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

[IanB]

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.

Bike lights (well mine, anyway) have a trapeziodal light pattern, so they have a more consistent illumination pattern when angled downwards. Plus side lobes to illuminate the kerb or verge.

I guessed that might be the case.

In the old days before LEDs, bike lights were dim and couldn't light up the road at all. Now, they could be almost as bright as car headlights. So it makes sense to have a beam pattern to avoid dazzling oncoming vehicles, as well as putting more of the light where it's wanted.

But a small LED light with the sole purpose of being seen might not need much in the way of a beam pattern, perhaps?

[mendip_discovery]

Just buy one of these,

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

What does legal stuff have to do with cycling? Its not like they can be told off or anything. Even these electric motorcycles are free for be used by everyone, the police are too busy to do anything about it.

[deadlylover]

Yeah I'd figure out a flashlight mount and just change the lens.

Buy something like a Convoy S21E and get an elliptical lens (they call it striped).

I like the Nichia 519A emitters, relatively neutral (though sometimes a bit above the BBL) with good CRI. Make sure you get the version with the Anduril driver, you'll be able to flash the version to Anduril 2, though I'm pretty sure Anduril 1 has a bike flasher strobe as well.

[Njk]

The lighting requirements depends on the untended use. A trail ride is a dumb case. To flood the front area with more light. Just attach any flashlight powerful enough to the bike and you're all set. But a road ride is a more complex case because generally, a well collimated beam of several degree of divergence angle is required (you can always add some diffusion if necessary, it's not a problem). According to the optics science (etendue etc.), the larger the aperture size (the lenses diameter), the more collimated beam can be produced with given light source aperture and target efficiency loss. That does not mean that such a beam can't be produced with a small lenses, I've old Inova X1 spotlight that has a lenses of the AA battery diameter and produces a beam like that of laser pointer. But that's with high losses. If you remember, old bicycle headlights were quite big, of more than 50 mm housing outer diameter. I presume that's because incandescence bulbs produce not so much light and it was essential to minimize the losses. But actually, a LED has less brightness density, it uses larger light emitting surface (source aperture) to produce higher perceived brightness. It's typical for a power LED to have 1x1 mm emitting surface area, which is much larger than that for the incandescence. That means that a LED requires even greater lenses aperture (at least 40 mm effective aperture diameter for automotive headlight applications AFAIR). While most of the modern bicycle headlights are much smaller. Perhaps that's because now it's not necessary to be an optics engineer to design and sell a cute LED lighting device packed with Wi-Fi, BT and Ant features.

One of my former colleagues was a railway automation engineer by education. According to him, it usually does not make sense to build a hermetically sealed housing for an outdoor equipment. It's not a diving equipment, after all. It adds cost with little to no benefits. Even with no leaks, the water will appear from the internal air as the temperature change. Soon, the vapors will reach the electronic components (no matter of conformal coating) and start the corrosion. It's possible to fill the internal volume with a pressurized inert gas, but that adds even more cost and maintenance burden. A better approach is to build a splash-proof housing and fill the inside with a sticky viscous substance, like grease, fat, etc. That makes a visual inspection during the maintenance a nightmare, but it really works and it's cheap. For a bicycle accessory device, the water-tightness is a nonsense. It's not technically feasible for a cheap and lightweight device. Instead, it shall be made such that user can easy take it apart for periodic drying, cleaning and possible parts replacement. It's a very important requirement for bicycle headlight, but currently I'm not aware of such a headlights too.

The images below are for B&M IQ-XS E headlight. The IQ2-Tec optics that uses additional small prism. It's a well known model so many reviews can be found on the internet (e.g. https://fahrradbeleuchtung-info.de/testbericht-busch-mueller-iq-xs-e) and some the images are not mine. It's not super easy to take it apart but that's perfectly doable with no damage using a plastic card of the right thickness. I'd used my old driving license for that. It's a E-bike version so there are no huge caps for energy storage inside. It's of recent batch with re-designed reflector for horizontally wider beam.

It's a lighting device so optics is king while electronics is of secondary importance. But here is an electronics forum so some words about. There is no MCU (isn't it very good?) since the automatic switching between the night and day modes is done in a simple HW way by the mean of phototransistor. The BOM:

IC1: TI LM3404MA (1.0 A CC buck regulator for high power LEDs)
IC2: TI LM2731XMF (1.6 MHz boost converter with 22V internal FET switch)
T1, T5: OnSemi FDC5614P (P-channel logic level MOSFET, 60V 3A, 105mΩ)
T2: Diodes DMN2058U (20V N-channel enhancement mode MOSFET)
T3: Diodes DMG3420QU (20V N-channel enhancement mode MOSFET)
T4: Diodes BSS138W (50V 200mA N-channel enhancement mode MOSFET)
T20: Osram SFH 320 FA (IR NPN phototransistor, 980nm, 120°), likely
LED1: Osram KW HHL532.TK (3.2W, 395 lm)

[Zero999]

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!

That's true, but flashing lights are better at attracting attention. This is why emergency vehicles and roadwork sites use flashing, rather than static lights.

I normally use flashing lights when it's not dark, but very cloudy or twilight, because it catches the attention of other road uses and drivers can still track me because I wear a fluorescent vest. At night, I use both a flashing and static light, which is the best of both worlds. Flash frequency is important. It mustn't be too high because it's annoying and can trigger photosensitive epilepsy.

Perhaps the original poster could use a light which is static, but pulsed at a higher intensity every second, or one static light and a flashing one.

[EC8010]

What does legal stuff have to do with cycling?

