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 Summary.
From the earliest days of artificial lighting the broadside type of unit
has been a fundamental lighting tool. Regardless of the light-source used
in such lamps-whether mercury-vapor tubes, carbon arcs, or incandescent
filament globes -the broadside is a lamp of the floodlight type, designed
to emit a relatively wide flood of soft, moderately powerful illumination.
It has withstood innumerable changes in lighting and photographic technic,
including the introduction and acceptance of Spot lighting, the change
from orthochromatic to panchromatic film, the changes from silent to talking
pictures and from arc to incandescent light-sources, and the present growing
popularity of natural-color photography.
The
paper traces the evolution of arc broadsides only, and comment upon the
design and performance of the early units. The evolution of the broadside
is followed the successive improvements in silent-picture usage; its decline
at the introduction of sound and Mazda lighting; through the relatively
recent rebirth of arc lighting due to the requirements of modern natural-color
photography; and the most recently introduced units of this type which
are replacing equipment designed less than five years ago at the introduction
of the three-color Technicolor process. Comparison is made between the
early, intermediate, and modern units as regards color distribution light
distribution, steadiness and length of burning period, indicating that
though less public attention has been given to these types than to the
more familiar spot. lighting units, the broadside has kept pace with advances
in lighting and equipment design.
The
first artificial light-sources used to illuminate motion pictures were
of the "broadside" or floodlighting type. From that day down to this,
the "broadside," regardless of the type of light-source it housed, has
remained a fundamental tool of motion picture lighting.
So
far as is known, the first installation of artificial lighting for motion
picture production was made at the original Biograph studio on 14th Street,
New York, N. Y., in 1905. The lamps used were primitive "banks" of mercury-vapor
tubes, suspended above the sets under the glass roof, to supplement to
daylight on dull days, and to replace it on dark ones.
Other
pioneer producers and technicians were not long in appreciating the commercial
advantages of artificial lighting, and in time virtually all the eastern
studios equipped themselves with mercury vapor lighting equipment. When
the industry began its migration to California, the vapor-tubes followed,
for in spite of the most enthusiastic claims, clouds do sometimes obscure
the California sun, and artificial lighting remained a commercial asset.
As
this development progressed, the mercury-vapor tubes were adapted to a
variety of units, all of the floodlighting type. In addition to the original
overhead units were "broadside" units of from six to eight tubes, mounted
on wheeled stands to permit their use on the stage floor; "goose-neck"
units which resembled the "broadside" banks but with the addition of a
second bank, mounted above the first and directed at a downward angle;
and in some instances-special low front-lighting units (usually of four
tubes) mounted horizontally on a low, wheeled carriage and used to throw
light upward against the faces of the players.
The
first arc-light unit to appear seems to have been the Aristo, introduced
not long after the introduction of the vapor tube. This unit, which was
an adaptation of similar street-lighting units, was an overhead floodlight.
It was a single arc, burning at about 28 amperes and 63 arc volts. It
was commonly fitted with a simple conical reflector reminiscent of those
on street lamps, and the arc was enclosed in a glass globe. With its small
dimensions and relatively high power for those days, it became very popular
for supplementing natural light on glass stages. The introduction of true
arc "broadsides"-that is, floodlighting units for floor use-appears to
have taken place about 1912. According to cinematographers active at the
time, the Wohl was one of the first, if not actually the first of these
units used. It, like most of its successors for a decade or more, was
an adaptation of units previously made for photoengraving. These pioneer
lamps were what might be called double-twin arcs, for they consisted of
a pair of twin arc units, each with a large, box-like reflector, mounted
one above the other on a common stand. The stand consisted of three upright
posts, arranged parallel to each other in a triangular formation; the
lamps slid up and down between the two front posts, while a counterweight
operated on the third post. The four arcs were wired in series-multiple.
They burned at 30 amperes when all four arcs were connected in series
across a 220-volt circuit, or at 60 amperes if each two arcs were burned
independently in multiple on a 110-volt line.
