Luminescence is emission of light not caused by a rise in temperature (the object emitting
light stays cold). The light is released by atoms returning from
"excited" (charged) state to normal "ground"
state. It means, an object which glows, first must absorb energy to
get into "excited state." That energy will be released (in form
of light) by the object returning to the ground state of energy.

The energy can be supplied in many ways, but in our particular case of glow sticks the
energy is supplied by a chemical reaction (what makes the "chemi"
in chemiluminescence). Typical glow sticks as chemical reactants use a
hydrogen peroxide solution (which is called the "activator"), a
solution of phenyl oxalate ester and a fluorescent dye (which makes the
color). The activator is stored in a thin glass capsule. When the glass
capsule is broken by flexing a glow stick the activator is released, and
mixing the components (shaking the glow stick) initiates the reaction.
Depending on components used, the chemical reaction can last (glow sticks
can glow) from a few minutes to many hours. When using glow sticks
as party supplies, wait until that last moment to shake them. Heating the glow sticks
(providing extra energy) will speed up the reaction, what will result in
brighter light but will shorten the glow time. The reaction will slow down
in low temperatures the light will dim, but the glow time will be longer.