Everything is "glowing" all the time simply by virtue of its temperature. It's just that to see this thermal glow with our eyes the object has to be very, very hot. Daylight comes from the white-hot light source that is the surface of our sun heated to 5,800 K by its nuclear fusion furnace. (K stands for degrees Kelvin and means degrees centigrade above absolute zero.) By reflection, this is also the source of moonlight and the light of the planets. The filament of the ordinary household light bulb at about 2,000 K may appear a bit yellowier. Its glass envelope is definitely very hot to the touch. Red coals of a fire are cooler but still hot enough to see.

However, the thermal glow from things that are at ordinary temperatures (or cooler) - like 300 K or less - is invisible to us. It can be seen only by sensitive instruments. That's why we have the dark of night. The remarkable primordial thermal glow from the birth of our universe (the "big bang") about 13 billion years ago is another example. It represents a perfect thermal light source at only 2.728 K And you can learn more about it at the NASA web site.

Now we know that a glowing glow stick can be worn on one's head. One can touch a lit Neon tube. A fluorescence light tube that is turned on is not very hot. The firefly is not hot (if it were it couldn't live!). Less obviously, the aurora borealis (northern lights) and the aurora australis (southern lights), lightning, or the spark from a spark plug are not hot. Yet all of these produce light that is visible to us. Evidently such visible light cannot be derived from thermal energy. These all must be "cold" light sources. They produce special colors that depend on the make-up of the material and how it is excited - not the temperature.

The Neon atoms in a Neon tube, the Mercury atoms in a fluorescence tube, the atoms and molecules in our atmosphere are energized by collisions with fast moving charged particles. These are energized by our electrical supply, the electrical discharge of clouds, or charged particles shot out from the sun and focused towards the earth's magnetic poles. The excited Neon atoms produce their characteristic orange/red glow. Bluish light from energized mercury atoms is absorbed by a phosphor coating on the inner surface of the tube to make cold, but white light.

By contrast the blue/green flash of the firefly and the many colors of the glow stick come from special chemical reactions. Such cold light is therefore called chemiluminescence. To see how a glow stick is actually built and how it works check out The London Glowstick Company.