Can someone explain overdriven?

Can someone explain the concept of overdriven vs underdriven? Does overdriven mean supplying a bulb with more voltage than is typical for that bulb? An underdriven light will not have good output? Thanks

I'm don't have a really technical understanding of it, but the basic term means driving an LED at a higher current than is recommended/rated by the manufacturer.

Different LEDs have different tolerances for current and heat based on their design. The manufacturer tests their product and recommends a level that is the best compromize between output and longevity of the LED. Generally speaking, pumping more through the LED than is recommended yeilds more light, but it may be at the expense of much of the life of the LED- some are more tolerant of this than others (for example, the Nichia LEDs are probably the most tolerant of overdriving among 5mm LEDs).

Underdriving does not mean the light won't have good output- many popular lights (the McLux PD for example) don't drive their LEDs at full spec. Underdriving generally results in greater efficiency (better lumens/watt due to much longer runtimes). The LEDs don't build up as much heat and will "live" much longer as well. Of course, the light won't be as bright, and if a luxeon is very underdriven, the color often shifts more to the yellow/red part of the spectrum.

Hope this helps a bit.

Almost all light emitters (bulbs leds etc) will have a certain voltage and current rating from the manufacturer.

Eg. a 3 volt lamp (incan).

When you apply more than 3 volts to it, it is then being overdriven. The added power will cause the filament to glow brighter and release more light, but at the expense of bulb life. Of course, too much overdrive will blow a bulb/led.

I thought i'd chuck this in as Solstice did LED's but not incans.

Thanks for the explanations, so a underdriven luxeon led will look more like light from an incandescent?

no, led are different and do not show the "browning-out" effect like incans.
The light output will decrease, but it still stays white.

(f.e. I like my lights to have a "low" level with around 50 mA to the led. Great for everything like reading, checking gadgets, ... with dark adapted eyes.)
((also needed current gets lower. In my 2aa / badboy lights, I prefer the high output to be about 300 mA to the led. Barely noticeable, but a great plus for runtime)

With incans, you gain efficiency with overdriving. When you apply a higher voltage than specified, the power goes up a little but the light output goes up even more. It's an exponential function.
With underdrinving, it's the total opposite.

With LEDs, it's often the other way around. Their efficiency maximum is often not at the specified current but much lower. A 750 mA-rated Luxeon is the most efficient at about 200-300 mA if I remember correctly and a standard 5 mm 20 mA LED is the most efficient at 12 mA. Therefore, you will loose a little bit light output but gain a lot more runtime with underdriving.

iamerror said:

so a underdriven luxeon led will look more like light from an incandescent?

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Not really. Incans change color if you over-/underdrive them but LEDs don't. Well, they do change, but very little compared to an incan bilb. They often go greener/bluer with underdriving but not that much. They will still have a much higher color temperature than incans, even when they are underdriven/dimed.

Not really. Incans change color if you change the voltage but LEDs don't. Well, they do change, but very little compared to an incan bilb. They often go greener/bluer with underdriving but not that much. They will still have a much higher color temperature than incans, even when they are underdriven/dimed.[/QUOTE]

Wow, I did not know about alll this. You say that LEDs do not change tint much with overdriving/underdriving but incandescents do. Does overdriving make an incandescent more yellow or more white, what about underdriving too?

Well, it's nothing you are supposed to learn is school or that is easy to find just by googleing so it's perfectly normal to not know this.
Don't get me wrong, I'm not saying you are dumb, but rather smart to ask these questions.

Yes, that's correct. LEDs change color/tint very little with over-/underdriving compared to incans.

If you overdrive a incan bulb, it will become more white (nicer and more efficient).
If you underdrive a incan bulb, it will become more yellow (horrible and less efficient).

dumb question about LEDs:
will they draw an infinite amount of current, if available? for example, i hook up an LED directly to a 3v power source, but i dont add any resistors to function as current regulation, will the LED blow?

pizzle,

No, that's an excellent question!

If your standard LED has got a forward voltage drop of less than 3 volt, it will blow. Just before it blows, it will try to draw as much current as you have got.

This is a truth with modification (I'm not sure that expression work in English, but you get the point) when it comes to really high power LEDs like Luxeons. They have a much flatter I-U curve and can be voltage driven instead of current driven. But for your standard 3, 5 and 10 mm LEDs, they will blow.

So in short:
Low power LEDs (5 mm and such): Yes, they will blow.
High power LEDs (Luxeons and similar): They might blow. Make sure before you try.

ah, much thanks, winny i've been wondering this for a while.
cheers!

Sorry, another beginner question... when you say "more efficient" are you saying the batteries will last longer before you need to change them, or something else? (this sounds important)

iamerror said:

Sorry, another beginner question... when you say "more efficient" are you saying the batteries will last longer before you need to change them, or something else? (this sounds important)

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they're referring to efficiency as amount of light per watt of energy used.

pizzle said:

they're referring to efficiency as amount of light per watt of energy used.

Click to expand...

Oh, thanks. Is there any advantage in having a more efficient bulb over a less efficient bulb if they both put out the exact same amount of light?

well, one will be more efficient that the other...

led's do change tint depending on the drive current. how they change depends on the bin that you started with. a more efficient emitter will give the same amount of light for a longer period of time. assuming you have two t bin led's with one being a a j and one an l, the j will give the same lumens for longer when compared to the l. the tint shift will depend on the tint binning, xo, v1 etc...

iamerror said:

Oh, thanks. Is there any advantage in having a more efficient bulb over a less efficient bulb if they both put out the exact same amount of light?

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yes, the more efficient bulb will use less energy, therefore have a longer battery life

So a more efficient LED will result in the following:

1. A slightly different tint
2. The light will last longer on the same pair of batteries than it would with an inefficient LED
3. A shorter bulb life than an inefficient LED

Is this all correct?

because the more efficient one uses less energy, it should have a longer life than the less efficient one.

pizzle said:

because the more efficient one uses less energy, it should have a longer life than the less efficient one.

Click to expand...

I thought that overdriving/making it more efficient shortened the life?

overdriving and making more efficient are two distinctly different things

overdriving: running more current or voltage than rated for.

something that is more efficient doesn't necessarily mean it is overdriven or will have a shorter life. not all incandescent bulbs or LEDs have the same design, therefore whats true for XXX model won't be true for YYY model.