The
advantages of arc lighting became increasing pronounced as cinematographers
drew away from the earliest flat lightings and began to experiment with
the possibilities of creating effects of contour and separation of planes
by contrasts in lighting. A considerable variety of arc "broadsides" were
built during the next several years by a number of manufacturers. Among
these might be mentioned one curious design in which a single arc of relatively
high power (3040 amperes) was mounted to burn horizontally in a semicylindrical
reflector, and another in which the carbons were placed at right angles
to each other. In general, however, the successful designs soon evolved
to the form familiar to all who have had any experience with production
prior to the early days of sound.
In
general, these lamps were of the twin-arc type with the two arcs placed
beside each other with the carbons vertical, and burning in series at
about 30 amperes. The lamp was mounted on a pedestal quite similar to
the types in general use today, with the necessary ballast resistance
at the base of the pedestal.
These
arcs were generally used in conjunction with the softer vapor tubes. Before
the introduction of arc spotlighting equipment, they were the only sources
of strongly directional "hard" light available. In some studios the way
in which the "hard" and "soft" lighting was mixed was left to the cameraman.
In others, a rigid studio policy dictated the lighting: in some such cases
all the vapor lights might be used overhead, and all arcs on the floor;
in others, vapor lights exclusively on the floor, and arcs overhead.
A
common malady throughout all the days of the early arcs was the so-called
"kleig eye," medically termed conjunctivitis. It was a painful inflammation
of the eye and eyeball. The cause was simply ignorance of the spectral
characteristics of arc lighting. Arc light has always radiated strongly
in the injurious, short-wave ultraviolet region. At that time, the lamps
were very generally used with no diffusion, or at best a simple scrim
of silk or tracing-cloth which, of course, failed to impede the ultraviolet
rays. Since the rebirth of arc lighting five or six years ago, modern
knowledge of spectral radiation has virtually eliminated this malady.
Ordinary lead glass absorbs all the injurious components of the ultraviolet
radiation. Accordingly modern arcs are always used with some sort of a
lead-glass window-clear, if no diffusion is wanted; translucent, if diffusion
is desired. And "kleig eye" is known only to press agents seeking imaginary
copy.
The
performance of the early arcs left much to be desired. Of course, when
motion pictures were the silent drama, it did not matter whether or not
lighting equipment burned silently; but then, as now, a steady-burning
light-source was important to good cinematography. Even the most enthusiastic
booster of these early lamps could not deny that they flickered badly,
and frequently went out at the most inopportune moments. It was probably
fortunate that the film used in those days was of relatively limited sensitivity,
for maintaining a mere exposure level of illumination usually required
the use of so large a number of overlapping lamps that the effects of
flickering by individual lamps were minimized.
In
a certain measure this performance was due to the then relatively limited
knowledge of carbon design and production. Fundamentally, however, the
flickery performance of all types of pre-talkie "broadsides" must be laid
to the crude methods of feeding the carbons. Some early lamps even used
a simple, hand-operated gravity feed. The majority made use of some type
of gravitational-magnetic feed, which fed both arcs simultaneously. The
result, of course, was an exceedingly intermittent feed. The lamps would
burn with less and less intensity and increasingly pronounced flicker
as the arc-gap grew wider. Then the carbons would suddenly feed, after
which the light would momentarily become abnormally brilliant, and then
diminish slowly as before. The electricians of those days used to keep
long poles available on the sets with which to beat or jolt the lamps
at the start of each "take," in the hope that the jolt would cause the
carbons to slip down and thus minimize flickering during the scene. Floor
lamps were often shaken, and the main switch flipped rapidly on and off
for the same reason. The percentage of otherwise good scenes spoiled by
lamp flicker was high.
Fig.
1 shows a curve made by one of these lamps with a General Electric recording
photometer. The lamp used was a typical twin-arc "broadside" of the later,
pre-Vitaphone vintage. It is possible that when the lamp left its maker's
hands some fifteen years ago its performance might have been considerably
more creditable; but time unfortunately did not permit completely reconditioning
the unit, and the test was made with the lamp in approximately the condition
it would be in under normal studio usage of its period.
