One is permitted to read Tehillim on Shabbat Kodesh by the light of a candle, and especially if one reads by the light of an electric bulb, for there is no concern whatsoever.
Sources and Explanations
Chazal decreed that on Shabbat one may not use the light of a candle for anything that requires much close attention, such as checking one’s clothes for lice or reading a book, even if one does not utter aloud what he is reading. This is a decree lest he forget and tilt the lamp to bring the oil closer to the wick so that it will burn well (Ben Ish Chai, Parashat Noach, Year 2, ot 18). However, regarding things that are fluent on a person’s tongue, one should not forbid, as the Ben Ish Chai writes (ibid., ot 20): “Reading with which a person is very familiar, such as mizmorim of Tehillim for a person who is accustomed to them, and all the more so the mizmorim of Shabbat, and likewise the reading that is recited before Kiddush to which he has become accustomed every Friday night, and likewise the first four chapters of Mishnah Shabbat which he is accustomed to recite at the table every Friday night, and in all of these he does not need to look in the book except for the beginnings of the sections, it is permitted to read alone by the light of the candle, since he does not need to study them so closely by the light of the candle that it must be bright, such that he would tilt it; even a dim light suffices for him.”
Today, when we read by electric light, most of the poskim have written that since there is no concern here of “lest he tilt,” one may be lenient freely. See Yabia Omer (vol. 1, siman 16), who cites many poskim who were lenient in this.
From the sefer “Shaf Veyativ – Laws of Saying Tehillim” by Rabbi Shay Tahan, Chapter 7: What Is Forbidden and Permitted When Saying Tehillim, Halacha 19 (p. 131 in the print edition). Translated from the Hebrew original.
