I read that fluorescents normally operate between +5 and +60 Celsius (41 and 140 Fahrenheit).
The winter temperatures in our country are sometimes below -10 °C (14 °F), rarely below -20 °C (-4 °F).

I have faint memories from my early childhood (some 35 years ago) - long T12(?) hanging over the street. Reportedly, the Soviet "Razno" were able to cope with these temperatures.

Today, the CFLs are used. In the last years, there are many new installations in our town. AFAIK, it's Osram DULUX L SP 36 W/840 2G11. "Optimum luminous flux at low ambient temperatures (+5 °C)." No low temperature limit specified.

I suppose, the old Soviet fluorescents had the problem solved chemically while today the electronic ballast does it...?

Ballasts engineered for higher open circuit voltage (OCV) will start lamps at low temperatures.  Modern T8 electronic ballasts do this, and so do older HO (800mA) and VHO (1500mA) and some other types of ballasts.  Preheat ballasts seem to be able to start lamps at low temperatures well since they make a big voltage spike when the starter opens.  I think any fluorescent cold temperature outdoor applications still should be enclosed so the lamps can reach proper operating temperature and light output.  In the mid-80s, a new supermarket opened near me and they used single bare VHO lamp strips outside.  They seemed to work well in the winter but these lamps have other problems like poor lumen maintenance.  This was in the northern USA where it sometimes gets below -20C in the winter.

There are engineering tradeoffs about mixing stuff in with the mercury (amalgam) to change the optimum operating temperature, but I don't know much about that. 

I saw a post here about the old Soviet street lights.  It sounds similar to old US streetlights that used HO and VHO lamps on rapid start ballasts.

Matt

There are two problems with fluorescents at low temperatures: Starting voltage requirements being too high for some ballasts and then maintaining mercury pressure during operation (so the efficacy).
The ballast tackle just the first problem. And in fact the preheat style ballasts (majority in Europe, as on 220..240V it means just a plain series choke for nearly all lamp types) deliver far enough voltage for ignition at virtually any temperature, provided the starter works there. But those have quite some margin, so no real problem with that.

The other story is the mercury pressure. Low temperature means the mercury condense and so there is not enough mercury in the atmosphere to generate light. The optimum mercury pressure is at about 30..40degC on the lamp cold spot. The amalgams attract the mercury, so lower the pressure at higher temperatures. Well, why the amalgam is important for cold operation? With compact format of the PL-Ls, they usually operate at temperatures way higher than the ambient, so it is not as big problem to heat up to ~+30degC even when outside is -20degC (with appropriate fixture without air drafts), what is almopst at the optimum for the pure mercury. But that means in summer, when the air could reach 30degC (at nigh and in the central Europe), this setup will correspond to temperatures exceeding 100degC, with pure mercury that would be too much (the streetlight should operate both in summer, as well as in winter). But when you use the amalgam, above the 30degC the pressure will be steered by the amalgam temperature. And as this is usually way higher, it is matter of internal component temperature control, e.g. from the filaments or if the need call for that, even a bi-metal could be eventually used to move the amalgam pellet closer/farther away from the hot electrode, so maintain it's temperature really constant over very wide temperature range.

And even below the "30degC" the situation is not lost: The optimum Hg pressure, so the cold spot temperature depend on the complete lamp fill mix, this was used mainly with T12.

So the compact shape of the PL-L is in fact easier to design it for wide ambient range than T12, for T12 at cold you have no other choice than the gas mix, while with the compact PL-L this problem is shifted below -10..-20degC just by the fact the lamp heats itself up...

And by the way the electronic ballast makes it more complicated: It's lower losses mean there is lower temperature in the fixture.
But on the other side the electronic could be designed with some thermal compensation, boosting the power at low temperatures.
But all PL-L's I've seen outdoor have just a preheat choke, no electronic...

Very interesting, thanks.

... even a bi-metal could be eventually used to move the amalgam pellet closer/farther away from the hot electrode, so maintain it's temperature really constant over very wide temperature range.

Never heard of it. I wonder if this kind was produced and used or there were just prototypes of this simple self-regulating system.

But all PL-L's I've seen outdoor have just a preheat choke, no electronic...

Yes, it seems that the performance on very low temperatures is worse. Possibly, there is also a slight light colour change.

Very interesting, thanks.

Quote from: Medved on April 14, 2014, 12:57:01 AM

... even a bi-metal could be eventually used to move the amalgam pellet closer/farther away from the hot electrode, so maintain it's temperature really constant over very wide temperature range.

Never heard of it. I wonder if this kind was produced and used or there were just prototypes of this simple self-regulating system.

It was meant as an example, what could be possible if you have to go so far. Normally the temperature is regulated by the filaments: Higher the temperature, less it becomes sensitive for absolute temperature differences, but the environment induce constant differences between summer vs winter operation.

Quote from: Medved on April 14, 2014, 12:57:01 AM

But all PL-L's I've seen outdoor have just a preheat choke, no electronic...

Yes, it seems that the performance on very low temperatures is worse. Possibly, there is also a slight light colour change.

It is, but what I observed here, most of the fixtures were designed for 2 lamps, but installed was only one of them. But that mean there is 1/2 of the generated heat compare for what the fixture was designed for, so no wonder the lamps have problems to reach full brightness at cold temperatures. And I would expect the same happen on other places as well. Usually these were put on poles originally designed for  80W MV with ~3500lm of mean / 3000lm minimum light output over the life without any beam control (just bare MV lamp with just a roof being the complete fixture), so a single 40W PL-L with partial beam control is sufficient there.

There are engineering tradeoffs about mixing stuff in with the mercury (amalgam) to change the optimum operating temperature, but I don't know much about that.

I dimly remember that Narva made in the old days such lamps, denoted as "kältefest". (Not what Narva today sells as "Igloo", lamps like the Philips Xtra Polar with an additional outer tube in T12 size.)

I saw a post here about the old Soviet street lights.

Weren't they in doubt MVs?


In practice I have seen so far no big problems with FL outdoor lighting in cold winter nights. There may be a drop in light output, but it's not too dramatic, at least when considering that in Central Europe wer'e talking about just a few nights every year.

I remember from such a cold morning the switch-on of the lights in an unheated storage hall: The lamps were pretty dim, but they all came up without problems. And I think after a while they got brighter, after warming up a bit.