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Then for these numerical values,
Y-V
r/ffiz
r
2x3x0.0004 2x3 2x3
r,soo
Which is equal to { 625p901 62,500 - 250.
Which is equal to 829 - 250, or
X : 579 hours.
By substituting in the equation (4) all of the above
lrulrr.., except ihat for current costr making "E''' !!"
cost per K. W. hour, 1.45 cents' and solving for X,
the time of use, which results in maximum economy'
is found to be 646 hours.
These two values check fairlY
found graphically and shown in
ure 1.
DISCUSSION ON
DR. LYNDON'S PAPER
well with those
the curves, Fig-
t s1 l
Mn. Fanmnala: The lamp manufacturers use
a method sbmewhat similar to that described by Dr.
Lyndon to determine the most economic and best
lamp life. By proper choice of the lamp efficiency
(filament temperature) the average life of lamps
may be controlled within wide limits. Based on
lamp renewal costs alone, if the cost of electrical
.n.igy is low and lamp costs very high, then it
*o*ld b" desirable to design the lamps for a fairly
long life and conversely if the energy cost is high
and lu-p cost low, it would be more economical to
operate the lamps at a short life. In the case of
Iamps used for general lighting service it has been
found that for the average energy rates prevailing
throughout the country an average life o{ about
500-600 hours gives the maximum light at lowest
cost,
In the case of lamps for studio lighting service we
have the additional important element of color of
the light. It would be desirable from the standpoint
of color rendition on the film to operate the
lamps at a very short life; i. e., 50 or 100 hours;
this, however, would make the lamp cost excessive.
In our study of the problem, it has been found that a
life of from 200 to 400 hours gives the best balance
between energy cost, lamp cost, and the photographic
rendition of colors.
Several studios are making the mistake of operating
their lamps at a long life, hoping to reduce
their lamp costs. While such a procedure may reduce
the lamp expense, it greatly reduces the quantity
of photographic light from the lamp with the
result that more equipment must be used to secure
sufficient light, and as equipments cost more than
lamps the net operating expense may be higher.
QuBsrrox: Has there been reached a comparison
between the two lights, the Arc and the Incandescent
as to the amount of light that we require
for a given amount of space? In large sets the Arc
lights seem to have a greater carrying power naturally
and without occupying a considerable amount
of space. Do the Incandescents have a tendency to
drop ofi in carrying power? As the light proceeds
from the lamp it is absorbed by the atmosphere.
Close to the lamp there would be a great deal of
energy. We have never come around to that point.
In other words, would Mazda illumination be possible
for general illumination without having to resort
to Arc lights for certain things at some future
time ?
Mn. Bar,r-: Who can answer? Mr. Jones.
Mn. JoNns: I did not get the import of the
question.
QursuoN: In the relative quality of the lights
in making up the comparison between the Arc light
and the Incandescent, it seems that the rays of the
carbon lamp will travel to a greater extent than the
Incandescent. The Incandescent has a greater falling
off power for a given area. A large set lighted
with Incandescents would require more lamps than
an Arc lighted set.
Mn. JoNrs: The question is rather complicated,
and the answer, I think, depends upon the definition
of the term "falling off." There are reliable data
relative to the penetrating power of difierent wave
lengths. In the case of the transmission of light
through the earth's atmosphere, which contains a
certain amount of diffusing or scattering material,
such as water, vapor and dust, red light will travel
with less loss of intensity than blue, which is scattered
to a greater extent. Light from the Incandescent
lamp is red, compared with that of the Arc,
and hence under the conditions mentioned above
should travel with less loss of intensity than Arc
light. In the studio, however, this atmospheric scattering
must be very small indeed, and hence will
have a negligible efiect. If the Arcs actually have
greater "carrying power" in the studio it is probably
due to difierences in the angular distribution of
the radiation from the light source, the light source
being defined as the actual source of radiation plus
its reflection fixture or housing. It may be also that
this opinion that the Arc carries better than Tungsten
light is based upon tests in which care has not
been exercised to be certain that the two sources
have identical candle-powers.
Mn. FanwHau: Mr. Jones' statements relative
to the greater power of red light in penetrating {og
and dust are correct. I should like to supplement
Mr. Jones' remarks with reference to the carrying
power of light from various sources. Ever since I
have made a study of the lighting problems in the
studios, the statement has been made that the light
from Incandescent sources falls ofi more rapidly
with increasing distance than does the light from the
Arc lamp. The illumination received on any surface
follows what is called the inverse .qrr"r. I"*,
and is independent of the nature of the source. A
simple statement of the inverse square law is: The
illumination intensity on a surface varies inversely
as the square of the distance between that sur{ace
and the light source. I should like, at this time.