So far I know Osram (factory Eichstätt/Germany) presented the 26mm T8 flourescent tube jan. 1978 for 35W T8 instead of T12 40W and 60W T8 instead of 65W. July 1978 presented Osram and Philips new T8 lamps for the market 18,36 and 58W. They wrote the lamps will be saleable in January 1979. GTE Sylvania Frauenaurach (Germany) presented for the market these typically T8 lamps in April 1979 with black end caps.
@TL8W: Where comes your 18W TLD of 1978 from? Has that lamp the brass end caps? 

When did the modern T8 fluorescent lamp came out for the US market? GTE Sylvania introduced the F32T8 Octron line in August 1981. Then Westinghouse followed suit shortly after with the Octolume line. GE was late in the game, the Trimline (now Starcoat) line came out around 1988-89.

Did the first Octrons have black ends or already aluminium? Interesting that in the States the T8 energysavers were introduced later than in Europe.

The 18w and 36w T8 line you guys are talking about is not widely used in the states. Reason, most of our F40T12 ballasts are rapid start and they can't start krypton filled T8 lamps because the starting voltage requirement is higher in these lamps than RS ballasts could provide. Also the thiner tube diameter is farther away from the grounding fixture surface, which aids in lamp starting. Instead, we got the 34w 4 feet T12 and 60w 8 feet T12 energy savers.

Such tubes weren’t available in Europe. The T12 are/were always full wattage.
The other way round on our VHO tubes the wattage was being increased like for example the original 120W 5 feet tube became 140W and the 100W 4 feet tube was later sold as 115W. Both were then stated as “Double Flux”.