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- Is this true or not? Yesterday I found a small flashlight in a store that had a white LED instead of a bulb. I was curious, so I spent the ten bucks and bought it. It is made by Brinkman, uses two AA batteries, and throws a bluish-tinged white light that seems not quite as bright as a Maglight AA flashlight, but pretty close. The blue/white light of the LED flashlight looks very similar to the color of new (US) car headlights and some streetlamps. The package says that the bulb “never needs replacing”. Never: that’s what it says. I had seen red LED flashlights for astronomy use, but the LED’s they used were regular ones only as bright as you’d expect, because a lot of light isn’t needed or wanted in that particular situation. This white-LED is far brighter than any LED I had seen before. I know that transistors lifespans haven’t been detirmined, and I dunno about LED’s, but this thing seems to put out a lot of illumination. Is the word “Never” just an assumption that a normal person will lose or break the flashlight before the LED burns out, or is it true that LED’s (even ones this bright) really will never burn out? - MC
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You’re right – “never” is a big word. If you look at the specs for Light Emitting Diodes you find the lifetimes rated at hundreds of thousands of hours. That’s decades of time, so obviously they don’t know from direct experience. It must be an estimate based upon theory. I don’t know what the breakdown mechanism of an LED is, but it certainly takes a long time. My guess is that these people are figuring that very few people will remember the claim of “never breaks down”, even fewer of them will complain about it, even fewer will send back the flash;ight for replacement, and the handful of flashlights returned can be paid for without breaking open the piggy bank.
You’re focusing (ouch!) on the wrong words. “Never needs replacing” is ad-speak for “when it breaks, you’re screwed.”
LEDs are considered “life-time of the product” components. Any failure of such a component marks the end of the life-time.
Recent advances in LED technology, esp. when used in clusters, have basically made standard incadescent and flourescent bulbs obsolete. Last a long time, consume very little energy for the lumens, etc. Just a couple more years for production to ramp up. You’ll tell your grandchildren about the old days of lights that were hot, burned out, etc.
BTW, you use the phrase “never burns out” which may not be on the package. But if it is, it’s still legit ad-speak since, technically, when they go out, they don’t “burn” out.
FtG aka GLP
The “lifetime” of an LED is in the tens of thousands of hours. The sites I have seen advertising LED flashlights claim 100,000 hours. Burning continuously, that would be 4166 days, or 11 years and 5 months. I dare say that that would last a normal person’s lifetime if used intermittently as most flashlights are. Even if the LED only holds out for 10,000 hours, when was the last time you left a flashlight turned on for a year and expected it to continue working?
According to This site (PDF) the MTBF (mean time before failure) of LEDs is HUGE. The MTBF for a widget is the time after which you would expect half of the widgets to have failed.
The test described in the above page resulted in zero failures that I could discern from reading the paper, but for the sake of calculating MTBF they essentially say “Let’s assume 1 failure happened in each of our tests otherwise this is a short paper.”
This gives MTBF for their particular LEDs of between 500,000 hours and 12 million hours, depending on conditions (mainly temperature.) That’s between 66 and 1400 years. Of continual operation. If you go with reasonable operating temperatures the MTBF for these LEDs is somewhere in the 200 year range. Of course, LEDs have not been around nearly that long, so it is possible something could degrade them over time. We’ll see in a few decades.
So, it appears that ‘forever’ means that something else will fail in the flashlight before the bulb. Or, as others have pointed out, it is ad-speak for ‘maintenance-free’ - i.e. a failure in this part indicates the end of the product’s life and thus it is somewhat of a circular definition.
I’d wager that a good deal of these LED flashlights will still have working LEDs long after I’m dead. Go ahead, just try to collect from me when I’m dead.
Not to hijack, but I thought this would be a good opportunity to discuss why incandescent bulbs are inferior to LED’s in many respects:
Reliability. As discussed above, LEDs are much more reliable than incandescent bulbs, especially in high-vibration environments.
Efficiency. All else being equal, and LED is more efficient (and therefore runs cooler) than an incandescent bulb.
Speed. LEDs turn on much faster than an incandescent bulb (almost instantaneously). This can be an important factor when using a light as an emergency indicator, e.g. the brake lights on an automobile.
Geometry. LEDs can be made in a bewildering array of shapes and sizes.
Of course, there are advantages to incandescent bulbs:
Brightness. It’s a piece of cake to make a very bright incandescent bulb, but difficult and expensive to do the same with an LED.
Radiation Pattern. For the most part, incandescent bulbs shine light characterized by a non-directional (spherical) wave front; if you want to focus the beam, it’s simply a matter of using mirrors. By contrast, LEDs inherently have a narrow beam width. That’s fine if that’s what you want, but sucks if you want a very broad beam or spherical pattern.
Power Requirements. Incandescent bulbs are equally happy running off AC or DC, and can be designed to operate over a very wide range of voltages. LEDs on the other hand are much more finicky about voltage and current levels.
CrafterMan, I just have to nitpick on this one:
Well, no, they don’t. I speak from experience here – I once tried to get an LED company to make me an LED with a specific beam shape/direction. It turns out that much of the focusing into a tight path comes from that front “bullet” shape that they put on the package. But they don’t place really tight specs on where the LED junction falls relative to the bullet, so there’s a LOT of variation in the far-field pattern. But the focussing is due to that bullet shape. The light pattern from the LED itself spreads out horrendously – it has to, because the junction is so small. Diode Lasers are notorious for their absurd far-field angles – you have to put a lens in front of them to collimate them, or use a diffractive filter.
Just to up the geek quotient a little:
I know RF Power Transistors, not LED’s, so this information may be wrong, but I bet it is not.
A regular bulb works by heating a tungsten filament to a very high temperature and using the glow of the wire as a light source. At these temperatures the tungsten is actually boiling off the wire and the temperature extremes from off to on put a lot of stress on the wires, hence they burn out.
An LED generates light as a by-product of the re-combination of electrons and holes. This process happens at at any temperature and does not use up any of the LED in any way.
In order to get a bright LED you need a lot of electrons and holes which means you need a lot of current. Because the wires and metalization paths on the LED are so thin (On the order of thousandths of an inch), the electrons flowing through actually knock the metal atoms out of their places and push them along in the direction of current flow. Because of the grain structure in the metal, you get voids and clumps. eventually a void grows to a size that the current can no longer flow and you have a failure.
This wearout can be controlled by adjusting the thickness of the metals, changing the metal itself (Gold is the best but the new copper metals in MPU’s work better than the most common aluminum.) and lowering the temperature. For my parts, increasing the temperature by 10 deg C cuts the lifetime in half.
Chances are that most lifetimes reported are for use at the maximum rated temperature, like 175 deg C. While the LED bulb in your flashlight gets hot, if it is held (by good design) to a temperature around 100 - 125 deg C during normal operation, it should last much longer than the published lifetimes.
Is that geeky enough for you?
Yes, I understand a semiconductor die spreads out the beam, but the most you can get is half a sphere, and LED manufacturers usually “tame” it by focusing the beam externally. I guess my point was that incandescent bulbs inherently emit a true spherical wave front, which can be advantageous when using the light source for general (non-research) lighting purposes (depending on the application).