| A few bulbs benefit from "soft starting", many and probably most do not. | Most (but not all) bulbs have zero or negligible fatigue damage to the | filament from a "cold start" despite a cold start jolting the filament to | cause a "ping" sound that is audible at close range.
I've found that this can be a benefit for the small candelabra style bulbs often used in small home chandeliers. Their filaments are constructed in a different way with typically 4 vertical segments. I've had these blow very often with full starting, and noticeably less often starting dimmed. Regular bulbs haven't noticed a change.
| There is a usual prelude-to-failure uneven evaporation of the filament. | That process causes a "thin spot" that is subject to a temperature | overshoot during a cold start. In most lightbulbs, such a "deadly thin | spot" is a deterioration mode of the filament that accelerates at a rate | worse than exponentially (during operation) once it becomes significant. | This means that for most lightbulbs, when they become unable to survive a | cold start their operating hours are numbered. And for most (but not all) | lightbulbs, cold starts do zero to usually-negligible damage until the | filament has aged enough for a cold start to be fatal.
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| True, but they usually don't blow out immediately unless the overload is | very severe. Mild to moderate overload merely shortens their life.
I have seen at times some strange bulb behaviour. And this without any dimmer involved. The bulbs sometimes start to hum. Or maybe they will modulate the light output around 10 Hz. In these cases I have learned they are "dead already". If others are around I'll just say "that bulb just burned out" to which they reply "but it's still giving out light". Then my reply is "when have you ever seen a light bulb just stop giving out light while its on" (it happens, but it's rare enough most people don't remember ever seeing it). I insist that it is already dead and add that it won't come back on when the light is turned off then back on. Often times someone is willing to actually try the switch and every time I've been proved right. Then they start wondering about me.
| Current surge from burnout is often worse than the current surge of a | cold start. Often when the filament breaks, an arc forms across the gap. | The arc can be encouraged by the voltage gradient across the filament to | expand and go across the ends of the filament, in which case the filament | is no longer limiting current through the arc. This is what causes the | "bright blue flash" that sometimes occurs during a burnout, especially a | burnout during a cold start (when the filament resistance is less and | allows more current to flow through the arc which makes the arc hotter and | more conductive). | Most lightbulbs have fusible links in one of their internal lead-in | wires so that a "burnout arc" does not pop a breaker or blow a fuse. | However, this may be inadequate for protection of dimmers.
I've had a few cases where the surge that resulted for a burn out arc has caused other bulbs in the same fixture to burn out. In one case, all
5 bulbs in a fixture blew at the same time. In that case, all 5 bulbs also showed multiple filament breakage, and arc damage in the base, such as melting through the base. In another case, the bulb became welded to the base. In another case, there was damage in the wiring itself. Two case tripped breakers (multiple bulb burnouts in these, too).
| I believe probably true. It gets more uncertain when you have a 600 | watt or 540 watt load on a 600 watt dimmer, and it gets worse when you put | more than one dimmer in the same box since each one adds heat to the | others (despite the loss in each dimmer being only a few watts).
Just put a 7 watt light bulb in a small metal case and leave it one for a while. Without good thermal dissipation, heat rise can be significant. Many a fire has happened from decorative items with even small bulbs used inside (such a Christmas light items).