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Last summer a small company called Intersource Technologies in Sunnyvale,
California, announced it had invented a domestic electric light bulb that
used neither filament nor electrode. The new bulb, its maker claimed, would
survive 14 years of normal use and consume only a quarter of the electricity
a conventional bulb uses.

Sounds absurd? Front-page newspaper reports talked of a global industry
being transformed overnight by this invention – a version of the induction
light bulb. The bulb, which its manufacturer calls the E-Lamp, turns electricity
into light using radio waves to induce a charge in gases enclosed by a glass
bulb. By separating the electrical components and the parts that actually
produce light, the induction lamp avoids the main physical and chemical
reactions which cause conventional filament and discharge bulbs to deteriorate
and fail. ‘It changes the technological base of the industry,’ says Martin
Scott, programme manager at General Electric, the US-based multinational
behind some of the household names in the business, such as Mazda, Thorn
and Tungsram.

The idea of induction lighting is an old one, but until now it has proved
impossible to turn it into commercial reality at a reasonable cost. The
problem is that a radio transmitter powerful enough to induce light in a
glass bulb will spread its signals far and wide, interfering with televisions,
communications and devices such as heart pacemakers. Containing these emissions
requires expensive electronics or a physical cage. The Dutch electronics
giant Philips, which launched an induction lighting system in 1991, charges
about £400 per device. The company makes its QL induction light for
use at sites such as road tunnels, where the cost of replacing bulbs is
enormous.

Intersource Technologies says it has solved the problem of interference
without expensive extra circuitry (the company won’t say how it’s done),
at a price of between £6 and £12 per bulb.

TURN ON TO TRADE-OFFS

Although researchers in the lighting industry are interested – and have
stepped up their own efforts to develop induction technology – insiders
are confident that conventional bulbs will not become obsolete overnight.
The image of an industry that profits by selling bulbs as short-lived as
possible is false: in fact lighting technology involves a constant trade-off
between efficiency, longevity, aesthetics and, crucially, price.

For most domestic consumers, purchase price and aesthetics (both shape
and light quality) come first, with efficiency far behind. Hence the survival
of the tungsten filament bulb, known in trade jargon as GLS, for general
lighting system. For municipal street lamps, on the other hand, efficiency
is the priority, with aesthetics a poor fourth. Low-pressure sodium lamps
with their yellow glow have fitted that bill.

The familiar tungsten GLS is still the industry’s mainstay. The basic
design has changed little from that patented by Thomas Alva Edison more
than 100 years ago. An electric current flows through a thin filament in
an inert gas, heating it until it becomes incandescent (at about 2500 degreeC
in a household bulb).

Tungsten bulbs are cheap to make – producing a 100-watt bulb costs a
few pence – but they have two flaws. They are inefficient, converting only
10 per cent of electrical energy into light; and have an expected lifetime
of only about 1000 hours.

A bulb’s life can be extended – by running it at lower than the rated
voltage and never switching it off. The record for longevity is probably
held by one in a fire station in Livermore, California, which has burnt
with only brief interruptions since 1901.

Another way to make bulbs last longer is to fit an electronic switch
which builds up power to the filament gradually, rather than in a surge
which creates rapid heating, thereby creating microscopic defects in the
metal’s crystalline structure. Such devices are on sale, but the £4
price tag puts most people off.

‘Anyone can make a 20 000-hour GLS,’ says Tony Everett of GE Lighting
(part of General Electric) in Enfield, north London. ‘but there’s a trade-off
– the longer the life, the less light.’

This does not mean that the technology of filament lighting has stood
still since Edison’s day. The 1960s saw a major step forward in efficiency
and longevity with the tungsten halogen lamp. The hotter an incandescent
lamp’s filament, the more efficient it becomes. In conventional light bulbs,
however, heat causes particles of tungsten to evaporate from the filament
and form an opaque black coating on the inside of the bulb. This reduces
the amount of light produced, and the thinner filament becomes more and
more prone to failure.

In the late 1950s, researchers discovered that a small quantity of halogen
added to the gas filling the bulb reacts with gaseous tungsten from the
filament to form a metal halide, which then settles on the cooler parts
of the filament. The discovery of the ‘halogen cycle’ meant engineers could
make a filament last longer, or run it at a higher temperature to produce
more light – or both. Today’s tungsten halogen lamps have double the efficiency
and several times the life of conventional incandescent lamps, but with
price tags of pounds rather than pence.

