Compact fluorescent lamps (CFL’s) are notorious for producing low output when they are first turned on, and this is especially true at very low temperatures.
Why are they so temperature-sensitive? Is it related to the vapor pressure of the mercury contained in the tube? Something about the phosphor coating?
Is there a temperature at which they won’t produce any light?
I don’t know the answer; however, I know of a fix. For places that are cold and need instant light such as motion-sensing outside flood lights, I use LED bulbs. They come up to full brightness nearly as fast as incandescent bulbs and use even less energy than CFLs. Of course they are pretty expensive.
Yep, I’ve got those on the outside of the garage. Inside the garage, I have four 150-watt-equivalent CFL’s, which light the place up nicely when they are at full temps. Currently, LED bulbs are not available with that sort of brightness.
Yes, it’s the Mercury.
Almost all (all?) chemical reactions occur more slowly at lower temps.
I’ll let a real chemist answer your last question but note that the freezing point of mercury is about -39 deg C.
Understood, but fluorescence is not a chemical reaction.
all fluorescent lamps behave like this; at cold temps it takes longer for the mercury to vaporize completely and generate enough UV to cause the coating to fluoresce. Per wiki:
“The light output and performance of fluorescent lamps is critically affected by the temperature of the bulb wall and its effect on the partial pressure of mercury vapor within the lamp.[18] Each lamp contains a small amount of mercury, which must vaporize to support the lamp current and generate light. At low temperatures the mercury is in the form of dispersed liquid droplets. As the lamp warms, more of the mercury is in vapor form. At higher temperatures, self-absorption in the vapor reduces the yield of UV and visible light. Since mercury condenses at the coolest spot in the lamp, careful design is required to maintain that spot at the optimum temperature, around 40 °C.”
the same seems to be true for most vapor/arc lights like mercury-vapor and high-pressure sodium lamps.
There are different gases used in CFL bulbs, but most of them contain some type of mercury. At colder temperatures, instead of being a nice mercury vapor (which is what is needed for proper light output), some of the mercury condenses into droplets. As the bulb heats up, more and more mercury goes into a vapor state and the bulb gets brighter.
I have motion-activated floodlights outside my house, and I have used one CFL and one incandescent PAR in the fixture. The incandescent one comes on instantly, even in Minnesota winters (like today, -7´F) while the CFL one takes a while before it reaches full brightness.
Don’t some CFLs’ circuitry intentionally start the bulb slowly? I think soft start is supposed to extend bulb life.
It would be nice if somebody from Tower, MN, would come in to answer the question about whether CFLs ever get cold enough that they don’t put out any light. Here in the lower half of the state we’ve noticed that our outdoor CFLs continued to put out an anemic glow even at -30F. However, we were forced to abandon CFLs for outdoor use by their short lifespan in Minnesota winters. Even the expensive ones were toast after a single winter.
you will get shorter lifetime out of CFLs if you don’t use them in motion activated lights.
hopefully soon LEDs will be as bright as needed for lower cost and be the best solution for small fixture outdoor lighting.