Paul Hovnanian P.E. said:
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.
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
