Another nice lamp! I wonder what years did GTE use the right hand etch or did they use both at the same time.

GTE used the right-hand etch? I think the lifelines used it to symbolize the plant it was made at.

So this is yours now? Cool to hear an update on the basement preheaters!

not this exact lamp. Mine has a different date code. I'll eventually get all the lamps and fixtures. Oen fixture is going to Aaron and another to Joe. I'll be keeping the other two 4ft fixtures and the 2ft fixture. So the original owner of these fixtures had used daylight lifelines for a while. all the 4ft lamps were daylight Sylvania lifelines except for a GE, a 1988 Philips F40CW, and a 80s or 90s Sylvania F40/W lamp. The 2ft fixture has two inside etch GE F20/CW lamps.

yep the fixtures aren't going anywhere so no worries! My uncle thought the lamps were all dead. These fixtures really are weird though lol. You can't tell of the fixture have power or not and if the lamps are good or not or if the starters are good or not or if the ballasts are good or not. One fixture had one lamp installed and that lamp worked but my uncle took out the lamp. the wide-spaced lamps fixture doesn't show any signs of life but it could just be a quiet ballast. the lampless fixture for Joe isn't connected to power nor is the F20 fixture.

Nice, that Philips F40CW is the same age as the ones at my house in CA!
In the one pic I thought the one lamp in the fixture with the low-profile top was a Norelco or a rare Westy with aluminum ends, but I guess not. Hope that GE turns out to be a Mainlighter or a 3!

when were the 3s made and when were the mainlighters made? (Example: 1982-1990)

3's and 3-pluses were made in the 60s I think, I know 3-plus came later. Mainlighters were made from 1969-1985 though. Mine are all late 70s vintage.

Oh wow a GE-3 lamp would be a nice find! I'm guessing it's probably a mainlighter or post-mainlighter though.

Maybe a rare pre-EPACT non- Watt-Miser F40CW? Those are kinda rare IMO since they were made for only a couple years, not decades like the Mainlighters.