It
will be observed that when first struck, the arc leaps to a relatively
high intensity, reaching a peak after about 30 seconds, after which the
intensity rapidly decreases, with frequent and strongly noticeable fluctuations;
until, after approximately 3 1/2 minutes burning, when the intensity has
declined to approximately 1/3 its original value, the lamp retrims itself,
without, however, regaining more than 2/3 of its initial intensity. Thereafter
the cycle of decline and retrimming repeats itself.
Similar
tests, covering a period of an hour's burning, were even more noteworthy.
The short-period fluctuations already noted stood out prominently, and
superimposed upon them was a pattern of longer-period fluctuations of
still greater intensity. These occurred at approximately 5-minute intervals,
and at the peaks the recording stylus was thrown completely off the scale.
FIG. 1. Characteristic of early type of lamp, prior to 1926.
Immediately
before these peaks, as the carbons in retrimming momentarily touched before
striking what for all purposes was a new arc, the intensity dropped to
zero.
It
will be seen that there was a triple flicker in these lamps, phased as
follows: first, minor variations in intensity at intervals of less than
2 seconds; second, fluctuations of 40 to 50 per cent at intervals of approximately
3 minutes; third, fluctuations of several hundred per cent at approximately
5-minute intervals. Thus while these lamps would actually burn for considerable
periods, it will be obvious that for true photographic effectiveness it
was seldom safe to burn them continuously for more than 3 minutes, or
at most 5 minutes without extinguishing for adjustment. Even during this
short burning period, they were only momentarily at their best performance.
The
coming of sound and the introduction of panchromatic film, occurring a
most simultaneously, spelled the doom of these early arcs. Even though
it was in time found that arcs could be silenced quite effectively by
the application of choke-coils, the much longer scenes general in talking
pictures demanded the use of steady, flicker-free illuminants. At the
same time, panchromatic film's stronger sensitivity in the yellow-red
region made the early arcs, which were deficient in this range, inferior
to the steadier and redder incandescents. High-intensity arc spotlights,
of course, continued in occasional use, since no other illuminant could
compete with their strong, intensely directional beams for certain dramatic
lighting effects.
The
arc was reborn about five years ago, with the introduction of the three-color
Technicolor process. With any process of natural-color photography or
cinematography the color of the light is of fundamental importance, both
technically and commercially. The color control possible in the camera's
separating filters, and in the multiple color-printing operations naturally
make a certain degree of compensation possible. Natural daylight, however,
is a fairly uniform blend of rays of all spectral colors. If the system
is balanced for this standard, there is difficulty in using it with light
which, like the incandescent, leans to the red end of the spectrum, or,
like the earlier arcs, leans to the blue end. Printing color-control alone
is seldom sufficient to compensate for such differences. The filter-balance
of the camera can, of course, be altered to make such compensation. But
this is not commercially feasible, for it would necessitate either readjusting
the camera filters, which are an integral part of its optical system,
or the use of completely different cameras whenever a company went from
an artificially lighted stage to naturally lighted exteriors. A further
complication is found in the general practice of using "booster" lights
to supplement natural light outdoors. To be useful, such artificial light
must mix imperceptibly with daylight.
The
logical requirement in lighting--the one that the Technicolor engineers
set up as a basic standard--would be that the artificial light must have
as nearly as possible the spectral distribution of natural light at mid-day.
Certain
other requirements, almost equally important, also existed. The light-losses
inevitable to distributing an image over three films, absorbing color-components
of each with selective filtering, necessitated, especially at the outset,
illuminants of high intensity. The requirements of talking pictures naturally
presupposed a silent lamp, while the length of scenes in such pictures
made flicker undesirable. The high sensitivity of the Technicolor process
definitely called for flicker-free lamps.
Arc
lighting seemed inherently more nearly suited to these requirements. Arcs
are the most intense illuminants thus far available for motion picture
lighting. Experience had shown how they could be silenced satisfactorily.
Their radiation, while not then ideally matched to the daylight standard,
even then seemed more nearly suitable and appeared capable of being made
more so. On the other hand, the arcs then available, especially the fundamental
"broadside" types, flickered badly. Since much scientific knowledge had
been amassed since the design of these early lamps, however, it appeared
hopeful that flickering could be overcome, or at least minimized. Accordingly
the Technicolor Motion Picture Corporation commissioned the Mole-Richardson
engineers to develop arc equipment suited to modern production in the
three-color Technicolor process.
