoke and sulfurous fumes are also damaging, as are fine dust and wind that blows into one’s eyes. Also too much walking and large strides, and excessive crying [are harmful], as the verse says, “My eyes are spent with tears.”⁹Eichah 2:11. Most detrimental of all is excessive sexual intercourse. By contrast, “the commandment of G-d is clear, enlightening the eyes.”¹⁰Tehillim 19:9.