Going off the colour, I'd say neon /argon

Love it!

Neon i reckon these were just philips S10s very good starters indeed

Doesnt seem like pure Neon (or maybe different pressure ?) Philips S10s are yellower than the old Chinese starters that really were Neon like an indicator. The starter is a newer (00's i think) Philips since in the 90s ones the capacitor was not positioned upright

The camera is being very generous with the exposure. It's only a thin film of orange but there is a purply tint which makes me think like angryhorse that its an argon/neon mix. The fittings aren't that old, late 90's 2000's were my guess for when these came out. I've been tempted as I have three to trim one down and make a fitting for my 14w 15inch T12 tubes. Should I do that or find a shitter fitting to trim down?

Indicator Neons have Argon in them too, but i think S10's might have some 3rd gas in them. I would not cut down a good luminaire. Make one out of glavanised sheet C profiles for drywall or metal cable raceways

I don't have many metalworking tools. I would have to go somewhere to get it done. The undersides of these fittings is rusted so I wouldn't feel too bad cutting one but at the same time it would be a shame as they are good 18w fittings. They might have krypton in them as the purply underglow does have a dim silvery colour to it

Thats the great thing with sheet metal profiles. They can be processed into a good fluorescent batten with just few cheap hand tools. Cut to length and make the cuts to fold the ends of the "box" with tin snips, fold by hand / with pliers / wood block and hammer, and secure with self drilling screws

Sounds fantastic! Will have to give that a go!