Since
the fundamental lighting tool was the "broadside" arc, and since the then-existing
"broadsides" were perhaps the least adequate of any existing units, the
first lamp to be developed for three-color Technicolor cinematography
was the "Side Arc" (MR Type 29). This unit has been thoroughly described
in previous papers, and little need be said in detail about it at this
time. While similar in appearance to previous arc "broadsides," in design
and performance it was revolutionary.
This
lamp, though it operated at 40 amperes, used carbons much smaller than
any previously used in arc "broadsides," and of different composition.
These carbons were specially developed for the purpose by the National
Carbon Company, and were known as 8-mm. Motion Picture Studio Carbons.
The light radiated was an almost perfect substitute for daylight. The
intensity of the light of these lamps was approximately 250 per cent greater
than that of previous "broadsides."
Like
previous arcs of the same type, the twin arcs were burned in series, with
a ballast resistance. Instead of feeding simultaneously, as did most previous
"broadsides," each pair of carbons was fed and controlled independently,
to maintain the required voltage across its arc-gap. This naturally did
much to eliminate flicker.
Fig.
2 shows a record of a test made with one of these lamps. It will immediately
be observed that the characteristic slow loss of intensity, and the longer-period
fluctuations of the previous type arcs have been eliminated, although
considerable minor variation still remains. However, judged by the "broadsides"
then existing, and by the arc spotlights then used, the Side Arc was considered
a flicker-less lamp. For overhead use a companion design (MR Type 27)
was made, mechanically the same, but mounted for overhead use. It was
known as the "Scoop."
During
the ensuing five years new and greatly improved types of arc spotlighting
equipment (MR Types'65, 90, and 170) have been brought out, as detailed
in previous papers.
FIG. 2. Characteristic of side arc.
Their performance was so improved that the imperfections of the Type
29 Side Arc became evident.
Two
improvements in arc "broadsides" were deemed especially necessary: first,
further reduction of flickering; second, longer burning periods without
retrimming or other attention. The latter was of definite commercial importance,
for much time was lost retrimming large batteries of arcs, especially
the overhead Scoops, on large sets.
Those
requirements have been met in a new unit, introduced only within the last
two months. Known commercially as the "Duarc" (MR Type 40), it embodies
principles not hitherto employed in studio floodlighting arc equipment.
Research
in connection with the design of high-intensity arc spotlights indicated
that in these rotary-carbon spotlights much of the flicker was eliminated
by continuous feeding of the carbons. Therefore, in the Duarc the carbons
are fed continuously. Each arc is, of course, fed and controlled individually.
Front
and rear views of the Duarc are shown in Fig. 3, while the same lamp,
without its covering, is shown in Fig 4. It will be seen that each pair
of carbons is fed by means of an endless chain; the carbon-holders are
mounted on opposite sides of this loop in such a way that as one holder
ascends the other descends. Each chain is ascends the other descends.
FIG. 3. Front and rear views of the Duarc.
Each chain is driven by an independent, slow-speed electric motor, which
requires only 600 revolutions to feed completely a trim of carbons. This
requires over 2 hours.
The
operation of these motors, and hence of the carbon feed, is controlled
automatically by the resistance across each respective arc. This is done
by an adaptation of the familiar Wheatstone bridge principle of balanced
resistances.
The
cycle of operation in the Duarc is as follows. When the master switch
is thrown, current is fed into the motors, causing them to revolve sufficiently
to bring the carbon electrodes into contact. As the current flows through
these electrodes, the motors immediately and automatically reverse themselves,
drawing the carbons apart to form the arc. When the carbons are so separated
as to give the most satisfactory arc, the motors again reverse and drop
to the very slow speed of 5 rpm.; then they feed the carbons continuously,
at a rate in each case dictated by the resistance across the individual
arc-gap, keeping the arc at its most favorable point until the carbons
are consumed. Special 8-mm. positive and 7-mm. negative carbons have been
developed for this lamp by the National Carbon Company.
