PHOTOGRAPHIC LIGHT SOURCES 



287 



exceeded. Table VII shows the relative photographic effects, in various portions of 

 the visible spectrum, of daylight and photoflash illumination. 



Table VII. — Relative Photographic Effects for Various Emulsions and Light 



Sources 



Plate 



Blue-sensitive plate. . . 

 Isochromatic plate. . . . 

 Orthochromatic plate.. 

 Panchromatic plate I . . 

 Panchromatic plate II, 

 Panchromatic plate III 



Relative photographic effect' 



Photoflash lamp 



Red Yellow Green Blue 



30 

 30 

 30 

 180 

 70 

 90 



15 

 30 

 20 

 80 

 60 

 50 



30 

 30 

 30 

 30 

 50 

 40 



160 

 160 

 180 

 100 

 120 

 120 



Daylight 



Red Yellow Green Blue 



30 

 30 

 30 

 90 



10 

 20 

 15 

 40 

 40 

 30 



25 

 30 

 30 

 30 

 40 

 30 



180 

 180 

 180 

 180 

 140 

 160 



1 From Philips Tech. Rev., vol. 1, no. 10, (1936). 



The light output of photoflash lamps is given in Table VIII. One of these lamps 

 produces a maximum intensity of about 360,000 candles, which is about twice that of 

 a 50-kw. tungsten lamp whose luminous intensity is about 166,000 candles, measured 

 perpendicular to the plane of the filament. The spectrum is largely continuous 

 although some superimposed lines of aluminum are present. 



The photoflash lamp is quiet in operation and does not produce any smoke or 

 objectionable odors, vapors, or gases since the combustion is confined entirely to the 

 interior of the glass bulb. Of course, when once used, the aluminum is changed to 

 aluminum oxides and the filament is usually burned out, so that the lamp can no longer 

 be used. 



It is sometimes found that photoflash bulbs operated at low voltage (3 volts is 

 common) fail to flash. This is probably due to lack of contact between the filament 

 and the crumpled aluminum. Such bulbs may be used on high-voltage circuits, 

 however, and will then perform satisfactorily. It has been found that when several 

 photoflash bulbs are used in the same reflector, igniting one lamp will serve to set off 

 the other lamps. For this reason, it has sometimes been suggested that only one lamp 

 in a group need be connected to the source of current. Such a procedure may be 

 entirely satisfactory for portraiture or similar types of photography where the subject 

 is relatively motionless and the shutter is opened during the entire duration of the 

 flash. However, the practice of flashing several bulbs by contact is not to be recom- 

 mended in those cases where the shutter is synchronized with the photoflash lamps, 

 as the bulbs do not all flash at the same time. Consequently, the shutter may be 

 closing before the "contact flashed" lamps actually ignite. 



Bulbs have been known to explode while being flashed. The resulting shattering 

 of glass can be dangerous. To safeguard against exploding lamps, photoflash lamps 

 have recently been manufactured with a disk of colored salt painted on the bulb or 

 the stem. These disks have one color in an absolutely dry atmosphere of oxygen but 

 change their color in the presence of the moisture of the atmosphere. If any cracks 

 or air leaks occur in the bulb, this salt changes color and indicates that the lamp is 

 defective and may explode. Such lamps should not be used. 



