Andrew Michael Ciaria, age 11, of Enid, Oklahoma, for his question:

How is heat produced in a light bulb?

Light bulbs are made to shed light, which they do. But they also create enough heat to make a lighted bulb too hot to handle. This is a nuisance and also very wasteful. Both light and heat are forms of energy. The heat from a bulb is wasted energy and we would like to convert it all into light. Fireflies can create light without heat, but so far our scientists have been unable to figure out how those pretty little beetles manage to do it.

A light bulb, naturally, uses electricity    and the current is created by moving electrons. These negative particles of matter are infinitesimally small and they move incredibly fast. They also pace together in astronomical numbers. The light from a glowing bulb is actually a traffic jam that occurs when armies of jogging electrons must squeeze through a narrow bottleneck. Their countless collisions create enough heat to make the metal filament glow.

An electric wire is a double strand of copper. It conducts the current from the generator. Along the way there are numerous outlets where we can plug in and use the electric current. In AC, or alternating current, this is the energy of electrons jogging back and forth in step, at so many times per second. They create energy throughout the circuit, but in the wires they have enough room to move without many collisions. This smooth traffic arrangement changes when we plug in a light bulb.

Then the electron traffic must detour through the thin wire system inside the glass bulb. It enters and departs through a pair of rather sturdy metal rods. But their tops are connected by a very thin wire filament. The electron traffic has to squeeze through this bottleneck. This .results in countless collisions, which release enough energy to heat up the thin filament. When we turn on the switch, in less than a second the detoured electron traffic in the bottleneck makes the filament hot enough to glow.

Hence, the bulb does not create heat as a byproduct. The light it sheds is actually a byproduct of the heat in the filament. The numbers and speeds of the electrons involved are fantastic. For example, suppose you switch on a reading lamp. You enlist armies of electrons, jogging back and forth at perhaps 60 times per second. Aboutbillion billion of them jog through the wiring and crowd through the narrow filament in the bulb. There they jostle each other and release the heat that causes the glow that lights the lamp.

This is a crude way to light electric bulbs because so much energy is wasted in unwanted heat. But at present, we do not know how to separate this energy of heat and light. Researchers are striving to find a more economical way to produce light without heat. Meantime, the fireflies refuse to share their secret recipe for making cold light.