They were not designed to fail with fire and lots of smoke if that is what you are asking. It is meant to be a silent EOL in case of normal EOL, and a "bang" and a little smell in case of something going wrong
The more scary effects are results of (what i suspect is) overlooked design flaws, and of cost cutting
The fuse in CFL is there to go off in case of a ballast failure, not normal tube EOL. So in most CFLs it will never be called upon to blow (up to and after the lamp EOL), but sometimes it will. What choices we have :
- Glass Ballotini fuse. Those were actually used in CFLs of the 90s
- Metal film resistor
- Ordinary resistor (like whats used for electronics)
- Thin track on the circuit board making a "fuse"
What we get with each option (sorta..) :
| Glass fuse | Metal film resistor | Ordinary resistor | PCB track fuse |
Protection from "high current" short circuit | Good | Good | Moderate | Moderate |
Protection from "limited current" short circuit | Good | Moderate | Absolutely No !!! (it catches fire) | Bad (it may leave a carbonized PCB behind, risk of arcing) |
Fuse itself limits the short circuit current | No | Yes | Yes | No |
Cost | High | Moderate | Low | Free |
We want the fuse to be effective against all sorts of faults, work safely, and we do want it to limit the fault current - so the CFL handles its faults on its own and does not trip breakers
(with 90s CFLs a ballast short would be more likely to cause a welded light switch or tripped breaker, but the ballasts were by far better built - which really minimized the chance of such failure to happen in the first place)
Quite obviously, the Metal film resistor is fair choice for the later, cheaper (higher chance of ballast failure) CFLs. But then there are some things to consider..
- If there is a low current fault, the resistor will heat up, but not enough to fuse. The hot resistor itself must not present a danger : Melting the CFL Plastic enclosure, setting it on fire, and so on. The resistor must be positioned so it isnt outright pushed against the Plastic from inside, and the Plastic must be non flammable (at temperatures to which it might get heated by the resistor)
- When the resistor fuses, it can shoot some (small) sparks. The CFL ballast enclosure gotta be made of sturdy enough Plastic to not melt through, and not have an opening right in front of the resistor so the sparks dont come out (and land on the user's bed below the CFL...)
One of the most common things i seen is use of ordinary resistor instead of the Metal film one. That is pure cost cutting, potentially even done by beancounters instead of by engineers : The engineers said X ohm resistor, so we found an equivalent one thats cheaper than that expensive one they specified...
But the fault in which the difference between the 2 resistor types will show up (limited current) is quite rare, so most CFLs (atleast here) have the ordinary resistor yet scary stories that come down to the wrong resistor type being installed are very rare
My personal thoughts on that are :
- Incandescents were ok all those years, but usually i want higher K temperature of the light and less energy use
- If not my parents ("Ashy, a lamp for $20 is WAY too expensive !!") back in the very early 00's (Osram Dulux EL's from Germany), we'd probably be using CFLs allready then - because i seen them somewhere and liked them. In reality i switched my house to CFLs around the mid 00's, when their prices started going down and i finally managed to convince my parents. Yep, the tradeoffs made to get the CFLs cost less are the ones that made them fail in nasty ways sometimes...
- Decent CFLs do contain their faults, even if they are not the best. They are not going to be dangerous
- I dont feel a need to be "safe" from a potential scary (but harmless) sudden "bang" surprise.. (which havent yet happened to me in ~12 years). If it happens, it happens..
- Most other lamps may fail with a bang too - Incandescents (arcing), LEDs (electronic driver short circuits), so CFLs are not particularly worse