Hi.

Today I found some old Airam 40W T12 warmwhite deluxe lamps but what is weird is that those are approximately 100cm long and not the typical 120cm. Is this some T12 version of modern 30w T8s or what? Those had that older airam logo so they dates pre 70s. Unfortunately my camera is broken right now so no pictures yet. What kind of ballast should I use to run those? I have to see if I can find some more of those next time.

Yes, there is 970mm 36W 0.556A and 1047mm 38W 0.43A T8's. The first need special ballast, not common with any other fluorescent due to different current rating, the second will run on generic "36/40W" ballast.

thats bad luck.... those are exactly those 970mm long lamps. There was actually this number printed in the etch and I first thought that would be the colorcode or something. Now, for what purpose these lamps were made? is it some old standart or what is the story behind these "special" lamps? I should probably go to check if there were any ballast for those lamps(found them in one demolition site) There were some fixtures but those were so weird shaped and ugly so I did not investigate any closer. There were huge bunch of these lamps but there is not much joy of these if you dont have a ballast to use them... Thanks for help anyway.

I think the 1 m lamps are mainly used in outdoor signs, at least that is the only place where I have seen them. The tubes are still available today, even 40 W T12 (at least at my supplier). I think this is because T8 drops to much light output at low ambient temperatures.

I checked Helvars catalog and there is ballast for 36w lamp with lamp current 0,53A so that kind of ballast is probably meant to use with these lamps(anyway the lamp current is very close). model number is L 42 T6 but getting that kind of ballast is probably not an easy thing to do. I have to go to do some dumpsterdiving to find out if I can find suitable ballast.

I just recalled from my memory: 0.5A are 35W MH, 0.6A are 50W MV. These are not so far from the 0.55A, so you might use this ballast, but in preheat circuit, of course. I guess these HID ballasts are usually less lossy, so you will get higher efficacy then from "fluorescent" ballasts
Or it would be at least good experiment to use the HV MH ignitor as instant start setup...

I went back there but the fixtures were gone. There was still some lamps thought and I found similar coolwhite deluxes. I have 50MV ballast somewhere so it will have to do.

@Medved: Yep, with HV ignitor you could probably make nice lamp tormentor  . I have one 4,5kV hps ignitor but its sure that I wont try it with these lamps. Maybe some less valuable lamp could be tested with that kind of connection. How much is the ignition voltage in instant start ballast? I bet way less than 4,5kV

I know Thorn Lighting still make 1 meter fittings which are now 38W T8s but I can't find any other manufacturers that make them. It seems to me like the 1 meter lamps were a failed attempt at creating standard metric size fluorescent lamps.

Based on what I've heard and read, the 36W-1 T8 and 38W T8 tubes were created for European (only?) shops with specific shelf lighting which have certain standardized shelf widths. Neither the 30W T8 (90cm) nor the 36W T8/40W T12 (120cm) matched the width of these shelves so that is why the inbetween-length 36W-1 and 38W T8 tubes were introduced.

Actually, the 36W-1 and 38W  versions were the successors of the T12 versions 40W-1 T12 and 42W T12 that came to the market at the end of the 60s. I still have a Philips 42W color 33 T12 at home from that era.

Ahaa, Thats interesting. How do the construction of these 40W-970 differ of standart 120cm long 40 watters? probably those have different cathodes but is there something else different?

I was just thinking what kind of changes they had to make to get same wattage for shorter lamp.

Ahaa, Thats interesting. How do the construction of these 40W-970 differ of standart 120cm long 40 watters? probably those have different cathodes but is there something else different?

I was just thinking what kind of changes they had to make to get same wattage for shorter lamp.

Simple:
Heavier electrodes. And shorter length mean lower voltage drop automatically, this was actually compensated by increasing the rated current.

I'd just run a 40W-1 tube on a 40W-1.2m electromagnetic ballast...

I'd just run a 40W-1 tube on a 40W-1.2m electromagnetic ballast...

Then you run it only at ~30W. I think it is not anymore healthy for electrodes, as they can run too cold (without auxiliary heating), so their emission may not reach required level to avoid sputtering.

The lamp will indeed run at reduced power but I expect the lamp current to stay at or slightly above the minimum required level needed to keep the electrodes sufficiently heated.

There a few alternatives however tht will run the lamp close to nominal power:

Find the correct ballast (tough to find)

Use 2 ballasts for European TL25W T12 (0.25A, 100V) in parallel

Use 2 ballasts for PL-C 26W (0.3A, 80V) in parallel

In Europe, this 970mm 36W T8 lamps are still in production (Osram), you can buy it. These lamps need also a higher preheat current of 0.73A. I've 36W-1 and 40W-1 lamps in my collection.