# XP-L or XHP for headlamp 10000 lumens



## Buoyen (Nov 10, 2015)

Hello. I need some advice on what to do. I'm building a bike helmet light for aggressive trail/downhill riding. The target is 10000 lumens.
The light will be powered by a 25V battery, 6x26650 cells.

At first I thought I would use this setup:
2x Aluminum housing with fins and enough room for 4 10mm sinkpads with XPL V6 and the 24mm Carclo quad optics with "XP-L mod" (from mtnelectronics).

8 LEDs and by using the calculator: http://pct.cree.com/dt/index.html
3A gives 8800 lumens with the efficiency 110 lumens/W (85 degrees C core temperature). With taskled driver I should be able to give more current, but with more power loss as well.

Then I saw the XHP series and I see the XHP35 will have better efficiency than the XP-L but cost more.
Will the XHP 35 fit the quad optic with the XP-L mod? And the most efficient bins of this series, are they available somewhere at this moment? Thinking about the E4 or F2?

Other choices? 
Thanks for all replies!


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## TheAngryPhoton (Nov 10, 2015)

Hello,

The LED cost is probably negligible for what you're really trying to do. You're talking about a couple dollars difference.

The battery doesn't make sense to me. A quick look at a 6-cell pack it looks like they make them for bike lamps but they are configured as 3x2, three parallel strings each consisting of two cells, 8.4V (briefly while fully charged, 7.4V nominal). Even if you put six lithium batteries in series (not recommended for charging reasons unless you have a crazy six-cell charger), you still only have about 3.7V*6=22.2V. Where'd you get 25V?

You should think about your drive circuitry. If you want a quality light you want to do better than throwing a battery across some LEDs. You may want to at least use constant-current drive circuitry, or better. And...umm... you'll need ~12V + compliance to drive the XHP35

DigiKey and Mouser both have various XHP35 parts stocked, not sure which bins.


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## Buoyen (Nov 11, 2015)

Yes, that's true. Fully charged the battery is 25.2, but nominel 22.2V

I did a build with taskled drivers some years a go, but I'm looking at the Taskled driver this time, it looks like that if the driver has sufficient cooling it should be able to suppport 100W or so.

The big question is what LED to use. The XHP 35 seems superior to the XL-P when it comes to efficiency ref. the calculator.
But do the optics fit? And is the E4 or F2 bin available somewhere?


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## TheAngryPhoton (Nov 11, 2015)

Just curious, what is the charger? Does it do balancing?

XPL dome height is 2.68mm R1.95. XHP35 dome height is 2.8mm R1.85. Both have footprint of 3.45mm^2. So the two are almost identical, the XHP35's dome is 120 microns taller. The XHP35 would probably fit in a cavity modified with an "XL-P mod"

I searched 4 or 5 of the major electronics distributors and nobody shows E4 or F2 in stock.

Go big. Throw the XHP70 in there, that thing's a monster!


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## Steve K (Nov 11, 2015)

I'm intrigued by the basic concept of putting 10,000 lumens on a helmet. Do people use this sort of thing?

When I think about the practical aspects of using it.. all I can think of is what happens if you happen to glance down at your handlebars or front wheel, and so much of that light is returned back to your eyes. Or is your night vision already worthless because of all of the light already hitting the ground nearby you?


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## DIWdiver (Nov 11, 2015)

The other thing is that it's going to need some serious cooling. 10K lumens is going to take something like 80W, of which something like 60% is turned to heat. 48W is an awful lot to dissipate off something that's mounted ON YOUR HEAD!


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## rsk_productions (Nov 12, 2015)

DIWdiver tell a big true. How will be your heatsink?


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## TheAngryPhoton (Nov 12, 2015)

DIWdiver said:


> The other thing is that it's going to need some serious cooling. 10K lumens is going to take something like 80W, of which something like 60% is turned to heat. 48W is an awful lot to dissipate off something that's mounted ON YOUR HEAD!



Exactly what I just logged back in here to post! Think of having an old 40W or 60W light bulb taped to your forehead.


