[emeritus]

No personal experience of lamp manufacture, but after GEC got out of the GLS lamp business I acquired a number of textbooks relating to electric lighting that were no longer required.

The existence of the lamp cartel was no secret.

The origin and development of the cartel is discussed in some depth in "The Electric Lamp Industry", (Bright), published in 1949 for MIT. Rather than seeking to shorten lamp life, the first cartel was established in Germany around 1903 with the objective of allowing the manufacturers to make enough profit to make lamps of good quality. Unlike the US and the UK, where the patentees could impose prices and quality control, there was no effective patent protection for lamps in Germany, resulting in savage price-cutting that resulted in lamps of poor quality and short life. At this date, the only known metal to make a reliable gas-tight seal was Platinum, and cheaper lamps often used iron wire that failed due to leakage.

Edison's original lamps lasted around 2000 - 3000 hours, but the light output soon fell to 80% of its initial value. Life was reduced to 1000 hours circa 1880 to improve luminous efficiency. Improvement in gas mantles in the 1890's gave gas a temporary superiority, meaning that Edison had to run his lamps even hotter to compete, thereby shortening their life to around 600 hours.

A detailed numerical analysis, including financial costings, of the relationship between lamp life, luminous efficiency, and cost of electricity, is set out in Westinghouse's "General Illumination Course" workbook of 1931. The 1000-hour life is presented as being a reasonable trade-off between lamp life and electricity cost for a given level of illumination for domestic users. Under-running a lamp certainly increases life, but reduces light output, leading to an overall increase in the cost per lumen. Over-running a lamp is actually slightly more economical in terms of cost per lumen.

Some extracts from these books are attached.

The conspiracy theory proponents do seem to ignore the practicalities of GLS technology and the cost of electricity. Until they moved house in the 1960's, my parents benefitted from a pre-nationalisation contract with the electricity board whereby 10/6d a year covered any maintenance needed on the installation, including free replacement of bulbs. I always wondered as a child why people paid money for bulbs when all we had to do was take the old bulbs into the electricity showroom and they would give us a replacement. No incentive for them to supply bulbs of short life. AFAIR, 2000 hour lamps were available in the 1970's. I did try a couple, but they certainly produced less light that the ordinary GLS versions.