||Although Sealed Beam reflector lamps have existed since their 1938 development by Daniel Wright at GE of America, it took a number of years before their initial restiction to special applications was widened to cover interior display lighting. Part of the reason for this was the large cost difference vs blown glass reflector lamps. The key stimulus that propelled sealed beam lamps into general lighting was the emergence of long-life mains voltage versions equipped with a user friendly screw cap, combined with extensive mechanisation of the manufacturing process so as to permit a cost reduction. The first sealed beam lamp engineered for this mass market was the PAR38 version, and it could be produced with a power dissipation up to approx 150 Watts.
To cater for applications requiring higher power, a 300 Watt lamp soon followed in the larger PAR56 envelope. This increased its cost quite significantly and luminaire design was somewhat more complex as these types made use of the two-prong GX16d caps as used on professional stage/studio lamps. The gap between the 150W and 300W ratings was bridged around 1950 in the USA, with the 200W PAR46 size employing a side prong cap.
This intermediate size was not offered in European markets, where the difference in luminous flux between the largest PAR38 of 150W and the smallest PAR56 of 300W left a rather large gap. In 1973 Thorn Lighting attempted to fill this with a 200W PAR46 engineered for European markets. Most unusually, this lamp made use of a standard E27 cap so as to keep costs low and simplify luminaire design. However the design did not prove very successful and within just a couple of years it had been discontinued.