Question: Transition lenses are glasses which change color based on the sun’s ultraviolet rays, such that when one walks outside, they lenses become darker and when one goes back indoors, they turn lighter and back into regular lenses. Does wearing them on Shabbat pose a concern of the prohibition of dyeing/coloring on Shabbat because of the lenses’ color change when they come in contact with ultraviolet rays?
Answer: Let us first point out that lenses changing color as a result of the sun’s rays certainly poses no concern of the Torah prohibition of coloring, for the Rambam (Chapter 9 of Hilchot Shabbat) writes that “one is only liable for dyeing on Shabbat when the color is permanent.” This means that the color must last for a long time; however, coloring which fades or is erased quickly is not prohibited by Torah law.
We must, nevertheless, determine whether or not this poses a concern of transgressing a rabbinic prohibition, for the Rambam (Chapter 22 of Hilchot Shabbat) writes that a woman may not apply makeup to her face on Shabbat since this constitutes a rabbinic prohibition of dyeing on Shabbat. We must therefore discuss whether or not the lenses changing color poses a concern of a rabbinic prohibition of coloring on Shabbat as well,
Maran Rabbeinu Ovadia Yosef zt”l writes that it seems to him that there is no concern of coloring here, for all of the forbidden works on Shabbat are derived from the works performed in the Mishkan (Tabernacle) meaning that any work which was performed in the Mishkan is likewise forbidden to be performed on Shabbat (see Shabbat 49b). In the Mishkan, the process of dyeing was carried out by placing a tangible substance onto textiles, such as coloring woolen strands with blue or purple wool. However, lenses made from a material which is sensitive to ultraviolet rays and therefore change color on their own are in no way comparable to the work performed in the Mishkan and there is therefore neither a Torah nor a rabbinic prohibition to wear such glasses on Shabbat.
After discussing this matter lengthily and proceeding to support his opinion with various sources, Maran Rabbeinu zt”l rules that there is concern of coloring or erasing on Shabbat whatsoever when one leaves one’s house on Shabbat wearing transition lenses (Responsa Yechave Da’at, Volume 2, Chapter 47).
On a similar note, Maran Rabbeinu zt”l rules regarding that which some customarily place apples around a green Etrog during the Sukkot holiday in order to turn it yellow quickly, that it is indeed permissible to do so on Shabbat and this does not constitute the forbidden work of coloring, for this is not the usual method of coloring; rather, the Etrog turns yellow on its own when surrounded by ripening apples since it ripens along with them (Chazon Ovadia-Sukkot, page 258 and Chazon Ovadia-Shabbat, Part 5, page 26).
Summary: One may walk outdoors wearing transition lenses which turn colors as a result of contact with ultraviolet rays on Shabbat and this does not pose any concern of coloring on Shabbat.
