Inside many electric light bulbs is a wire called a filament, made of tungsten. When current is passed through the wire, it glows white hot, giving off light and some heat. As the oxygen has been removed from the bulb, combustion cannot take place, so the wire does not bum out immediately.
Electricity flows through a thin tungsten wire in the light bulb called the filament. The filament used in a bulb has a property called “resistance.” Resistance is the amount of friction that an object will put against electricity flowing through it. A filament has a lot of resistance to electricity. As a result of this resistance, the filament heat up and start glowing, converting electrical energy to light energy. This is because of the Joule-effect, which means that resistances heat up when an electrical current runs through them. This produces light and heat illuminating its surroundings.
The brightness of the filament can be varied by changing the amount of current flowing through it (the amperage), or the voltage between ends, as the amperage is related to the voltage by Ohm’s law. Also, as the filament ages, its brightness will diminish somewhat and its light will get redder and redder. Eventually, all filaments will slowly vaporize and fail due to the high temperature caused by the electricity flowing through it.
By design, a light bulb has no oxygen in it. The manufacturer fills it with an inert gas like argon or nitrogen. However, this does not prevent atoms from popping off the surface of the filament due to the intense heat. This makes the filament thinner and thinner. Eventually, it becomes so thin that it breaks. For a short period of time, the two broken ends are very close to each other, and electricity can jump across in a bright blue spark. However, the two broken ends soon fall away from each other, breaking the spark, and the bulb will light no more.
Light bulbs themselves, if used properly, are not dangerous. Although their primary function is to produce light energy, as a side effect they also produce heat.
Light bulbs are sold according to the number of watts they use – the higher the number, the brighter the bulb is, and the more energy it uses. Despite getting hot, light bulbs don’t explode. However, the outer glass of a light bulb which has been on for some time is quite hot, and can cause minor burns, or the broken edges might cut the skin.