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Light sticks are really cool — literally. When a light stick is ‘cracked’, it emits light with no perceptible heating effect. If you hold an uncracked’ light stick near a black light (ultraviolet light source) it will fluoresce. That is because one of the ingredients inside the light stick is a fluorescent dye. When the two main ingredients of the light stick are mixed, a reaction produces energy that activates the fluorescent dye.

Inside the light stick there is a breakable glass vial containing the ‘activator’, which is hydrogen peroxide, H2O2. In the main chamber, there is a mixture of the fluorescent dye solution and phenyl oxalate ester. When the activator and the phenyl oxalate ester mix a series of reactions occur that release energy to the fluorescent dye. This energy is ultimately released as light, in the colour of the particular fluorescent dye being used.

You can control how bright the light stick is by varying its temperature. Place the light stick in a cold fridge, and it will give off very little light. Place it in a cup of hot water and it will glow more brightly. Of course, the brighter it glows the shorter its useful life will be.

Question: What form of energy does the unused ‘light stick’ have? Into what form of energy is it converted when you ‘crack’ the light stick?

These light sticks have not been ‘cracked’. They are illuminated by an ultraviolet lamp of the type available at novelty stores.