I would like to build my own LED bicycle headlight ...

[DiTBho]

so
It's Septermber, Summer is ending, September brings with it far fewer sunny days, more dark days.
I am fully back to work and It's been raining cats and dogs for three days.

Autumn and Winter days will have less light in the late afternoon since I don't have time in the morning, but I can only train after work, so after 6:00 pm, I will almost certainly return home with little light.

After the bad accident I talked about here, which was caused also by not having a bright enough headlight on the bike, I would say that it is time to get a suitable one!

I found some light products that seem reliable and good for cycling on dark roads

• Garmin Varia UT800, see here
• Topeak Whitelite HP500, see here
• Vis Pro1000 Trail, see here
• ...

However they are very costly and limited by an internal battery.

After the incident, I found my wheel-set is gone, too damaged to be repaired, it must be replaced.
So, I would like to use a front dynamo hub for the new front wheel, and take advantage of its dynamo hub.

I have a 3 Watt one here, and it would be nice to avoid being limited to 1-2 hours of LED lighting due to an internal lipo battery, which you can not even replace.

-

So, I would like to build my own LED bicycle headlight, and I would like to build it as a smart lighting device, with an ambient light sensor and an accelerometer that automatically modulate the PWM.

Like Garmin did with the Varia UT800, but powered by the dynamo, and with full control of its firmware to avoid being frustrated as you can read in some product reviews, because users want to use the light in one way, and the Garmin' firmware does not allow them to.

I would also like to add a button on the ergopower, to activate the boost mode, on the sections of road that are particularly worrying. In addition to the dynamo, I would also like to use super capacitors (from the material of a fake water bottle) to give extra current to the LED in the boost mode.

There are no problems for the electronic/firmware part, but I am a bit stuck on the optical part where to find the lens.

* * *

Which lens to get, etc. Do you know of anything I can use? 

[Njk]

It's difficult. Sure you can come up with all your design files and find an affordable CNC machining service in your area. But custom optics manufacturing service can be much more expensive, I guess. While it's not an option for a bicycle headlight to use a COTS architecture lighting lenses

[dave j]

For the optics/housing, is repurposing an old bike light designed for incandescent bulbs worth looking at? There's got to be loads of old ones knocking around that people have replaced with LED lights and don't want any more.

[Njk]

For the optics/housing, is repurposing an old bike light designed for incandescent bulbs worth looking at? There's got to be loads of old ones knocking around that people have replaced with LED lights and don't want any more.

One problem is that for an incandescent bulb, cooling is less critical than that for a LED. The old housings are not designed with that in mind. Very substantial changes will be required.

[themadhippy]

Nip down the local motorbike scrappy and have a mooch

[dave j]

One problem is that for an incandescent bulb, cooling is less critical than that for a LED. The old housings are not designed with that in mind. Very substantial changes will be required.

Even if the housing itself isn't suitable, it could be a cheap way of getting a suitable lens and reflector.

[Nominal Animal]

modulate the PWM

For the love of dog and all that is furry, please don't let it visibly pulse or flicker.  (Anything above 100Hz is fine, although I personally prefer much higher.)

I'm one of those people who cannot tolerate light flicker.  When I go for a walk in the late evening when a bit tired already, those low-Hz bright pulsing bike lights make me nauseous.  In actually photosensitive people, they can trigger an epileptic seizure.  I understand it prolongs battery life by 2×-5×, but the problems they cause to myself and others makes me believe they should be made illegal.

[nctnico]

modulate the PWM

For the love of dog and all that is furry, please don't let it visibly pulse or flicker.  (Anything above 100Hz is fine, although I personally prefer much higher.)

I'm one of those people who cannot tolerate light flicker.  When I go for a walk in the late evening when a bit tired already, those low-Hz bright pulsing bike lights make me nauseous.  In actually photosensitive people, they can trigger an epileptic seizure.  I understand it prolongs battery life by 2×-5×, but the problems they cause to myself and others makes me believe they should be made illegal.

Not only that. When driving a car you can't follow where a blinking light is coming from or going to. So it actually doesn't help to be safer as you can't determine whether the bike is on a colission trajectory or not!

Back to the design: I'd start out with high efficiency LEDs and put those into a suitable reflector housing. For riding off-road it could make sense to have two headlights. One with a narrow beam and one with a wide beam. But I think there are readily made headlights available with are good. I have a bike from a brand called Batavus (well known Dutch A-brand) and the LED headlamp that came with it is fine for riding when it is pitch black dark. Or put differently, the trick is to avoid the crap they mount on cheap bycicles.

