Incandescent over light bulb demise

Roger Jewsbury, Head of Department of Chemical and Biological Sciences, University of Huddersfield

Taking them off the shelves isn’t such a bright move

Of all the imposed changes in recent years, few have rankled as much as the phasing out of the incandescent light bulb — identified as the third greatest invention of all time in a recent poll.

At the time of the announcement newspapers lamented its passing, families gave up their Saturday afternoons to empty supermarket shelves of this so-called redundant technology and many sighed in collective disbelief at the bureaucrats in Brussels.

This disappearance, however, of the traditional incandescent light bulb on the grounds of energy inefficiency may be misguided in the UK, where the surplus heat that is generated is not wasted.

The incandescent or filament light bulb is simplicity itself, with the bulb consisting of a thin wire or filament that glows when an electric current passes through it.

First demonstrated publicly by the British scientist, Sir Humphrey Davy, over 200 years ago, it became commonplace during the last century as a result of the commercialisation by Briton Joseph Swan and the American Thomas Edison and the availability of mains electricity.

The principle is simple. A current passes through the filament, which heats up and emits light.

There are some technical details of course. Many metals will melt before emitting light. Humphrey Davy used platinum, but this was (and remains) expensive. Edison used the cheaper tungsten, which has the highest melting point of all metal elements at over 3,000C.

To avoid the tungsten reacting with oxygen it was necessary to keep it out of contact with air and today the filament is in a glass envelope containing the un-reactive gas argon. The life of the bulb is then limited by the eventual evaporation of atoms of tungsten or the failure of the glass seal with the base of the bulb.

About 90 per cent of the energy is converted into heat rather than light and in today’s more energy conscious world, this is considered inefficient.

Indeed in many parts of the world it is, but not here in the North of England. The reason is simple, most of us heat our houses for a major part of the year.

When we don’t, it is during the summer months when with extended daylight hours we don’t need to use artificial lighting.

So when the light is on the energy is not lost, it is usefully used to help heat the room. In other countries the situation is different. In tropical SE Asia, where heating is never required, the old style fluorescent tube lighting has been used for decades, long before there was any talk about energy saving bulbs, which are based on the same principle.

In the fluorescent lamp, the electricity excites mercury atoms which emit ultra-violet light which itself causes chemicals on the inside of the glass, known as phosphors, to emit visible light.

The lamp is more complex since it also needs some electronics to control the current.

This is usually separate and known as the starter in fluorescent tubes but is built in to the compact “energy saving” bulbs.

These are more expensive to make but under ideal conditions this is compensated for by a longer life. Heat is still generated by the electronics but the compact fluorescent bulbs are three to four times more efficient in light emission than the filament bulbs.

There are some risks with these fluorescent bulbs, as there are with most technology.

Mercury is poisonous so the tubes should be disposed of via a recycling centre and not broken deliberately particularly indoors.

Of greater concern to the public is that they are not identical replacements for the filament bulbs.

They have a warm-up time and do not reach full brightness for up to five minutes. The brightness also deteriorates over the life of the bulb and depending upon the chemical nature of the phosphor, they may not emit light of the same colour as the traditional bulbs. For some people, the flicker that is characteristic of fluorescent bulbs can be unpleasant. Finally although they are sold as having a longer life, it does depend upon how they are used.

They are more affected by being switched on and off than the older bulbs and this can markedly shorten their life.

In the end probably you will have to switch, but by that time reliable and inexpensive LED bulbs may be available.