Dimming a TL tube in the past

[AgX]

This is a historic/academic question.



I just found in an old Katalog a Kindermann darkroom luminaire based on a regular Philips TL29 tube, which got a built-in dimmer allowing 11 light-outpt settings. The luminaire is from 1966 or earlier.
The tube is without starter, thus likely permanently heated.

I know of electronic power supplies for plain TL tubes which allow dimming of the tube.

I do not remember (well, my memory...) ever having read in old electrotechnics literature about dimming a TL tube. I mean, that was in times before phase-fired control.

Any ideas how that was achieved back then?

 

[AgX]

Well, in a lamp manufacturer's handbook from that time I found a hint at phase-fired control of TL-tubes. This was achieved by using thyratron tubes. However the same source stated that such was that costly that even in cinemas it would be more cost effective to install just incandescant lighting and dim that at lower investment costs.
On the net I found hints though at thyratrons installed at cinemas.

So I am not much wiser, but still the thyratron is my best bet., as you keep silent.

 

[Billy Axeman]

I have a stand-alone vertical TL design lamp in my living room which I dimmed somewhat by adding an extra ballast inductor in series with the existing one. This reduces the current through the lamp after it has started. The effect though is limited and the color of the light shifts to reddish.

p.s. These links on Wikipedia suggest a 'dimming ballast' for fluorescent lamp so there might be existing solutions for that

Fluorescent lamp
https://en.wikipedia.org/wiki/Fluorescent_lamp
Link: Dimming ballast

Electrical ballast
https://en.wikipedia.org/wiki/Electrical_ballast
... Dimmable ballast.

 

[AgX]

Yes; I thought that maybe a larger ballast coil was used, that had several taps, but I found no hint whatsoever at old literature that just reducing the current had worked. And you indeed experienced disadvantages with such approach. (But to be fair, reducng the current at incandescant lamps reduces the colour temperature too, and we accepted that..)

The link at Wikipedia refers to a ballast controlled by a form of thyristor. But that is technology from afer the period I am investigating on.