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National Mazda Grid Filament Stereopticon |
Within one year of the 1913 introduction of coiled tungsten filament lamps for general service lamps, this new technology was applied to stereopticon projection lamps. At first the filament was bent into a series of parallel sections, arranged in a wreath shape similar to general lighting lamps but rather more compact so as to attain a higher brightness light source. However the depth of the filament assembly prevented it being brought into the focal plane of the projection apparatus. Moreover the light from some filament segments was partially blocked by other parts of the filament. This limitation was overcome by arranging the parallel coiled filament sections into the shape of a planar grid, having approximately the same square shape and aspect ratio as the images to be projected. The result was an immediate improvement in the brightness of projected images for a given lamp power. Around the same time, the design of the bulb envelope was also reduced from the former G-30 spherical bulbs to the new T-20 tubular bulb featured here. This allowed the filament to be brought closer to the optical system, thereby realising another increase in screen brightness.
It is believed that this development took place between approximately 1915 and 1921 - GE literature of 1915 still refers only to the bunch-filament G-30 design of stereopticon lamps, and this lamp features its exhaustion tip on the bulb crown - thereby dating it to prior to 1921 when the tip was relocated to the inner stem area.
| Manufacturer: | National Lamp Works of GE | |
| Lamp Power: | 400 Watts | |
| Lamp Voltage: | 115 Volts | |
| Lamp Current: | 3.48 Amperes | |
| Cap Type: | E26s | Brass & Vitrite |
| Bulb Type: | T-63 | T-20 in eighths/inch |
| Bulb Finish: | Clear | Borosilicate |
| Filament Type: | C-13 | Monoplane Grid |
| Atmosphere: | Argon-Nitrogen | Red phosphorus getter |
| Luminous Flux: | 10,000 Lumens | |
| Luminous Efficacy: | 25 Lumens per Watt | |
| Beam Intensity: | N/A | |
| Beam Distribution: | N/A | |
| Colour Temperature & CRI: | CCT: 3000 Kelvin | CRI: Ra 100 |
| Chromaticity Co-ordinates: | CCx: 0.452 | CCy: 0.409 |
| Rated Lifetime: | 50 hours | |
| Burning Position: | Vertical base down | |
| Overall Length: | 140 mm | 51/2 inches |
| Light Centre Length: | 76.2 mm | 3 inches |
| Factory: | U.S.A. | |
| Date of Manufacture: | Approx. 1920 | Date Code: p4 A5 |
| Original Value: | ||