Increasing the gas pressure also slows down the evaporation of the tungsten,
making the lamp both more efficient and longer-lasting. But tungsten lamps
are cost-effective only for jobs where compactness is important, such as
car headlights.

But the technology that the industry has pushed hardest is that of discharge
lamps. These create light by exciting a gas or vapour with an electrical
charge. Discharge lamps are vastly more efficient than incandescent bulbs,
producing up to 200 lumens per watt instead of the 12 lumens of a GLS bulb.
They also last much longer. But discharge lamps have several disadvantages.
The most efficient types have a narrow colour spectrum (in the case of sodium,
yellow). They also take time to reach their full intensity. They need control
circuits to maintain the arc, and are hard to make in ratings below about
150 watts.

The lighting industry has invested huge amounts of money in overcoming
these disadvantages. Increasing the gas pressure in sodium lights spreads
the frequency across more of the visible spectrum, producing a ‘friendlier’
glow. Alternatively, the ultraviolet light emitted by a discharge through
mercury can excite a fluorescent coating on the inside of a tube to produce
red light which balances the mercury’s blue and green. This is the basis
of the familiar fluorescent lamp, which produces up to 90 lumens per watt.
The discharge arc operates in a clear glass tube containing mercury vapour
in a mixture of argon and krypton, and coated on the inside with phosphor
powder. The electrical discharge produces some blue and green radiation,
but mostly invisible ultraviolet. The phosphor coating converts the energy
in the ultraviolet into a mixture of visible wavelengths, which appear white.
The colour depends on the phosphors used, but it is still less like daylight
than that of an incandescent bulb. Standard fluorescent lamps score about
54 on the industry’s Ra scale, where natural daylight is 100. The value
indicates how well the spectrum resembles sunlight.

The peak of discharge lamp technology is probably the high intensity
discharge (HID) bulb, which combines high efficiency with natural colour.
A 150-watt bulb known as the Arcstream, which is assembled in a clean room
at GE’s Leicester plant, is six times as efficient as an ordinary filament
bulb. The snag is that at 150 watts, producing 12 000 lumens, it is too
bright for domestic use. That and its price, about £50 per bulb, confine
it to uses such as shop windows.

WHAT WILL REPLACE THE OLD BULB?

The high cost reflects the difficulty of making HID bulbs. ‘It’s the
hardest lamp there is to make in the world,’ says Gary Caunt, production
manager at GE in Leicester, because the tiny components and precise quantities
of dosing chemicals have to be assembled under computer control, in perhaps
the most advanced manufacturing process in the lighting industry.

But powerful and attractive as the HID is, it will not replace the 100-watt
bulb in the hallway. This is the role the lighting industry has chosen
for another technology, the compact fluorescent lamp, which it has spent
tens of millions of pounds developing and promoting. Their attraction is
that they consume one-fifth the electricity of ordinary tungsten lamps yet
last eight times longer. The breakthrough was the development of new phosphors
which had colour ratings of Ra 84.

Calogero Di Gesu, GE’s product manager for compact fluorescent lamps,
says the economic advantages are obvious. ‘The total cost (over its life)
of a compact fluorescent and its electricity will be £25.84. That
compares with £63.20 for eight incandescent lamps and their electricity.
In places where the lamp is left on for a long time – more than 12 hours
a day – you get a payback in less than two years.’

The snag, Di Gesu admits, is that most consumers do not think this way;
they are happier to pay out an endless stream of 50 pences for new bulbs
rather than invest up to £15 in one go. Only some 2 million compact
fluorescents are bought in Britain each year, of which industry accounts
for some 70 per cent. It is this niche that the induction lamp will attack.

The coming battle between the two technologies is likely to hinge on
claims of ‘greenness’ as well as cost and efficiency. Manufacturers have
already found this to be a more complex issue than energy consumption. Each
compact fluorescent, for example, contains about 12 milligrams of toxic
mercury, while a thorough environmental audit of induction lighting should
also include the impact of manufacturing its complex circuitry. It might
even turn out that the throwaway and apparently wasteful tungsten bulb is
the greenest lamp of them all.

Michael Cross is a freelance journalist.