1 & 3-Watt LED, Overdrive or Underdrive

I'm sorry if this this question has been asked before. I was wondering if the anyone can answer this complicated question.

The simple question is: Is it better to overdrive and over heatsink a 1-Watt Luxeon or to get a 3-Watt Lux, heatsink, and underdrive it?

That was the simple question. I was thinking along the lines of light output, longevity and efficiency.

My thought would be the 1-Watt would be brighter and probably bluer while an underdriven 3-Watt would have a warmer light if they were from the same bin. True of false?

Thought #2. The overdriven 1-Watt would last just as long as an undriven 3-Watt Lux if it is heatsinked enough. My thinking is in this analogy: A car engine can have a 6-cylinder engine or a V-8. The 6-cylinder can live just as long and run just as powerful as a V-8 if it is taken care of. A 6-cylinder could be more efficient than a V-8 simply because there is less internal mass to move. But that is in the mechanical world. I'm thinking electronics here and that is the 4th dimension. Any thoughts?

I think underdrive would be more efficient. Anything that makes too much heat means loss of efficiency. Over driving will also affect longevity negatively.
Experts can tell you more.

One of the Many things! I truly desire is a M*g 3D with a 3W >>>WHITE<<< LED driven at around 800 to 1000ma.

After seeing how my Madmax looks in a M*g C/D reflector, I REALLY want a 3W!!!!!!!

Alas...

/ubbthreads/images/graemlins/broke.gif /ubbthreads/images/graemlins/broke.gif /ubbthreads/images/graemlins/broke.gif
/ubbthreads/images/graemlins/jpshakehead.gif /ubbthreads/images/graemlins/jpshakehead.gif /ubbthreads/images/graemlins/jpshakehead.gif
/ubbthreads/images/graemlins/banghead.gif /ubbthreads/images/graemlins/banghead.gif /ubbthreads/images/graemlins/banghead.gif
/ubbthreads/images/graemlins/sick.gif /ubbthreads/images/graemlins/sick.gif /ubbthreads/images/graemlins/sick.gif

What KFC said. Underdrive will be better, simply because you waste less energy as heat.

The LEDs will remain the same colour no matter how hard you drive them, except that the phosphor on the white ones can be eventually driven to saturation, and beyond that, any light put out by the LED comes out as blue. That's why Arc AAAs and other overdriven white LEDs normally appear blue.

Other than that, I'm not sure the difference between the 1W and 3W LEDs. I think that it's simply a matter of efficiency at higher drive currents.

I would like a more complete answer to this question as well. I have a bunch of incomplete information mixed together with paranoia/overcautiousness, so I use 3W exclusively if I'm running a HD constant-on at 500mA or above. I have 1W SEs, and I would like to know what a reasonable cutoff is.

[ QUOTE ]
Chop said:
The beam characteristics of the 1W and 3W luxeons are the same. At levels under 700mA, the 1W will arguably be brighter. The color of the 3W at underdriven levels might be off a little too, although I've had good luck driving them at 500mA.

[/ QUOTE ]
Re: thought #1, the 1W would perform in-spec for color and with appropriate increases in brightness. The 3W, depending on current, may have some color shift, but I've read that it's unpredictable, since binning is done at spec current. Both of my Lux3T sandwiches appear a little green when run on low, but I have no idea what their tint bin is. It would make sense if they were TX0?, but that's not necessarily the case.

Re: thought #2, my impression is that the 1W will have a decreased life because it is not as robust internally, but this decrease will not be appreciable in any sort of normal use. Adequate heatsinking goes a long way towards preventing failure and maintaining lifespan.

3 watt is the newer and improved product. /ubbthreads/images/graemlins/thumbsup.gif
It costs about 1.5 as much as a 1 watt, is more rugged, longer lasting, slightly more efficient, and usually whiter. /ubbthreads/images/graemlins/smile.gif

If you're aiming for a certain light output (let's say 40 lumens), it is better (i.e. more efficient, less chance of blowing out the LED) to obtain that light output by underdriving a 3-watter rather than overdriving a 1-watter. In fact, I'm philosophically against overdriving $10+ LEDs at all for economic reasons, although I do experiment overdriving 20-cent Hong Kong LEDs. All that being said, if the needs of a project can be met by slightly overdriving (meaning 10% or less) a 1-watter rather than underdriving a 3-watter, then I would chose the 1-watter and save the money. On the other hand, I wouldn't even entertain any thought of overdriving a 1-watter by 50% or more. For one thing, lifespan is an inverse exponential function of drive current, meaning a 50% overdrive might reduce lifespan from 50,000 hours to perhaps a few hundred hours. Second, the possibility of an unpredictable catastrophic failure negates one of the primary advantages of using an LED in the first place-namely reliability. Also note that these things work in reverse when underdriving (provided adequate heatsinking is provided). Running a 3-watter at, say 400 mA, might very well result in a lifespan of over 300,000 hours. Maybe not important for flashlights, but this might be very important for a light in a difficult to replace area which may need to run continuously for decades.