Last night I turned on the kitchen light-two ceiling fixtures-one went on, the other one was dead. These are two-bulb (CFL type), and I installed them about 3 years ago. I was looking at the replacement bulbs-they are 10,000 average life rated. Figuring about 8 hours/day usage, that works out to about 3 1/2 years…so the failure time is reasonable…but being statistically independent, what is the probability of both failing at the same time? Should be a pretty low number.
You’d need to define what “the same time” means. Technically, the probability that they burn out at PRECISELY the same time is zero, because time is a continuous variable. If you define a range of possible times (say, both burning out in the same hour) then it’s still a tough question because there are so many possibilities. Think of it this way: each bulb is more likely to blow out around 10,000 hours of use than at around, say, 12,000 hours. So the likelihood of both blowing out around 10,000 hours is also higher than the likelihood of both blowing out around 12,000 hours.
You’d also need to know the standard deviation of the lifespan of the bulbs.
I’m speaking through my hat here, but a momentary power surge, or an extended period of higher than normal voltage (?) could have caused both bulbs to fail around the same time.
No kidding i had all 4 100w CFL bulbs, all new, in same box, go out in one day. They were installed in 4 outdoor sockets outside, under the roof that overhangs my garage.
So i got four new bulbs, same specs, also from Walmart, but slightly more expensive GE brand bulbs…these are still going strong.
The others were Walmarts “Great Value” brand. It was not yet freezing outside, in fact unusually warm. All went out over a 24 hr time frame, but each was hours apart…so i doubt a power surge. And not in same sockets.
I would just be guessing what the cause was , however I will never buy Great Value brand again.
What brand were yours?
I replaced a lot of bulbs with CFLs at the same time and also went through a period, about 6 years later, where a group on the same switch (so same usage) all went out within a few days.
They were some “made in China” off brand.
The low beam lights on my wife’s car burned out on the same day. My mechanic said its not the first time he’s seen it with that particular model.
may want to try those new LED bulbs…they are dropping in price, but still lots more than CFL…Don’t see the top section of them being colored yellow, and think they are bug lights.
My guess is, the yellow filters out the bright blue light associated with white LED’s.
I have read nothing but positive reports on them, IIRC, you can dim them, and they run very cool, and require less wattage in your cottage. Find them at Home Depot.
Give a few as Xmas gifts, and use close friends or relatives as a guinea pigs…let us know how they liked it.
No. Most brands use “white” LEDs, which are blue with a yellow phosphor in the LED. Philips uses blue LEDS and puts the yellow phosphors in the top section instead of the LEDs.
If you’re happy with CFLs, you will be happy with LEDS. If you hate CFLS, you may or may not hate LEDs. (They still can’t match an incandescent in color rendering or dimmability, but are an improvent over CFLs and they are just as good as incandescent for cold weather and instant turn-on).
To speculate the OPs question, yes, maybe a surge. There’s a surge when you turn on a filament lamp with a switch which is why it’s common for a bulb to blow at that moment. Since I added soft-start dimmers to every socket in my house I’m replacing bulbs a lot less.
… maybe cheap electronics don’t like surges anymore than regular bulbs. Also, on LEDS, like CFL’s they still throw light differently than incandescent bulbs. This may not be a problem depending on the fixture. The Philips LED throws more light down than other LEDS or most CFLs, but the shadows of the sides can be seen if the bulb is close to the fixture globe. It’s OK in my nightstand lamps but they look awful in the globes of my dining room fixture.
Whatever you do, don’t ask how many Dopers it would take to change two lightbulbs…in a recent thread, I couldn’t even get a consensus on how many Dopers it would take to change one.
No Dopers, they would stand back and watch it screw itself.