Lamps / luminaires for walk-in freezers

Any fluorescent lamp will have an issue with this being way off it's optimum operating temperature. This creates two problems:- The lamp will be very dim. If you fit a thermal sleeve to the tube, it will eventually warm up, but this can take half an hour, so it's not suitable for occasional use. Secondly, the tube starting voltage will be much higher than usual, which can make the lamp much harder to start -- depends heavily on the control gear. 6' and 8' tubes would be impossible to start using regular switch-start control gear, and even 5' would be difficult.

5' tubes on SRS (Semi-resonant start) control gear used to be the norm for very low temperature on 240V mains as it generates 500V across the tube for starting, but this has vanished from the scene with the advent of electronic control gear. If you go the electronic control gear route, you will probably have most luck with instant start type, but you might have to do some trial and error to find a ballast make that works reliably.

How come a GLS lamp in a walk-in freezer is being subject to rough handling? On the assumption that the lamp doesn't need to be left on, a filament lamp is probably the best choice. What you could try for very low outlay would be an energy saving lamp in the same socket. Pick one with an outer bulb over the tube, as this will help the tube to heat up, but you'll still have the same problem with long run-up, just supposing the control gear generates enough voltage to start the lamp in the first place.

I work in a walk in freezer and just use a standard screw in florecent and it works fine as long as it does not get turned off... if it does i leave the door open for a few minuter and it works fine ps. my light has a glass shield around it if that matters...

Maybe the folks over on sci.engr.lighting can throw some light on this. Here's my thinking:

A standard incandescent lamp shouldn't have trouble in this application. If anything, the various fluorescents you are considering may have far more problems at such low temperatures. The reduced life of an incandescent might be due to the lower filament resistance at low temperatures, when the bulb has been off and cools down. The resulting inrush will be higher and might be over stressing the filament. One thing to try would be to use a bulb with a higher voltage rating (130V instead of 120V). If that doesn't help, some sort of 'soft start' series device might help. I seem to recall a little button shaped device intended for insertion into a standard lamp socket that was supposed to extend lamp life by reducing the warm-up inrush.

It's not clear if the OP means that the life of the GLS lamp is shorter than expected, or that it meets its life spec but life is shorter than desirable. I think he meant the latter.

I also don't think that the temperature of the freezer will increase the surge current enough to make a noticeable difference in life. After all, the operating temperature of the filament is about 2700 K, so decreasing the cold temperature by about 50C doesn't change the resistance ratio by very much.

It's possible to use fluorescent lamps in insulating sleeves that are designed for cold ambient temperatures. These are designed for outdoor applications in locations where winter temperatures are cold. However, if this walk-in freezer is used for food or any similar material, I would be concerned about mercury contamination if (or more accurately when) one of the lamps breaks.

Until recently the only non-mercury option would be incandescent lamps, but if the short life of incandescent lamps is a serious problem, it is becoming possible to use LEDs for this type of application - though the initial cost will be very high. The efficacy will be higher than GLS lamps, especially on a 230-volt system and especially when compared to long life GLS designs. But the efficacy will be significantly lower than fluorescent sources, by at least half.

The other option is a fiber optic light guide or light pipe system that locates the lamps outside the freezer. This removes both the waste heat and any potential mercury contamination from the freezer. But, this option also has high initial cost.

GLS are rated 750 or 1000 hrs. Converting to 12v filament would enable you to use common 2000 hr and 4000 hr 50w halogen bulbs. It should also be a low cost conversion.

12v would also enable the use of 2x or 3x 20w halogen lamps. When one dies, you still have light output. With 2 lamps you need to replace one twice as often compared to using one, but you dont lose your light at the time, and if necessary you can go longer between relampings, since the combined life will be more than the life rating of a single identical lamp.

What issues there may or may not be from the food safety angle I wouldnt know.

NT

It may not be the inrush (I agree with your point about it being a small shift in power) but it could be thermal shock. Typically different materials expand and contract at different rates, for situations with wildly varying temperatures, the lamp companies match their materials so that the stresses remain managable in the operating range, but possibly not outside of it. What might be happening here is that the stresses in the pinch or adjacent are just too much, particularly as the glass starts at -30=B0C and quickly the metal is at

2400=B0C (at least at the filament). A little crack here, a leak there and suddenly you have fried filament.

And the LEDs might actually last their design life in this environment!!! Subcooling 50=B0C would certainly drop the operating temp all the way in to the silicon. Wow, I've found somewhere I believe LED data for! Thanks Vic!

I don't know that this would prove beneficial unless you're able to ensure that the interface through the insulation is sufficient to prevent more heat flow out through the light pipe than the light source originally produced. Normally I'd say fine, but we have a 50=B0C differential driving quite a lot of thermal flux. The fiber optic would probably work pretty well though. PMMA might get quite brittle - I remember installing some .75" harnesses in Seoul in the snow in a building without a facade. It took a day and a half to simply unroll six harnesses very slowly. Glass fiber would be more expensive, but might be better suited to the environment.

My big question is: Is this fridge continuously lit, or only when there is someone in it? If it is intermittent, you have more shock on the lamp, but the rate at which the lamp is being used is relatively slow. The inefficiency and heat added by an incandescent isn't important in this case, as opening the door will have much bigger impact. On the other hand, fluorescents don't start well at low temperatures, but can be kept warm (as you pointed out) with a sleeve insulating it at roughly optimum operating temperature. If on permanently, a well glass fitting with a small metal halide might actually be a good solution. A preheat lamp could be used for startup.

