homemade Petzl Ultra clone- optics advice

[aUtOnOmOuS_Robot]

Hi all,

I'm an avid mountaineer and I'm looking to replace my Petzl Myo XP with something brighter. When you're ascending a 14er with 1000ft drops on either side of you in pitch darkness anything short of searchlights is inadequate. I like what I've seen of the Petzl Ultra but there are a few improvements I'd like to make, and being an amateur robot builder I think I can do it myself.

I really like the myo xp's diffuser lens so I'd like to have this on my lamp. Rather than try and build a sliding lens I think I'll just have two groups of leds, some that throw and some that flood.

I like Petzl's approach of lots of leds underdriven for improved efficiency but I'd like to be able to fully drive them if I so desire. I'm thinking 8 P4's, 4 with wider optics and 4 with spot optics. I would like this to be fairly compact so I'm thinking about designing a pcb to put the leds on rather than using a bunch of stars. Will that be able to dissipate enough heat?

I plan on using two 1A buckpucks pwm'ed by a microcontroller to drive them. I'm using two pots to separately control brightness of the wide angle/spot. I have ~1" diameter weatherproof knob covers for the pots as well as on/off switches that fit into the ends.

I'll be CNC'ing the housing from aluminum. I'll design a li-ion battery pack using 18650's.

I think I have a pretty good handle on every aspect but optics. What should I use?

Thanks,
Scott

 

[ahorton]

I also like the idea of having two different sets of LEDs for Spot and Flood.

Personally, I think you can do better than P4s.

If you are serious about throw, then you'll want Cree XR-Es with some sort of aspheric lens.

How much spot you need is up to you. I find that one XR-E, driven to a full amp behind a good lens can easily give you 200m range. Beyond that is not very useful (again just my experience with making headlights).





As for Flood, I think the Cree XP-G with 10mm optic is the best way to go, or possibly a SST-50 or SST-90.

4 XP-Gs or a single SST-50 will put out more light than 4 SSC P4s at the same drive current (and the SST-90 will be even more again). The 4 XP-Gs or a single SST will only take up as much room in the headlight as one P4 with a 20mm optic.

I'm a rock climber and adventure racer myself and I've been making my own headlights for my friends for a while now. I initially had a design similar to yours with lots of LEDs but settled down to a single XR-E behind an aspheric for flood and 2 XP-Gs with 10mm lenses for flood. I realise that doesn't sound like enough LEDs since you're thinking of 8 and I'm suggesting 3, but when compared to the Petzl Ultra it does very well.

The Ultra gives up to 350 lumens while 2 XP-Gs can give 700 lumens.

The Ultra claims a range of 120m but from what I've seen I think it's only about 75m of useful light. A single XR-E will give 200m of good range.

Anyway, that's a description of the light that I make and sell to my friends. I look forward to seeing what you come up with.

If you like, have a look at the parts I have for sale in my signature line below. The kit may be of interest to you since it has an aluminium body ready to take LEDs and optics of your choice.

 

[aUtOnOmOuS_Robot]

Why would I go with an XP-E for flood and an XP-G for throw? Wouldn't the same led with different lenses work?

I liked the P4's knowing since that's what's in the Ultra and they're cheap at DX but there's something to be said for the simplicity of a single LED. The only problem I see with the multi die leds like the sst50 and 90 is that I'd "need" a bigger driver circuit to even remotely push them to their limits.

I ran across this post with testing of the sst90

http://www.candlepowerforums.com/vb/showpost.php?p=3098815&postcount=336

I'd like the most efficient led I can find, is the SST90 any better than the 50 at low (<2A) currents?

I think a 2 led setup with sst50's will do me fine. I think I'll go with your aspheric lens for throw but what should I use for flood? What distance should I use between the led and your lens? Is there another driver that could push higher currents than the buckpuck?

Thanks,
Scott

 

[Th232]

Why would I go with an XP-E for flood and an XP-G for throw? Wouldn't the same led with different lenses work?