FIG. 4. Front and rear of the Duarc, with covers removed.
The
practical result of these improvements is shown in Fig. 5. From this curve,
made under conditions similar to those of the two previously shown for
earlier types of "broadsides," it will be seen that while minor fluctuations
still exist in the light-flux of the "Duarc," they average less than 1/6
the magnitude of those of the Type 29 Side Arc, and less than 1/25 the
magnitude of the pre-talkie "broadside." They are scarcely evident, either
visually or photographically. The several superimposed fluctuation patterns
of greater magnitude and longer period, evident in the, earlier lamps,
have wholly disappeared. For all practical purposes it may be said that
the long-sought goal of an absolutely flickerless; are "broadside" has
at last been attained.
At
this point may be mentioned one of the frequent instances where the performance
concepts of the engineer and the practical cameraman do not agree. Measurements
of the intensity of the light-flux radiated by the Duarc, made by Mole-Richardson
and Technicolor engineers, indicate that there is very little difference
between the intensities of the new Duarc and the older Type 29 Side Arc.
FIG. 5. Characteristic of the Duarc.
This
is as it should be, for increased uniformity of light-flux, rather than
increased intensity, was the aim from the start.
Several
cinematographers, on the other hand, after using the new lamp on production,
have reported that they obtained better results with the new lamp, used
8 feet distant from the subject, than they did with the earlier Side Arc
at half the distance.
A
number of practical improvements in design have been possible by virtue
of the radically different principles involved in the new unit. For one
thing, earlier "broadsides" were generally fitted with a hinged cover
over the upper part of the carbon-feed mechanism. This cover was almost
invariably opened when the lamp was in use, for better ventilation. In
the Duarc, asbestos insulation is applied behind the sheet-metal housing
of the unit, and between the reflector and the mechanism. The latter,
especially, insulates the mechanism from the heat of the burning carbon
electrodes. More accurate knowledge of convection currents within such
a lamp also dictated the design of ventilating ports and inner light-baffles.
As a result, the operating mechanism of the Duarc is semi-permanently
sealed. In actual use there is no reason for opening this compartment
save for rare major repairs which would, of course, never be made on the
set.
The
only manual operating controls are the main switch and two knobs which
project from the front of the lamp, directly below the reflector. Each
of these is connected to one of the two carbon-feed chains. Their purpose
is to permit quick separation of the upper and lower carbon-holders when
the lamp is to be retrimmed.
The
carbon-holders are of the quick-release type, consisting of a split bushing
compressed by a small coil-spring. The butt-ends of the carbons are simply
inserted in these holders, after which the spring-loaded bushing holds
them fast. No tools are needed for trimming or retrimming the lamp.
Another
innovation is found in the diffusing screen and its mounting. Previously,
because of the heat radiated from the arc, such diffusers had necessarily
to be made of relatively narrow strips of glass, mounted in a frame that,
for better ventilation, was simply hung rather loosely over the front
of the lamp.
The
diffuser used in the Duarc is constructed of a single sheet of translucent
pyrex heat-resisting glass, mounted in a rigid cast aluminum frame. This
frame fits closely over the lamp opening. For trimming or inspection,
the frame slides up and off a tongue-and-groove joint like a window-screen,
Ventilation is cared for without the necessity of any opening between
the lamp and the diffuser, while, of course, the use of pyrex virtually
eliminates heat-breakage risks. The frame design prevents undesired "spilled
light," including both visible and ultraviolet rays. The diffuser frame
is hinged to open like a book, so that the diffusing screens may be replaced
easily, while in the somewhat rare event that no diffusion is needed,
a pane of clear pyrex may be used. Hooks are provided by which additional
diffusing media, silks and the like, may be hung over the regular diffuser
as desired by the cameraman.
The
Duarc is a twin-purpose unit. Ordinarily it is mounted on a conventional
three-lift pedestal for floor use, allowing a wide range of adjustment
from very low to very high positions. Alternatively, special chain hangers
are available by which the same units may be utilized either singly or
in banks for suspended overhead units, replacing the older "scoops" previously
referred to.
