Daylight Visible Bike Light - Front/Rear Combo - 100 Lumens on 2 AA's

Picture of Daylight Visible Bike Light - Front/Rear Combo - 100 Lumens on 2 AA's
The Ultimate Combo Bike Safety Light - It's a front/rear combo light with two 3-watt high-power LED's, all powered by just two rechargeable AA's. No heavier than your old setup but 10x brighter! All for only $20, and you can re-use the case from your oldest crappiest bike blinker to make this one!

- Daylight Visible!!
- Combo front headlight & rear blinker, or front/rear blinkers - 100 lumen total
- Full 360 degree safety light visibility
- Full brightness with rechargeable batteries (with option for alkaline use)
- Just 2 AA batteries power both lights (with option for AAA's)
- 8 hour runtime (with option for longer runtimes)
- fully waterproof and durable
- Total parts cost: $20
- Option for rear blinker only
- Simple electronics project using a proto-board and easy-to-solder parts.

See it in action! Side-by-side comparison videos below showing (on the right side) a top of the line commercial tail-light with 10 LED's, the Cateye TL-LD1000, and on the left side - the ultimate bike blinker front/rear combo.

close-up walkaround:


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Step 1: What you need

Picture of what you need
you will need the following stuffs to make the ultimate rear-only "AA battery" blinker:
(parts appearing in the circuit schematic are noted)

- old bike light, providing a good waterproof battery holder and bike mount
- LED1: Luxeon 3-watt red/orange high power led (part# LXHL-LH3C)
- L2optics 5x20 lens (OP-520)
- L2optics lens mount (OH-S35)
- prototyping board (such as: schmartboard 201 or vector V2018)
- SW1: waterproof on-off switch (such as: E-Switch 100AWSP1)
- cmos 555 timer chip (such as: TI TLC555CP)
- Q1: ultra low threshold PFET (such as: Fairchild NDP6020P)
- R1, R2: 2 x 6800 ohm resistors (such as: Xicon 291 series)
- C1: 10uF capacitor (such as: Xicon 140-SRL series)
- 18-22 gauge stranded wire, 2 feet
- 22 gauge solid wire, 2 feet

additional parts for the front light option:
- LED2: Luxeon 3-watt yellow high power led (LXHL-LL3C)
- L2optics lens (OP-520)
- L2optics lens mount (OH-S35)
- 2 pairs of spade-lug crimp connectors (or other connector)
- R4: 1-ohm, 1-watt resistor (such as: Xicon 294 series)
- handlebar mount from old bike blinker, or hack something together.

additional parts for "AAA battery" option:
- R3, R4: 1-ohm and 2.2ohm, 1-watt resistors (such as: Xicon 294 series)

additional parts for alkaline battery option:
- D1: 1-amp standard diode (such as: 1N4001 with a DO-41 package)

additional parts for both alkaline & rechargeable battery compatibility option:
- D1: 1-amp standard diode (such as: 1N4001 with a DO-41 package)
- exchange the SW1 on-off switch for an "on-off-on" SPDT toggle switch (E-Switch 100AWSP3)

where to get the parts:

LED's & lenses: the cheapest place to get these ($3.50 per LED and $1 for lens and lens mount) is from future electronics also see here - the 2nd link is a direct search for the LED's and buckpucks. for the lenses, here is the direct search to find them. You can also get the LED's from or in Europe, dunno if they have lenses though.

All the other electronics are available from
normally I use digikey but mouser was one of the only places stocking the Q1 transistor needed, so all the other part numbers above are available at mouser.
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that's great, very clean circuit too. Maybe you wish to read my BBB instructable ;-) (

mquiring12 years ago
"Stop Police" :-D
nerdzilla6 years ago
In many places, you can get heavily fined, because from a distance the lights resemble an emergency vehicle.
True, but police would be more likely to encourage than discourage their use. It's much better than riding at night without lights, which many bike riders do and don't get stopped for.
Ha, then you do not live in my country. 3rd brake lights for cars were forbidden, but as the general undesatnding was that these would increase safety, a date was set for them to become legal.
Eventhough everybody agreed that these increased safety and eventhough the law was written to make them legal, police were fining people who had these lights till midnight of the day before the law came into practice, After all, 'rules are rules'
These lights on my bike would no doubt get me shot.

