Measure their diamerers, you'll probably find that the Philips is an A-60, whilst the G.E. is an A-55. Most of our last G.L.S. in Australia from the Sidorjo plant south of Surabaya, where A-55's. A-55 was never made at E.L.M.Australia in the later years, although this bulb size was used for 15w vacuum refrigerator lamps with 5WR filaments in the 1950's and 60's at E.L.M.Australia.

The first step to these smaller size A55 bulbs came simultaneously from Philips and Osram, if I remember rightly in 2001. It was done purely as a way of reducing costs by shrinking the packaging and transport volumes. GE went a step further and uses still smaller A50 bulbs. What they don't tell you however is that the rate of lumen depreciation during life for A55 and in particular A50 is considerably more rapid than the original A60's. The evaporated filament material is deposited over a smaller surface area on the bulb, and as a result is somewhat thicker and blocks more light. Additionally the smaller size lamps run hotter, and occasionally this has given problems for the 100W rating in particular. Due to the higher glass temperatures, the glass is more likely to release residual impurties into the bulb atmosphere, which react with the tungsten filament and lead to still faster rates of blackening. If the production processing is of excellent quality it shouldn't be a problem, but in reality that's not always the case! In conclusion, the original A60s are, on balance, usually somewhat superior to the modern miniaturised lamps.