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.

[mendip_discovery]

Just buy one of these,
https://www.aliexpress.com/item/1005006723526188.html



TBH I know it's heavy etc but can't you fit an LED headlight unit from a motorcycle, use a 12V battery pack from a UPS. At least you would have dip and main.

Other options include looking at what they offer for the off road motorcycles, Polisport makes some headlight kits and if you feel rich then look up Touratech.


If I can ride a 1961 Matchless G3LS at 6V at night while at times going more than 60mph it should be enough light or you need to slow down.

[IanB]

Rather than use a purpose designed bike light, I would be inclined to consider a regular torch (flashlight) with a suitable mounting bracket. These are regularly designed with removable batteries (typically 18650 lithium ion or some such), so you are not limited to duration of a built-in battery. You could easily carry one or two spares with you. The optics of such a torch will be way better than anything you can concoct yourself.

If you are really keen, you could cannibalize such a light by replacing the internal battery with the external supply from the dynamo, or arrange a charging circuit to keep the torch battery continuously topped up. But this seems like a lot of work, and I don't know if it would be worth it.

[DiTBho]

Just buy one of these,

Well, I'm not one to spend money on aerodynamic accessories ...
such as { aero helmet, aero water bottle, aero fork, aero seat tube, aero wheels ... }
but ...  I do trips of 120km, and that big thing at 30-35km/h average ...
... certainly creates so much air resistance that it gives me a sore neck

[Nominal Animal]

If you mostly drive at night with minimal extra weight, ignore this post.

Edit: IanB basically said this better above.

How about designing the power side so that you have a removable rechargeable battery pack, and lets you choose between charging it from your dynamo, isolating it and using only the dynamo for the light, or using only the battery pack for the light?

You could even make different capacity packs for different types of trips.  When going on a holiday trip without a support car, you'll have many kg of cargo anyway, so having an additional battery pack is likely not a big deal.

Add optional 5V output regulation, and in an emergency, you could charge your phone with the dynamo enough to make a quick call.

[radar_macgyver]

Battery pack: you can make a pack from 18650s, shrink-wrap them with poly film and zip-tie to a clip-on bottle holder to make them easily removable for charging/theft prevention. Waterproof barrel plugs are available (meant for dive lights, apparently). Alternately, use an old bike water bottle (I used one that got leaky), this makes the batteries waterproof, and you can use a standard bottle holder. This does make the wires a bit longer though.

[DiTBho]

Rather than use a purpose designed bike light
...
If you are really keen, you could cannibalize such a light by replacing the internal battery with the external supply from the dynamo

I listed 3 products in my previous post.
They are all no less than 100 euro.

The Garmin Varia UT800 costs 130 euro.
Would you cannibalize it?

They usually have waterproof protections, and designed to avoid you to be able to replace the battery.
I do not even how to open them without breaking them.

The XOSS XL-400 has a lens and rear cap glued with resin: how do I open it? 

It was damaged in the impact, the lens is horribly scratched and there are quite deep dents, so much so that they have damaged something, because it no longer turns on.

For me it is to be thrown away, and I am tempted to use a mini Dremel to cut along the cap, which unfortunately they have glued, so I can open it.

[IanB]

I listed 3 products in my previous post.
They are all no less than 100 euro.

You listed three specialized bike lights.

My suggestion was to think outside the box and not look at bike lights, but look at regular "tactical" flashlights combined with a mounting bracket.

A few years back, everything had removeable batteries, either AA or 18650. Now it seems times have changed, and most lights have a built-in battery and USB C charging. You need a time machine 

However, apart from the lights you listed, brands like Olight and Fenix have bike light offerings. If they have a USB C charging port, you could connect the dynamo to a USB C charger, and plug that into the light, so it would charge as you ride along. You would have to check that it can be charged while in use.

If you did this, you would not have to cannibalize anything.

But my suggestion was to possibly modify a $30 light, not a $100 light. There are inexpensive lights that take 4 AA cells, nominal 6 V, which would be compatible with a dynamo output.

[themadhippy]

Just buy one of these,

not road legal in the uk,all bike lights are supposed to be fixed to the bike

[IanB]

For example, this inexpensive light has a nice adjustable beam pattern from wide to narrow, it is bright, and it runs from 4 AAA cells (nominal 6 V). It apparently has a regulation circuit inside to control the brightness of the light, so any approximately 6 V DC supply should work.

https://www.harborfreight.com/590-lumen-tactical-led-flashlight-black-59362.htm

Maybe you can find something similar in the UK, or online?

To add an external power supply, you could drill a hole in the side, run a cable through, and seal it up with silicone. Or even fit a waterproof power jack and wire it up internally.