The Lamp Room

What's the story with these?
I can't find much information on them besides that they exist and you can buy them.
Was it an older standard like how older 5ft tubes were 80W?
Are they any brighter than a standard 2ft?

I guess that they are meant to be "half 80W" tube - to be able to run 2 in series on 80W gear. Correct me if i am wrong. For us it means that 2 40W T12s in series may work ok on 80W Merc ballast or 2 36W ballasts in parallel, with S2 starters

They are supposed to be 2x brighter than 20W, assuming same efficacy. (but it would be less efficient than 40W 4ft tube). Also they probably handle better being run in cold ambient (outdoor signs etc)

Yes, that's correct! These can be run in series on old 80w gear. Most fittings I've seen these in run the tubes as a pair anyway, quite uncommon to see a single 2' 40w T12 fitting. they tended to be used in streetlighting, road signs and the like where a longer tube would have meant a larger, bulkier lantern. All the fittings I have that run them are streetlights, with the exception of one 'explosion-proof' fitting and a couple of battens I've converted myself. You can run a single 2' 40w tube on 2x 20w ballasts wired in parallel. That's how the fitting I use to test my 2' 40w tubes is wired. Good luck ever finding a genuine 2' 40w ballast to run a single tube. they exist, but VERY hard to find indeed!

I see now.
I did assume they'd be running on 80W gear.
I think I'll order one to take a look at as I have a spare 20W ballast I could beef up a fitting with.

If you do mod a fitting, make sure the ballast pair you use are identical to eachother!

For the 2 switchstart chokes in parallel, i think it is not really required that they be identical. After all their electrical characteristics are very similar regardless of exact design / manufacturer

(Chokes of different efficiency classes like EEI=C and EEI=B1 may have somewhat different current phase angle that may result in slightly underdriving the lamp when in parallel, but i think the effect will be insignificant and you can pick pretty much any chokes you want)

Yes, that's correct! These can be run in series on old 80w gear. Most fittings I've seen these in run the tubes as a pair anyway, quite uncommon to see a single 2' 40w T12 fitting. they tended to be used in streetlighting, road signs and the like where a longer tube would have meant a larger, bulkier lantern. All the fittings I have that run them are streetlights, with the exception of one 'explosion-proof' fitting and a couple of battens I've converted myself. You can run a single 2' 40w tube on 2x 20w ballasts wired in parallel. That's how the fitting I use to test my 2' 40w tubes is wired. Good luck ever finding a genuine 2' 40w ballast to run a single tube. they exist, but VERY hard to find indeed!

Do you by any chance have a wiring diagram for 80w mbfu choke wired in series with 2 x 2ft 40w tubes that can show how the starters are wired on to the tubes? - for example using 2 standard switchstart starters?

This basically (shamelessly nicked off the net). Exactly the same circuit you'd use for 2' 20w tubes on a 40w ballast, 8w tubes in pairs, or any other series circuit for that matter.