Thomas Paterson

Maybe not exactly what you are looking for but could these be LED refrigerator lights be adapted to work?

IME, one test I did with philips CFs indicated that they start just fine at -22C, but that was only once, and I haven't tried it for reliability purposes, it was just to see if my garage lights will go on if it's really really cold.

I still don't think that 50C added differential could name enough difference to notice. But, I'm certainly open to being proven wrong with some test data.

Well - folks here who have read my comments about LED for many years will be surprised that anyone thinks of me as an LED supporter :-)

The fiber is long and thin and constructed from low thermal conductivity material. The light only makes it from one end to the other because of the internal reflection. As long as the fiber does not transmit IR there is little heat transfer. Fibers have been used for this application for a number of years.

It is 50C at 270K or so, which does make a fair difference to the inrush current, which would exacerbate existing filiment problems.

I don't know enough about incandescent filaments to know whether it is a problem but it's possible that there could be a phase transition between room temperature and the temperature of the freezer that could make the filament more brittle at low temperatures.

Certainly there is an old story that claims that Napoleon's sodliers' tin buttons disintegrated in the cold temperatures experienced during the retreat from Moscow. Whilst possibly apocryphal, pure tin does have a ductile/brittle phase transition at 13.2 degrees C (from beta/white to alpha/grey tin).

David

It's a 50C adder to the difference between the starting or cold temperature and the operating temperature. While the glass-to-metal seals do not operate at 3000K, they still operate well above 270K.

No test data, but you're changing the pinch from heating from 20=B0C to

300=B0C (280=B0C range) to -20=B0C to 300=B0C (320=B0C range). It's a significant percentage, and importantly outside of the design criteria the engineers worked to. I'm not saying this is the mechanism, solely that I'd definitely believe it.

Never considered you one - nor am I, hence the surprise. Actually designing a $500K LED install at the moment, so I do use them in the right circumstances.

Quite right, fiber is fine. I was refering to light pipe. That's a nice little air volume with its own convection currents due to the lamp at one end, and now extra cold world behind it.

Thomas.

Too many years ago now, I was involved in a project involving low temperature testing of incandescent, halogen incandescent, fluorescent and mercury HID lamps. As I recall, the military wanted to know the characteristics of various lamps used for lighting at bases in Greenland.

We took the systems down to -30F (-34.4C) which was the limit of our test chamber and tested both bare lamps and lamps in sealed fixtures.

All of the lamps worked just fine and lasted their normal rated lives -- even the fluorescent with a bit of tinkering. Incandescent lamp materials didn't seem affected by the temperature differential -- no seal or bulb cracking as long as moisture was not dripped onto a hot lamp envelope. Halogen lamps just didn't care about anything we did to them. They were the

500 and 1500 watt linear lamps with quartz envelopes. They would be my overall choice for instant reliable light in very cold or wet conditions -- as long as there is minimial shock or vibration.

Fluorescent lamps were surprisingly good performers. Once started, however, they have to be in an environment which will let the lamp "cold spot" warm to its rated value, typically with a layer of air at 25C surrounding the lamp. We used 1.5 ampere T10 lamps since they draw enough watts to heat their surrounding air quickly.

Subsequently, a fixture was developed for the T10 lamps that made operation at very low temperatures (below -20F) routine. It was a 2-lamp weatherproof unit plus an incandescent lamp on a timer. When switched on, the incandescent lamp came on immediately and heated the air inside the lamp enclosure. The fluoresent lamps were powered on at the same time and started. As the air heated, from both sources, the fluorescent lamp came to full brightness. The incandescent lamp was then automatically switched off and the fluorescent lamps easily maintained the optimum lamp compartment temperature.

Later on, the major lamp companies simply enclosed the T10 lamp with a glass outer jacket and thermal end caps and called it a "T10J". That lamp is rated to at least -20F, is still listed and will operate at lower temperatues with a slightly reduced light output. T10J lamps are, I believe, still commonly used in commercial food freezer facilities.

Mercury lamps took a few seconds longer than normal to start probably so the starting glow could vaporize a bit more of the liquid metal into vapor. I wish we could have tested the mercury lamps below the freezing point of mercury (about -40 C or F).

One surprise was the number of ballast failures. In our tests, the ballasts were also in the low temperature environment. We thought at the time the failures were due to the electrolytic capacitors freezing and shorting, but I don't remember if that was confirmed. Anyway, we recommended for food freezer applications that the ballasts be mounted outside of the low temperature area.

Terry McGowan

That must to had been an interesting project.

As for the mercury ballasts being unprotected, there might had been more condesation on the windings. This in turn could lead to a higher posibility of short circuit among turns. Did you try any potted ballasts?

Would asume that aided start HID (HPS and MH) would work fine. At the most the ballast might need to offer a higher starting current, to insure a proper start.

No. But that is a good idea.

I've heard that HPS lamps do very well in -20F and below temperatures. They lighted the construction work on the Alaska pipeline during the 1970s, for example. I don't believe that any special ballasts or other equipment was required.

Terry McGowan

Interesting. What was the thinking behind the dual lamp setup given evidence that fixtures seem to operate well at these temperatures by themselves?

If you don't find any let me know. I only know of one company in Mexico that pot their ballasts.