The 15 Watt boards you linked (with fake xhp70 on it) is certainly compact.
And if they burn and stop working, I’ll replace them with a new ones. They are dirt cheap, maybe $2 on aliexpress each. I’ll wire these lights with a relay and a fuse so my battery will stay protected if anything goes wrong.
I also had this Idea, I think it should work.
Use this dc converter to step down to desired voltage (to 9V or 7,5V). They seem waterproof and fire proof if something goes south.
https://www.aliexpress.com/item/1005004360654374.html?spm=a2g0o.detail.1000013.5.1fb3ccc6qFAvaN&gps-id=pcDetailBottomMoreThisSeller&scm=1007.13339.291025.0&scm_id=1007.13339.291025.0&scm-url=1007.13339.291025.0&pvid=46627d7f-9494-4b8c-bf9e-f9da021d0c37&\_t=gps-id:pcDetailBottomMoreThisSeller,scm-url:1007.13339.291025.0,pvid:46627d7f-9494-4b8c-bf9e-f9da021d0c37,tpp_buckets:668%232846%238115%232000&pdp_ext_f={"sku_id"%3A"12000028902964162"%2C"sceneId"%3A"3339"}&pdp_npi=2%40dis!EUR!9.8!8.53!!!!!%402101f6b516713149554514812e5cef!12000028902964162!rec
And then use any cc 2S flashlight driver to drive my led.
But I don’t have enough room inside a bike for it
Just keep in mind that automotive environments are NOT the same as crowbarring a cell that supplies pretty smooth voltage whether at 4.2V out of the charger to 2.8V when giving up its last gasp.
Even buck/boost converters are counting on a smooth trouble-free supply voltage.
Automotive doodads are specced to see everything from 9V or less, to 15V or more, in normal operation, AND need to be able to be able to withstand 35V spikes due to alternator “load dump”, which can be significant.
Throwing a resistor at a “12V” LED will likely end up with it being pretty much off when at the low end of the voltage range, while frying the LED when at the high end.
So yeah, buck-boost would be needed, but you’d have to “prefilter” its input (suppress or at least block spikes, maybe have a filtering cap too).
However, there is a regulator between battery and the alternator.
I think one critical point is the motor ignition.
To avoid problems switch on module afterwards.
He can try several ways and report most reliable system
And load-dump is what happens when the magnetic field suddenly collapses when the engine’s shut off, “regulator” or not.
(The regulator only controls rotor current in the alternator. It’s not a post-regulator like a 7135 or 7812 or anything.)
I have managed to source Ledil lenses that suit my project. Now I have a choice between reflector and TIR lenses. They both have the same specifications regarding the beam and dimensions.
What would be better, reflector or TIR?
You want distinct hotspot + spill, go for the reflector.
You want a smoother, more homogeneous beam, go for the TIR.
Thanks 
.
That’s why, unless I’m really going for a pencil-beam, I like TIR lenses better.
Plus, it’s rare to get a fried-egg beam with TIRs, while that’s usually the norm with reflectors.
you can't get flat/oval beam from off the shelf reflector, so for fogs you need tir, but for spot, either one will do.
Thanks again
TIR ordered.
Lights finished, you can check the Build topic: