Why does a light BURN out?

Answer 1

Because the tungsten filament is evaporating. As the filament becomes thinner, resistance and temperature become higher, evaporation speeds up. Eventually the filament becomes so thin that it melts.

A 100 watt incandescent light bulb radiates 98 watts of heat and 2 watts of light. In summer, it takes 50 watts of air conditioning to get rid of the 98 watts of heat. A 20 watt compact fluorescent produces the same 2 watts of light while consuming 85% less electricity, and absence of heat makes it last ten times longer.

Answer 2

The voltage is too high.

The filament has a finite resistance. As the voltage is increased, then so is the current drawn, as per Ohms law. When the current gets too high the filament will burn up.

If you mean, 'in normal use', with no changes in voltage?

Just before a bulb fails, it sometimes burns really bright just before going out.

What happens here, is that the filament breaks. One end of the broken filament hangs down and touches the support wires supplying the power.

This shorter length of filament is then powered up, but because it is now shorter than the full filament, the resistance is lower and a larger current flows through, burning it up.

Answer 3

An incandescent light bulb contains a glass casing which holds a near-vacuum atmosphere [although some bulbs do contain some inert "backfill gases] and a tiny, fragile filament stretched between a hot lead and a neutral lead. When electricity flows through the light bulb, the filament, due to its resistance heats to a very high temperature resulting in a glowing (incandescence)]. Thus it "burns." Because the atmosphere of the bulb is sucked out, the lack of oxygen keeps the filament from incinerating [actual combustion]. The fragile nature which allows the filament to glow so brightly also makes it susceptible to the slightest imperfection, or even vibration.

Physics being what it is, "slightest imperfections" abound in nature. Dust collecting on one side of the bulb may cause warping and breaking of the filament. Heating and cooling as the filament is turned on and off causes wear and tear. Vibration is another hazard. So: dust your light bulbs, avoid touching them with bare hands, Try to keep table lamps from high traffic areas.

There are other causes too. For instance, DC bulbs might not last as long due to the nature of chemistry. Electricity is the flow of electrons, and when using direct current, the electrons flow in only one direction. That causes migration of minerals with time, causing one side of the filament to weaken.

Power surges are another cause of blown bulbs. If the power jumps up to 150 volts or more coming into your house, the bulb might burn out, even if it happens for a split second, and especially if you just turned it on and a spike occurred. For DC bulbs, using the wrong battery and bulb combination can cause this, or otherwise using a voltage higher than what is recommended.

Answer 4

Bad ballast can cause this, if you are using T12 tubes , upgrade the ballast to a newer T8 ballast and use T8 tubes.

Answer 5

Higher that normal voltage will tend to shorten the life of fluorescent tubes.

Answer 6

Excessive build up of heat