LS 1W vs 5W

Forgetting the cost difference and all other things being equal (2 AA batteries, same circuit), if you put a 5W LS in place of a 1W what would the effect be? (brighter/dimmer, draw more/less current, Run hotter/cooler?) I'm just curious if it would be better to underdrive a 5W LS in a MiniMag or overdrive a 1W? Could you use the same circuit or would you have to 'tune' it for a particular LS?

It would depend upon the circuit being used. Underdriving the 5W Luxeon at 1W would require the circuit to put out about twice the voltage at half the current. Some circuits could deal with this, others couldn't. None of the direct drive circuits could deal, and any circuit which needs to be tuned for individual LED variation would probably need component value changes.

However the general boost circuit designs would still work.

Running the 5W LS at lower power will likely result in increased efficiency. The 5W LS has larger cross section, which means less resistive losses, and also has better heat sinking, which means lower junction temperature. The 5W LS at 1W will certainly be more efficient than current 1W LS units, but it might not be more efficient than the new 'high dome' 1W units which are expected this summer.

-Jon

Thanks for the reply. If the 5W does turn out to be more efficient I think it makes more sense to underdrive the 5W in a Minimag. You'd have plenty of room to push it until the heat sinking became an obstacle. Other than cost, I think it's the way to go. Why push the 1W to it's limits? Am I wrong?

Keep in mind that the variation in Luxeon forward voltage is significant, and it may be that the forward voltage will be lower...which would mean that the direct drive with a 7.2V system could produce surprisingly high currents.

PeLu reported on a sample device which he had, which produced results which were better than the datasheet suggests.
Luxeon 5W

sflate,

My sentiments exactly. I'd rather have an elegantly small, bright flashlight with an underdriven Luxeon LED than a big honker that's brighter.

I can't wait to see what Peter has up his sleeve.

The published graphs for the 5W LS combine to show the following output characteristics which show a modest increase in efficiency as wattage drops quickly in a fairly narrow voltage range:

Forward
Voltage Amperage Lumens
6.8 0.700 100% of 120 = 120
6.6 0.500 77% of 120 = 92
6.5 0.400 62% of 120 = 75
6.3 0.300 50% of 120 = 60
6.1 0.200 36% of 120 = 43

This inclines me to think that a 7.2 V NiMH battery pack direct-driving 3@ 5W LS potted into a Mag D head is likely to be driven somewhere between the upper two ranges given voltage drop of the NiMH's under a 1.5 A to 2.1 A load.

Jon:

Given that 6.1 V might draw 700 mA within the LED to LED variations, what is the simplest effective circuit or resistor you would recommend for use with a 7.2V NiMH power supply? Does this potential variation mean that you wouldn't recommend energizing three 5W LS's in parallel?

lemlux,

I plan to use a 5W lS in a DB6AA using NiMhs and will test this 6cell combo - if it works out with or without a resistor will depend on load (my 1 LS setup vs your 3LS setup) and the LS voltage variation and heatsinking as well - we will know when we have the parts and did the first tests.

IMO one error in the above mentioned discussion of an underdriven 5W LS vs an 1W LS in a 2AA MiniMag or equivalent is that a booster gets less efficient when the voltage difference is higher - so you might very well lose the efficiency gain of the underdriven 5W LS in the booster and gain nothing or not much - let me add that using more cells this is not the case but I´m referring to the 2AAs discussed above.

Just my 2 cents

Klaus


Klaus

Sorry for bringing this post back up, but I had a question about the luxeon and didnt want to start a new topic.

I made my own luxeon flashlight which I love....just a simple resistor w/3 Ni-Mh batteries running a 1W luxeon. I have it in an eight "AA" battery holder (fits perfectly in the hand). The batteries fall out during "missions" sometimes, so I wanted to transfer the package into a 4 "AA" battery holder that has the battery cover, switch, and wires coming out.

Now, is there any advantage to filling the pack with the full 4 batteries to even it out and run the luxeon off 4 batteries with a resistor instead of 3? I'm not good with the math like you guys are

I've got an extra Surefire E2 (is it possible to have an EXTRA one?)...

Would it be possible to convert it to a 5W Luxeon (running on 6V), if normally used for short spurts only. I'm assuming that some sort of booster circuit would also be utilized? This would make an ideal sized light IMHO !
-bucken-

A previous LS 5W thread said 120 lumens can only be produced at -20C or below freezing temps, implying we will never see 120 lumens out of a driven-to-specs LS 5W.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by carl:
A previous LS 5W thread said 120 lumens can only be produced at -20C or below freezing temps, implying we will never see 120 lumens out of a driven-to-specs LS 5W.<HR></BLOCKQUOTE>

I humbly disagree - otherwise that couldn't be referred to as a "Typical" lumen output as described in the Lumileds datasheets. Perhaps that thread was talking about the 1W in liquid nitrogen or something...

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Doug S:
Actually, Hotfoot, carl is quite right about this. A careful reading of the datasheet shows that the 120 lumen typical is at a junction temperature of 20 C. I have noticed that many here on this board seem to be missing this point. I have been thinking about making a post about the difference in the Nichia and Lumiled methods of rating outputs. Since it is of more general interest, I will start a new thread on the topic.<HR></BLOCKQUOTE>

Doug S,

Good point made on reminding us about the somewhat optimistic figures on the datasheets. But Carl is still quite wrong (sorry Carl).

While I won't disagree with you on your reading and understanding of the datasheets, I'd certainly still have to maintain the incorrectness of Carl's assertion that we're not likely to see a 120-lumen 5W driven to spec.

Carl's post mentioned 120lumen *only* being possible a temp of -20C, not +20C (as the datasheets say) - and suggested below-freezing temps before we could see the advertised performance. The datasheets, on the other hand, do clearly state (as you have pointed out) that the LSs *will* deliver a typical of 120 lumens when driven to spec(electrically) at +20C. All things being equal, the same standards are applied to the 1W, so relatively speaking here, we are all taking apples and apples.

