The T8 is a Marine Land F18T8, which is exactly the same length as a standard 24" T12, so you can switch from F20T12 to those and claim you converted to T8 xD
IIRC the 18w was designed as a preheat lamp while the 17w was originally designed as a trigger/rapid start lamp. I've seen a old magnetic RS ballast for them on eBay before.
They actually use the 18w as a energy saver alternative to the 20w lamp overseas much like how 36w preheat T8s are used as a energy saver to the 40w lamp instead of our 32w RS T8 lamp.
Oh and the 18w lamp is most commonly used here as a appliance and aquarium lamp but I don't think the 36w T8 is used here...a shame cause I believe they actually run on North American preheat ballasts and save some energy unlike those 34w ballast cookers.
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They actually use the 18w as a energy saver alternative to the 20w lamp overseas much like how 36w preheat T8s are used as a energy saver to the 40w lamp instead of our 32w RS T8 lamp.
Oh and the 18w lamp is most commonly used here as a appliance and aquarium lamp but I don't think the 36w T8 is used here...a shame cause I believe they actually run on North American preheat ballasts and save some energy unlike those 34w ballast cookers.