Why do my light bulbs keep going and why do they trip out my fuse switch?

Back to Ask the Experts

Traditional bulbs, or ‘lamps’ as they’re called in the trade, have a tungsten filament and are filled with an inert gas such as Argon. The filament lights up when we turn on the power at our light switch but less than 10% of the energy we put in comes back out as light; the rest produces heat that sometimes reaches temperatures over 2000°C. The filament loses some tungsten during use and this causes thin spots to occur on it’s surface. Even with good quality lamps, this is usually within 1000 hours and often is much less with cheaper ones.

The voltage within your house could be slightly higher than normal, which can also affect lamp life, along with poor connections or using the wrong size wattage lamp in a light fitting. Examples of this would be using a 60W or 100W lamp in a fitting designed for 40W. The extra wattage results in overheating, shortening of the lamp life and potentially damaging the wiring.

Your fuse switch (also known as a ‘miniature circuit breaker’ or MCB) trips out when the lamp blows to protect your home. Sometimes the glass in tungsten lamps has been known to shatter completely. When the filament in a lamp blows it can cause an arc that draws hundreds of amps, seen as a blue colour when you hear the ping. The 6 amp MCB does its job by turning off when it detects this excess current.

The traditional tungsten lamps are being phased out of domestic use on a global scale, in favour of the newer compact fluorescent lamps (CFL / low energy bulbs). These can last up to 10 times longer than tungsten lamps and use about 75% less energy. Many stores now sell energy saving bulbs on special offers and are cheaper to buy than their tungsten predecessors. Another option would be to purchase LED (light emitting diode) lights. They are more expensive than the CFL bulbs but will last even longer and are even cheaper still to run.

Original questions from Simply Holbeach and answers provided by Kelvin Goulden

Back to Ask the Experts