We saw that light sticks use energy from a chemical reaction to emit light. This chemical reaction is set off by mixing multiple chemical compounds.
Compounds are substances made up of atoms of different elements, bonded together in rigid structure. When you combine two or more compounds, the various atoms may rearrange themselves to form new compounds. Depending on the nature of the compounds, this reaction will cause either a release of energy or an absorption of energy.
The reaction between the different compounds in a light stick causes a substantial release of energy. Just as in an incandescent light bulb, atoms in the materials are excited, causing electrons to rise to a higher energy level and then return to their normal levels. When the electrons return to their normal levels, they release energy as light. This process is called chemiluminesence.
The chemical reaction in a light stick usually involves several different steps. A typical commercial light stick holds a hydrogen peroxide solution and a solution containing a phenyl oxalate ester and a fluorescent dye. Here's the sequence of events when the two solutions are combined:
- The hydrogen peroxide oxidizes the phenyl oxalate ester, resulting in a chemical called phenol and an unstable peroxyacid ester.
- The unstable peroxyacid ester decomposes, resulting in additional phenol and a cyclic peroxy compound.
- The cyclic peroxy compound decomposes to carbon dioxide.
- This decomposition releases energy to the dye.
- The electrons in the dye atoms jump to a higher level, then fall back down, releasing energy in the form of light.
The light stick itself is just a housing for the two solutions involved in the reaction -- essentially, it is portable chemistry experiment. Next we'll see how bending the light stick sets this experiment in motion.