GE-Mazda Blue Photoflood DKE 5000K
This strongly tinted photoflood lamp has a much deeper colour than usual, and was designed for portraiture with black and white film materials. This was found to deliver especially beautiful rendering of skin tones. The original literature claims a colour temperature of 5200K vs the 4800K of normal blue photofloods, however measurement reveals a much higher CCT of 11000K. The measured flux is only 5500lm vs the claimed 9400lm, perhaps due to large variations in the thickness of the hand-blown bulb glass.

The bulb is heavily frosted on its inside surface and delivers a softly diffused light which is easy on the subject's eyes, and does not lead to such severe pupil contraction as other high intensity lamps. It can also be used as a supplementary light source with 'Daylight' film materials, but owing to its unusual spectrum was not recommended as the sole light source - some extra light from standard 4800K photofloods being preferred to attain a more natural colour balance

Aside from the particularly elegant blue glass bulb, the rest of this lamp is similar to standard versions. It employs a single-coil tungsten filament driven at around 3200K, achieving about 300 hours life - considerably longer than the 10 hours of the equivalent 3400K clear and 4800K blue photofloods. The filament is supported on a conventional soft glass stem assembly, and a baffle plate of mica in the neck serves to reduce cap temperature. The mica is of the expanded type, having been treated in a hydrogen furnace to cause partial delamination and improve its infrared reflectivity. The cap is of brass & vitrite, affixed to the bulb with the typical cementless crimping system as found on other GE high wattage mogul screw-based lamps.
Manufacturer: General Electric U.S.A.
Lamp Power: 1165 Watts
Lamp Voltage: 120 Volts
Lamp Current: 9.73 Amperes
Cap Type: E39s Mogul Screw, brass & vitrite
Bulb Type: PS-165 PS-52 in eighths/inch
Bulb Finish: Inside Frosted Deep blue glass
Filament Type: C-7A Wreath-Vee
Atmosphere: Argon-Nitrogen
Luminous Flux: 5,500 Lumens
Luminous Efficacy: 4.7 Lumens per Watt
Beam Intensity: N/A
Beam Distribution: N/A
Colour Temperature & CRI: CCT: 11000K (measured) CRI: Ra93
Chromaticity Co-ordinates: CCx: 0.278 CCy: 0.276
Rated Lifetime: 300 hours
Burning Position: Universal
Overall Length: 332 mm 131/16 inches
Light Centre Length: N/A
Factory: USA
Date of Manufacture: August 1945 Date Code: 68
Original Value: US $14.75 (1961)
 
References: 1) GE Photographic Lamp Guide, c.1950, U.S.A.
2) GE Photolamp Price Schedule, 27 September 1961, U.S.A.
3) Photoelectric Measurement.