The fully automatic operation of the Duarc gives a very practical advantage
for this latter use. Much time is ordinarily lost with "scoops" of conventional
type when used on large sets, due to the relatively frequent need for
retrimming. Such units are suspended from the roof-trusses of the stage,
directly over the set. They are in most cases quite inaccessible. Retrimming
means that the lamps must be lowered to the floor so, that the electricians
can get at them; in only rare instances it is possible to reach them by
ladders. In any event, reaching and retrimming large batteries of such
lamps is a serious interruption to shooting. In a modern production, where
overhead costs may mount up at several hundred dollars an hour, such delays
are not only inconvenient, but expensive.
The
Duarc, however, has an unusually long burning period, as it burns both
carbons down to stubs less than three inches long. Under both tests and
practical operating conditions, these lamps have burned without attention
for periods in excess of 2 hours, on a single trim.
In
practice, this means that with only reasonable care to turn the lamps
off during nonproductive periods between takes, the Duarcs, used as overhead
lamps, may be used without retrimming for not less than half a day. Under
some conditions, where production for other reasons is slow, the lamps
may well operate for a full day on one trim. In any event, no shooting
time need be lost, as the lamps can be retrimmed at the noonday halt,
and need no other attention during the day.
Since
the lamps automatically strike their arcs whenever the current is switched
on, they may be operated either singly or in banks by remote-control switches.
An interesting fact revealed in recent tests of these lamps is that by
the use of a conventional dimming rheostat it is possible to fade these
lamps in and out with no appreciable flicker-a valuable asset in certain
types of dramatic effect-lightings. Since the Duarc strikes its arc almost
noiselessly, and settles down immediately to steady burning with no initial
period of abnormal strength, these lamps may also be switched on or off
as required in the middle of a scene.
It
is evident that in the approximately 26 years since the introduction of
the industry's first arc "broadsides," the design, performance, and operation
of these fundamental units have made genuine progress. Yet during much
of the period, "broadside" design remained actually almost static, as
the more spectacular spotlighting units were introduced and developed.
The original principles of "broadside" design, borrowed from other fields,
had seemed good enough. Only when more scientific methods of design were
applied, together with a willingness to cast aside previously conventional
practices and develop lamps wholly intended for motion picture use, was
radical progress made. The same has been true of spotlighting equipment--as
witness the advances made when previously conventional ideas were supplanted
by the modern Fresnel-lens spotlight designs, originated solely for motion
picture lighting--and the same must be true of virtually every other phase
of equipment design for motion picture apparatus. Having attained the
status of a major scientific industry, the motion picture should no longer
be satisfied to borrow and adapt, but can strike out for itself, designing
and using equipment planned exclusively for the special requirements for
making better motion pictures.
DISCUSSION
DR.
GOLDSMITH: How close can you bring a broadside like that to an actually
recording microphone without the microphone picking up anything from the
motors during automatic feeding?
MR.
MOLE: We have placed this new lamp within six feet of the microphone and
have found it very satisfactory. It depends entirely on the particular
dramatic effect that you are trying to accomplish in recording.
A
short time ago, in a picture in which Shirley Temple was the principal
artist, these broadsides were used and we were confronted with a problem
of recording the scene in a very low key. Nevertheless, we were able to
use these lamps within about six feet of the microphone with satisfactory
results.
MR.
FINN: What is used for the mat surface diffuser?
MR.
MOLE: The diffuser, which is placed in front of the lamp, is pebbled and
sandblasted glass. It gives a soft, diffused light on the subject. The
reflector is chromium.
DR.
GOLDSMITH: So you get your efficiency of reflection from the chromium-plated
reflector and depend on the diffusers for the quality of the light, that
is, the softness or diffusion?
MR.
MOLE: Yes.
DR.
GOLDSMITH: Have you ever tried to any extent successfully using a hard
spot with a diffuser on it, when you have to place the lights quite a
way off from a set, and yet desire controlled diffusion?
MR.
MOLE: Sometimes they use a 150-ampere Sun arc, with a diffusing glass
in front of it, to give a large diffused surface.
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