Hi Guys,
I recently posted a thread, where I was looking for a host for a cree xhp70. I didnt get a lot of feedback, because I didnt really know, what I was looking for. I was thinking of building a bike light with the xhp70 but I dont know, whether that is a reasonable idea. Does anybody have an oppinion on the xhp70 for a bike light and if it is possible, can anybody recommend me a host?
Greetings devryd
Bike lights usually should have a long runtime and run without any heat problems
XHP70 is quite overkill,
any decent Bike Light with 2 XML2 LEDs would do it, running at about 1000-1500 lumens off 2 18650 batteries
On a bike light the beam shaping plays a big role not just the usual round flashlight beam
The long runtime shouldnt be a problem, because I usually dont do long rides at night. If it lasts for about 40 mins, it will be far more than enough. The heat is a far greater problem I guess, But I have a racing bycicle, so it should get a decent amount of airflow, at least. Is there a host, you could recommend for that, or is it just dumb to use the xhp70 for this usecase?
Normal flash light
Bike light low beam
Bike Light low and high beam
You can use a xhp70, but what I would consider first is what beam size and intensity you need for your riding, then design the light with that in mind.
If you are doing fast road riding I would say you want at least 30kcd. If you are on public roads where you’ll have oncoming traffic you should pay more attention to the glare and beam cutoff.
Then, would you prefer a traditional flashlight form factor where the battery is in the light? Or one with a separate battery pack? If it’s a separate battery pack you will probably have more than enough battery energy and you will be just limited by heat. On the other hand if you only have the one cell in the flashlight your brightness might be limited by battery energy.
I am driving on public roads and i do that rather fast, up to nearly 60 km/h hilldown, so a bright light would be good. I dont really mind, what formfactor the light is, as long as i can fit it on my bike.
German laws specify StVZO compliance for bike lights used in country. That severely limits the number of available lights since most countries other than Germany don’t have such strict regulations so there are many bike lights out there that are not compliant.
I know that germany is really specific about regulating everything, but I live in a pretty low populated part of germany. I have only been once in a police control with my car and I dont know anybody, who was controlled on the bike. I would take a good, not allowed light over a bad, allowed one.
Of course it mustn’t blind the other traffic
Raveman has been making cut off beam bike lights for a long time and has the bugs pretty much worked out. Personally I’m starting to not like cut off beam lights out in the country. I have had some problems with two oncoming cars, the second one waiting for a chance to pass the first one. It usually ends up with me against the grass and an oncoming car doing over 100 km/hr right next to my elbow. I also can’t see a thing because two cars are blasting me with light.
A more powerful/ annoying light makes it easier to be spotted in this situation. Maybe they think it’s a motorcycle, maybe the don’t know what it is that is that bright and are just more cautious. If I’m using a helmet light I point the light down and towards the ditch when the cars get closer. If its a bar light I just put a hand over it to cut the beam off or bump it and point it down, but only after I’m sure they know I am there. The way the new car headlights are people are getting used to getting flashed anyway.
Kaidomain has an xhp70 light with modes customized for a bike light. Nothing worse than hitting a bump at speed as you are switching modes and winding up in moon or blinky. It does a pretty good job of lighting up the sides of the road so you don’t get surprised by dogs or wildlife. Four sense resistors so plenty of places to add resistors and bump up power a bit. Their battery packs are pretty good, sound like you could get by with a two cell.
http://kaidomain.com/bike-lights-and-bike-accessories/Bike-Lights/KDLITKER-Bike%20Lights
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Hi Lexel
What brand of bike light do you use in this example
Thanks for that @WTF, i hadnt considerd, that it might be good to blind the traffic to a small degree.
But I am looking for a host, primarily, because I already have a xhp70 and possibly a driver and want to use them
The intent is not to blind them but to make them aware of you at a distance, although getting the attention of a driver preoccupied by their phone or conversation seems to require more stimulus these days.
Yeah I know what, you meant, I should have put the blind in “”.
But I think I want something a little less “blindy” than this light. I just saw a picture on a different page and it is a little too much light for the oncoming trafic
As for a host it’s going to need a big reflector. I have used a Kaidomain c8.2 flashlight that came with a boost driver and 6v xhp50 and replaced it with an xhp70. Bought an orange peel reflector made for and xhp70 and insulating gasket off of Aliexpress. Works ok for fast maintain biking but to get enough throw at road speeds might require higher power levels and then you have to worry about managing battery runtime.
I ended up moving that setup into a convoy M21A because of the bigger 21700 battery. Anything bigger than that is going to need a pretty solid mount.
How efficient is the xhp70 @32W?
How much of the power will be heat?
The xhp70 does generate a lot of heat so you need good heatsinking, and for sustained running at 32W you need good batteries, probably 2S2P if you want more than 25 min run time at full power.
I know that it generates a lot of heat, but I was looking for numbers. I already have a light with a xhp70 and on full load it gets hot really fast. I was just wondering, if anybody had some numbers for me, so I can try to get a cooler for it and build a light without a host, since nobody can recommend anything
From djozz’s test of the xhp70 it does about 113 lumens/W at 5A (33W). From the Wikipedia article on luminous efficacy 260-300 lumens/W is 100% efficient for a white LED so the xhp70 is 30-40% efficient.
Do you have a driver in mind? That is a big factor in determining what hosts you can use. As sirstinky said if you want to run it at 32W you probably want at least 32Wh of batteries which would require multiple cells so most likely an external pack.
I can give you a little guidance for the size of the reflector which will determine the beam intensity. Based on my experience the xhp70 will have a luminance of approximately 30 cd/mm^2 at 5A. So to get 30kcd you need about 1000 mm^2 of reflector area which is about what a C8 reflector has. So look for hosts with head diameter 45 to 55mm. There are a lot of bike lights like in kaidomain and gearbest, but most people here are unlikely to have experience with them.
As far as heat dissipation, a C8 sized light or maybe a bit bigger might be able to shed the necessary heat with a constant 15mph wind. My convoy S2+ running at 3A (so about 10W) does not get too hot on my mountain bike rides.
I dont have a driver in mind. I mean I have one here, but it only does 4.8A without modes, which might be a little high for constant operation. So I am open for any help, because I am really new to the flashlight comunity.