||Following the 1958 launch of the first linear halogen lamps, their compact dimensions and stable output quickly caught the attention photographic and projection equipment makers. GE's Photo Lamp department was quick to respond to their requirements, which were primarily for a lamp having a more compact filament than was employed in the first double ended types for floodlighting applications.
The 420-watt lamp illustrated on this page is not only the original double ended lamp which founded the compact 2⅝" family, but also the first halogen lamp engineered for use in audio-visual equipment. It was classified by ANSI with the reference FAL, and by the LIF as type A1/227. It employs a compact coiled-coil filament less than half an inch long, and although such a source was unsuitable for slide projection, it was entirely adequate for use in Overhead Projectors. Its high colour temperature of 3200K and relatively long 75-hour lifetime (by comparison with similar incandescent types) made it ideally suited to AV applications.
Shortly after its launch, it was joined by the 460W 3400K DWW version, realising a 50% increase in lumen output. However the life of its successor dropped to a mere 10 hours, making replacements too frequent for AV applications. It was quickly superseded by the 600W 3200K FFJ, whose life was returned to 75 hours and thus offered the high output and long life required for the OHP market.
This lamp operates on the tungsten iodine cycle, and thus shows a distinct greenish light when in operation. This was rectified from the early 1970s when both lamps in the 2⅝" family were modified to bromine chemistry.