The XP-G has twice the die area than the XP-E, but has a lower surface brightness, hence while it may output more lumens it won't throw as well. I can't see where ahorton mentioned XP-Es though, so I'll also say that for throw using an aspheric, the XR-E is still king due to the higher surface brightness and its spatial distribution. As for using an SST-50 or -90 for throw, you'll get a much bigger hotspot, but it definitely won't throw as far.

 

[aUtOnOmOuS_Robot]

XR-E not XP-E, my mistake. Okay, so I should use an XR-E with an aspheric for throw but I really want 300+ lumens and I don't want to run a single led at 1A at the cost of efficiency. I need 30-40 hours of battery life so a small improvement in efficiency will save a lot of weight in batteries. Could I mount multiple XR-E's behind the same aspheric lens?

Would a couple XP-G's or a single SST-50,90 be better for flood? What lens/optic would be best? I'm looking to duplicate the flood of a myo xp but brighter.

 

[Th232]

This reply got a bit longer than I expected. In short:

For maximum throw, power considerations and total OTF lumens be damned: XR-E at 1000 mA + aspheric.

For good throw but also good efficiency: XR-E at 1000 mA + Polymer Optics #207. For better efficiency and/or output, but slightly worse throw would be an XP-G + Polymer Optics #202.

For the flood component, I'd go for two XP-Gs over one SST-50, no experience with the Myo XP so I can't really help you with the optics part of the question.

Now for the reasoning behind the throw answers I've given.

Mounting multiple LEDs behind an aspheric has generally produced crap results due to the LED die not being on the axis of the aspheric. Also note that if you run two XR-Es behind separate aspherics at 500 mA, you'll get more output, but since the surface brightness is lower, it still won't throw as far as one XR-E driven at 1000 mA. Of course, it also makes your headlamp heavier and bulkier. Further, an aspheric doesn't capture more than about 60% (someone confirm?) of the light emitted due to the distance you need to place it from the LED, so it's highly unlikely you'll get 300 lumens out of an XR-E + aspheric.

If throw is your one and only concern, then I would highly recommend an aspheric. However, if you're interested in efficiency and OTF lumens as well, then things change.

I've actually spent a fair amount of time thinking about this problem when designing my own lights, and one solution that I personally like is an XR-E combined with a Polymer Optics #207. Throw isn't as good as with an aspheric but efficiency is greatly improved, and +/- 2.5 deg is still pretty tight. Of course, neither of those solutions may produce enough throw for you. Second to that would be an XP-G with PO #202, same optic but the holder is slightly different to account for the different die height. Even more efficient, but throw is again reduced by a bit.

One tip that I can give you is that in normal usage, you won't notice *much* of a difference between running an XR-E at, say, 900 mA as opposed to 1000 mA. Perhaps you could experiment to see at what point the reduction in brightness is negligible for you?

I think ahorton is too polite to say this, but it sounds like his headlamp setup is almost exactly what you're looking for, barring the efficiency part.

Hope this all helps and hasn't confused you further.

 

[aUtOnOmOuS_Robot]

ahorton's kit certainly looks nice but I'm looking for a little more customization in mine. Specifically I'd like mounts for a pcb with the buckpuck, microcontroller and associated circuitry as well as the external pots and weather proof switches. Besides, building stuff like this is why I have a CNC!

I like the look of that XR-E + #202 optic and the hexagonal shape will let me pack efficiently. I'll look around for a similar optic for flood with an XP-G. I think I'll use nested rows in a 2-3-2 arrangement, with the 3 being XR-E's and the 2's being XP-G's. What about using a 6 XR-E Cutter board in place of the XP-G's? (or is there something similar with XP-G's?)

http://www.cutter.com.au/products.php?cat=LED+Kits

 

[aUtOnOmOuS_Robot]

Looks like I can't read, they have triple XP-G's on that page I linked to! Oops!

 

[ifor powell]

This got posted over on MTBR today a good source of inspiration for you. A bike light but I suspect it would be mountable on the head with a very good headstrap. Very similar to what you were thinking of 2 sets of 4 XPGs independently contralable one with a narrow optic one with a more floody optic. The controll is 2 bflexs so a clicky interface, I suspect two pots will give a far easier UI but bflexes do have nice thermal and battery features.