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## Steve K (Nov 12, 2015)

DIWdiver said:


> The other thing is that it's going to need some serious cooling. 10K lumens is going to take something like 80W, of which something like 60% is turned to heat. 48W is an awful lot to dissipate off something that's mounted ON YOUR HEAD!



to play devil's advocate, I will note that bike helmets consist primarily of stryofoam, so there's a good bit of insulation.
Also, there should be plenty of airflow over the heatsink. 

Besides.. heat rises, so what could go wrong??


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## DIWdiver (Nov 12, 2015)

Steve K said:


> to play devil's advocate, I will note that bike helmets consist primarily of stryofoam, so there's a good bit of insulation.
> Also, there should be plenty of airflow over the heatsink.
> 
> Besides.. heat rises, so what could go wrong??



Actually, I was thinking of the size and weight of the heatsink, not burning (well, heating anyway) your head. But that's a good point too!


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## rsk_productions (Nov 13, 2015)

Im working with 30W and I must to mount a big heatsink with fan. So I reduced the size. You must to include the dissipation of driver too.


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## Buoyen (Nov 15, 2015)

TheAngryPhoton said:


> Just curious, what is the charger? Does it do balancing?
> 
> XPL dome height is 2.68mm R1.95. XHP35 dome height is 2.8mm R1.85. Both have footprint of 3.45mm^2. So the two are almost identical, the XHP35's dome is 120 microns taller. The XHP35 would probably fit in a cavity modified with an "XL-P mod"
> 
> ...



Nice work. I was too lazy to check the dimensions myself.
XHP70 is a good idea. 3 of that is cheaper than 8 XP-L and putting the numbers into the calculator it would be more efficient at 125 lumen/Watt at 8800 lumen. Cutter has the P2 bin in stock so I ordered 3 on TPAD stars with 30mm Carclo TIR optics. Woohoo! 

The battery includes a board like this that has balancing and protection functions like this:
http://www.batteryspace.com/pcmwithequilibriumfunctionandfuelgaugefor222vbatterypackat10alimit.aspx



Steve K said:


> I'm intrigued by the basic concept of putting 10,000 lumens on a helmet. Do people use this sort of thing?
> 
> When I think about the practical aspects of using it.. all I can think of is what happens if you happen to glance down at your handlebars or front wheel, and so much of that light is returned back to your eyes. Or is your night vision already worthless because of all of the light already hitting the ground nearby you?



For fast trail riding at night you need a lot of light. 10000 might not be neccesary, but I wanted to point out that this light should have extreme output.
It might be that I barely use more than 6000 at maximum i.e., but even then I have spare power at least.



DIWdiver said:


> The other thing is that it's going to need some serious cooling. 10K lumens is going to take something like 80W, of which something like 60% is turned to heat. 48W is an awful lot to dissipate off something that's mounted ON YOUR HEAD!



According to this thread:
http://www.candlepowerforums.com/vb/showthread.php?311740-LEDs-waste-75-as-heat
A LED dissipates 75% as heat as a rule of thumb. Harder driven LED will have lover efficiency. So in this case I think we can assume at least 80% will be heat.
Power at 10000 lumen is about 85W. That's 68W of heat.

With a simple calculation based on the nusselt-number for a laminar flow of fluid over a plate I find that with 550 cm^2 area the plate temperature will be 80C at a speed of 15km/h speed and 10C ambient. Plate temperature of 80 will mean core temperature of at least 110 C (with 0.9K/W in the LED itself it is 25K increase). A bit high and that means the output is reduced to 9000 lumens...
I call this the worst case scenario.

Then I found some round extruded aluminium heatsinks on ebay. I'll put it in the lathe and make a housing and then cut off the sides so they can be put next to each other like this is the plan:




Weight of the heatsinks as shown is 105g and has the 550cm^2 area I used in the heat calculation.
I have drawn a GoPro mount, but I have to think a bit on the placement. I haven't really made a weight estimate yet, but if I can keep it under 250g I'm happy.

So what do you think?


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## The_Driver (Nov 15, 2015)

10.000 Lumens with small optics doesn't make much sense in a bike light. It will blind you so much that you will see less far than with a dimmer light. Even in difficult terrain. If you really want to make the light practical (not just for showing off) you need to use relatively large optics (diameter is the important characteristic). You want as much lux as possible. 

