A Pair of Glasses, a Spoon, and a Bottle of Beer Walk Into a Halachic Debate

Rav Moshe Feinstein, zt”l, addressed two potential Shabbos prohibitions regarding photochromic lenses: Tikkun Maneh (completing or perfecting an item) and Tzovaya (dyeing).

The prohibition of Tikkun Maneh forbids completing or perfecting an object for its intended use on Shabbos. One might argue that since photochromic lenses are not functional as sunglasses until they darken, wearing them outdoors effectively completes their function. However, Rav Moshe Feinstein cast shade on this reasoning. Since these lenses are specifically designed to transition between shaded and clear states, their darkening does not constitute a new function but a built-in design feature.

A helpful analogy is that of a door: No one would claim that closing a front door completes the construction of a house, as doors are meant to be opened and closed. Similarly, objects designed for multiple states – such as folding tables, playpens, and strollers – may be opened and closed on Shabbos without concern for Tikkun Maneh.

The Torah prohibition of Tzovaya applies to permanent dyeing, but Chazal extended this prohibition to include temporary coloring as well. As a result, applying cosmetics on Shabbos is forbidden since it temporarily tints the skin. One might argue that photochromic lenses, which darken when exposed to sunlight, undergo a temporary color change and should therefore be prohibited under Tzovaya Mi’deRabbanan.

Rav Shlomo Zalman Auerbach, zt”l, however, shed some light on this issue. He ruled that this is not a concern. He explained that simply walking outside cannot be considered a prohibited action on Shabbos. The person is not actively causing the color change; rather, the sun naturally darkens the lenses.

The Orchos Shabbos questions this reasoning, drawing a comparison to the case in Sanhedrin (77a). There, the Gemara states that if someone ties another person outdoors in the sun and the victim subsequently dies from sun exposure, the one who restrained him is liable for murder. Although the victim was already outside, the murderer is held responsible because he ensured that the person remained in a deadly situation. Similarly, in the case of photochromic lenses, while the wearer may not initiate the color change, he is responsible for the glasses being outdoors, allowing the sun to alter their shade. Thus, one could argue that the wearer bears responsibility for the transformation caused by the sunlight.

Rav Moshe Feinstein, zt”l, offered an additional rationale for permitting photochromic lenses on Shabbos. He maintained that the shading effect of these lenses is extremely temporary and fleeting. Because of this, it does not even meet the criteria to be considered Tzovaya Mi’deRabbanan.

Thus, there are (at least) two distinct reasons to permit photochromic lenses on Shabbos: The wearer does not perform any direct action to color them; the change in color is considered too transient to be classified as Tzovaya; the distinction between these two reasons affects the permissibility of other items.

Shemiras Shabbos Kehilchasa (40:2) discusses plastic thermometer strips placed on the forehead. If the numbers are always visible but change color upon heating, the strip may be used on Shabbos. However, in footnote 8, Rav Shlomo Zalman Auerbach, zt”l, warmed up to this leniency only for a miktzas choleh (someone who is slightly ill).

Despite this, Rav Shlomo Zalman permits the use of photochromic lenses on Shabbos (ibid 18:18) for everyone. The distinction he makes is that wearing these glasses outdoors does not involve any direct action by the wearer; the darkening occurs passively due to exposure to sunlight. In contrast, placing a thermometer strip on the forehead is an intentional action that initiates color change, which is why it is only permitted for a choleh.

A similar discussion arises regarding children’s bowls and spoons that change color upon contact with hot or cold food. When dipping such a spoon into a bowl of cold milk, one actively causes a color change. If this is analogous to the thermometer strip, it could be considered Tzovaya and thus prohibited. However, Rav Moshe Feinstein maintains that such temporary color change is not considered Tzovaya at all.

Rabbi Shmuel Fuerst, a rav and Dayan of Agudas Yisrael in Chicago and a talmid of Rav Moshe, ruled that using these color-changing utensils on Shabbos is permitted. Similarly, Rav Dovid Feinstein, zt”l, permitted using a black mug on Shabbos that changes color when hot liquid is poured inside. This suggests that the temporary nature of the color change, similar to photochromic lenses, does not constitute Tzovaya.

Rav Avigdor Nebenzahl, who generally follows Rav Shlomo Zalman’s rulings, discussed a bottle of Coors beer that changes color when it becomes cold. He ruled that one should not put the bottle in the fridge with the intention of changing its color, as this would constitute an action promoting color change. However, if one simply places the bottle in the fridge and the color change is just a cool bonus, it is permitted. It would seem that Rav Moshe Feinstein would permit placing the Coors bottle in the fridge regardless of one’s intentions.

Regarding photochromic lenses, the vast majority of Poskim permit their use on Shabbos. Rav Yitzchak Berkowitz, shlit”a, has stated that the widespread custom is to be lenient. So if someone is glancing for a halachic ruling on photochromic lenses for Shabbos, the outlook seems pretty clear: most poskim see no reason to darken the experience.