I would avoid using batteries of any kind. I specifically modified my bike to also power the rear light from the dynamo as changing the batteries is cumbersome and you never know when they cut out. Driving without proper lights on a bycicle in the dark is dangerous. People won't see you.

[Njk]

Even if the housing itself isn't suitable, it could be a cheap way of getting a suitable lens and reflector.

Perhaps. But that lenses are typically of glass. What you'll do when it's accidentally broken? It can be a problem to find exactly that lenses for replacement. Moreover, you can't make as many products as you want. Generally, it's better to avoid a non-scalable solution.

And from the engineering perspective, you'll be forced to use a classic optical scheme, where the light source is located at the focal point of the reflector. It's the only practical scheme for a bike light with an incandescence lamp. While with LEDs, it's possible to use a more advanced schemes, where the light from the source is rotated by the reflector (what Busch+Muller and Outbound Lighting does). That allows for better cooling and beam forming. So with old parts, all the design efforts will result in outdated product, in best case

[DiTBho]

For the love of dog and all that is furry, please don't let it visibly pulse or flicker.  (Anything above 100Hz is fine, although I personally prefer much higher.)

Yup, usually, it's 1kHz.
The control unit that does the dimming on the LED panels in the helicopter hold is even 10Khz.

[DiTBho]

I have a bike from a brand called Batavus (well known Dutch A-brand) and the LED headlamp that came with it is fine for riding when it is pitch black dark. Or put differently, the trick is to avoid the crap they mount on cheap bycicles.

The night of the accident, I was using a LED headlight made by XOSS

• XOSS, XL-400, see here

It costs between 20 and 30 euros, it's what Amazon suggests the most. The brand XOSS is not that bad, but I have to say that specific LED headlight didn't give enough light for the road conditions I was on, certainly not the 400 lumens declared, in addition to the fact that the battery lasts really little, again less then how declared.

In my case, the bicycle is an old 90s steel road frame.
For the front dynamo hub, I have two alternatives

• Shimano Nexus, Shimano DH-C3000-family, 3W/6V, 36H, quick release mechanism
• Sturney Archer X-FDD, 3W/6V, 36H, It also integrates a drum brake, has bolt tightening

For this specific bicycle, which is my training one, I already have the Shimano hub at home, and I would leave aside the Sturney Archer alternative for two reasons

• It weighs 1.2Kg, and I don't need a drum-brake on that bike. The RIM-brake is fine.
  I will need it on a bicycle I will use in Norway, but that's another story, and another bicycle
• Not having the quick release mechanism is a real problem to take the wheels on a plane because you can't put them in the classic "bicycle bag" since the hubs have a protruding axles on both sides

You need specific bags, made to measure, nobody produces them.
I have already talked about it in another topic, it's a problem that I'm solving, but that I haven't solved yet.

* * *

In any case, both hubs offer 3W/6V, which is not much in terms of current.

[nali]

If those hub gennys are like my Schmidt, they'll provide more than 3W over 20kph; in essence they act as a speed-dependent voltage source with a maximum current of around 500mA. So as a little side project you could build a MPPT regulator and switch in extra LEDs as an automatic "high beam".

It's one of my "never got round to" projects 

[langwadt]

start with a cheap LED torch ?

[radar_macgyver]

You can buy aluminum-backed LED boards here:
https://www.ledsupply.com/leds/cree-xlamp-xhp35-high-density

There are many models to choose from, with different LEDs, color temperatures, etc. Once you've settled on an LED type and board, you can pick from the optics available on the same site. When I built a bike light, I chose an elliptical spot lens so that the beam is confined vertically to avoid dazzling oncoming cars, while giving a decent horizontal spread.
https://www.ledsupply.com/led-optics/10510-carclo-lens-3-up-elliptical-spot-led-optic

They have many other lens vendors available, suitable for LED boards with different numbers and types of emitters. The single-emitter lenses also need a plastic holder to keep it aligned with the board. You can also find housings and compact LED drivers on the same site:
https://www.ledsupply.com/led-heatsinks/dynamic-led-heatsink-housing
https://www.ledsupply.com/luxdrive-constant-current-led-drivers

Mouser seems to carry the lenses under "LED lighting optics", and are cheaper, but the parametric search doesn't have anything useful to search on.