Why the 5 watt in the ARC5

I'm still new to the technology of led's so I'm not familiar with the technical aspects of it yet. Can someone please explain for me if they can?

Why did Peter choose the 5 watt for the ARC5?

I may be mis-informed but I think I read here somewhere that the 5 watt led has a lifespan of "only" 500 hours. Does that mean that the technology of this led is not yet mature like the 1 watt that lasts 100k hours. I think it's a huge trade-off for just wanting a brighter light.

At just 500 hours, wouldn't it cause headaches for Arc with it's 10 uyear warranty. For people who use this light a lot, it would most probably fail before the warranty runs out.

Isn't there a better alternative without this compromise? I think most people would be skeptical to buy a $250 that lasts only 500 hours.

The quoted figures for luxeon life span refer to the time it takes for luminous output to drop by 50%. It will still be putting out light, just not as much as it used to. Also, i understand that the ARC5 will underdrive the LED at 3 watts which should greatly improve the life span.

Peter will underdrive this 5W in ARC5, so I guess the short lifespan shouldn't matter, as the LED will last a lot longer. This quoted short lifespan is only for the 5W driven within spec.

If Peter is going to underdrive it anyway, isn't there a 3W led already existing with a rated lifespan of 50K+ hours? Will an under driven 5W be more efficient than a fully driven 3W under the same conditions?

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billson said:
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Will an under driven 5W be more efficient than a fully driven 3W under the same conditions?

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YES, it will put out a beautiful and usefull side spill /ubbthreads/images/graemlins/grin.gif

I am not entirely sure, but I believe here is the basis for that decision.

1). My recollection is the life on the 5 watt part is now up to several thousand hours. You are going to get tired of buying batteries long long before you run out LED life.
Even 500 hours is a long long time in a flashlight.

2). The issue with underdriving LED's, especially white one's, is it can change the output characteristics, so it is best done with a slight of hand. The LED driver is controlled by a Pulse Width Modulator, so while it on, it is full power, but you adjust the total output with the duty cycle. As long as the Pulse frequency is well above about 70Hz, the flicker will be undetectable by the human eye. PWM driving also tends to improve battery life, and minimizing power dissipation in the driver.

3). The 5 watt product probably has better thermal characteristics at 3-5 watts, so if you want Maximum output, you can probably get it for longer with the 5 watt, and you can have more 'boost' available.

My thoughts anyway.

This does bring one question to mind for me: if the Arc4 can barely run on full power with a 3V lithium (and only on quality batteries), then how on earth is the Arc5 going to run a 5W LED, even at 3W, with a single CR123? Is Peter going to have to abandon the 1x123 for the Arc5 in favor of the 2x123, and if so, is this a feasible EDC? And if the Arc5 does get bumped to "Mission" status, will there be a redesign?
There's my slippery slope.

I guess that was more than one question.

It should work OK, after all, there are plenty of people who run a 5 watt SureFire head from an L4 on a single cell E1E body (including me).

This is a a 5 watt Luxeon running on a single 123 battery, it's been nick named the TW4.

The "TW4" puts out about twice as much light than my Arc LS does and has a 65-70 min. run time.

Al

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SRue said:
This does bring one question to mind for me: if the Arc4 can barely run on full power with a 3V lithium (and only on quality batteries), then how on earth is the Arc5 going to run a 5W LED, even at 3W, with a single CR123? Is Peter going to have to abandon the 1x123 for the Arc5 in favor of the 2x123, and if so, is this a feasible EDC? And if the Arc5 does get bumped to "Mission" status, will there be a redesign?
There's my slippery slope.

I guess that was more than one question.

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Yes, the Arc5 is meant for more than an EDC light and will only have the full brightness options available with TWO 123 cells. That said, it WILL run for a short time (I've read) at the higher brightnesses with only a single 123. Also, the 5W LED in the same reflector as a 1W will not have as tight a beam, which is fine by me, as I like a wide beam for many of my uses anyway.

Peter can make the Arc5 work on one 123a battery buy carefully selecting low voltage binned 5 watt Luxeons. Say he gets a load of W and X binned Luxeons with a very low forward voltage of a T binned...say around 6.3 volts. Underdriving it will drop the voltage required even more...say 6.1 or 6.0 volts.

Since he "calibrates" the Arc4 for brightness, not current... he can pull it off by using ultra-premium binned 5 watt Luxeons. The middle of the U binned Luxeons put out 100 lumens at full 700mA of power. An X bin will punch out 220 lumens at full power so you can see the greatness of it. An X bin would put out more light running at 2.5 watts than a U bin at full 5 watt power.

Then, look at the forward voltage of the LEDs. An X3T running at full power has an average full output forward voltage of 6.63 volts X .700 amps = 4.64 watts. A U3V has a forward voltage of 7.60 volts X .700 amps = 5.32 watts. Only around 10% difference but every bit helps in a small light.

I can see the Arc5 Premium running W or X binned Luxeons with low forward voltage at around 2.5 to 3 watts for a seriously blinding light.
I do know one thing, it will be interesting to see things take shape for the Arc5+

If Peter is actually planning to do what BentHeadTX suggests above, then I'm going to pass on the Arc4 and wait for the ARC5. Imagine 220 lumens on boost for an light the size of the LS. Even for just a few seconds would be awesome.

Sorry to burst your bubble, but there's no way in heck that an Arc5 would even come close to 220 lumens.

Those ratings are hardly conservative and they are set forth for a certain die temperature (typically 25 degrees C). With an 'X' binned (which are ridiculously hard to find) LS in there it would generate incredible amounts of heat thus greatly reducing the amount of light coming out. The L4 already puts out around 60 lumens and Peter already mentioned that the 5W will be underdriven, probably much like the L4. 220 Lumens out of an X binned 5w in such a small package would require much higher voltage and amperage than 6 volts and 700mA.

The 220 lumen rating was at full power, the Arc5 won't be able to push it that high. Peter is going to run it at around 3 watts so a single battery can handle the load. My concern is around 80 to 100 lumens which can be done with a W at 3 watts. As always, have fun trying to find a bin that high in any kind of quantity.

Peter does have the right idea with a thermal sensor, the light can be pushed as hard as heat levels and electrical energy will allow. Throw a copper slug under the 5 watter and some fins on the head for cooling and grip and things might work out nicely. The head will have to be larger and heavier to withstand the thermal loading expected from the 5 watt beast. A two 123a battery pack will supply the power necessary for full operation if Peter ever allows the curcuitry to drive that hard.

The 1.2 watt Luxeons bins have really jumped in the last 15 months but the 5 watters have lagged some. Hopefully, the bins will improve in the upcoming months while the Arc5 is under developement. Eventually, the W's and X's will be plentiful enough for the Arc5 to really shine. Peter knows that the bins will improve and the Arc5 will only get better with time. I thought my BB500 N binned light was bright 15 months ago, the R2H has really shown me how far this hobby has come in that short amount of time.

I want a W binned Arc5+ under my tree next Christmas, hey... it could happen! /ubbthreads/images/graemlins/rolleyes.gif /ubbthreads/images/graemlins/grin.gif

There's no harm in dreaming. Even if the Arc 5 manages just twice the amount of light the Arc 4 can produce at full power, it would still be great.

I think it would be safe to expect it should be more than that or Peter would not have made this partifcular choice. Why use a 5W if you don't plan to use it the way it was designed for?