The sun., 1907-08-18
THE LAMP or THE FUTURE
WIN Give IAsht without Heat-ProbabIy n
Gas or VapOr.


Many attempts have been made TO in
crease the efficiency Of our present electric
incandescent lamps. says a writer in Cas-
sier's Ma0dxine. -.
Light is only by-product in all known
illuminants, for the production of light
| depends on incandescenoe, that is, the shin
ing Of hot bodies. because they are hot.
Such q hot body radiates a variety Of
waves. but very few Of these are useful -
light. The useful light rays only appear
when the temperature is fairly high; below
that only long heat waves appear. BY in
creasing the temperature the percentage
OF useful light rays increases.
As long as we only know the way to pro-
duce electric light by incandescenoe We
can only increase the efficiency by Increasing
the working temperature.
Naturally there must be certain tenn
perature where The percentage Of visible
radiations reaches the maximum, and this
is supposed to be between 1900 and 5000
degrees Centigrade. But even at this tenn
peratAre the efficiency only amounts TO about
per cent. 80 that there is an absolute limit
in lighting by incandescence,
The familiar electric incandescent lamp
consists OF filament Of carbon enclosed In
a vacuum. The carbon fiament is heated
by the electric current and forms our hot
body. Now, carbon Ii apparently the most
refractory OF all substances, its boiling
point being about 1900 Centigrade.
Unfortunately we cannot use such high
temperature in the carbon incandescent
lamp, for our limit ID not the boiling point
but the temperature at which the evapora-
tion becomes 30 great as to limit the life
of>our lamps. The temperature at which we
work carbon In our lamps b about f.so0 de-
grees. =. - - 80 .'51
The efficiency Of the incandescent lamp
can therefore be increased by using ma
terial which has lower vapor tension at q
higher temperature.
Nernsf was the FIRST 10 devote hisstsention
70 the problem and brought out the well
.iss" prncipsly E ~ uroona ams9e mssoesam SSn
oxide and a small amount Of the oxide Of the
yttria group.
Great hopes were entertained when the .
Nernst lamp appeared on the market, but
these have not been realized, for the lamp
had one great disadvanta &c which bas never
been overcome, namely, the filament does
not conduct and consequently does not
light up st ordinary temperatures.
The success with these experiments led
scientists to turn their attention TO other
rare metals, of which the following have
been used with success: tantalurn, tungsten,
chromium and iridium.
The 'tantalum lamp has SD far been the
most successful Of all metallic filarnent
lamps and thousands are nov in use in Lon
don alone. There 10 no doubt that within
very short time we shall have at our COM
mand metallic filament lamps which from
practical point of view will eoual the
present carbon lamp and have an eflIcienay
OF watt per candle.
This will be a great achievement. but it w{n
not be the lamp Of tine future. FOR a.
shown In the beginning of this article we
We aro absolutely limited as long as We
cling TO incandescent bodies for light pro-
duction
Heatt although capable OF making liquid
or solid incandescent. cannot make q gas
incandesosnt, but merely increases it's
pressure. We can. however. set gas mole
cules in vibration by chemical reaction or
electric stress, such as l. done when an
electric current 's passed through vacuum
tube. w. .r .,
Theoretically. there is no limit to the efyi-
cheney OF q luminescent gas. Within the
last few. years good eff,ciences have been
obtained with the Moore vacuum tube illu-
mination. and this method Of light produce
tion has great future before H. The light
OF the future will be q lamp giving light With
out hcat and tho probabilities are, that this
will be either a luminesoent gas or vanee.