We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
perature of a HI projection arc burning regular HI positives close to maximum current has been found to be 5500° K, very close to that of standard noon sunlight (5090° K).
The approximate color temperature of average daylight (sunlight + diffused skylight) is in the neighborhood of 6500° K, while north skylight varies from 10,000° K to infinity, with 25,000° K a fair average. This is a white which is definitely bluish, and hence relatively weak in the red and orange end of the spectrum.
Illuminants which emit light of a pinkish, lavender, or greenish cast simply cannot be described on the basis of color temperature. The light emitted by blackbody radiators varies from orange-red, at the lowest color temperatures (800-900° K), through amber-white, yellow-white, white, bluish white, and, at an infinitely high temperature, pale lavender-blue. There is no place in the scale for tints of other colors. Perhaps the best method for designating the colors of illuminants is the determination of trichromatic color coordinates on a standard chromaticity chart.
Xenon and Mercury Spectra
Figure 4 includes the spectrophotometric curves of two modern projection illuminants superposed upon those of the noon sun and the HI carbon arc for comparison. These new light sources, extensively used in Europe, are the xenon discharge lamp and the mercury-vapor impulse lamp, the latter being employed as a pulsed-light source in shutterless projectors.
Except for its excessive heat and the peak in the blue region of the spectrum (which may slightly exaggerate the blue tones in color films), the xenon lamp is visually very satisfactory. Although less bright and optically less efficient than the rotating-positive HI carbon arc, it serves as an improved substitute for the LI arcs still used in the smaller European theatres. It is fairly economical and has the outstanding advantage of a much whiter light. Xenon light is, in fact, just perceptibly lavender-blue.
The high pressure mercury vapor impulse lamp gives a light which is visually blue-white, but so uneven in its spectral-energy distribution that it plays unpleasant "tricks" with the dye images on color prints.
This illuminant has very sharp and intense emission peaks in the violet (405 nm), the blue-violet (435 nm), the yellow-green (546 nm), and the fellow (580 nm). There are also strong peaks in the ultraviolet (particularly at 312 and 365 nm); but the few faint emission lines present in the infrared are not important. More than any other projection light source, the
^
■t*
•4. ><
^^*~ "■* '
1
*-\
■8
J*
•
r L.I. AR
y^<T
400
500 600
Nanometers
700
FIG. 3 — Spectrophotometric curves in the visible spectrum of average noon sunlight, the high-intensity and low-intensity carbon arcs, and the tungsten-filament lamp. Note that only the HI carbon arc accurately duplicates natural white sunlight.
A Short Cut to Brighter Pictures
^^^
Strong Glass Reflectors
II lamphouse mirrors constantly deteriorate,
lose reflectivity, waste light and power.
[1 eplace yours now -and regularly.
our dealer has the size you need.
THE STRONG ELECTRIC CORPORATION
31 City Park Avenue
Toledo 1, Ohio
International Projectionist
January 1961