But it sure is a good instructable
but you might get shot by a drug dealer :s
nerdzilla nande5 years ago
one can only hope.
Yakumo5 years ago
the idea and the instructable is nice but can it be that i'm the only one who thinks that this amount of light is kind of dangerous? i mean if i would drive behind you, i would at least be distracted or slightly blindet (only seeing cyan dots all over the place). even my flashlight replacement (5red leds each 6000mcd 20°) (thats about 0,5 lumen per led) has this effect if someone looks directly at it. i don't even want to imagine how it is with a 100 lumen led at eyelevel on a dark road.
I can only hope that yes, you are the only one who thinks this amount of light is dangerous. How bright is 100 lumens compared to car tail lights? Or car headlights? Probably 30% as bright as tail lights and 5% as bright as headlights. Those also are at eye level, and are much bigger and brighter than any bike light you can buy or make. My reasoning goes like this: Cars and trucks are big hunks of metal that are hard to miss, yet evidently they need a lot of bright lights at night to make them visible to others. So what on earth makes anyone think that a cyclist (which is easy to miss even in the daytime) should just ride along with the usual piddly 20 lumen flasher? Furthermore, cars and trucks are relatively safe places to be in a crash, and yet they still have lights galore. Bikes, on the other hand, are very dangerous in crashes, and yet some people think cyclists should be apologetic about having bright lights that announce "I'm here, don't hit me!"
I didn't expect an answer after that time but okay ^^

My problem isn't really the amount of light that's shining in my eyes, it's the blinking. I quote myself here: "only seeing cyan dots all over the place".
The other problem is the time when the LED is off, maybe it's not much maybe only about 1/10 of a second, but with 100 km/h (that is legal standard outside of towns in Germany and trust me on that: no one is driving that slow if no one is around) that are still 2,8 meters where the bike is invisible.
For the sake of argument...lets make that 1/100 of a second, how close was it the last time you where passed? Yes, that's the moment where you should think of the guy that almost killed you. Was it more than 28cm? Even if it's blinking faster as long there is no light while someone passes you IT IS DANGEROUS! If the cyclist makes any sudden sidemovements (maybe because of a dead rabbit or because he's drunk, doesn't matter) no light at the wrong moment can and end up someone getting hurt.

2 of this Lights max 10 cm apart, one lit up while the other is off would be awesome. Very visible from long range because of blinking and not too distracting while being close. Maybe connecting one led with a pnp and on with a npn transistor/mosfet after the 555 timer could do that.
tuberc4 years ago
Must the transistor be able to handle 24amps? It's alot easier for me to get a p-channel that handles 100V 10A, sorry but haven't used one of these in years.
amitrane4 years ago
What is the value of Q1 transistor ultra-low-threshold PFET ????
tltaylorsw5 years ago
Nice light, I am a bike paramedic and would like to use a PIC (16F628A) in place of the 555 to provide 2 alternating flashing lights. would the same moset placement work for me?

Thanks in advance
nande5 years ago
Can I forgo the circuit board modification and just replace one of the existing led with the high powered led? someone please tell me please cos I really really wanna do that...
imakethings5 years ago
m new to electronics can u tell me the use of the circuit you build?
moisture6 years ago
I just finished mine! I tried to make the blinkers and circuitry easily detachable from the bike so I can take it all inside when I park. I also put a 5k pot as R2; dialing it to zero gives a solid light. And damn, it is bright. Thanks, Dan.
kudoskun6 years ago
The lumiledsfuture link is a parked link. You should update that section. How about using one of the leds from They have 1 watt lights, would it be better to have 3x1watts vs. 1x3watt light? Perhaps you can spread the light out better.
Gopher6 years ago
Can I use the same components and run the circuit on 4AA 2700mha Rechargeable and thus have more power from the 3W luxeons? IE will the extra power available simply make the LED brighter with no ill effect on components, obviously the led will need heat sink but what about the FET? or should it be heatsinked anyway for safety Basically I just want a single 3W led to blink at as high a brightness as possible from 4AA batteries
civilpd6 years ago
I think I am going to build your light. What are the possibilities of using one the radio sh*ck 7.2v or 9.6v NiCad rechargeables? Would it overheat the LEDs or have other negative results?
shortman6 years ago
This is good and you could also use a bike light generator th keep batteries charged as you drive. You would only need voltage reducer from 6 volts to 3.
jimhensel7 years ago
Just made a rear flasher (pictured here) and an independent front flasher. Used Urine Specimen bottles -- every thing tucked in quite nicely. Thanks for the Instructable. Just unscrew to access the batteries.
dan (author)  jimhensel6 years ago
damosk7 years ago
Anyone have experience building LED systems to run off dynamo hubs?
kuan.fl7 years ago
You must be getting super specials deals; when following your sourcing links, I get $7 per LED +$9 shipping. Any better deals?

Love of the idea of the project, but I have a couple of questions.

