GE Sealed Beam Automotive / Pin Spot #4515

The model #4515 sealed beam lamp was introduced in the 1940s for automotive spotlighting applications, employed in hand lamps which could be powered from cars having a 6-8 volt electrical system to serve as a long-range spotlight. This application soon disappeared, especially with the widespread introduction of streetlighting which made a mobile spotlamp redundant. However its uniquely narrow beam with razor sharp cutoff soon attracted the interest of theatrical lighting technicians, and today long after the disappearance of its automotive application it continues to be mass produced for entertainment lighting, as a so-called Pin Spot.

It features a specular reflector and clear lens, combined with a compact filament of unusually low voltage to deliver an exceptionally narrow beam. Extremely sharp cutoff is achieved thanks to the anti-glare shield which blocks stray light from the filament, such that virtually all light rays exiting this lamp have been collimated by the reflector.

Interestingly this lamp shows a residue of one of GE's early processes in PAR lamp manufacturing, the electrical tipoff. Traditionally small gas flames are used to seal the exhaust tube at the rear of the lamp, but this does not allow the pressure in the bulb to be greater than atmospheric, and for PAR lamps can lead to cracking if the flame plays too much on the glass reflector. GE therefore developed the process of electrical tipping, in which the tubulation is first painted with an electrically conductive graphite coating, and then sandwiched between a pair of spring-loaded metal blocks. These deliver a high current through the graphite, and pinch the glass together as it softens, preventing any blowout in case positive internal gas pressures are used.
Manufacturer: General Electric U.S.A.
Lamp Power: 30 Watts
Lamp Voltage: 6.4 Volts
Lamp Current: 4.6875 Amperes
Cap Type: Screw Lugs
Bulb Type: PAR-114 PAR-36 in eighths/inch
Bulb Finish: Clear Lens Aluminised Reflector
Filament Type: C-6 Single Coil Transverse
Atmosphere: ~10% Nitrogen in Argon Positive Pressure
Luminous Flux: N/A
Luminous Efficacy: N/A
Peak Intensity: 55,000cd
Beam Distribution: Oval 5°x10° to 50% peak intensity
Colour Temperature & CRI: CCT: 3000K CRI: Ra 100
Chromaticity Co-ordinates: CCx: 0.452 CCy: 0.409
Rated Lifetime: 100 hours to 50% survival
Burning Position: Universal
Overall Length: 70 mm 2¾ inches
Light Centre Length: N/A
Factory: Trumbull, Warren U.S.A.
Date of Manufacture: April 1950 Date Code: 4 0
Original / Present Value: Unknown Unknown
References: 1) GE Miniature Lamp Catalog 3-6478, USA, 1964?