Sadly, it matters when you have an accident. I've been knocked off my bike twice by the Police (and my wife reminds me that I was nearly run over on a foot path by a Police car). First time, policeman suddenly opened his car door in front of me which I wrecked with my knee before sailing over the top to land in the road. Second time, going off-duty special constable turned right across my path forcing me to brake so hard that I stood the bike on its nose and saw his rear wing pass by about 6" from my nose. It wasn't a stable position and I broke my arm when I landed. In both cases, driver tried to find fault with me (cyclist). Nevertheless, despite not having a witness, I fought the cases and obtained compensation. Have an accident at night and even if your light is perfectly good and you are in the right it will be harder to fight your case.

[thm_w]

Having built ~10 bike lights, its not really worth it for a front light, unless you need a very specific feature. For accent lighting or helmet lights it can be worth making your own.

Buy a magicshine EVO1700 (cbl1600), or similar, and then use the dyno output to charge it over USB: https://www.aliexpress.us/item/3256806555421828.html
- 1700lm with a flat cutoff
- 4000mAh battery
- wireless remote
- downside: not good for daytime use, better at night

[Nominal Animal]

That's true, but flashing lights are better at attracting attention.

Yes; but the flashing one doesn't need to be the main nor the brightest one.  That's the objectionable configuration.

Things like reflectors in both your shoes and your head can make you more recognizable, too, because of the movement pattern; just a simple blinking light is not enough for some idiots humans to recognize there is something to consider there.  Some just don't associate a blinking light with a bicyclist or a pedestrian or a pet on a leash, just think of it as a blinky light.

I've found the clip-on red LEDs some pet walkers use at night very intuitive; and when there are a couple in the leash also, very easy to detect from quite far off, and thus predict the movements of.  Just something to consider, mind you.

or one static light and a flashing one

If it matters any, I don't ever recall getting nausea (I don't get seizures, so not "true" photosensitivity) from a static front light and flashing notification lights (like say the common red one in the rear reflector, or a weaker flashing white one in your hat); I've only gotten it from the main front white flashing one.

(Blue lights are not legal here, they're reserved for emergency vehicles only.  Some bike lights are too cold/blue.)

[DiTBho]

Things like reflectors in both your shoes and your head can make you more recognizable, too, because of the movement pattern

uh, I spent yesterday afternoon checking the pedals. I had bought them only five days before the accident and wanted to check their mechanical condition before thinking about removing the scratches and polishing them.

Luckily I didn't mount the Campagnolo Super Light pedals made in the late 80s with titanium axle (~150..200 euro NOS) but the cheap japanese MKS Sylvan track (35 euro + 14 euro for a couple of ceramic ball-cages) still in production, because unfortunately, once inspected, I discovered that the axle of the right pedal is bent and the ball cage is damaged, or rather a pair of ceramic balls, a much harder material than aluminum, has deformed the internal raceway creating a hollow, something that now compromises the smoothness of the balls, you hear a terrible creaking, and that's the sound of what is not worth repairing them and you'd better thrown away.

I don't like "road pedals", I prefer "track pedals", which are 1 inch shorter and usually without the extra protection for dust cups.

Track pedals usually don't have any reflectors installed and don't even have a hole to screw them in.

For strange reasons all orders in my area of that model of pedals have a two month waiting period, but Good News!!! I found exactly the same pedals second hand in perfect condition and with an interesting modification: two M4 holes to install reflectors!

I was thinking of drilling them myself, but hey? Good Job already done 

[Zero999]

(Blue lights are not legal here, they're reserved for emergency vehicles only.  Some bike lights are too cold/blue.)

I nearly had an accident because some idiot had blue lights on their bike, on a cycle track which has blue illuminated studs, near the edge. It was dark and foggy and I thought the cyclist was the edge of the cycle track, until I got close and realised.

Track pedals usually don't have any reflectors installed and don't even have a hole to screw them in.
For strange reasons all orders in my area of that model of pedals have a two month waiting period, but Good News!!! I found exactly the same pedals second hand in perfect condition and with an interesting modification: two M4 holes to install reflectors!

Alternatively you could stick reflectors on your shoes.

Or how about designing some lights to sick on your shoes? A flexible PCB, high brightness amber LEDs (phosphor converted might be the best), a lithium ion cell and charging IC, are all that's required. You could cover it in a few layers of conformal coating to keep the moisture out.

[Nominal Animal]

I'd say reflectors on shoes or pedals or calves suffice.  Also, one or two reflectors in the spokes of each wheel makes one very distinctive when seen from the side; the dual motion is key.

There are huge differences between reflectors, though.  Some of the reflective tape I've seen is amazingly reflective/effective.  I've seen many quite poor red ones (as used at the back) and amber ones (spokes) and even white ones (for pedestrians), that look like they should work but when tested in dark do not reflect at all well, so pay attention to what you use and check before trusting.

Having the bike helmet reflect light is particularly useful, because even the oblivious ones associate such reflections with a human head.  (I don't mean it should be completely reflective, just that any part on it reflecting light, combined with static or moving reflections on the bike, is almost always associated with a bicyclist.)

Using the quirks of human perception to convey the idea of a bicyclist being there is what I'm driving at.  Pardon the pun.

[themadhippy]

and amber ones (spokes)

So last century,  strip of individually addressable rgb leds  on a spoke is were its at,the rotation of the wheel enables some pretty good animations and patterns

[Someone]

There are huge differences between reflectors, though.  Some of the reflective tape I've seen is amazingly reflective/effective.

Cheap too, quick way to add night time visibility to any hard surface.