What I will have to concede is that while a 5W may start off at 120lumens or so, this figure may steadily decline as the junction temp rises. I had a breakfast meeting with the chief Lumileds rep in my region (AsiaPac) and he reaffirmed that the datasheets only reflect an average of the luxeons that you get. Output and consumption/drive characteristics *will* vary from specimen to specimen. One other CPF member has actually tested an example of the 5W LS driven to spec and clocked in 130lumens!

I'm not "defending" Lumileds, but manufacturers simply post their typical findings at given repeatable ideal test conditions (which in most cases, do not mirror real-world ideals), but this is beside the point. Is +20C impossible? No. Impractical? Perhaps, for some apps (like flashlights). But certainly possible in freezing ambient temps like winter. Nothing here to suggest that Lumileds was indicating unrealistic or unattainable performance.

At the end of the day, that's all good and fine on paper for the moment, but until we can actually hook one up and measure one for ourselves in *our* respective real world conditions, the utility and mileage we get out of the 5W can only be based on the datasheet.

On a last note, I've seen and messed about with that 3xCR123 5W Luxeon flashlight that Luxeon reps carry around with them and I *can* tell you that this thing will still utterly shred an E2 for output

Actually, Hotfoot, carl is quite right about this. A careful reading of the datasheet shows that the 120 lumen typical is at a junction temperature of 20 C. I have noticed that many here on this board seem to be missing this point. I have been thinking about making a post about the difference in the Nichia and Lumiled methods of rating outputs. Since it is of more general interest, I will start a new thread on the topic.

Carl, Doug S,

I re-examined the 5W LS datasheets again and I almost had to swallow my words in my posts above, then I realized *why* you gentlement arrived at the conclusions that you did.

In the previous post, Carl stated that the datasheets indicated a junction temperature of -20C before 120 lumens could be achieved. Upon an initial glance, it seemed he was right (thus my near lexico-fiesta). But, look again - the Y axis is calibrated in % *not* lumens! So, if you re-examine chart, the output is actually 100% at 25C (which lines up nicely with all the other charts they give on the datasheet) and about 115% when Tj is at -20C!! Thats really about 138 lumens!

I wouldn't blame you fellas for missing that - it certainly almost caught me off too! But I'm extremely happy to know that the figures have finally made some sense

Carl said that the temperature (in general, not necissarily at the junction) would have to be -20. At 20C ambient temperature, with no additional heat sinking, the junction wont even be near 20c, more like 70c most likely after even just a minute. And at a JUNCTION temp of 70C (even though we are still at an ambient of 20C), you won't get 120 lumens. His point about -20C means that would have to be the ambient temperature before the junction would be able to stabilize at 20C, thus outputting around 120 lumens.

Spud

BTW, this is all assuming I read that other thread right.

Actually, Hotfoot, I misread Carl's post. I thought that he was talking about +20, not -20 [I choose to ignore that the spec is at 25C, not 20C as it was irrelevant to the point that I *thought* Carl was trying to make]. The point I thought he was making, and which I am in agreement with, is that a Luxeon which meets the 120lm typical *as specified by the datasheet* will not yield anywhere near 120lm as operated in the manner as is typically encountered by CRFers. Sloppy reading on my part.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Tater Rocket:
Carl said that the temperature (in general, not necissarily at the junction) would have to be -20. At 20C ambient temperature, with no additional heat sinking, the junction wont even be near 20c, more like 70c most likely after even just a minute. And at a JUNCTION temp of 70C (even though we are still at an ambient of 20C), you won't get 120 lumens. His point about -20C means that would have to be the ambient temperature before the junction would be able to stabilize at 20C, thus outputting around 120 lumens.

Spud

BTW, this is all assuming I read that other thread right.<HR></BLOCKQUOTE>

Excellent point, Spud - yeah, I guess in the real world, what we'd have is a bright-to-spec light when switched on, but quickly degrading as the temp rises. I'm also seeing why Doug S brought up the issue of how Nichia and Lumileds respectively rate their products for the datasheets.

Great info guys - but - back to my orginal question. For a Minimag with a Lamda and/or Madmax 167x circuit would you be better off using a 5W and underdrive it or a 1W and overdrive it? Would the 5W be as hot? Use more/less current (runtime)? Since the 5W isn't out yet I guess it's wishfull thinking, but I'm curious as to what the prevailing thoughts are of the experts on this board. (In other words I need one of you to make up my mind already )

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by sflate:
Great info guys - but - back to my orginal question. For a Minimag with a Lamda and/or Madmax 167x circuit would you be better off using a 5W and underdrive it or a 1W and overdrive it? Would the 5W be as hot? Use more/less current (runtime)? Since the 5W isn't out yet I guess it's wishfull thinking, but I'm curious as to what the prevailing thoughts are of the experts on this board. (In other words I need one of you to make up my mind already

)<HR></BLOCKQUOTE>

The 5W will be slightly brighter by specs, but that remains to be seen. As far as which is hotter, 2 watts is 2 watts; if both are consuming the same power, no difference. However, the 5W may be able to be driven with less power to get the same amount of light. But, maybe not enough to account for the increased price.

Next thing everyone needs to understand: the 5W and 1W HD are square chips with the phosphor only on the chips. They will produce a square image of the chip in the beam. To further compound this, the lens will project a round spot from indirect light collomated. Perfect alignment is required of the lens so the square and spot merge into one, otherwise you get this weird shaped barbell beam spot.

The current batwing 1W makes a nice round spot because the phosphor is gobbed into the reflector cup.

How well everyone likes the square beam spot will interesting.........