You should also de-dome the LEDs or use ones without a dome (Cree XP-L HI, Cree XHP-35 HI etc.). It will improve overall system usability by a lot (i.e. making the light as compact as possible and/or producing more lux). You get ~90% more lux (with the same optics) and ~10% less lumens.

Another good tip is to use elliptical optics to reduce wasted light. You don't have to do this on all of the LEDs, but I would do it on most of them. Obviously you would orient the optics horizontally so that the light goes more the sides and less into the trees.


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## Steve K (Nov 15, 2015)

Buoyen said:


> I have drawn a GoPro mount, but I have to think a bit on the placement. I haven't really made a weight estimate yet, but if I can keep it under 250g I'm happy.
> 
> So what do you think?



I've never mounted a half pound of stuff on a helmet. Will that tend to pull the helmet fore or aft, or to one side? 
Will it be mounted at the top to keep the weight centered?

As with a lot of projects, I think I'd prototype it and see how it performs before sinking real money into it.


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## Buoyen (Nov 16, 2015)

The_Driver said:


> 10.000 Lumens with small optics doesn't make much sense in a bike light. It will blind you so much that you will see less far than with a dimmer light. Even in difficult terrain. If you really want to make the light practical (not just for showing off) you need to use relatively large optics (diameter is the important characteristic). You want as much lux as possible.
> 
> You should also de-dome the LEDs or use ones without a dome (Cree XP-L HI, Cree XHP-35 HI etc.). It will improve overall system usability by a lot (i.e. making the light as compact as possible and/or producing mor elux). You get ~90% more lux (with the same optics) and ~10% less lumens.
> 
> Another good tip is to use elliptical optics to reduce wasted light. You don't have to do this on all of the LEDs, but I would do it on most of them. Obviously you would orient the optics horizontally so that the light goes more the sides and less into the trees.



Thank you for the input. I agree it's a waste if a lot of the light is outside of the target area, but for technical stuff I do like to see what is close to me as well. Having a lot of light directly in front of me will just blend, I agree. I need to experiment a bit I think how much light I want in front of me.

I have considered elliptical. Maybe one or two of the three would be a nice try. Carclo have one 30mm elliptical with FWHM: 45 X 19






Interesting what you say about de-dome. I haven't tried it nor thought so much about the oportunity.
What you say do make sence. Here is a comparison of the XHP35 HD and the XHP35 HI medium optics:

HD:





HI:





If I read this right we see that at the same total ouput (?) the HI have more light in the area we actually want the light to be. At 20 degrees the HI has 220 Cd and the HD 250 Cd. Max 1500 vs 1250. Rough numbers from the graphs, but just to illustrate. So less light around, but what about just going with a narrow optic then?

HD narrow:







Steve K said:


> I've never mounted a half pound of stuff on a helmet. Will that tend to pull the helmet fore or aft, or to one side?
> Will it be mounted at the top to keep the weight centered?
> 
> As with a lot of projects, I think I'd prototype it and see how it performs before sinking real money into it.



Good idea. My current helmet light weights 160g and isn't noticeable at all. I'll try to add 100g just to make a feel for it, but I think it won't be a problem. I usually use the lighter open helmet on the trails, but when riding in the park or at certain competitions I use the full face which weight over 1 kg so you could say I'm used to have some weight on my head. 

Yes top mounting is the plan.


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## Harold_B (Nov 16, 2015)

So basically you want to bolt this to your head: http://heiseled.com/index.php?main_...id=119&zenid=7cb957d9dcdf6cdfee172d9df1adf77f


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## The_Driver (Nov 16, 2015)

Buoyen said:


> Thank you for the input. I agree it's a waste if a lot of the light is outside of the target area, but for technical stuff I do like to see what is close to me as well. Having a lot of light directly in front of me will just blend, I agree. I need to experiment a bit I think how much light I want in front of me.
> 
> I have considered elliptical. Maybe one or two of the three would be a nice try. Carclo have one 30mm elliptical with FWHM: 45 X 19
> 
> ...



