In another thread, it was mentioned that CFLs and LEDs
last longer than incandescent bulbs.
We all know incandescent bulbs fail due to the filaments
being made so thin that they oxidize and burn up, over time.
But, what causes CFL bulbs to fail?
And, what causes LED bulbs to fail?
On Friday, January 25, 2013 7:24:18 AM UTC-8, Joe Mastroianni wrote:
I remember thirty years ago, you wouldnt even think about breaking a fluorescent lamp while replacing it. In fact you hardly ever had to replace them. Now they make the class thinner than an eggshell and if youre not VERY careful it breaks before you even finish putting it on, and even if you manage to put it on, the glass doesnt last long once it gets hot. Glass is mostly made of silica which is cheap, so its not that the Chinese are saving money by making it thinner and if its not to save money then the only reason they would have to do so would be so you keep having to replace them and buy more.
Not sure what glass thickness weight has to do with anything. I have
never broken a bulb while installing it and never heard of fluorescent
lamp glass overheating and failing. If anything modern fluorescent lamps
last longer especially when using electronic ballasts.
I believe incandescents fail because tungsten evaporates (the bulb
blackens somewhat) and hot spots develop. Small lamps are under vacuum.
At about 40W they are gas filled (not including oxygen). The gas reduces
evaporation of the filament.
In halogen lamps, the halogen transports the evaporated tungsten back to
the filament. As a result the filament can run hotter, producing a
smaller percentage of heat.
I suspect in a significant percentage it is the ballast electronics that
In general, flourescents have a filament, or cold cathode, at each end
that produces electrons. The electron emitting surface slowly fails and
when it gets too low the lamp won't start. Sometimes the filaments open.
I would guess cumulative damage from heat. Semiconductors (and
electronics in general) don't like heat.
One of the problems in LED lamp design is removing the heat from the LED.
In my experience CFLs fail so rarely that I was never interested in why and
never investigated - always looked like a random event anyhow.
LEDs, on the other hand, failed so frequently that I did look and, basically,
the reason is two-fold. They require bringing the voltage across each individual
LED to 3.5-3.6V Given that you start out with 120V power, they string 20+ of
them together so the power supply of the LED bulb does not have to lower it down
too much and they also very frequently skimp on the design and the components of
the power supply. I can't say for the higher-end LED bulbs which I've not yet
gotten any due to costs and my general skepticism about their life expectancy,
but the lower-end ones I've opened often even lack some component that are
clearly labeled on the PCB inside. For example, an inductor that's intended to
limit the inrush current through the string of the diodes, is often labeled on
the board but missing (replaced by a wire short) because it's kinda expensive
(about $1). I'm also pretty sure the LEDs themselves and every other component
inside were picked from the lowest cost (lowest quality) bins.
One other intrinsic issue with LEDs due to their low voltage and consequent
stringing of a couple of dozen together is that life expectancy of such serial
circuit drops dramatically. It's pretty much false advertising when they print
on the box "30,000 hours life" because even if one LED might really last 30,000
hours, the probability of the string of 24 failing in the first 1000 hours or
less is much higher - the probabilities of each LED failing compound and bring
the entire circuit's way down.
Greed on the part of the manufacturers (for all light bulbs which do not
last long). The bulb burns out, you buy a new one and they make more
This bulb has worked for over 110 years...
On both CFL: and LED the drive electronics are more likely to fail
suddenly than the lamps themselves. Both LED and CFL loose output
slowly with age - both use phosphours to create the visible white
light, and those phosphours deteriorate with use (photon production)
I remember back in the 70s seeing a tour of Thomas Edison's Florida
home and they had a bulb of his burn so many hours a day since he
left. I guess it was like 50+ years then and still burning well. So
I got to believe what most people say in this thread as true.
That poor thing doesn't put out a whole lot of light either.
Take a 100 watt 120 volt bulb and run it on 80 volts - particularly
9f you can feed it DC - - the light will be a warm yellow. equivalent
to something like a 40 watt bulb - and will last for decades.
On 01/26/2013 04:33 PM, email@example.com wrote:
It's an efficiency thing though... say you have a 120W, 240V
incandescent running on 120V. The light out of that bulb will be dimmer
than a 60W, 120V bulb running on 120V, as the filament won't be as hot
and therefore won't glow as brightly. You're trading life for efficiency...
replace "roosters" with "cox" to reply.
as i learened from my copier repair days the last 5 volts make a major
difference in light output.....
our building was old and the power line voltage varied a lot. which
caused to light too dark copy complaints.....
The graph I have goes to 90% voltage. At that point the life is
increased 50% (and rising fast). The lumens are 70%. At half voltage the
lumens would be a rather low percentage (far lower than 60W equivalent).
As you lower the voltage the spectrum shifts toward red and infrared (as
you more or less said) That means a much higher percentage is heat.
With higher voltage the spectrum moves toward blue and a higher
percentage is in the visible spectrum. Photographers used to run bulbs
at overvoltage. Stadiums sometimes did the same thing.
Last time I was in Menards they had some long life bulbs with appalling
low lumen ratings for the wattage.
One more factor.... efficiency...
The lighting goes down fast,... the heat output ("light" we can't see)
goes up fast ...
Hint: Incandescents, at lower voltage are great in seasons where
we would like more heat that light..... In the summer... not so
Not really, if you burn an incandescent lamp below its design voltage
you will see the color shifts to yellow because the filament is much
less hotter and much less efficient as an illumination source but it
also last for a lot longer.
I used to use a 300 watt incandescent bulb on a dimmer for my grandma
who couldnt see well....
bulb life was forever however the inside of the bulbs turned black
over time, eventually so little light even at full dimmer output i
couldnt read a paper. grandma was bothered i replaced the bulb before
it burned out
i have had a copuple CFLs die while i used spray wax in their
vicinity. fire came out of one... it appears the spray wax vapor
causes a short of some sort..
dont use a lot of wax but these days if i do i make certain the
lights are off and cold, then i wrap a rag around the CFLs do my
waxing, and remove the rags before powering the lamps back on.
sometimes i just remove the bulbs if they are dsty and spray the glass
part with water, then let it dry a long time
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