||Following GE's invention of the blown reflector incandescent lamp in 1936, a natural progression was to adopt similar designs for infrared heating applications. GE's first industrial infrared lamps were made in G-30 spherical bulbs for use with an external reflector, and the integrated reflector versions in R-40 bulbs made a dramatic step forward both in terms of initial performance, and also because a new, clean reflector was provided with each lamp replacement.
Initially the R-40 infrared reflectors were made in soft glass bulbs, even up to the most powerful 375W rating. Their high operating temperature rendered them liable to shatter with some violence if splashed with liquids or touched against cold objects whilst in operation, due to the low thermal shock resistance of soda-lime type glasses. Additionally, the highly focussed infrared beam resulted in uncomfortable levels of glare arising from the concentration of visible light into the same area. Both problems were elegantly solved with the 1946 launch of the lamp featured on this page, which set new standards in the infrared lamps business.
The bulb is blown in borosilicate hard glass which exhibits excellent thermal shock resistance. The front area of the bulb crown is externally coated with a deep red colour organic laquer, and its transmission is controlled so as to allow unhindered passage of the infrared wavelengths while blocking the majority of the visible light emission. The lamp cap was also changed at this time from an expensive mechanically-locked skirted screw base to a simple standard screw cap affixed with high temperature cement. A ceramic baffle plate in the lamp neck serves to keep the cap temperature low enough to permit this change.