Re: A Narrative History of the Light Bulb
- From: "James Hooker" <jdh@xxxxxxxxxxxxxx>
- Date: Sun, 01 Apr 2007 15:17:31 GMT
These energy saving lamps were made by US firm Duro-Test. It was developed
together with MIT and marketed briefly under the trade name of the "MIT
Wattsaver Lamp".
Basically this was the earliest work on Infra-Red Conserving (IRC)
incandescent lamps. Duro-Test was the pioneer in this concept, disclosing
its first prototype in a 1977 issue of Lighting Design & Application. Later
in 1979 they discussed a lamp concept which had demonstrated the possibility
for 30% energy savings.
It's a fascinating story of an excellent idea turning into a commercial
disaster, there were too many problems that were never fully solved. There
were 3 key areas that had to be developed for this lamp - firstly the
coating, secondly the spherical glass bulb, or rather a method of accurately
mounting the filament directly at the centre of the bulb, and thirdly the
filament metallurgy.
The coating is of a Fabry-Perot design consisting of three layers -
basically a sandwich of metallic silver between two dielectric films. It
was orignally developed by MIT for coating flat solar cell plates, but a
special sputtering technique had to be developed to achieve a uniform
coating on the internal surface of the bulb. It is an outstanding infrared
reflector and absorbs only a small amount of visible light, at the red end
of the spectrum (hence the greenish appearance of the bulbs). It's more
efficient than the coatings used on many of today's Halogen IRC lamps, but
has the drawback of deteriorating at high bulb wall temperatures - hence the
bulb of this lamp had to be increased in diameter to the G-30 size.
Furthermore it was found that for the IRC effect to work, the filament had
to be mounted precisely at the centre of the bulb. A deviation of only 1mm
in filament position was enough to lose half of the IRC effect. Standard
incandescent lamp production methods are unable to achieve such accuracy in
filament mounting. So Duro-Test adopted a 2-part bulb design, consisting a
pair of glass hemispheres. The lower hemisphere is essentially like the
pressed glass reflector of a PAR38 lamp. The filament assembly could be
very accurately mounted at the optical focus point of this hemisphere. Then
the second upper hemisphere of the bulb was fused to the first around the
rim at the maximum diameter, just like making a PAR lamp.
However the final problem which emerged was that of filament sag during
life. This was sufficiently severe that fairly early in life or during
ageing, the filament would move away from the optical axis. To counteract
this problem it was necessary to grow a very stable and coarse grain
structure in the filament. This has the unfortunate drawback of making the
filament rather brittle. Special filament mounting techniques also had to
be developed because it would simply fracture if clamped into the leadwire
as normal.
By 1983 Duro-Test had solved the problems to the best of its ability, and
put the lamp on the market, having invested some $3 million in their
production line. It demonstrated real energy savings of about 30%. But it
was difficult to manufacture and plagued with problems of fragile filaments.
Apparently the lamp was never suitable for distribution via normal channels
in supermarkets etc - the vibrations encountered during shipping would break
the filaments. This naturally closed off the bulk of the envisaged market.
Last year one of the former Duro engineers sent me one of these lamps by
post - typically it arrived with the filament in pieces! By 1988 the
company was forced to pull the plug on the project. It was unfortunate that
despite more than a decade of dedicated research this problem of tungsten
metallurgy was not solved.
In the mean time Toshiba in Japan had developed a much more commercially
viable lamp with IRC coating in the form of the linear halogen types. GE
later commerciallised an almost identical design. The advantage of choosing
the linear halogen design was the possibility to use multiple filament
supports to keep it from sagging, and right on the optical axis of the
coated tube. Additionally the early lamps were only available in relatively
high wattages of 300-900W - these types having thicker filaments which
better resisted sag. Exceptional work in tungsten metallurgy, primarily led
by GE later allowed smaller lamps down to about 60W to be created.
Incidentally this technology for low wattage IRC lamps is still completely
unavailable in lamps suitable for the European and Asian line voltage of
230V. Higher voltage lamps require thinner tungsten wire for the filament,
and it is still not possible to produce a 230V filament lower than about
200W which is sufficiently sag-resistant to realise an IRC lamp. IRC lamps
can only be used here in conjunction with a step-down transformer, so the
market has evolved around types having 12-volt capsules instead.
James.
"TKM" <nomail@xxxxxx> wrote in message
news:2cCPh.223204$5j1.63688@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
"Victor Roberts" <xxx@xxxxxxxxxxxxxxxxxxxxx> wrote in message
news:4ggr03t98vbf91fv1q337cfsn4qujlb8ee@xxxxxxxxxx
On 30 Mar 2007 17:50:56 -0700, "Adam Aglionby"
<ledlight@xxxxxxxxx> wrote:
Photographic exhibition might find a few interested here...
http://www.wirtzgallery.com/exhibitions/2007/2007_04/wagner_2007_frame.html
Puzzler though are the " Energy Efficient Experiment, 1980's" lamps,
hwta the heck are they look like some sort of discharge lamp?
Thanks
Adam
The three with transparent bulbs clearly have filaments.
These may be early experiments with IR reflectors. It was
first though by some that IR reflectors could be applied to
"normal" bulb shapes. Through these experiments we all
learned that the filament positioning in an A-Line or Globe
bulb was not precise enough for IR reflection to be
effective and it was better to mount the filament in a
cylindrical filament tube and then put the reflector on the
outside of the filament tube.
--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.
That's what I recall as well, Vic. I've forgotten the name of the company
and those involved; but I do recall that the U.S. Dept. of Energy funded
the development of the work somewhat to the dismay of the of the lamp
industry at the time who didn't think the idea would work. Later, the
"halogen IR" technology did work and made possible 900 watt linear halogen
lamps with the light ouput and life ratings of conventional 1500 watt
halogens. Those lamps are still available and the technology has, of
course, been applied to other halogen types including those used in
stage/studio and automotive lighting.
Terry McGowan
.
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