Halakhah su Salmi 19:9

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.

It is written, “Serve the Lord with gladness” (Ps. 100:2)¹Berakoth 31a. and “Serve the Lord with fear” (Ps. 2:11), but how so? ²The Midrash on Psalms, trans. William Braude (2 Vols.; New Haven, Conn.: Yale University Press, 1959), II, 147.(both fear and gladness?) If a man is over-joyful, let him recall the day of death,³Berakoth 31a. this is fear. If he is sad, let him rejoice his heart with matters of the Law,⁴Shabbath 30b. as it is written, “The precepts of the Lord are right rejoicing the heart” (Ps. 19:9).

To not conclude the judgment by estimation: That a court only kill the accused with witnesses that testify about the same matter about which he is to be killed; that they actually saw him with their eyes, [not] that they testify against him based on strong indications. And about this is it stated (Exodus 23:7), "and an innocent one and a righteous one you shall not kill" - meaning to say, be very careful not to kill a person about whom it is possible that he did not do what they said that he did. And so is it explained in Mekhilta d'Rabbi Yishmael 23:7:2, as there they said, "If they saw him pursuing another to kill him, the knife in his hand, and they [warned him, 'If you kill him, you will be killed.' And the witnesses] averted their eyes [and did not see him striking him] and afterwards they found him (the victim) in the death throes, the knife dripping blood in the hand of the murderer — I might understand that he is liable [for execution. Hence,] we learn to say, 'and a clean one and righteous one you shall not kill.'" Behold, because they averted their eyes at the time of the striking, this one is exempted. And the matter is proper and fitting to be like this. As if the Torah had permitted to establish the parameters of punishment with strong possibilities, it would come out from the matter that sometimes we would kill people for something they did not do, as there is great breadth to the possible. And know this and understand it, as it is a clear thing. And therefore, He, may He be elevated, closed this gate and commanded us about it. And all of "the precepts of the Lord are just, rejoicing the heart" (Psalms 19:9). And also included in this negative commandment is one about whom two witnesses have testified that he committed a [different] sin; for example, that one testifies that he did work on Shabbat and one testifies that he worshiped idolatry, such that this one is not condemned by their testimony, as it is stated, "and an innocent one and a righteous one do not kill." And so did they, may their memory be blessed, say (Mekhilta d'Rabbi Yishmael 23:7:2), "If one testified against another that he worshiped the sun, and another, [that he worshiped] the moon, I might understand that they combine (to constitute the necessary two witnesses). [Hence,] we learn to say, 'and an innocent one and righteous one you shall not kill.'"