Glow sticks have four components: an outer tube made of a semi-pliable plastic, the fluid contained by the outer tube, an inner glass ampule and the fluid it contains. Activation requires bending the outer tube enough to break glass ampule. Shaking the glow stick to mix the chemicals creates a chemical reaction that produces the glow. But the glow doesn't last forever, only about four hours once activated. You can keep the glow for a while longer and reactivate it --- for an extra 30 minutes --- once it's gone flat.
Keep glow sticks in cool dry places and in their original packaging to ensure they will glow to their maximum potential. Activate glow sticks any time, but note that usage in warm temperatures cause them to glow brighter and for shorter periods of time. Use glow sticks in cool temperatures to increase the lifespan of the chemical reaction. Observe that the glow stick glows more dimly but for longer periods.
Extend an activated glow stick's life by placing it in the freezer. Notice that the glow stick grows dimmer then seems to stop glowing once the chemical reaction slows down. Be aware that the chemical reaction doesn't stop, it only slows down. Remove the glow stick from the freezer the next day and observe the chemical reaction return to normal levels and the glow return. Take note that the total glow time will still be up to four hours, when the chemical reaction comes to an end.
Fill a pan half way with water and heat the water to boiling. Use a pair of tongs to place the "dead" glow stick into the boiling water and allow it to boil for 30 seconds. Use the tongs to remove the newly reactivated glow stick from the water. Be aware that the reactivation only lasts for about another 30 minutes and may be dimmer than the original glow.