Wenn you have too much light directly in front of you your pupils get smaller. This means you will see less in the distance. See here for an example.

When you have ~10.000 lumens there will be enough spill light even if you use large, tight optics and de-domed LEDs.

Also remember that the battery will get relatively big and heavy if you really want 10.000 lumens.

Please take a look a this bikelight that somebody here in Germany built for himself. It does some of the things we talked about. He used three warm-white XM-L2 LEDs in combination with three medium-large (45mm) Gaggione optics. He used two horizontally orientated elliptical optics (Gaggione LLC49E) for the wider light in the foreground and a normal, tight spot-optic (Gaggione LLC49R) for things in the distance. He also mounted the two elliptical optics at an off angle to the left and right (very smart!). For maximum usefulness he did not give all the LEDs the same current. The spot LED got 82% of total power (total power only 17W in this beamshot). This creates a very balanced "carpet" of light in front of the bike. 

If you want to improve his concept and make the light brighter you should add additional LEDs with spot optics and use small LEDs without a dome. I would try the XP-L HI. I would also go for a higher color temperature of 4000-5000K (depending on preference). I find it easier to concentrate during biking with these higher color temperatures. It will also make your light more efficient. I would refrain from going higher than 5000K since it makes everything in nature look "dead". 

Regarding de-doming: if you have a given optic and compare the XP-L HD (or XM-L2) with the XP-L HI, the HI will give you a 50% smaller spot with ~90% more Intensity (Lux). Since you want as much lux as possible (within realistic size constraints) the XP-L HI will allow for a more efficient design.
Since you have so much power available you should also think about using de-domed XP-G2 LEDs instead of XP-L HI LEDs. They again have a 50% smaller spot and ~65% higher Intensity compared to the XP-L HI. The downside of the de-domed XP-G2 LEDs is that you might get a green tint (nasty side effect of de-doming) and they are a bit less efficient. The upside is that you can use smalle roptics and still get the same size spot as with the XP-L HI. You need to carefully think this through. I would probably go for the XP-L HIs though because of less hassle and a nicer tint.


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## Buoyen (Nov 17, 2015)

I don't really understand why he want so much light on the sides?

I think something like this. A wider beam that provides enough light to the sides and near me, and then spots that light up ahead.


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## The_Driver (Nov 17, 2015)

Buoyen said:


> I don't really understand why he want so much light on the sides?
> 
> I think something like this. A wider beam that provides enough light to the sides and near me, and then spots that light up ahead.



In you first post you mentioned that you want to use the light for "aggressive trail/downhill riding". This means there will be a lot of tight turns. With a normal bike light you will always have tunnel vision and not see much in turns. Making the spill this wide will drastically reduce this effect and make you feel safer and allow you to go faster. The other reason is that the spot optics also produce some spill light which is enough for the area directly in front of your bike. Especially if you want to able to see far into the distance (to go fast on straight parts of the trail).

The circles you drew on the picture are way to small too ride fast in a safe manner. They limit your peripheral vision. 

If you make the light good enough you can probably skip the helmet mount and just put it on the bike. This is certainly much more comfortable since the light will be quite heavy.

I think you just need to buy some optics and LEDs and try different combinations to see what works best for you.


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## Buoyen (Nov 17, 2015)

That's a good point!
Ellpiptic lenses here I come.. hehe.


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## mhanlen (Nov 17, 2015)

I guess my question would be, have you simulated this with any lights close to 6000-10000 lumens? Like everyone said, expect to add considerable weight to your helmet, and make it top heavy. I don't know how well a helmet would secure safely to your head during agressive downhill riding, and stay in place. I'd run some simulations with a weighted helmet, and see if you need a different approach to a helmet design, or use something different than a standard bicycle helmet. Also take into account having a bunch of metal with heatsinks strapped to a helmet, may make a helmet suddenly dangerous, if you were to have to use one for it's intended purpose. There are a lot of logistics you have to work out before your basic task of constructing that light.


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## Buoyen (Nov 17, 2015)

Yes, what helmet I use dempends on what riding I intend to do. I'm not worried about the weight, but in case of a crash I would want the light out of the way  Especially on the trail helmet.
Either this 






or this:


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