May one activate a glow stick on Shabbos? (In other words, is there a prohibition on activating the chemical reaction which produces the light in a glow stick?)
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Aside from the chemical reaction (about which I don't know whether that would be permissible on Shabbos), there is also the fact that in activating it you're breaking the inner glass tube. At the very least, if we consider this מקלקל (a destructive act), then I would think it would be prohibited Rabbinically.
It's discussed by Rabbi Mordechai Torczyner, along with the chemical reaction causing self-heating meals, in this mp3. (Also see his source sheet.) It's been discussed in some Hebrew-language halacha journals recently.
It appears to be at most rabbinically prohibited, at least at first glance.
I hope that this is more helpful.
I am a rabbi in Birmingham. When we have tornadoes which knock out power we recommend people use light sticks. There is no heat generated, the light is a simple chemical reaction. breaking the inner glass is not mekalkel as what you are doing is not destructive it is in fact constructive. Think of cutting a cucumber for salad...yeah you are breaking something but it is for a constructive purpose so it is not mekalkel.
Not every cutting act or breaking act is forbidden. It must fit into a category of melakha. The three categories of cutting are Gozez and Kore'a and mekhatech.
Gozez requires that the cutting be done inorder to improve the item that it is being cut off from the av melakha only applies in animals and people but the toladot apply globally (bekhorot 24b, tosafot bekhorot 25a, Eglei Tal Melekhet Gozez). This is shearing a sheep or getting a hair cut.
Koreya: requires that the tearing be done inorder to sew back. This means that if you have two pieces of cloth that are coming apart you may not separate them so that you can resew them. This melakha only applies to soft bendable materials (cloth etc.) and not to things like metal or wood or glass (minhat chinuch shabbat 24 and elsewhere I cant remember or find at the moment) and though not the main stream view may pasken that it only applies to woven materials.
Mekhatekh, this only applies when cutting something to a specific size or shape (rambam 11, chayei adam)
The category of breaking is only applicable if you in the process do a melakha. Or if it is destroying inorder to build however, if there is no constructive nature to the act there is no issur (maybe baal tashchit though it wouldnt apply in this case) The gemara posits that even if a man is breaking something inorder to show his anger in his household that may not be completely non-constructive.
All this being said, I dont let my children play with the light sticks on shabbat and we don't take them out unless there is a power outage. I dont think that it would be assur for them to do so but I dont think that it is shabbostik (it is not in the spirit of shabbat). In the case that you really need them for light it is certainly better than any alternative such as a flashlight. So in summary I think that it is permitted but I think that it lessens the shabbat experience (except for when it doesn't)