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Union University Department of Physics

The Science Guys



Science Guys > August 2002

August 2002

I have heard a light bulb has glass around it to keep air away from the filament. Can a light bulb burn in space where there is no air without glass around it?

We may have all heard of interesting things happening in space where there is a weightless environment (not gravity free) or where there is no air. For example, what is the shape of a candle flame burning in a chamber of air on a spacecraft? It is not tapered as it is here on Earth. Thus phenomena that we experience here on Earth act differently under the weightless conditions found in "space."

The typical incandescent light bulb contains a thin wire (usually tungsten) called a filament that has a high electrical resistance. This filament gets very hot when an electric current passes through it. The intense temperature makes the filament glow brightly. If oxygen were present the glowing hot filament would burn up. For combustion as we know it, oxygen must be present. In order to keep oxygen away from a light bulb’s filament on Earth, some bulbs have most of the air removed, others are simply filled with an inert gas (one that does not burn or aid combustion). Thus on Earth the glass globe around the filament is necessary to keep the filament isolated from the oxygen in the air. (It also protects us from the exposed wires and hot filament.)

Since there is no air (oxygen) in outer space, a filament without a glass covering would simply glow and not be consumed by traditional burning.

Actually, the filament gets so hot it literally boils off atoms and electrons. Sometimes this material collects as a dark spot at the top of the bulb. Eventually the filament deteriorates, becomes weak, and breaks, thus ending the life of the light bulb. In some cases the presence of a gas can actually inhibit the filament’s deterioration to a certain degree. With a gas present the filament’s atoms cannot boil off as readily, so the filament’s life is prolonged. In some bulbs the filament can even burn hotter and thus give off more light if a particular type of gas is present in the bulb. Today, halogen gases are often used in bulbs to improve the quality of light bulbs. These bulbs are currently promoted as giving longer life and more light.

In summary, bulbs on Earth have most of the air removed or are simply filled with an inert gas (one that does not burn or aid combustion) in order to keep oxygen away from a light bulb’s filament. Thus the globe is necessary to keep the filament isolated from the oxygen in the Earth’s atmosphere. In space a bulb could burn for a considerable time without a globe but the emptiness of space could hasten the evaporation of the filament and eventually the filament would break just as it does on Earth.