Download Report - Academy of Motion Picture Arts and Sciences

Mn. BnowNrNc: You mean the Tungsten filament
is an element and not a composite material ?
Mn. I)rr,nnav: That can easily be explained.
When the filament of a lamp is removed from the
glass bulb, leaving the amount intact, and a current
of the required voltage allowed to flow through the
filament while it is exposed to the air, the Tungsten
filament will almost immediately oxidize, forming a
yellowish-white oxide of the metal Tungsten. Tungsten
is an element.
N{n. Bar,r,: Any other questions ?
Mn. FanxHanr: I should like to supplement
some o{ the points brought out by Mr. Deleray. In
general the designed voltage of the lamp determines
the filament length, and in order to secure grearer
source concentration, low voltage lamps have been
tried. However, due to the larger diameter of the
filament wire, because of the greater current, the
gain in concentration is not as great as would be
expected. The use of transformers or some other
{orm of voltage reducing device {urther complicates
the problem. In regard to universal burning lamps,
while they are nominally called "universal burning,"
nevertheless when they .are burned in any
other position than base up their life is reduced
about 30 per cent. Thus in designing equipment
to use these lamps it is desirable to position the
lamps so that they will operate generally base up
and thus secure maximum life. With re{erence to
standard vs. special lamps, it is, of course, desirable
to use a standard lamp wherever possible, but I do
not believe it wise to restrict the motion picture
studios to standard types alone. For example, the
C-5 filament construction has been standard {or the
round bulb lamps used for spot lighting service, but
in our work in the studios we have found that the
monoplane, or C-13, construction gives a more uniformly
illuminated spot as well as more light. While
this is a non-standard lamp, nevertheless I feel it
justified because of the better results.
Mn. Ponrun: One point Mr. Farnham brought
out is perhaps a little confusing. I rather fear that
he gives the impression that all lamps burn better
when burned base up-that is all right for the
lamps that are designed {or base-up burning. They
have a fairly long neck bulb, but the concentrated
filament lamps are all designed for burning base
down and they will not burn in a base-up position.
Mn. Drr,rnay: As previously stated, the T type
of bulbs can be burned in any position within 25
degrees of base down. The G type of bulbs can be
burned in any position, except within 45 degrees of
vertically base-up, and the PS type may be burned
in any position.
Mn. FanNrrav: My preceding remarks relative
to lamps burning better in a base-up position applies
only to the PS or pear-shaped bulb lamps. The
tubular bulb lamps must, of course, be burned base
down or within 25 degrees of base down to get satisfactory
performance. The round bulb lamps have
to be burned in almost any position because the spot
lights in which they are employed are often pointed
directly downward and even upwards. Thus it is
necessary that these lamps be made to operate in
almost any position, except possibly base-up. However,
these lamps give their best performance when
operated in a base or nearly base-down position, and
they should be so placed in the equipments that they
will operate in this position as much as possible.
Mn. RavroN: I have occasionally had lamps
fail the first time the current was turned on with
the development of dense white fumes within the
bulb. This is evidently due to too much air in the
bulb.
Mn. DBLrnav: There is evidently a flaw or
leakage in the glass which has allowed air to replace
either the vacuum or inert gas. As soon as
the lamp is lighted the Tungsten filament oxidizes
and causes a yellowish-white coating to be formed
on the inside of the bulb.
Mn. Rayror.r: Working recently with a 250-
watt coiled-coil filament lamp, as soon as the current
was turned on the lamp exploded; the bulb
flew in a thousand pieces all over the room. Can
you explain this behavior ?
Mn. Dnrrnay: It would be difficult to give a
specific reason. It might be that in the filling of the
bulb too much gas was permitted or it might be due
to a weak spot in the glass bulb itself or again it
most likely would be due to an arcing of the filament
caused by the filament coils coming in contact
with one another.
Mn. FanNnarr: Referring to Mr. Rayton's
question on the coiled-coil filament lamps. For some
peculiar reason we have had quite a number of just
such failures with the coil-coil filament lamps. The
coiled-coil filament lamps are constructed by coiling
the filament wire on one mandrel and then coiling
this coil on a second mandrel, thus obtaining a high
source concentration, however, should such a filament
short circuit, the voltage developed across such
a short would be higher than in the usual types and
there might be quite a rush of current if the circuit
is not adequately {used, resulting in the sudden
development of considerable heat which would
cause the bulb to shatter.
Mn. AnNoro: Is there any way of eliminating
some of the heat from incandescent lamcs ?
Mn. DBrnnay: Cold light has been the subject
of attention for many years. In the incandescent
lamp we know that approximately 3% of the light
developed is in the ultra-violet'and approximately
94% in the infra-red. Heat may be eliminated by
the use of screens or possibly by water radiation.
QuBsuoN: Is there any way o{ eliminating
infra-red ?
Mn. Drr,Bnay: .The infra-red can be somewhat
eliminated by increasing the light output of the
lamp but as you decrease the infra-red you shorten
the life of the lamp.
Mn. Far.Nualr: Practically all the heat we feel
standing in front of a lamp comes from the infrared
region (radiation in wave lengths longer than
7000 Angstrom units). The most promising way
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