Would a configuration of 5 cells (6.0V) driving 2 LEDs serially work as well? Or 3 NiMH cells (3.6V) + dropping resistor (0.6 V)? Don't know how circuit would have to change to accomodate these 2 scenarios. The reason I ask is as follows.

Without taking into account wiring/circuit losses or voltage suppression of NiMH cell in winter biking weather(~20-30 F), for most of the runtime, I expect supply voltage from 2 NiMH to be 2.2-2.4 V (2 x 1.1-1.2V).
According to pg 10,11 of the datasheet
at those voltages, I should get 300-600 mA, which translate to 0.2-0.5x relative to "normal" flux.
Isn't 20% a bit on the low side?
The datasheet say these LEDs take 2.31 V minimum, 2.95 typical, 3.51 max. On the plus side, at winter temps, looks like the red/orange/amber LEDs are more efficient.

I'm an electrical noob, so any comments appreciated.
fghgh kuan.fl7 years ago
skeen that was perfect and fabulas
dan (author)  kuan.fl7 years ago
sure you can do it with more cells, one of my goals was to only use 2. under-driving the led means no resistor is needed and the efficiency is very high, and run-time is improved.
kuan.fl7 years ago
Thanks for the feedback Dan. Why a P-channel MOSFET vs N-channel? From research, N-channel is more efficient. I'm not sure which stat to look at to judge whether "comparable"? Is it the Gate Threshold Voltage (V(gs(th)))?
Fairchild specs (min=-0.4V, typ=-0.7V, max=-1.0V)
Would this MOSFET work
ON specs (min=1.0V, typ=1.5V, max=2.0V)

Thanks in advance.
rs20007 years ago
Dan, awesome rear light, thanks, when I turn mine on it flashes at various different rates then after about a minute it just stays on steady - any idea what is most likely to be at fault? Thanks
dan (author)  rs20007 years ago
i assume it is fairly random flashing each time? either a loose connection somewhere, on a total disconnect on the gate of the mosfet (floating gate can randomly switch)
rs2000 dan7 years ago
Thanks Dan, my connections seem good, I might try swapping the mosfet out. Cheers
agathman7 years ago
I built both a front and rear flasher for myself, and made one for my daughter too. Great instructable. I actually dispensed with the old bike light housing and used a trailer clearance light (about $2 at WalMart), with all the innards removed. Then I attached a hose clamp to the housing to put it on the bike. Works great!
Mr_Squidge7 years ago
Hi Dan This looks like a great light and I fancy having a go at putting one together. I'm going through the parts list and I always struggle with getting the right capacitors (I'm fairly new to electronics). I can't find any reference to the Xicon cap that you mention and am looking for a suitable alternative. What material is the cap that you have used? It looks from your diagram that it is polarised? Any help you could give would be appreciated. Paul P.S. Anyone in the UK found a place to pick these parts up easily? Realy struggling with matching specs.
Can 'anyone' help with what type of capcitor that is? I'm pretty new to this and whilst I can put things together, I always struggle with the parts list.
dan (author)  Mr_Squidge7 years ago
any kind of cap is fine
windriver7 years ago
Hi Dan, Like everyone else it seems, I love your instructables and have read and re-read them a zillion times. I'm building this one (we all reallly need better bike lites), and have plugged the circuit into a breadboard. I'm new to electronics, and without real knowledge, I don't know how to debug the result. The light shines but doesn't blink. R1 and R2 are 10K ohm, C1 is 10uF (long leg connected to pin 6 of the timer, short leg goes to ground). The rest is stock per your instructions from Mouser. The LED (LXHL-LH3C) lights, but doesn't blink when I connect the positive side of the led to Pin 2 of the PFET, and the neg side to ground. I've tried replacing R1 and R2, C1, and even the timer (TLC555CP) -- all with same effect. Is the PFET bad? Is there a reasonable way for me to debug this? I hope this is the right place to ask this question. Thanks a lot for any insights, and the great instructables -- keep up the great work.
dan (author)  windriver7 years ago
try connecting regular red led to pin 3 of the 555, it should blink.
windriver dan7 years ago
Great - thanks Dan. It blinks. I must have blown up the PFET. With Alkalines and no zener diode, the circuit would run at 3 V instead of 2.4 for rechargeables. Is that too much voltage for the LEDs (hot), or too much voltage for other circuit components (burn out)? I was thinking the diode was to keep the LEDs from getting too hot without a heat sink, but then with even a 50% duty cycle, they're only on half the time....
billbob7 years ago
great instructable:) do the leds need a heatsink?
dan (author)  billbob7 years ago
no - average power for them is under a watt so the 'star' is enough heat sink.
salibon1 dan7 years ago
Are you selling any for those of us who do not have a clue as to your schematics or any of your electrical thingees.
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