Blowing light bulbs

[Chris Lewis]

Random responses:

These are brand-new (less than a year old) ceiling pot fixtures. A "standard" HD brand of some sort. Cheapies, but reasonably well built. Rated at 100W I believe.

BR30s are medium size incandescent flood lights, 60W apiece - the fixtures are designed specifically for this size. The halogen equivalent is "PAR30" IIRC.

So heat is unlikely to be a problem. We haven't even installed the fixture bezels yet.

Vibration is certainly a possibility, but we're aware of it (I wrote the FAQ on that! ;-), and some of the lights that are dying aren't anywhere near floor space likely to have much vibration. CFs on the same area (in previous ceiling mounted J-boxes, same switches) also _seemed_ to have a relatively shortened lifespan.

There is no aluminum on (or upstream) of this circuit. The only aluminum is a subpanel feed to the garage.

No, we're not having dimming/brightening problems. Many other bulbs in the house have more than adequate lifetimes (ie: 10 year+ on some reasonably well used flood lights). So it's not an overall voltage problem.

As we've not had a lot of luck with CFs on this circuit already, I'm hesitant about going for them until I understand what's happening.

[Our kitchen ceiling lights also have similar problems, despite being on a dimmer.]

I should check the voltages on this circuit just in case. A pair of new switches is probably a good idea too.

[Doug Kanter]

In case you want to spend a few bucks to prove or disprove the vibration theory, Home Depot carries an incandescent bulb by Philips, specifically labeled for use in ceiling fans. My fan was blowing bulbs almost weekly due to a nasty vibration transmitted through the ceiling from the monster of an exhaust fan in the bathroom 20 feet away. (I'll be dealing with that later this summer). I switched to the Philips bulbs - problem gone. They're 40 watt bulbs, shaped like normal lamp bulbs, but maybe 30-40% smaller in size. Might be worth a shot.

[Chris Lewis]

According to les :

[Technically, it's not 2 phase. It's simply a center-tapped transformer winding.]

Yes.

If the neutral is not making a solid connection back to the center tap of the transformer, the apparent neutral-real ground voltage can be quite extreme, resulting in one leg of the feed being significantly lower than 120V and the other much higher. It simply becomes a voltage divider between whatever devices you have attached to the two legs.

[Doug Kanter]

I've never found a rough service bulb whose light color wasn't ugly. I wonder why?

[Doug Kanter]

Other than some Philips frosted fan bulbs I mentioned elsewhere in this thread, my experience with rough service bulbs has been those labeled as "Good for trouble lights". Weird, overly warm color, more so than your run-of-the-mill light bulbs. Doesn't matter so much in a trouble light, but there have been some other instances over the years when I could've used them, in basement fixtures, for instance, where foot traffic above seemed to be causing early bulb failure.

[Chris Lewis]

According to Harry :

Standard recessed light fixtures and the bulbs that they're designed for installed as per instructions and electrical code aren't "proper"?

"Pinch and squeeze" 120V permanent fixture wiring?

Proper?

Good gracious me. Not.

I'm quite good at running wire, thank you.

[Bud]

Looking at 75W bulbs, the rough service bulb is 62% of the light output of a normal bulb. Part of this is losses from more filament supports. But they probably run the filament at a lower temperature to make it more shock resistant. Lower temperature shifts the spectrum toward the red.

Bud--

[Don Klipstein]

Fixtures as described above are notoriously hard on compact fluorescents. (Less of a problem for most CFLs 13 watts or less, as well as Philips SLS excluding versions 25 watts or more or dimmable). So I suspect rough heat situation for early failure of compact fluorescents, and fair-good chance of a different reason for early failure of incandescents - most likely bad brand or bad lot of bulbs, after that significantly high line voltage or vibration.

If you are using the dimmer as a soft-starting means, please be aware that soft-starting usually increases incandescent lifetime only a little. Some incandescents even suffer vibration problems from the spiky current waveforms when dimmed by usual dimmers, to an extent such that dimming only slightly extends their lives. (Most incandescents have major life extension from dimming, although with energy efficiency decreasing badly enough for cost of achieving a given level of lighting to actually increase.) Most halogens have an aging mechanism slowed only a little by dimming and a few halogens have contaminants that dominate and wreak havoc when major dimming is done.

- Don Klipstein ( [e-mail])

[Don Klipstein]

Outright true, but for most lightbulbs this stress is within the "endurance limit" (threshold of causing metal fatigue), and less than the stress of having people dance or dribble basketballs on the floor above or slamming nearby doors. And yes I do know that a lightbulb experiencing a cold start can have its filament mechanically jolt enough to produce a "ping" sound that is often audible within a foot or two away. NOTE - the filament is much weaker when hot, and the main mechanical stress of a cold start occurs when the filament is not so hot, and much stronger than a hot filament whether it is ductile or brittle.

Most dimmers when turned all the way up will reduce RMS voltage to a lightbulb roughly 2-3 percent, and that reduces light output about 3 times that and can account for a life extension of 20-40%.

In general, "rough service" bulbs have much longer life expectancy than "standard" bulbs even where there is no damaging vibration present due to the filament being designed to run cooler, since most such bulbs are used where labor has to be paid to replace them. Also, they are less efficient to such an extent that a 60 watt "standard" bulb usually outshines a 75 watt "vibration resistant" or "rough duty" one. Over 1,000 operating hours, 15 watts of electricity usually costs more than a lightbulb does.

- Don Klipstein ( [e-mail])

[anoldfart2]

What are pot fixtures?

[Joseph Meehan]

Your basic recessed light.